Supplementary Material

1. History of environmental regulations

SM Table 1 Acts and regulations in terms of regulating atmospheric emissions in Singapore (Oon & Saparudin, 2014)

Acts and regulations for general pollution2018 Environmental Protection and Management Act (Amendment of Second Schedule) Order

20182009 The Environmental Public Health (Toxic Industrial Waste) Regulations 2009.2002 Environmental Protection and Management Act (CHAPTER 94A)2000 Environmental Pollution Control (Air Impurities) Regulations 20001999 Environment Pollution Act (replace the Clean Air Act, Drainage Act, The Water Pollution and

Drainage Act)Acts and regulations for air pollution

1990 Clean Air (Standards) Regulations, Revised Edition, 19901980 The Clean Air Act (Amendment of Schedule) Notification, 19801978 The Clean Air (Standard) (Amendment) Regulations, 19781975 The Clean Air (Amendment) Act, 19751973 The Clean Air (Prohibition on the Use of Open Fires) Order, 19731972 The Clean Air (Standard) Regulations, 19721971 The Clean Air Act, 1971

2. Method of National Emission Inventory

2.1. General methods

2.1.1. Data sources

Contemporary data of the intensity of Cr-related activities, or P, from 1990 onwards, were mainly

retrieved from national statistics databases (Anti-Pollution Unit, 1971; Singapore Pollution Control

Department, 1986; Singapore Department of Statistics, 2018b) and related company websites.

Historical data of P, e.g., brick production of individual companies, were obtained from an online

archive of newspapers of Singapore (NewspaperSG, 2019) that includes The Strait Times (in its

various guises), TODAY, New Nation, Business Times.

Emission abatement efficiencies, r, were determined from a combination of the national statistical

database (Anti-Pollution Unit, 1971; Singapore Pollution Control Department, 1986; Singapore

Department of Statistics, 2018b), expert consultations (see SM section 2.1.2), and any released

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reports, including newspaper articles, dating to the period immediately following implementation of

a relevant piece of legislation. The latter was implemented to account for differences in levels of

enforcement and the effectiveness of environmental regulations relating to Cr pollution.

2.1.2. Expert consultations

Consultations were carried out with Singapore-based experts who wished to remain anonymous in

any write-up of the research, cited as a personal communication in the manuscript. For the

production subsystem, email and phone interviews were conducted with two authors of technical

reports of relevant Cr-related activities. For the consumption subsystem, three senior managers

(length of service > 25 years) from companies were interviewed in person in terms of the detailed

industrial procedures, pollution control measurements, histories and outlooks of the industry, etc.

Each interview lasted two hours on average. Two site visits were conducted in three companies

forming part of the disposal subsystem, to have a comprehensive understanding of relevant disposal

procedures. The average length of the site-visits was one hour.

2.1.3. Data validation and cross-checks

Data source triangulation (Carter et al., 2014) was conducted to validate the authenticity of the

newspaper-sourced data. For instance, estimates of the total production of conventional bricks,

electricity, total volume of incinerated waste, were compared with the estimated sum of the

production/operation capacities of individual concerns.

2.2. Subsystem 1: Manufacturing of Cr-containing products

2.2.1. Steel manufacturing

Industry introduction and Production (Psteel)

Before the 1960s, steel demands in Singapore were mainly met by import. Local manufacturing

depended on hand-operated re-rolling mills, the production of which was only 2,000 tonnes of steel

bars per year ("Task Ahead," 1964). There were no large-scale steel mills in Singapore until National

Iron and Steel Mills Limited (NISML) commenced in 1964; the output was 48,000 tonnes, using

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electric arc furnaces ("All in step with progress," 1973). Over the years, many other steel mills were

set up in Singapore. For instance, Leong Huat Industries Pte. Ltd and Webforge ("Remarkable growth

in the face of recession in world trade," 1974). The nation-owned NISML, however, was always in a

monopolistic position; its production accounted for 80% of the total steel output of Singapore in the

early 1980s ("Strong balance sheet puts NISM on firm footing," 1983). By 1989, NISML was the only

steel manufacturer remained in Singapore ("National Iron planning Malaysian joint venture," 1989).

Production of steel (Psteel) in Singapore increased from 190 thousand tonnes in 1970 to a maximum

of 764 thousand tonnes in 2008; the production dropped to 596 thousand tonnes in 2017 (see SM

Figure 1) ("National Steel Mills quadruples its spending on hi-tech," 1985; International iron and

steel institute, 2019).

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SM Figure 1 Steel production in Singapore from 1900-2017

Emission factors (EF steelair )

There are many emission factors (EFs) of Cr emissions to the atmosphere from steel manufacturing

process (EF steelair ), ranging from 0.1 g/tonne-steel to 4.5 g/tonne-steel(see SM Table 2). However,

those numbers are only valid with specific dust removal devices. Uncontrolled Cr emissions were

reported as up to 450 g/tonne-steel (Nriagu & Nieboer, 1988). In this paper, for uncontrolled

emissions from steel manufacturing, the EF steelair was set as 225 g/tonne for low emission scenario

(LES) and 450 g/tonne for high emission scenario (HES).

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SM Table 2 Emission factors for atmospheric emission from steel manufacturing

Location Year EF steelair Reference

China 2014 2.3 g/tonne-steel-steel and 4.5 g/tonne (Cheng et al., 2014)Worldwide 2001 4 g/tonne-steel (Pacyna & Pacyna, 2001)Worldwide 1988 4-40 g/tonne-steel (Nriagu & Pacyna, 1988)Worldwide 2006 0.28-16.5 wt.% of steel plant dust (Ma)The US 1988 Uncontrolled: up to 450 g/tonne steel

Controlled with Venturi scrubber: 0.1-9 g/tonne-steelControlled with bag filters: 0.1-4 g/tonne-steelControlled with electrostatic precipitator: 13.5-36.1 g/tonne-steel

(Nriagu & Nieboer, 1988)

This study-LES 225 g/tonne-steel for uncontrolled emissionsThis study-HES 450 g/tonne-steel for uncontrolled emissions

Efficiency of the dust removal device (r)

Cr emissions from steel manufacturing process were reported as exclusively in the form of particles

(Nriagu & Nieboer, 1988). Responding to the new movement of anti-pollution and abided by the

‘Clean Air Act 1971’, in 1970, NISML promised to install equipment to lessen the smoke from the mill

("Getting 'on top of old smokey'," 1970), and the company claimed that there would be “no dust and

no smoke emitted” ("Steel factory leads war on the smog," 1970). Regarding that, the efficiency of

the dust removal devices (r) in this paper was set to steadily increase from 10% in 1971 to 95% in

1980, 95% for 1980-1989, 99% for 1990-1999, and 99.5% from 2000 onwards.

Main calculation methods (E steelair )

E steelair =EF steel

air × P steel×(1−r) Equation 1

2.2.2. Conventional Brick manufacturing

Industry introduction and Production (Pbrick)

Conventional bricks refer to construction bricks that are made from clay with limited heat resistance.

The first modern brickworks, Alexandra brickworks Ltd., was established in 1899 (Labrado &

Alexandra Heritage Tour, 2017). There were many small brickworks in the 1920s; however, rather

rudimentary methods were adopted that depended on cows or buffaloes to step on earth; bricks

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were hand-shaped by workers. The turn-out was between 10,000 and 20,000 bricks each month (Sin

et al., 2015). The industry flourished over the years. Before World War II, there were at least 20 kilns

in Singapore (Zaccheus, 2014). However, during the Japanese occupation (1942 -1945), several local

small brickworks were destroyed ("Bricks Meet Demand in Singapore," 1946); the total brick

production drastically dropped to 22.2 million pieces ("Bricks Meet Demand in Singapore," 1946),

which was at the same level as the initial production of Alexandra brickworks in 1899 (Labrado &

Alexandra Heritage Tour, 2017). After the war, the brick industry revived rapidly due to the demand

from post-war constructions. However, in 1950, high retail prices of local bricks, large numbers of

imported cheaper bricks, and low demand for housing (thus low demand for bricks) heavily

impacted on the local brick industry. There were 14 brickworks in 1956, while only half remained in

1960 ("Big expansion plan for brick works," 1960). Total production of bricks gradually increased in

the following decade and reached 310 million in 1972, 70% of which were contributed by Alexandra

brickworks, the biggest brickworks in Singapore ("Builders run short of bricks, sand," 1972).

However, Alexandra brickworks ceased operation the second year because of land acquisition (Ho,

2016). The total brick production reduced to 98 million in the following year, and Jurong brickworks

became the biggest producer (Sin et al., 2015). In the meantime, the Singapore government also set

up a nation-owned brickworks ("HDB sets up $4.5 million brickworks," 1973). The brick industry

continued expanding in the following decades attributing to the island-wide public housing

construction. The brick production in 1984 reached 473 million pieces ("Building material prices

decline," 1986). In the late 1980s, however, the industry shrank due to rigid air pollution regulations

("Pollution under control here," 1989) and impacts of cheaper imported bricks from neighboring

countries where had less stringent environmental regulations ("Brick makers complain of foreign

threat," 1982). Most of the brickworks ceased operations at the end of 1990s (Sin et al., 2015) and

there was no local bulk production of bricks after 2005 (Kien, 2014) (see SM Figure 2).

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SM Figure 2 Productions of conventional bricks in Singapore from 1900 to 2017

Emission factors (EF brickair )

Emissions of Cr mainly came from fuel burning and clay baking process. Emission factors of Cr

emissions to the atmosphere from conventional brick production (EF brickair ) was reported as

0.0255g-Cr/tonne-brick (United States Environmental Protection Agency, 1997). Many countries

have adopted this EF for inventory analyses, including Australia (Australia Department of

Environment and Energy, 1998), China (Tian et al., 2015) and the UK (Passant et al., 2002). Due

to the lack of relevant experimental data, EF brickair was set as 0.0255 g-Cr /tonne-brick - 20% for

for LES, and 0.0255 g-Cr /tonne-brick +20% for HES.

Efficiency of the atmospheric emission abatement equipment (r)

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SM Figure 3 shows, at least by the end of 1950s, the biggest and the most modernized Alexandra

brickworks was mainly dependent on high chimneys to disperse pollutants. Environmental

pollution had become a significant public concern in the 1980s as residents were suffering from

the soot and dust emitted from smoking chimneys of brickworks; the Environment Ministry

received 137 complaints about pollution from brickworks in 1983 (Anti-Pollution Unit, 1971;

Stricter measures to control pollution from brickworks, 1987). In the early 1980s, a new brick

making technique which hardens bricks by chemicals instead of burning in kilns were introduced

in Singapore. However, not many brickworks adopted the new technique ("Brickmakers prefer

to use old methods to meet shortage," 1981). The Environment Ministry also started to regulate

emissions from brickworks in the early 1980s. However, no significant alleviation was achieved

("Stricter measures to control pollution from brickworks," 1987). In 1987, another regulation

was imposed on these brickworks in Jurong district, urging them to upgrade their equipment,

change fuel types and install smoke meters ("Stricter measures to control pollution from

brickworks," 1987; "Pollution under control here," 1989). However, efficiencies of the pollution

control equipment (r) were not available. In this paper, the efficiency of the pollution control

equipment, including equipment installation rates and effectiveness of environmental policies,

was set as 0% before 1970, 10% from 1970 to 1980, and gradually increasing to 95% from 1981

to 2005.

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SM Figure 3 A painting of Alexandra Brickworks in the late 1950s, Painter: Ng Eng Teng

Main calculation methods

Ebrickair =EF brick

air × Pbrick ×(1−r ) Equation 2

2.2.3. Refractory material manufacturing

Industry introduction and Production (Prefractory)

Refractory materials refer to fire bricks or construction products that are resistant to high

temperature (> 538 °C) (United States Environmental Protection Agency, 1995). These materials are

usually used in furnaces and reaction chamber. Refractory manufacturing in Singapore has the same

length of history as that of conventional brick manufacturing, because the oldest brickworks,

Alexandra brickworks, also produced high-quality fire bricks. However, the production was not on a

large scale. Almost seven decades later, in 1966, fire bricks and other refractory construction

materials were recognized as pioneer products by the Minister of Finance despite its long

manufacturing history in Singapore ("More pioneer products for Singapore," 1966). At the end of

1960s, Singapore was predicted to become more self-sufficient in refractory materials ("Refractory

products from Jurong," 1969); Gob Bee fire-bricks Pte Ltd, one of the major refractory material

manufacturers, had a production capacity of 800 tonnes/month. By 2016, there were at least two

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companies supply refractory materials in Singapore, namely Echelon Engineering Pte Ltd (Echelon

Engineering Pte Ltd, 2018) and NSL Chemicals (NSL Chemicals, 2016). The latter has three

manufacturing factories across Southeast Asia, one of which is in Singapore (Eastech Steel Mill

Services (M) Sdn Bhd). The total output from the three factories is about 50,000 tonnes/year,

consisting of five types of refractory products, all of which contain components of either chrome ore,

magnesia-chrome or chrome-magnesia (NSL Chemicals, 2016). Due to the lack of detailed

production data (Prefractory), we did not consider the refractory production before 1966 in this

calculation. Prefractory from 1966 to 2016 were linearly interpolated based on the production data of

Gob Bee fire-bricks Pte Ltd and Eastech Steel Mill Services (M) Sdn Bhd.

Emission factors (EF refractoryair )

Emissions of Cr happen when processing Cr-containing ore to produce refractory products (United

States Environmental Protection Agency, 1995). Suppose producing one unit of refractory product

needs 1/3 unit of Cr-containing ore. Emission factors of Cr emissions to the atmosphere from

refractory production EF refractoryair was set as 0.035 kg/tonne- chromite-magnesite ore processed for

LES and 0.13 kg/tonne- chromite-magnesite ore processed for HES (United States Environmental

Protection Agency, 1995).

Efficiency of the atmospheric emission abatement equipment (r)

The efficiency of the atmospheric emission abatement equipment over the period from 1966 to

2005 was adopted from those reported in SM Section 2.2.2. For contemporary efficiency,

considering the main pollution control equipment is fiber filter, r of which was reported as 99%

(United States Environmental Protection Agency, 1995). Therefore, in this paper, r was set as 99%

for the period from 2005 to 2017.

Main calculation methods

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Erefractoryair =EFrefractory

air × Prefractory × 13

×(1−r ) Equation 3

2.2.4. Cement manufacturing

Industry introduction and Production (Pcement)

Singapore did not have cement industry until the 1960s, before which cement was all imported. In

1961, the first cement work Hong Leong Co. Ltd was established to serve the growing demand from

constructions of public housing across the country. The cement work had a production of 180,000

tonnes/year ("Singapore's first cement works to open in April," 1961). By 1972, Hong Leong Co. Ltd

was the only cement work in Singapore, and its production could not meet the domestic demand

("Singapore again faces a shortage of cement," 1972). Cement industry increased rapidly in the

1970s. By 1979, there were five factories, namely Jurong cement (500,000 tonnes/year, the biggest),

Asia Cement, Singapore Cement, Ssangyong, and Pan Malaysia cement works. The five plants had an

annum production of 2.5 million tonnes, which significantly surpassed the domestic demands (1.3

million tonnes) ("Better times ahead for cement industry," 1979). Despite the oversupply, cement

production continued to increase and reached 3.1 million tonnes/year in 1983. During the Singapore

financial recession (1985-1986), the price of cement dropped significantly, which made locally

produce cement no longer profitable. The total production of cement decreased to 1.9 million in

1985 ("Cement firms face a tough time this year," 1984). Cement industry in Singapore, however,

was still expanding. The sixth cement work commenced in 1986, which raised the total production

capacity to 5.5 million tonnes. By contrast, local demand for cement dropped to 2 million tonnes

("Cement makers claim they fall prey to dumping," 1986). Due to the high cost of labor and land and

increasingly stringent environmental regulations, the cement industry of Singapore shrank rapidly

and gradually shift away from manufacturing to trading. In 2005, the total production of cement was

150,000 tonnes (Hargreaves, 2013), which was even lower than that in 1961.

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Emission factors (EF cementair )

Emission factors of Cr emissions to the atmosphere from cement production (EF cementair ) were set as

1.0 g/tonne for LES (Cheng et al., 2014) and 2.0 g/tonne for HES (Nriagu & Pacyna, 1988).

Efficiency of the dust removal device (r)

Same as in section 2.2.2.

Main calculation methods

Ecementair =EFcement

air × Pcement ×(1−r ) Equation 4

2.2.5. Petrochemical industry - Cooling tower operations

Industry introduction and consumption (Cwatercirculating)

Cooling towers refer to evaporative cooling systems that remove heat through evaporation

(Singapore Public Utilities Board, 2017). Many industrial plants, such as power plants and

petrochemical plants, install cooling towers for cooling purposes. To prevent corrosion,

hexavalent Cr is usually added to circulated water as corrosion inhibitors (United States

Environmental Protection Agency, 1989). Singapore has a long history of utilizing cooling towers

for heat removal. In 1916, a 15-foot cooling tower was installed in a rubber factory ("Local

Industries," 1916). Singapore also hosted the largest cooling tower manufacturer (Marley

cooling tower) and the main distributor (Boustead Engineering) in Southeast Asia ("Trade Talk,"

1983). A poorly designed cooling tower emits hexavalent Cr- and bacteria-containing water

aerosol. The latter could cause infection of Legionnaires, which is a disease with a high mortality

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rate. In the 1990s, with the wide application of cooling towers, the infections of Legionnaires

increased in Singapore (Veloo, 1992; Nadarajah, 1997).

Hexavalent Cr emissions from cooling towers are associated with the total amount of water

circulating in the cooling system (Cwatercirculating). The total water consumption is proportional to the

quantity of processed oil: 1.5 barrels of freshwater is needed for processing one barrel of crude

oil; 80%-90% of the water is consumed in cooling systems (Henderson, 2016). Data on the

quantity of processed oil in Singapore were adopted from an online database (BP, 2018). SM

Figure 4 shows the water consumption from cooling systems. The water consumption rose

rapidly in the 1970s and had increased steadily in the following four decades, except a plunge in

1998 resulting from the global economic crisis. The water consumption reached 110 million

cubic meters in 2017.

Water consumption of a cooling tower consists of three parts: 1) evaporation loss 2) drift (loss of

droplets of water carried by air) 3) blowdown or bleed off (removed concentrated circulating

water) (Singapore Public Utilities Board, 2017). Evaporation loss (Pwater evap) is associated with a

temperature difference between inlet and outlet and is also dependent on meteorological

factors, such as wind and related humidity. Considering the high humidity (mean 85%) weather

of Singapore, evaporation loss from cooling towers before 1990 was estimated as 0.85% and 1%

of total circulated water for LES and HES, respectively ("Cooling towers that are light, compact,"

1976); from 1990 onward the evaporation loss was set as 0.65% and 0.85% of total circulated

water for LES and HES, respectively (CHECALC, 2016).

The volume of blowdown (Pwater blowd) is dependent on the amount of Pwater evap

and the number of

cycles of concentration (COC). The latter represents the number of times that water circulates

within a cooling system before discharge as blowdown (Singapore Public Utilities Board, 2017).

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The higher COC, the more saving on circulated water. Best Practice of Water-saving (Singapore

Public Utilities Board, 2018) recommends that COC should be at least 7 and 10 for portable

water and Newater, respectively. In this paper, from 2015 to 2017, COC was set as 7 and 10 for

LES and HES, respectively. From 2010 to 2015, COC was set as 6 and 8 for LES and HES,

respectively. From 2000 to 2010, COC was set as 5 and 7 for LES and HES, respectively. From

1980 to 2000, COC was set as 4 and 6 for LES and HES, respectively. Before 1980, COC was set as

3 and 5 for LES and HES, respectively. Pblowdown can be thus estimated by Equation 5 (CHECALC,

2016):

Pblowdown=Pwater evap

COC−1Equation 5

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SM Figure 4 Water consumption in cooling system operations in petrochemical plants from 1969 to 2017

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Production of blowdown-LES (m3) Production of blowdown-HES (m3)

SM Figure 5 Production of blowdown from cooling system operations in power plants from 1969 to 2017

Emission factors (EF coolingtowerair )

Hexavalent Cr emissions to the atmosphere from cooling towers mainly come from drift (United

States Board of Public Works, 1995). Water quality of both drift and blowdown are

approximately equal to circulating water in cooling systems (Kunz et al., 1980). In this paper, the

content of hexavalent Cr was set as 15 ppm hexavalent chromium per liter of circulating water

for LES and 20 ppm for HES (Kunz et al., 1980); Evaporated water does not contain any chemicals

(United States Board of Public Works, 1995), thus it is not considered here.

Efficiency of the drift removal device (drift generation rate) (∂)

There was no law to penalize building owners for not maintaining their cooling towers until 2002

when the Singapore government promulgated the Environmental Public Health (Cooling Towers

and Water Fountains) Regulations ("Environmental Public Health Act," 2002). All cooling towers

have since been obligated to run with pollution eliminators.

In the United States, drift loss (∂) from cooling towers that were built before 1970 was 0.1% to

0.2% of total circulated water; for cooling towers that were built after 1970, drift loss was

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reduced to 0.002% to 0.005% (Kunz et al., 1980). In the latest cooling towers technical reference

report from Public Utility Board of Singapore (Singapore Public Utilities Board, 2017), new

towers often have a drift emission of 0.02% of the recirculation rate or less. Modern drift

eliminators can achieve a drift loss of less than 0.002%. In the mid-1990s, there was a global ban

on the use of hexavalent Cr in cooling towers (United States Board of Public Works, 1995). An

interview of a government official confirmed the effective execution of the ban on the use of Cr

in cooling towers in Singapore (Anonymous, personal communication, November 8, 2018).

Considering the promulgation of the Environmental Public Health (Cooling Towers and Water

Fountains) Regulations in 2002 and the increasing premature death from Legionnaires in the

1990s, in this study, ∂ was set as 0.1% and 0.2% for LES and HES, respectively, before 2000.

From 2000 onwards, there were no Cr emissions from cooling towers in Singapore.

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SM Figure 6 Production of drift from cooling system operations in petrochemical plants

Main calculation methods

Ecoolingtowerair =EFcoolingtower

air ×Cwater circulating× ∂ Equation 6

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2.3. Subsystem 2: Consumption of Cr-containing products

2.3.1. Inland transportation – Fossil fuel combustion and tire worn

Industry introduction and consumption (C fuelcar and C tyrecar

)

Inland transportation refers to four-wheel private and public transportation. Emissions from

inland transportation consist of two parts, fossil fuel combustion and tire worn. Both types of

emissions are dependent on the number of vehicles. In 1915, the number of cars (N car) in

Singapore was 840 ("Growth of Motor Traffic," 1917). In the past century, the car numbers in

Singapore had an average increasing rate of 7% per year (see SM Figure 7), especially after

World War II ("The 60,000 mark" 1960; "Number of car trebles in 10 years" 1963). The number

of cars reached 578,233 in 2016 (Energy Market Authority, 2017).

Transportation-related fossil fuel consumption was 8000 barrels of oil (with 178,767 cars) in the

1970s("Singapore's oil pipelines," 1977), which is equal to a fuel consumption per car (α ) of 2.22

tonne of oil equivalent (toe). α reached 4.26 toe/car in 2015 (Energy Market Authority, 2017).

Total fuel combustion by car (C fuelcar) was estimated by Equation 7 (SM Figure 8). Tire worn per

kilometer traveled (∂) was set as 80 mg-tire/km (Samaras et al., 2005) and travel distance per

liter petrol (δ ) was set as 10 km/L (Land Transport Authority, 2009). Tyre-worn from cars (C tyrecar)

was estimated by Equation 8.

C fuelcar=N car × α Equation 7

C tyrecar=C fuelcar

× ∂× δ Equation 8

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SM Figure 7 Numbers of cars in Singapore from 1917 to 2017

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Traffic related patroleum consumption (toe) Tyre worn (kg)

SM Figure 8 Transportation-related petroleum consumption and related tire-worn in Singapore from 1917 to 2017

Emission factors (EF fuelair ∧EFtyre

air )

The EFs of total Cr emissions to the atmosphere from fossil fuel consumption by transportation

were set as 5.6 ug/kg for LES and 7.4 ug/kg for HES, respectively (Pulles et al., 2012). The EFs of

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total Cr emissions to the atmosphere from tire worn were set as 0.4 mg/kg for LES and 6.73

mg/kg factor for HES, respectively (Samaras et al., 2005).

Efficiency of the dust removal device (r)

In the early 1960s, motor vehicles (168,110 cars) discharged about 103,000 tonnes of various

pollutants to the atmosphere ("'Air pollution will worsen' warning," 1971). To control traffic

pollution, from 1972 onward, all new cars were required to install crankcase emission control

devices, which could reduce emissions by 30% ("Nature's defences help Singapore," 1972). In

this paper, the vehicle scrappage rate in Singapore was set at 10% per year (Singapore Land

Transport Authority, 2019). Therefore, all cars that were registered before 1971 were scrapped

by 1981, all cars that registered after 1981 had installed with the emission control devices.

Main calculation methods

Ecarair =EF fuel

air ×C fuelcar×r+EF tyre

air ×C tyrecarEquation 9

2.3.2. Power generation- Fossil fuel combustions

Industry introduction and production (C fuelcoal , C fuel

oil ∧C fuelgas)

Emissions from power plants come from combustions of fossil fuels and solid wastes. The former

includes coal, fuel oil, and natural gas. The consumptions of fossil fuels (C fuelcoal , C fuel

oil ∧C fuelgas) were

estimated from the generated electricity (Pelectricity). In Singapore, electricity was first available at

the beginning of the 20th century; Municipal Commissioners, Singapore Tramways Company's

generation station in Mackenzie Road was the first company to supply electricity to the city from

1905 to 1924 ("The Electricity Supply" 1927). In 1924, the first official power station, St. James

power plant, started operations and generated 30,000,000 units (kwh) per year ("The Men Who

Lighten Our Darkness," 1933). With steady population growth, electricity generation increased

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by an average growth rate of 11% per year. The speed, however, slightly slowed downed over

the past four decades with an average rate of 6% per year (Singapore Department of Statistics,

2018a). In 2017, there were seven power generation plants in Singapore (except waste-to-

energy (WTE) plants) (Energy Market Authority, 2018). The total capacity of electricity

generation increased from 2 megawatts (MW) in 1926 ("The Electricity Supply," 1927) to 13,355

MW in 2017 (Energy Market Authority, 2018). Data of Pelectricity from 1971 onwards are from

Singapore Energy Statistics (Singapore Department of Statistics, 2018a). Data before 1971 were

estimated based on the correlation coefficient (β) between Pelectricity and electricity consumption

(C electricity) using Equation 10 (International Energy Agency, 2014; Singapore Department of

Statistics, 2018a), which has been reported back to 1931 ("Municipality of Singapore," 1931).

Pelectricity=Celectricity × β Equation 10

190519121919192619331940194719541961196819751982198919962003201020170

10,000,000,000

20,000,000,000

30,000,000,000

40,000,000,000

50,000,000,000

60,000,000,000

0.96

0.98

1.00

1.02

1.04

1.06

1.08

1.10

1.12

Electricity generation Ratio of generation to consumption

Elec

trici

ty g

ener

ation

Elec

trici

ty g

ener

ation

: co

nsum

ption

SM Figure 9 Total amount of electricity generated and the ratio of generated electricity and consumed electricity from

1905 to 2017

The energy structure was drastically changed over the past century (SM Figure 10). The first power

station St. James was powered by coal. With increasing the price of coal, however, all the power

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stations had switched to fuel oil to generate electricity from 1937 onwards, until the early 1990s, the

percentage of fuel oil started to reduce ("The Men Who Lighten Our Darkness," 1933). Aside from

fuel oil, in 1985, WTE plants commenced operation and generated electricity from the combustion of

solid wastes (De Koninck et al., 2017). However, WTE plants never aimed to generate electricity; the

primary purpose is to reduce waste ("Plans for 5th incineration plant for solid waste," 2013). The

electricity generated from WTE has only accounted for a small portion of the total power generation

(around 1- 3%) (De Koninck et al., 2017). In 1992, Singapore started to substitute fuel oil with natural

gas to reduce atmospheric pollution ("Natural gas now makes up 95.5% of fuel mix; renewable

energy on the rise," 2015). The ratios of electricity generated from natural gas (γgas) had since

increased rapidly. In 2004, natural gas became the primary energy source of Singapore (De Koninck

et al., 2017). In 2016, γgas rose to 95.2%, whereas the ratio of electricity generated from fuel oil (γoil)

dropped to 0.7%(Energy Market Authority, 2018). In 2014, Singapore re-started to use coal as one of

the power sources, which accounted for 1.1% of the total generated electricity (Energy Market

Authority, 2018). The electricity generated from coal (Pelectricitycoal ), fuel oil (Pelectricity

oil ) and natural gas (

Pelectricitygas ) over the past century can be estimated by Equation 11-13.

Pelectricitycoal =Pelectricity × γcoal Equation 11

Pelectricityoil =Pelectricity × γoil Equation 12

Pelectricitygas =Pelectricity × γ gas Equation 13

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201720112005199919931987198119751969196319571951194519391933192719211915190919030%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Coal % Oil % Gas % WTE%

SM Figure 10 Energy structure of Singapore from 1905 to 2017

Different types of fuel have different energy densities. One short ton of coal has an energy density of

26.57×109 J (∂coal); one barrel of crude oil has an energy density of 41.87×109 J (∂oil); 1000 ft3 of

natural gas has an energy density of 1.055×109 J (∂gas) (Bodansky, 1991). Fuel consumption is also

dependent on power plant thermal efficiency (α ). St. James power plant had a α of 16.8% for coal

combustion ("The Men Who Lighten Our Darkness," 1933). Nowadays, modern power plants can

reach an average α of 33.2% (Bodansky, 1991). Therefore, the total amount of coal (C fuelcoal), fuel oil (

C fueloil ) and natural gas (C fuel

gas) that used for electricity generation can be estimated by Equations 14-

16.

C fuelcoal=

Pelectricitycoal

α × ∂coal

Equation 14

C fueloil =

Pelectricityoil

α ×∂oil

Equation 15

C fuelgas=

Pelectricitygas

α × ∂gas

Equation 16

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201720102003199619891982197519681961195419471940193319261919191219050

50,000

100,000

150,000

200,000

250,000

300,000

350,000

400,000

Co

nsu

mp

tio

n o

f co

al (

t)

SM Figure 11 Coal consumption for power generation in Singapore from 1905 to 2016

201720102003199619891982197519681961195419471940193319261919191219050

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

8,000,000

Co

nsu

mp

tio

n o

f fu

el o

il (t

)

SM Figure 12 Petroleum consumption for power generation in Singapore from 1905 to 2016

201720102003199619891982197519681961195419471940193319261919191219050

50000000000

100000000000

150000000000

200000000000

250000000000

300000000000

Co

nsu

mp

tio

n o

f n

atu

ral g

as (

ft3

)

SM Figure 13 Natural gas consumption for power generation in Singapore from 1905 to 2016

Emission factors (EF coalair , EFoil

air∧EF gasair )

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EFs of total Cr emissions to the atmosphere from coal combustion (EF coalair ) was set as 1.7g/tonne

for LES(Pacyna & Pacyna, 2001) and 7.7 ppm for HES (Belkin et al., 2009); EFs for heavy fuel oil

were set as 1.4 mg/GJ for LES, and 5.5 mg/GJ for HES; EFs for natural gas combustion were set as

0.2 mg/GJ for LES, and 2 mg/GJ for HES(Nielsen et al., 2013).

Efficiency of the dust removal device (r)

According to interviews with local power plant managers (Anonymous, personal communication,

November 15, 2018), there is no adoption of any dust removal devices for natural gas

combustion. For fuel oil combustion, electrostatic precipitators were equipped to capture dust

with an efficiency of 80%-90% (90% is the design efficiency; nonetheless the actual operation

efficiency was usually lower than that) and flue-gas desulfurization (FGD) was installed to absorb

SO2, which is also efficient in reducing dust with around 90% of efficiency. These two dust

removal devices work in tandem; the efficiency of the whole dust removal system thus could be

98%-99%. Before 1970, there was no evidence that those old power stations installed pollution

reduction devices (Singapore Public Utilities Board, 1965, 1970). Therefore, the efficiency was

set as zero before 1970.

Main calculation methods

Epowerplant fuel

air =(EF coalair × C fuel

coal+EF oilair × C fuel

oil +EF gasair ×C fuel

gas )×(1−r) Equation 17

2.4. Subsystem 3: Disposal of Cr-containing wastes

2.4.1. Solid Waste treatment

Industry introduction and disposed of wastes (Dincinerated and Dlandfilled)

With rising GDP, per capita generation of municipal solid waste in Singapore increased from 0.22

kg/cap in 1900 (estimated from the low-income country (World Bank, 2016) to 1.37 kg/cap in

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2017 (Singapore National Environment Agency, 2019). The increase eventually leads to a rapid

rise in the total production of solid waste (Psolidwaste) (SM Figure 14). Before 1980, solid waste

grew with an average rate of 4% per year. From 1980 onwards, the rate increased to 6% per

year. Psolidwaste in 2017 was 7.7 million tonnes (Singapore National Environment Agency, 2019),

which is seven times that of the level in 1980 and 161 times that of the level in 1900.

In 1900, there was only one incineration plant, Jalan Besar incinerator, which had a capacity (CP

) of 29,700 tonnes per year ("Smells at Government House," 1900). In the following six decades,

there existed three more incinerators in Singapore, namely Alexandra incinerator (1911-1932),

Serangoon Incinerator and Kolam Ayer incinerator (1932-1959) ("Destroying Refuse," 1911; "It

All Ends In Smoke," 1936). These incinerators mainly incinerated refuse of households, garbage

of the streets, and rotten carcasses ("Destroying Refuse," 1911). Due to high operation cost

($250,000 a year for Kolam Ayer incinerator) compared with landfill, all the incinerators ceased

operations before 1959. The colonial government considered that the 40 acres of Kolam Ayer

Basin would fill up in five years and could thus be turned to a building area, which was

profitable. In the meantime, the government was promoting a low-cost type of incinerator,

placed next to trash bin centers to reduce refuse volume locally ("'Keep clean' drivein

Singapore," 1959). Another reason for abandoning incinerators is that there was no matured

atmospheric pollution control technique for clean incineration ("Machines to join battle against

trash in S'pore," 1971). Therefore, from 1960 to 1978, all collected solid wastes were locally

burned and/or landfilled. By the end of the 1970s, however, Singapore was running out of

swamp areas to dump refuse ("$50m set aside for a central refuse complex," 1972). In 1979,

after almost 20 years, a new incinerator, Ulu Pandan Incinerator (1979-2009, capacity of 584,000

t/yr), was set up on Toh Tuck Road ("Mr. Lim will open Ulu Pandan Plant today," 1979). By 2017,

there were four incinerators in Singapore, operating with a total CP of 2.8 million tonnes

(Singapore National Environment Agency, 2017a; Keppel Seghers, 2018).

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The total amount of incinerated waste (Dincinerated) is dependent on solid waste collection rate (δ

) and solid waste recycling rate (∂). In the 1930s, only the town center had the solid waste

collection; the δ was only 35%, the remainder was directly disposed to dumping grounds

("Singapore's Economic Progress Remains Steady," 1933). After years of slowly increase, δ

reached 47% in 1976 and rapidly raised to 96% by 1986. The uncollected wastes, including

unburnable wastes and chemical refuse, were still dumped at two sites: Near Tampines in the

north-east and at the end of Lim Chu Kang Road in the north-west ("So you think it's just a lot of

rubbish," 1980). Due to the large volume of solid wastes, after 1986, the government started

promoting waste recycling, especially for industrial wastes. The waste recycling rate (∂) had

increased from 0% in 1986 ("Putting more rubbish to good use," 1986; "Singapore may need to

recycle more waste," 1989) to 61% in 2017(Singapore National Environment Agency, 2017b).

The total amount of collected and unrecyclable solid wastes (DSW ) were estimated by Equation

18. Parts of DSW were burned in incinerators (Dincinerated, see Equation 19), whereas those

exceeded the total CP of incinerators were directly landfilled (Dlandfilled, not including burning

bottom ashes, see Equation 20). Dincinerated was 8,800 tonnes in 1900. The amount increased to

2.88 million tonnes in 2017. The direct landfilled wastes Dlandfilled was peaked in 1977 with

almost 1.3 million tonnes, and gradually reduced to 96,500 tonnes in 2017, attributing to the

increasing recycling rate and incineration capacities.

DSW =Psolidwaste × δ ×(1−∂) Equation 18

Dincinerated={DSW ,∧DSW <CPCP ,∧DSW ≥ CP Equation 19

Dlandfilled={ 0 ,∧DSW<CPD SW−CP ,∧D SW ≥ CP

Equation 20

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190019061912191819241930193619421948195419601966197219781984199019962002200820140

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

8,000,000

9,000,000

0%

20%

40%

60%

80%

100%

120%

Collected waste (t) Uncollected waste (t) Recycling rate % Collection rate %

SM Figure 14 Total generated solid wastes (Psolidwaste), collection rates (δ ) and recycling rates (∂) from 1900 to 2017

201720112005199919931987198119751969196319571951194519391933192719211915190919030

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

3,500,000

4,000,000

Total disposed wastes (t) Total incineration capacity (t)

SM Figure 15 Total amount of safely disposed wastes (DSW ) and capacities of incinerators (CPincinerator) from 1900 to

2017

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201720112005199919931987198119751969196319571951194519391933192719211915190919030

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

3,500,000

Incinerated solid waste(t) Direct landfilled solid waste(t)

SM Figure 16 Total amount of incinerated solid wastes (Dincinerated) and landfilled solid wastes (Dlandfilled) from 1900-

2017

Emission factors (EF flyashair )

SM Table 3 Productions and emission factors of fly ash

Location YearFly ash production

(β flyash)Cr content of

fly ash (EF flyashair ) Reference

Singapore 1991 0.01% of the total weight

(Tay & Goh, 1991)

Singapore 1993 0.023% (Goh & Tay, 1993)

Singapore 1990 0.03% by weight (Hwa, 1991)

Singapore 1997 670 mg/kg (Tan et al., 1997)

Singapore 247 ppm (37 ppm – 651 ppm)

(Bradl, 2005)

The United States 10-30 kg/tonne of feed waste

From 140 mg/kg to 530 mg/kg

(Kalogirou et al., 2010)

This study- LES 10 kg/tonne 0.01%This study- HES 30 kg/tonne 0.03%

Efficiencies of the emission reduction devices (r) and recycling rate of incineration ash (∂)

Before 1971, Singapore did not have adequate legislation and techniques for regulating atmosphere

pollution (Oon & Saparudin, 2014). Therefore, in this paper, r of emission reduction devices was set

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499

to zero before 1959. In 1979, the new incinerator installed electrostatic precipitator units to

minimize dust emissions to abide by the Clean Air Act 1971. r of the dust removal device was 99.5%

("Mr. Lim will open Ulu Pandan Plant today," 1979). Therefore, we set the efficiency as 99.5% for the

period from 1979 to 2018.

According to the Singapore National Environment Agency (2018), the recycling rate of incineration

ash (∂) had gradually increased from 7% in 2013 to 13% in 2016. Before 2013, ∂ was set to be equal

to zero.

Main calculation methods

E solidwasteair =Dincinerated× β flyash × EF flyash

air ×(1−r) Equation 21

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3. Method of Econometric Analysis

3.1. Data preparation and analysis procedure

Estimates of foreign direct investment for the period 1950-1970 were based on the quadratic

polynomial correlation between foreign direct investment and gross domestic product per capita

using data from 1970-2017 (R2=0.91). The extrapolation was conducted with three considerations: 1)

the close relationship between foreign direct investment and gross domestic product per capita can

guarantee a reasonable prediction (Chowdhury & Mavrotas, 2006). 2) This extrapolated period

covers the period before and after the independence of Singapore (1965). 3) A significant economic

improvement in the mid-1960s was witnessed in the rapid growth rate of gross domestic product

per capita and in the substantial increase in foreign-invested pioneer firms that set up in Singapore

(29 in 1963 and 111 in 1966) (Hughes & Seng, 1969).

In this study, the decision-making route for econometric analysis was chosen as follows (SM Figure

17): Step 1, test stationarities of all variables (result: all variables are stationary at first differences).

Step 2, test cointegration relationships (result: cointegration relationships exist among variables).

Step 3, run Vector Error Correction Model to test long-run and short-run relationships among

variables (result: manuscript Table 2). Step 4, run diagnostic tests for the model (result: passed all

diagnostic tests).

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SM Figure 17 Economistic analysis decision making procedure.

3.2. Unit root test

The Augmented Dickey-Fuller test checks unit root in time-series under three types of models (SM

Table 4). Null hypothesis (H0) is that the tested time series is stationary, ρ=1; H1 is that the series is

nonstationary,ρ < 1.

SM Table 4 Three types of models used in the unit root test

Type of model Equation Augmented Dickey-Fuller No intercept no trend y t=ρy t−1+μt

μt N (0 , σ2 ) ∆ y t=(ρ−1) yt−1+∑i=1

n

∂i ∆ y t−i+μt

With intercept but no trend:

y t=a+ ρyt−1+μt

μt N (0 , σ2 ) ∆ y t=a+(ρ−1) y t−1+∑i=1

n

∂i∆ y t−i+μ t

With intercept and trend y t=a+ ρyt−1+γt+μ t

μt N (0 , σ2 ) ∆ y t=a+(ρ−1) y t−1+∑i=1

n

∂i∆ y t−i+γt+μt

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534

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538

In this study, y = CR, GDP, GDP2, FDI, IE, and ER, respectively;ρ∧∂i= coefficients of the lagged term

of y; a=intercept ;∆ y t=yt - yt-1 ; n = lags included in the unit root test, for annual data as used in

this study, n=2 was adopted (Bhaumik, 2015).

If the probability of ρ=1 is smaller (larger) than the chosen level of statistical significance (P<0.05),

then reject (accept) H0, and accept (reject) H1 that the series is nonstationary.

One anonymous reviewer suggested that we should consider structural breaks in unit root test.

Therefore, we also conducted Zivot-Andrews unit root test (SM Table 5).

SM Table 5 Three models used in the Zivot-Andrews unit root test

Type of model Equation DenoteIntercept

∆ y t=c+αy t−1+ϵ t+γ DI t+∑i=1

n

∂i ∆ y t−i+μt

μt N (0 , σ2 )

D is a dummy variable that is used to represent the structural shift at a possible break-date. It only has two values,

DI t={0 , if t<breakdate1 , otherwise

DT t={ 0 ,if t <breakdatet−breakdate , otherwise

Trend∆ y t=c+αy t−1+ϵ t+θ DT t +∑

i=1

n

∂i ∆ y t−i+μt

μt N (0 , σ2 )With intercept

and trend ∆ y t=c+αy t−1+ϵ t+γ DI t+θ DT t+∑i=1

n

∂i ∆ y t −i+μ t

μt N (0 , σ2 )

3.3. Akaike Information Criterion, Schwarz Information Criterion and Final Prediction Error for

optimal lag selection

Akaike information criterion (AIC), Schwarz information criterion (SIC) and Final Prediction Error

(FPE) (SM Table 6) were all adopted to estimate the optimal number of lags (regressors) in this study.

The number of optimal lags is confirmed when the residual sum of squares (RSS) is the smallest. To

achieve the aim, including more regressors will significantly reduce the RSS. However, problems of

overfitting and compromising the degree of freedom might also emerge. Both AIC and SIC criterions

include a penalty term to balance the increasing number of regressors.

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SM Table 6 Equations for Akaike information criterion (AIC), Schwarz information criterion (SIC) and Final Prediction Error (FPE)

Criterion Equation after natural log transformation

AICAIC=2k

n+¿(∑ ui

2

n)

SICSIC= k

n∈n+¿(∑ ui

2

n)

FPEFPE=ui

2 (n+k )(n−k )

where, n = number of observations, in this study n= 68; k = number of lags (regressors); u=RSS ; 2kn

and kn∈n are the penalty terms of AIC and SIC, respectively. The smallest statistics of each criterion

indicates the selected optimal lag.

3.4. Johansen Cointegration Test

Cointegration exists when there are common trends among time-series variables. Cointegration rank

(r) is the number of common trends that exist among the time-series variables. With n variables, a

maximum of n-1 cointegration rank can exist to link those variables in a dynamic system. If r≠0, then

confirms the existence of cointegration relationship(s).

Two likelihood ratio (LR) tests, Maximum Eigenvalue statistic tests (Equation 22) and trace tests

(Equation 23), were adopted to test the null hypothesis to determine the cointegration rank

(Lüutkepohl et al., 2001). The first step involves a test of the null hypothesis H0, r=0, against H1, r=1.

If the p-value is larger than the chosen level of significance, then accept H0 and confirm there is no

cointegration relationship among time-series variables. Otherwise, if p-value shows the rank is

significantly different from H0, then reject H0 and accept H1 and confirm the existence of one

cointegration relationship, and continue to test a new H0 , r=1 against a new H1 , r=2. The process

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continues until the first time when H0 cannot be rejected, then the value of r can be determined

(Johansen & Juselius, 1990).

LRmaximum (r )=−T log (1−γr+1) Equation 22

LRtrace (r )=−T ∑i=r+1

n

log (1−γ i¿)¿ Equation 23

where, T is the number of observations; γi is the maximum eigenvalue.

3.5. Vector Error Correction Model (VECM)

Equation 24-28 listed short-run relationships of non-dummy variables:

∆ CRt=θ1+∑i=1

n

δ11i ∆ CRt−i+∑i=0

n

δ12 i∆ GDP t−i+∑i=0

n

δ 13i ∆ GDP2t−i+∑i=0

n

δ14 i ∆ FDI t−i+∑i=0

n

δ 15i ∆ IE t−i+δ 16i ERt+δ17D t+φ0ect t−1+μ1 t

Equation 24

∆ GDP t=θ2+∑i=1

n

δ21 i ∆ CRt−i+∑i=0

n

δ 22i ∆ GDPt−i+∑i=0

n

δ23 i ∆ GDP2t−i+∑i=0

n

δ 24 i ∆ FDI t−i+∑i=0

n

δ 25i ∆ IEt−i+δ26 i ERt+δ 27Dt +φ1 ect t−1+μ2 t

Equation 25

∆ GDP2t=θ3+∑i=1

n

δ31 i∆ CRt−i+∑i=0

n

δ32 i ∆ GDPt−i+∑i=0

n

δ33 i ∆GDP2t−i+∑i =0

n

δ34 i ∆ FDI t−i+∑i=0

n

δ35 i ∆ IE t−i+δ36 i ERt+δ37 Dt+φ2ectt−1+μ3t

Equation 26

∆ FDI t=θ4+∑i=1

n

δ 41i ∆ CRt−i+∑i=0

n

δ42 i ∆ GDPt−i+∑i=0

n

δ43 i ∆ GDP2t−i+∑i=0

n

δ 44 i ∆ FDI t−i+∑i=0

n

δ 45 i∆ IE t−i+δ 46 i ERt +δ 47Dt+φ3 ect t−1+μ4 t

Equation 27

∆ IEt=θ5+∑i=1

n

δ 51i ∆ CRt−i+∑i=0

n

δ52 i∆ GDP t−i+∑i=0

n

δ 53i ∆ GDP2t−i+∑i=0

n

δ54 i ∆ FDI t−i+∑i=0

n

δ 55i ∆ IE t−i+δ 56i ERt+δ57D t+φ4 ect t−1+μ5 t

Equation 28

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where, ∆= deviation or first difference operator; n= optimal lag number; φ0~φ4 = error-correction

coefficients; θ1 θ5 = constant terms; δ 11i δ57 i = short-run coefficients; μ1 t μ5 t= error terms.

3.6. Granger causality test

Granger causality test measures the direction of short-run relationships through comparing the RSS

of a regression of a variable (y) with its own past (yt-1, yt-2,… yt-i) (denoted RSSR) with the RSS of a

regression of a variable with its own past and another variable’s past (xt-1, xt-2,…) (denoted RSSU). If

including the lagged terms of other variables significantly improves the regression outcome, then it

confirms that x granger causes y. The test consists of three steps (Asteriou & Hall, 2015):

First, calculate the RSS for individual time-series variables in a model only contains the lagged terms

of each variable itself.

y t=a+∑i=1

n

γi y t−i+μt Equation 29

where, y= CR, GDP, GDP2, FDI, IE, and ER; a= constant term; n= number of lags, in this case, n=3; μt=

white noise. The obtained RSSs ware denoted as RSSR-CR, RSSR-GDP, RSSR-GDP2, RSSR-FDI, RSSR-IE, RSSR-ER, and

RSSR-D.

Second, calculate the RSS for each time-series variable in a model contains the lagged terms of each

variable and lagged terms of another variable.

y t=a+∑i=1

n

γi y t−i+¿∑i=1

n

∂i x t−i+μt ¿ Equation 30

where, if y = CR, then x=GDP, GDP2, FDI, IE, ER, and D, respectively; if y= GDP, then x= CR, GDP,

GDP2, FDI, IE, ER, and D respectively, etc. Each pair of variables is examined; the obtained RSSs are

denoted as RSSU-CR-GDP, RSSU-CR-GDP… , and RSSU-ER-D.

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Third, the null hypothesis H0 : x does not granger-cause y; H1 : x granger causes y. Therefore,

calculate the F-statistics of each pair of RSSR and RSSU , e.g. RSSR−CR with RSSU−CR−GDP.

F=( RSSR−RSSU )/m

RSSU /(n−k )Equation 31

where, m= number of lagged terms of x, in Eviews, m = n, and k = n+m. If the F test statistic is larger

(smaller) than the critical value, then reject (accept) the H0, and accept (reject) H1 that x (does not)

granger causes y.

3.7. Breusch-Godfrey Serial Correlation Lagrange Multiplier (LM) Test

The Breusch-Godfrey Serial Correlation LM Test includes three steps:

First, estimate the residuals of ect t, denoted μt, and the goodness-of-fit R2 the long-run relationship

based on Ordinary Least Squares estimation procedure.

Second, regress μt with its lagged terms.

μt=∑i=1

p

γi μ t−i+ϵ t Equation 32

where γi= regression coefficients; ϵ t= white noise term. Null hypothesis, H0: there is no serial

correlation,γ1=γ2=…=γ p=0, thusμthas no relationship with its lagged terms; H1: not all

regression coefficients are equal to zero.

Third, test the null hypothesis using the chi-square method.

chisquare=(n−p )× R2 Equation 33

where, n= number of observations. When the value of chi-square is larger (smaller) than the critical

chi-square value at the chosen level of significance, reject (accept) H0, and accept (reject) H1 that

there exists serial correlation.

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3.8. Breusch-Pagan-Godfrey test for heteroskedasticity

Similar to the Breusch-Godfrey Serial Correlation LM Test, the heteroskedasticity test consists of

three steps:

First, estimate the residuals of ect t, denoted μt, based on the Ordinary Least Squares method.

Second, use Breusch-Pagan-Godfrey to formulate an artificial regression for μt squared (Equation

37). Calculate the goodness-of-fit R2 of artificial regression. H0: heteroskedasticity is not present, and

H1: heteroskedasticity is present.

μt2=β1GDPt+β2GDP2t+ β3 FDI t+β4 IEt +β5ERt+ β6 Dt+α0+ectt Equation 36

Third, test the null hypothesis using the chi-square method:

chisquare=N × R2 Equation 37

where, N = number of observations. The calculated chi-square has a chi-square distribution with S-1

degrees of freedom. If the estimated value of chi-square is larger (smaller) than the critical value of

chi-square with S-1 degrees of freedom, reject (accept) H0, and accept (reject) H1 that

heteroskedasticity is present.

4. Results

4.1. Results of national emission inventory analysis

4.1.1. Steel manufacturing

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201720112005199919931987198119751969196319571951194519391933192719211915190919030

10000

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50000

60000

70000

80000

90000

Total Cr emissions to air-LES (kg) Total Cr emissions to air-HES (kg)

SM Figure 18 Total Cr emissions to the atmosphere from steel manufacturing

4.1.2. Conventional Brick manufacturing

201720112005199919931987198119751969196319571951194519391933192719211915190919030

10

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Total Cr emissions to air-LES (kg ) Total Cr emission to air-HES (kg)

SM Figure 19 Total Cr emissions to the atmosphere from conventional brick manufacturing

4.1.3. Refractory material manufacturing

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Total Cr emissions to air-LES (kg) Total Cr emissions to air-HES (kg)

SM Figure 20 Total Cr emissions to the atmosphere from refractory material manufacturing

4.1.4. Cement manufacturing

201720112005199919931987198119751969196319571951194519391933192719211915190919030

1,000

2,000

3,000

4,000

5,000

6,000

Total Cr emissions to air-LES (kg) Total Cr emissions to air-HES (kg)

SM Figure 21 Total Cr emissions to the atmosphere from cement production

4.1.5. Petrochemical industry - Cooling tower operations

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201720

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19731971

19690

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Cr VI drift from cooling tower (kg) - LES Cr VI drift from cooling tower (kg) - HES

SM Figure 22 Hexavalent Cr emissions to the atmosphere (through drift) from cooling system operations in petrochemical

plants

4.1.6. Inland transportation – Fossil fuel combustion and tire worn

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Total Cr emissions to air by fuel-LES (kg) Total Cr emissions to air by fuel-HES (kg)

SM Figure 23 Total Cr emissions to the atmosphere from inland transportation in Singapore

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201320082003199819931988198319781973196819631958195319481943193819331928192319180

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Total Cr emissions to air by tyre-LES (kg) Total Cr emissions to air by tyre-HES (kg)

SM Figure 24 Total Cr emissions to the atmosphere from car tyre-worn in Singapore

4.1.7. Power generation- Fossil fuel combustions

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Total Cr emissions to air-LES (kg) Total Cr emissions to air-HES (kg)

SM Figure 25 Total Cr emissions to the atmosphere from fossil fuel combustion for power generation

4.1.8. Solid Waste treatment

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Total Cr emissions to air-LES (kg) Total Cr emissions to air-HES (kg)

SM Figure 26 Total Cr emissions to the atmosphere from centralized combustion of solid wastes

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4.2. Results of Econometric analysis

4.2.1. Unit root test

SM Table 7 Results of the Augmented Dickey-Fuller Test for Unit Root for each time-series variable except dummy variables

Variable Abbreviation

None Intercept Trend and InterceptLevel First

differenceSecond

differenceLevel First

differenceSecond

differenceLevel First

differenceSecond

difference

CR 0.2713

0.0000** 0.0000** 0.0797

0.0000** 0.0000** 0.1029 0.0000** 0.0000**

GDP 1.0000

0.0000** 0.0000** 0.9999

0.0000** 0.0000** 0.9060 0.0000** 0.0000**

GDP2 0.9994

0.0075** 0.0322** 0.9999

0.0000** 0.0000** 0.9928 0.0054** 0.0000**

FDI 1.0000

0.0000** 0.0000** 0.9996

0.0000** 0.0000** 0.9866 0.0000** 0.0000**

IE 0.9948

0.0000** 0.0000** 0.9673

0.0000** 0.0000** 0.3737 0.0000** 0.0000**

Augmented Dickey-Fuller Test, MacKinnon (1996) one-sided p-values. CR: Cr atmospheric emissions per capita; GDP: gross domestic product per capita; GDP2: GDP per capita squared; FDI: Foreign Direct Investment inflow; IE: Trade openness.Level: raw data, first difference: xt-xt-1, second difference: xt-xt-2. * reject the null hypothesis at 0.1 level, ** reject the null hypothesis at 0.05 level.Results show that all variables are stationary at the first difference.

SM Table 8 Results of Zivot-Andrews unit root test. The test includes three models, namely intercept, trend, and intercept and trend. The table reports all the probability values of the three models for data at level and at first differences, and the corresponding breakpoints.

Zivot-Andrews test statistics Models Level Prob. First different

prob. Chosen Breakpoint

CR

Intercept

0.0214** 1964

GDP 0.0083** 2004

GDP2 0.0022** 2006

FDI 0.0002** 2006

IE 0.0125** 2000

CR

Trend

0.1142 0.0013** 1979

GDP 0.0187** 1986

GDP2 0.0002** 2002

FDI 0.0000** 1999

IE 0.0321** 1983

CR

Intercept and trend

0.0003** 1976

GDP 0.0083** 2004

GDP2 0.0749* 1998

FDI 0.0041** 2006

IE 0.1143 0.0120** 2007

Null hypothesis: CR has a unit root with a structural break * reject the null hypothesis at 0.1 level, ** reject the null hypothesis at 0.05 level.

684

685

686

687688689690691692

693

694695696

697698699

SM Table 9 Results of multiple breakpoint test on the dependent variable CR.

Multiple Breakpoint test statistics on CR

(H0 vs H1*)F-statistic (critical value) Chosen Breakpoint

0 vs 1** 26.1520 (8.58) 1981

1 vs 2** 199.0255(10.13) 1964

2 vs 3 6.0381(11.14)* H0 number of breakpoints, H1 number of breakpoints +1;** Significant at the 0.05 level. Critical values are from Bai-Perron (2003).

4.2.2. Optimal lag selection

SM Table 10 Results of Akaike Information Criterion, Schwarz Information Criterion and Final Prediction Error for optimal lag selection

NO. of Lags Final Prediction Error(FPE)

Akaike information

criterion (AIC)

Schwarz information

criterion (SIC)1 8.78E+26 81.89848 83.56537*2 7.54E+26 81.69996 85.033733 9.92E+26 81.84115 86.841794 4.45E+26 80.75806 87.425595 5.74e+25* 78.18618* 86.52059

The lag number is indicated by the smallest statistic of each criterion, denoted by *.

4.2.3. Johansen Cointegration Test

SM Table 11 Results of Johansen Cointegration Test for cointegration relationship among variables

Hypothesized No. of Cointegrating

eqn(s) (r)Trace Statistic Prob.(trace)** Max-Eigen Statistic Prob.( Max-Eigen)**

H0: r=0 * 241.80 0.0000 86.53 0.0000

H0: r≤1 * 155.27 0.0000 65.90 0.0000

H0: r≤2 * 89.36 0.0007 38.28 0.0140

H0: r≤3* 51.08 0.0241 28.80 0.0348

H0: r≤4 22.28 0.2832 13.60 0.3985

* denotes rejection of the H0 hypothesis at the 0.05 level. **MacKinnon-Haug-Michelis (1999) p-values.Trace and Max-Eigen tests both indicates four cointegrating equation at the 0.05 level.

700701

702703704705706

707708

709710

711

712

713714715

716

717

718

719

720

4.2.4. Diagnostic tests

SM Table 12 Results of diagnostic tests for serial correlation and heteroskedasticity

Diagnostic test Null Hypothesis (H0) p-statistics Decision

Breusch-Godfrey Serial Correlation LM Test Exist no serial correlation 0.2024 Do not reject the H0 at the 0.05 level.

No serial correlationHeteroskedasticity Test: Breusch-Pagan-

GodfreyExist no heteroskedasticity 1.000 Do not reject the H0 at the 0.05

level.

No heteroskedasticity

721

722

723

724

725

References

$50m set aside for a central refuse complex. (1972, May 28). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19720328-1.2.52.1?ST=1&AT=filter&K=Singapore+incinerator&KA=Singapore+incinerator&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,incinerator&oref=article

The 60,000 mark. (1960, July 7). The Singapore Free Press. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/freepress19600707-1.2.64?ST=1&AT=search&k=Singapore%20number%20of%20cars&QT=singapore,number,of,cars&oref=article

'Air pollution will worsen' warning. (1971, May 21). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19710521-1.2.122?ST=1&AT=filter&K=air+pollution+control+singapore&KA=air+pollution+control+singapore&DF=&DT=&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&P=2&Display=0&filterS=0&QT=air,pollution,control,singapore&oref=article

All in step with progress. (1973, February 27). New Nation. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/newnation19730227-1.2.62.1?ST=1&AT=filter&K=Singapore+steel+production&KA=Singapore+steel+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,steel,production&oref=article

Anti-Pollution Unit. (1971). Anti Pollution Unit Annual Report -1971-1985. Asteriou, D., & Hall, S. G. (2015). Applied econometrics: Macmillan International Higher Education.Australia Department of Environment and Energy. (1998). Emissions Estimation Technique Manual

for Bricks, Ceramics, & Clay Product Manufacturing. Retrieved from http://www.npi.gov.au/resource/emission-estimation-technique-manual-bricks-ceramics-and-clay-product-manufacturing

Bai, J., & Perron, P. (2003). Critical values for multiple structural change tests. The Econometrics Journal, 6(1), 72-78. doi:10.1111/1368-423x.00102

Belkin, H. E., Tewalt, S. J., Hower, J. C., Stucker, J., & O'Keefe, J. (2009). Geochemistry and petrology of selected coal samples from Sumatra, Kalimantan, Sulawesi, and Papua, Indonesia. International Journal of Coal Geology, 77(3-4), 260-268.

Better times ahead for cement industry. (1979, August 14). New Nation. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/newnation19790814-1.2.77.2?ST=1&AT=filter&K=Singapore+cement+production&KA=Singapore+cement+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,cement,production&oref=article

Bhaumik, S. K. (2015). Principles of Econometrics: A Modern Approach Using EViews: Oxford University Press.

Big expansion plan for brick works. (1960, August 26). The Straits Times, p. 10. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19600826-1.2.106?ST=1&AT=filter&K=Jurong+brick+works&KA=Jurong+brick+works&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=jurong,brick,works&oref=article

Bodansky, D. (1991). The Energy Source Book. New York: American Institute of Physics.BP. (2018). BP Statistical Review of World Energy- Singapore Oil Refinery Capacities.

https://ycharts.com/indicators/singapore_oil_refinery_capacitiesBradl, H. (2005). Heavy Metals in the Environment: Origin, Interaction and Remediation: Elsevier

Science.Brick makers complain of foreign threat. (1982, October 26). Business Times. Retrieved from

http://eresources.nlb.gov.sg/newspapers/Digitised/Article/biztimes19821026-1.2.10?

726

727728729730731732733734735736737738739740741742743744745746747748749750751752753754755756757758759760761762763764765766767768769770771772773774775

ST=1&AT=filter&K=Jurong+brick+works&KA=Jurong+brick+works&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=jurong,brick,works&oref=article

Brick Shortage Holds Up Spore Housing. (1947, January 9). Malaya Tribune. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/maltribune19470109-1.2.23?ST=1&AT=filter&K=singapore+clay+production+bricks&KA=singapore+clay+production+bricks&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=singapore,clay,production,bricks&oref=article

Brickmakers prefer to use old methods to meet shortage. (1981, July 6). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19810706-1.2.107.1.3?ST=1&AT=filter&K=singapore+clay+production+bricks&KA=singapore+clay+production+bricks&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=singapore,clay,production,bricks&oref=article

Bricks Meet Demand in Singapore. (1946, November 11). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19461111-1.2.24?ST=1&AT=filter&K=Alexandra+Brickworks+output&KA=Alexandra+Brickworks+output&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=alexandra,brickworks,output&oref=article

Builders run short of bricks, sand. (1972, February 29). New Nation. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/newnation19720229-1.2.32?ST=1&AT=filter&K=Alexandra+Brickworks+output&KA=Alexandra+Brickworks+output&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=alexandra,brickworks,output&oref=article

Building material prices decline. (1986, March 21). Business Times Singapore. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/biztimes19860321-1.2.12.9?ST=1&AT=filter&K=Brick+production+in+Singapore&KA=Brick+production+in+Singapore&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=biztimes&CT=&WC=&YR=1986&QT=brick,production,in,singapore&oref=article

Carter, N., Bryant-Lukosius, D., DiCenso, A., Blythe, J., & Neville, A. J. (2014). The use of triangulation in qualitative research. Oncology nursing forum, 41(5), 545-547. doi:10.1188/14.ONF.545-547

Cement firms face a tough time this year. (1984, May 28). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19840528-1.2.35.7?ST=1&AT=filter&K=Singapore+cement+production&KA=Singapore+cement+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,cement,production&oref=article

Cement makers claim they fall prey to dumping. (1986, June 5). Business Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/biztimes19860605-1.2.25.2?ST=1&AT=filter&K=Singapore+cement+production+5.5+m&KA=Singapore+cement+production+5.5+m&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=&WC=&YR=1986&QT=singapore,cement,production,55,m&oref=article

CHECALC. (2016). Cooling Tower Makeup Water. Retrieved from https://checalc.com/solved/ctmakeup.html

Cheng, H., Zhou, T., Li, Q., Lu, L., & Lin, C. (2014). Anthropogenic chromium emissions in China from 1990 to 2009. PloS one, 9(2), e87753.

Chowdhury, A., & Mavrotas, G. (2006). FDI and growth: what causes what? World economy, 29(1), 9-19.

Colony's Motor Traffic. (1924, September 17). The Singapore Free Press and Mercantile Advertiser. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/singfreepressb19240917-1.2.22?

776777778779780781782783784785786787788789790791792793794795796797798799800801802803804805806807808809810811812813814815816817818819820821822823824825

ST=1&AT=search&k=Singapore+number+of+cars&P=7&Display=0&filterS=0&QT=singapore,number,of,cars&oref=article

Cooling towers that are light, compact. (1976, April 18). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19760418-1.2.84.9?ST=1&AT=filter&K=cooling+tower+water+consumption+singapore&KA=cooling+tower+water+consumption+singapore&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=cooling,tower,water,consumption,singapore&oref=article

De Koninck, R., Hai, P. T., & Girard, M. (2017). Singapore's Permanent Territorial Revolution: Fifty Years in Fifty Maps: National University of Singapore Press.

Destroying Refuse. (1911, March 1). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19110301-1.2.62?ST=1&AT=search&k=cement%20dust%20eliminate%20Singapore&QT=cement,dust,eliminate,singapore&oref=articlehttp://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19340720-1.2.95?ST=1&AT=filter&K=Alexandra+Road+incinerator&KA=Alexandra+Road+incinerator&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=alexandra,road,incinerator&oref=article

Echelon Engineering Pte Ltd. (2018). Company Profile. Retrieved from https://echelon.sg/The Electricity Supply. (1927, October 20). The Straits Times. Retrieved from

http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19271020.2.54Energy Market Authority. (2017). Singapore Energy Statistics. Retrieved from

https://www.ema.gov.sg/cmsmedia/publications_and_statistics/publications/ses17/publication_singapore_energy_statistics_2017.pdf

Energy Market Authority. (2018). Singapore Energy Statistics. Retrieved from https://www.ema.gov.sg/cmsmedia/Publications_and_Statistics/Publications/SES17/Publication_Singapore_Energy_Statistics_2017.pdf

Environmental Public Health Act, G.N. No. S 37/2001, Environmental Public Health (Cooling Towers and Water Fountains) Regulations § 133, Chapter 95 Stat. (2002 31st Jan 2002).

Getting 'on top of old smokey'. (1970, April 23). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19700423-1.2.90?ST=1&AT=filter&K=air+pollution+control+singapore&KA=air+pollution+control+singapore&DF=&DT=&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&P=2&Display=0&filterS=0&QT=air,pollution,control,singapore&oref=article

Goh, A. T., & Tay, J.-H. (1993). Municipal solid-waste incinerator fly ash for geotechnical applications. Journal of Geotechnical Engineering, 119(5), 811-825.

Growth of Motor Traffic. (1917, August 25). The Singapore Free Press and Mercantile Advertiser. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/singfreepressb19170825-1.2.56?ST=1&AT=search&k=Singapore+number+of+cars&P=6&Display=0&filterS=0&QT=singapore,number,of,cars&oref=article

Hargreaves, D. (2013). The Global Cement Report: Tradeship Publications.HDB sets up $4.5 million brickworks. (1973, January 11). New Nation. Retrieved from

http://eresources.nlb.gov.sg/newspapers/Digitised/Article/newnation19730111-1.2.56?ST=1&AT=filter&K=singapore+clay+production+bricks&KA=singapore+clay+production+bricks&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=singapore,clay,production,bricks&oref=article

Henderson, R. (2016). Water Consumption in US Petroleum Refineries. Retrieved from the United States: https://greet.es.anl.gov/files/refineries-water-2016

826827828829830831832833834835836837838839840841842843844845846847848849850851852853854855856857858859860861862863864865866867868869870871872873874875

Ho, S. (2016). Alexandra. Retrieved from http://eresources.nlb.gov.sg/infopedia/articles/SIP_2016-06-21_114707.html

Hughes, H., & Seng, Y. P. (1969). Foreign Investment and Industrialisation in Singapore. Canberra, Australia: Australian National University Press.

Hwa, T. J. (1991). Leachate of fly ash derived from refuse incineration. Environmental Monitoring and Assessment, 19(1), 157-164. doi:10.1007/BF00401308

International Energy Agency. (2014). Electric power consumption (kWh per capita). https://data.worldbank.org/indicator/EG.USE.ELEC.KH.PC

International iron and steel institute. (2019). Steel Statistical Yearbook 1978-1978. https://www.worldsteel.org/steel-by-topic/statistics/steel-statistical-yearbook-.html

It All Ends In Smoke. (1936, February 26). Morning Tribune. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/morningtribune19360226-1.2.73?ST=1&AT=filter&K=Singapore+incinerator&KA=Singapore+incinerator&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,incinerator&oref=article

Johansen, S., & Juselius, K. (1990). Maximum likelihood estimation and inference on cointegration—with applications to the demand for money. Oxford Bulletin of Economics and Statistics, 52(2), 169-210.

Kalogirou, E., Themelis, N., Samaras, P., Karagiannidis, A., & Kontogianni, S. (2010). Fly ash characteristics from waste-to-energy facilities and processes for ash stabilization. Paper presented at the ISWA World Congress.

'Keep clean' drivein Singapore. (1959, September 16). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19590916-1.2.115?ST=1&AT=search&k=Kolam%20Ayer%20incinerator%20closed&QT=kolam,ayer,incinerator,closed&oref=article

Keppel Seghers. (2018). Waste-to-Energy Plants. Retrieved from http://www.keppelseghers.com/en/content.aspx?sid=3028

Kien, L. C. (Producer). (2014). Building Singapore Brick by Brick. Retrieved from http://justinzhuang.com/posts/tonneag/lai-chee-kien/

Kunz, R., Hess, T., Yen, A., & Arseneaux, A. (1980). Kinetic model for chromate reduction in cooling tower blowdown. Water Pollution Control Federation, 2327-2339.

Labrado & Alexandra Heritage Tour. (2017). Former Alexandra Brickworks. Retrieved from http://www.mycommunity.org.sg/tonneour-2/150-8-former-alexandra-brickworks.html

Land Transport Authority. (2009). Land transport statistics in brief 2009. Retrieved from Singapore: https://www.lta.gov.sg/content/dam/ltaweb/corp/PublicationsResearch/files/FactsandFigures

Local Industries. (1916, April 26). Malaya Tribune. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/maltribune19160426-1.2.49?ST=1&AT=filter&K=Singapore+cooling+tower&KA=Singapore+cooling+tower&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=singapore,cooling,tower&oref=article

Lüutkepohl, H., Saikkonen, P., & Trenkler, C. (2001). Maximum eigenvalue versus trace tests for the cointegrating rank of a VAR process. The Econometrics Journal, 4(2), 287-310.

Ma, G. (2006). Cr (VI)-containing electric furnace dust and filter cake: characteristics, formation, leachability and stabilization. University of Pretoria.

Machines to join battle against trash in S'pore. (1971, August 7). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19710807-1.2.56?ST=1&AT=filter&K=Chua+Chu+Kang+dumping&KA=Chua+Chu+Kang+dumping&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=chua,chu,kang,dumping&oref=article

876877878879880881882883884885886887888889890891892893894895896897898899900901902903904905906907908909910911912913914915916917918919920921922923924925926

The Men Who Lighten Our Darkness. (1933, September 10). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19330910-1.2.49?ST=1&AT=filter&K=Singapore+coal+consumption&KA=Singapore+coal+consumption&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,coal,consumption&oref=article

More pioneer products for Singapore. (1966, June 20). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19660620-1.2.95?ST=1&AT=filter&K=refractory+bricks+singapore&KA=refractory+bricks+singapore&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=refractory,bricks,singapore&oref=article

Mr. Lim will open Ulu Pandan Plant today. (1979, July 30). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19790730-1.2.134.3?ST=1&AT=filter&K=Singapore+incinerator&KA=Singapore+incinerator&DF=&DT=&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7cILLUSTRATION&WC=&YR=&P=2&Display=0&filterS=0&QT=singapore,incinerator&oref=article

Municipality of Singapore. (1931, August 24). Malaya Tribune. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/maltribune19310824-1.2.3?ST=1&AT=filter&K=MacRitchie+Reservoir+water+level&KA=MacRitchie+Reservoir+water+level&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=macritchie,reservoir,water,level&oref=article

Nadarajah, I. (1997, June 13). Bacteria Found in over Half of Cooling Tower Samples. the Strait Times. National Iron planning Malaysian joint venture. (1989, July 10). BUSINESS TIMES. Retrieved from

http://eresources.nlb.gov.sg/newspapers/Digitised/Article/biztimes19890710-1.2.34.8?ST=1&AT=filter&K=Singapore+steel+production&KA=Singapore+steel+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=1989&QT=singapore,steel,production&oref=article

National Steel Mills quadruples its spending on hi-tech. (1985, May 7). Singapore Monitor. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/singmonitor19850507-2.2.15.1?ST=1&AT=filter&K=singapore+steel+production&KA=singapore+steel+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=&WC=&YR=1985&QT=singapore,steel,production&oref=article

Natural gas now makes up 95.5% of fuel mix; renewable energy on the rise. (2015, July 21). the Straits Times. Retrieved from https://www.straitstimes.com/singapore/from-the-straits-times-archives-singapore-opts-for-cleaner-energy-sources

Nature's defences help Singapore. (1972, April 26). New Nation. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/newnation19720426-1.2.62.1?ST=1&AT=filter&K=air+pollution+control+singapore&KA=air+pollution+control+singapore&DF=&DT=&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&P=2&Display=0&filterS=0&QT=air,pollution,control,singapore&oref=article

NewspaperSG. (2019). An online archive of Singapore's newspapers. http://eresources.nlb.gov.sg/newspapers/

Nielsen, M., Nielsen, O.-K., & Hoffmann, L. (2013). Improved inventory for heavy metal emissions from stationary combustion plants: 1990-2009. Retrieved from https://dce2.au.dk/pub/SR68.pdf

Nriagu, J. O., & Nieboer, E. (1988). Chromium in the natural and human environments (Vol. 20): John Wiley & Sons.

Nriagu, J. O., & Pacyna, J. M. (1988). Quantitative assessment of worldwide contamination of air, water and soils by trace metals. Nature, 333(6169), 134-139.

927928929930931932933934935936937938939940941942943944945946947948949950951952953954955956957958959960961962963964965966967968969970971972973974975976

NSL Chemicals. (2016). Refractory. Retrieved from http://www.nslchemicals.com.sg/our-business/refractory

Number of car trebles in 10 years. (1963, April 12). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19630412-1.2.104?ST=1&AT=search&k=Singapore%20number%20of%20cars&QT=singapore,number,of,cars&oref=article

Oon, S., & Saparudin, K. B. (2014). Clean Air Act of 1971. Retrieved from http://eresources.nlb.gov.sg/infopedia/articles/SIP_2014-04-07_110024.html

Pacyna, J. M., & Pacyna, E. G. (2001). An assessment of global and regional emissions of trace metals to the atmosphere from anthropogenic sources worldwide. Environmental Reviews, 9(4), 269-298.

Passant, N. R., Peirce, M., Rudd, H. J., Scott, D. W., Marlowe, I., & Watterson, J. D. (2002). UK particulate and heavy metal emissions from industrial processes. Retrieved from https://uk-air.defra.gov.uk/assets/documents/reports/empire/AEAT6270Issue2finaldraft_v2.pdf

Plans for 5th incineration plant for solid waste. (2013, September 11). The Straits Times. Retrieved from https://www.eco-business.com/news/plans-5th-incineration-plant-solid-waste/

Pollution under control here. (1989, July 16). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19890716-1.2.23.3?ST=1&AT=filter&K=air+pollution+control+singapore&KA=air+pollution+control+singapore&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=air,pollution,control,singapore&oref=article

Pulles, T., van der Gon, H. D., Appelman, W., & Verheul, M. (2012). Emission factors for heavy metals from diesel and petrol used in European vehicles. Atmospheric Environment, 61, 641-651.

Putting more rubbish to good use. (1986, June 20). Business Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/biztimes19860620-1.2.11.7?ST=1&AT=filter&K=low+cost+incinerator&KA=low+cost+incinerator&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=&WC=&YR=&QT=low,cost,incinerator&oref=article

Refractory products from Jurong. (1969, November 10). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19691110-1.2.138.aspx?q=refractory&mode=advanced&ct=article&t=beritaharian%2cdailyadvertiser%2ceasterndaily%2ckabarslalu%2cmalayansatpost%2cmiddayherald%2cnewnation%2csingchronicle%2csingdailynews%2csingmonitor%2csingweekherald%2cstraitsadvocate%2cstraitschinherald%2cstraitseurasian%2cstraitsmail%2cstraitsobserver%2cstraitstelegraph%2cstoverland%2cstweekly%2cbiztimes%2cnewpaper%2cfreepress%2csingfreepressa%2csingfreepressb%2cstraitstimes%2ctoday%2cweeklysun%2cnysp%2cscjp%2clhzb%2clhwb&page=2&sort=relevance&token=refractory&sessionid=b63a3b38c407434f8fd1126387ef8ee6

Remarkable growth in the face of recession in world trade. (1974, September 26). New Nation. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/newnation19740926-1.2.34.1?ST=1&AT=filter&K=Singapore+steel+production&KA=Singapore+steel+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,steel,production&oref=article

Samaras, Z., Ntziachristos, L., Thompson, N., Hallb, D., Westerholm, R., & Boulterd, P. (2005). Characterisation of Exhaust Particulate Emissions from Road Vehicles. Retrieved from https://tonnerimis.ec.europa.eu/sites/default/files/project/documents/20100310_132356_74824_Particulates%20Final%20Publishable%20Report.pdf

Sin, J., Tham, S., & Low, L. (2015). Jurong Heritage Trail. Singapore: National Heritage Board.Singapore's Economic Progress Remains Steady. (1933, August 24). The Straits Times. Retrieved from

http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19330824-1.2.95?

977978979980981982983984985986987988989990991992993994995996997998999

1000100110021003100410051006100710081009101010111012101310141015101610171018101910201021102210231024102510261027

ST=1&AT=filter&K=low+cost+incinerator&KA=low+cost+incinerator&DF=&DT=&AO=true&NPT=&L=&CTA=&NID=&CT=&WC=&YR=&P=2&Display=0&filterS=0&QT=low,cost,incinerator&oref=article

Singapore's first cement works to open in April. (1961, November 3). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19611103-1.2.73.4?ST=1&AT=filter&K=Singapore+cement+production&KA=Singapore+cement+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,cement,production&oref=article

Singapore's oil pipelines. (1977, January 28). New Nation. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/newnation19770128-1.2.65?ST=1&AT=filter&K=Singapore+electricity+consumption&KA=Singapore+electricity+consumption&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,electricity,consumption&oref=article

Singapore again faces a shortage of cement. (1972, January 5). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19720105-1.2.118?ST=1&AT=filter&K=Singapore+cement+production&KA=Singapore+cement+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,cement,production&oref=article

Singapore Department of Statistics. (2018a). Electricity Generation, Consumption and Tariffs 1975-2017. http://www.tablebuilder.singstat.gov.sg/publicfacing/createDataTable.action?refId=14602

Singapore Department of Statistics. (2018b). Statistics Singapore. https://www.singstat.gov.sg/Singapore may need to recycle more waste. (1989, December 5). The Straits Times. Retrieved from

http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19891205-1.2.31.10?ST=1&AT=filter&K=refuse+recycle+singapore&KA=refuse+recycle+singapore&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=refuse,recycle,singapore&oref=article

Singapore Land Transport Authority. (2019). Certificate of Entitlement (COE). Retrieved from https://www.lta.gov.sg/content/ltaweb/en/roads-and-motoring/owning-a-vehicle/vehicle-quota-system/certificate-of-entitlement-coe.html

Singapore National Environment Agency. (2017a). Tuas South Incineration Plant. Retrieved from https://www.nea.gov.sg/docs/default-source/e-services-forms-docs/forms/tonnesip-brochure.pdf

Singapore National Environment Agency. (2017b). Waste Statistics and Overall Recycling. Retrieved from http://www.nea.gov.sg/energy-waste/waste-management/waste-statistics-and-overall-recyclingSingapore National Environment Agency. (2018). Waste Statistics and Recycling Rate 2003-2017. Singapore National Environment Agency. (2019). Waste Disposed Of And Recycled, Annual.

https://data.gov.sg/dataset/waste-disposed-of-and-recycled-annual?resource_id=7918b229-0e79-4d74-b725-e34183a56c01

Singapore Pollution Control Department. (1986). Pollution Control Report 1986-2003. Retrieved from Singapore:

Singapore Public Utilities Board. (1965). Souvenir Brochure: Commemorating the opening of Pasir Panjang 'B' Power Station. Singapore.

Singapore Public Utilities Board. (1970). Jurong Power Station will be officially opened by Dr. Goh Keng Swee. Retrieved from Singapore:

Singapore Public Utilities Board. (2017). Technical Reference for Water Conservation in Cooling Towers. Retrieved from https://www.pub.gov.sg/Documents/tonneechnicalReference_WaterConservation_CoolingTowers.pdf

102810291030103110321033103410351036103710381039104010411042104310441045104610471048104910501051105210531054105510561057105810591060106110621063106410651066106710681069107010711072107310741075107610771078

Singapore Public Utilities Board. (2018). Best practice guide in water efficiency buildings, version 1. Retrieved from https://www.pub.gov.sg/Documents/PUB_Water_Efficiency_Guidebook.pdf

Smells at Government House. (1900, May 31). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19000531-1.2.50?ST=1&AT=filter&K=Singapore+incinerator&KA=Singapore+incinerator&DF=&DT=&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7cILLUSTRATION&WC=&YR=&P=2&Display=0&filterS=0&QT=singapore,incinerator&oref=article

So you think it's just a lot of rubbish. (1980, February 29). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19800229-1.2.108.11.1?ST=1&AT=filter&K=national+iron+and+steel+dust+singapore&KA=national+iron+and+steel+dust+singapore&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=national,iron,and,steel,dust,singapore&oref=article

Steel factory leads war on the smog. (1970, March 11). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19700311-1.2.59?ST=1&AT=filter&K=national+iron+and+steel+dust+singapore&KA=national+iron+and+steel+dust+singapore&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=national,iron,and,steel,dust,singapore&oref=article

Stricter measures to control pollution from brickworks. (1987, February 19). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19870219-1.2.34.9?ST=1&AT=search&k=HDB%20brickworks%20production&QT=hdb,brickworks,production&oref=article

Strong balance sheet puts NISM on firm footing. (1983, December 3). SINGAPORE MONITOR. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/singmonitor19831203-1.2.19.8?ST=1&AT=filter&K=Singapore+steel+production&KA=Singapore+steel+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,steel,production&oref=article

Tan, L., Choa, V., & Tay, J. (1997). The influence of pH on mobility of heavy metals from municipal solid waste incinerator fly ash. Environmental Monitoring and Assessment, 44(1-3), 275-284.

Task Ahead. (1964, January 31). The Straits Times. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/straitstimes19640131-1.2.153.4?ST=1&AT=filter&K=Singapore+steel+production&KA=Singapore+steel+production&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE%7CILLUSTRATION&WC=&YR=&QT=singapore,steel,production&oref=article

Tay, J.-H., & Goh, A. T. (1991). Engineering properties of incinerator residue. Journal of environmental engineering, 117(2), 224-235.

Tian, H., Zhu, C., Gao, J., Cheng, K., Hao, J., Wang, K., . . . Zhou, J. (2015). Quantitative assessment of atmospheric emissions of toxic heavy metals from anthropogenic sources in China: historical trend, spatial distribution, uncertainties, and control policies. Atmospheric Chemistry and Physics, 15(17), 10127-10147.

Trade Talk. (1983, June 8). Business Time. Retrieved from http://eresources.nlb.gov.sg/newspapers/Digitised/Article/biztimes19830608-1.2.14.6?ST=1&AT=filter&K=Singapore+cooling+tower&KA=Singapore+cooling+tower&DF=&DT=&Display=0&AO=true&NPT=&L=&CTA=&NID=&CT=ARTICLE&WC=&YR=&QT=singapore,cooling,tower&oref=article

United States Board of Public Works. (1995). Factsheet: Eliminating Hexavalent Chrome from Cooling Towers. Retrieved from Los Angeles: http://www.gfxtechnology.com/CR6.pdf

10791080108110821083108410851086108710881089109010911092109310941095109610971098109911001101110211031104110511061107110811091110111111121113111411151116111711181119112011211122112311241125112611271128

United States Environmental Protection Agency. (1989). Locating and Estimating Air Emissions from Sources of Chromium-Supplement (EPA-450/4-84-007G). Retrieved from https://www3.epa.gov/tonnetnchie1/le/chromium.pdf

United States Environmental Protection Agency. (1995). AP-42: Compilation of Air Emissions Factors: Refractory Manufacturing. Retrieved from https://www3.epa.gov/tonnetnchie1/ap42/ch11/final/c11s05.pdf

United States Environmental Protection Agency. (1997). Compilation of Air Pollutant Emission Factors, Volume 1: Stationary Point and Area Sources, fourth edition, AP-42. Section 11.3 Bricks and Related Clay products. Retrieved from https://www3.epa.gov/tonnetnchie1/ap42/ch11/final/c11s03.pdf

Veloo, R. (1992, June 7). Five in S'pore die from Legionnaires' disease. The Straits Times. World Bank. (2016). MSW Composition by Country Retrieved from

http://siteresources.worldbank.org/INTURBANDEVELOPMENT/Resources/336387-1334852610766/AnnexM.pdf

Zaccheus, M. (2014, September 26). Patching heritage cracks. The Straits Times.

112911301131113211331134113511361137113811391140114111421143

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