Air and Air Pollution

de Nevers, N. 1995: Air Pollution Control Engineering, McGraw-Hill

Questions

• Do you know any kinds of air pollution?

• Air pollutants?

• What is “air pollution”?

Photochemical smog?

Acid rain

Fine particle pollution ~ haze

Climate change?

Basics and Data

Gas % ppm

H2O 0~7

CO2 0.032

CH4 1.5

CO 0.1

O3 0.02

NH3 0.01

NO2 0.001

SO2 0.0002

H2S 0.0002

Minor components of clean air Atmospheric stratification

Stratospheric ozone layer depletion

Tropospheric ozone is being increased

The major “green house gas”

Distribution depends on local conditions

The only substance that can undergo phase

changes under natural conditions, with dramatic

latent heat release or absorption, so that plays an

important role in climate change.

Air Pollution and Weather

• Air pollution and weather are linked in two ways. One way concerns the influence that weather conditions have on the dilution and dispersal of air pollutants.

• The second way is the reverse and deals with the effect that air pollution has on weather and climate.

• Air is never perfectly clean.

• Examples of “natural” air pollution include:

– Ash,

– smoke and windblown dust

Air Pollution Occurrences

• The most obvious factor influencing air pollution is the quantity of contaminants emitted into the atmosphere.

• However, when air pollution episodes take place, they are not generally the result of a drastic increase in the output of pollutants; instead, they occur because of changes in certain atmospheric conditions.

• Two of the most important atmospheric conditions affecting the dispersion of pollutants are:

– (1) the strength of the wind and

– (2) the stability of the air.

Inversion

This is an example

of a generalized

temperature profile

for a surface

inversion.

Temperature-profile

changes in bottom

diagram after the

sun has heated the

surface.

Air Pollutant Types • Although some types of air pollution are recent creations,

others, such as London's infamous smoke pollution, have been around for centuries. One of the most tragic air pollution episodes ever occurred in London in December 1952 when more than four- thousand people died.

• Air pollutants are airborne particles and gasses that occur in concentrations that endanger the heath and well-being of organisms or disrupt the orderly functioning of the environment.

• Pollutants can be grouped into two categories:

– (1) primary pollutants, which are emitted directly from identifiable sources, and

– (2) secondary pollutants, which are produced in the atmosphere when certain chemical reactions take place among primary pollutants.

Directly emitted from sources or transformed in atmosphere, e.g., O3 in photochemical smog, sulfates and nitrates in acid rain, …

Air Pollutants

• Gaseous pollutants:

– SO2, combustion of coal, sulfur containing ores

– NOx (NO and NO2), combustion, high temperature or with HCs

– VOCs, petroleum, lubricants, solvents, paints, …(non-methane)

– CO, HCs (none-methane), …

• Particulates: (aerosols)

– TSP, total suspended particulate matter, diameter < 100μm

– PM10, respirable particulate matter, diameter < 10 μm

– PM2.5, fine particulate matter, diameter < 2.5 μm

– falling dust, tons per month per km2 (not a concentration)

Air Pollutants

• Special air pollutants – Toxic chemicals

– Lead (Pb) and mercury (Hg)

– Radioactive substances

– CFCs

– Green house gases • Natural effects: H2O, CO2, CH4, N2O, O3…

• By Kyoto protocol: CO2, N2O, CH4, SF6, HFC, PFC

• Regulated air pollutants – China: before 2000, TSP, SO2, NOx; after 2000: PM10,

SO2, NO2

– O3 and PM2.5 are also taken in some countries

• “Grey” haze problem

Combustion is the main Source of Air Pollutants

• Fossil fuels

− Coal burning: soot, SO2, NOX, … CO, C, Hg, …

− Oil combustion: NOX, CO, HC, …(SO2 from heavy oil)

− Natural gas: H2S, …

• Generation mechanism of SO2 and NOx

− SO2: combustion of contaminated fuel, coal, heavy oil,

sulfuric ores..

− NOx: thermal (high temperature), prompt (with HC

elements), and N;

− VOCs: a variety of sources, paints, oil, …

Air Pollution: From Local to Global

Local: London smog (coal burning type)

The Great Smog befell London starting on December 4, 1952, and lasted until March of

1953. It was a great disaster that killed thousands and formed an important impetus to the

modern environmental movement.

In early December of 1952, a cold fog descended upon London. Because of the cold,

Londoners began to burn more coal than usual. At the same time, the final conversion of

London's electric trams to diesel buses was completed. The resulting air pollution was

trapped by the heavy layer of cold air, and the concentration of pollutants built up

dramatically. The smog was so thick that it would sometimes make driving impossible. It

entered indoors easily, and concerts and screenings of films were cancelled as the audience

could not see the stage or screen.

Since London was known for its fog, there was no great panic at the time. In the weeks that

followed, the medical services compiled statistics and found that the fog had killed 4,000

people—most of whom were very young or elderly, or had pre-existing respiratory problems.

Another 8,000 died in the weeks and months that followed.

These shocking revelations led to a rethinking of air pollution. The disaster demonstrated to

people around the world that it was a real and deadly problem. New regulations were put in

place restricting the use of dirty fuels in industry and banning black smoke. These included

the Clean Air Acts of 1956 and of 1968, and the City of London Act of 1954.

City size (medium): Los Angeles smog

(automobile effluent type) • In the 1950s a new type of smog, known as photochemical smog, was

first described. This forms when sunlight hits various pollutants in the air and forms a mix of inimical chemicals that can be very dangerous. A photochemical smog is the chemical reaction of sunlight, nitrogen oxides (NOx) and volatile organic compounds (VOCs) in the atmosphere, which leaves airborne particles (called particulate matter) and ground-level ozone.

• Nitrogen oxides are released by nitrogen and oxygen in the air reacting together under high temperature such as in the exhaust of fossil fuel-burning engines in cars, trucks, coal power plants, and industrial manufacturing factories. VOCs are released from man-made sources such as gasoline (petrol), paints, solvents, pesticides, and biogenic sources, such as pine and citrus tree emissions.

• This noxious mixture of air pollutants can include the following:

• All of these chemicals are usually highly reactive and oxidizing. Photochemical smog is therefore considered to be a problem of modern industrialization. It is present in all modern cities, but it is more common in cities with sunny, warm, dry climates and a large number of motor vehicles. Because it travels with the wind, it can affect sparsely populated areas as well.

Regional: acid rain

• Acid rain" is a popular term referring to the deposition of wet (rain, snow, sleet, fog, cloudwater, and dew) and dry (acidifying particles and gases) acidic components. A more accurate term is “acid deposition”. Distilled water, once carbon dioxide is removed, has a neutral pH of 7. Liquids with a pH less than 7 are acidic, and those with a pH greater than 7 are Alkaline. “Clean” or unpolluted rain has a slightly acidic pH of over 5.7, because carbon dioxide and water in the air react together to form carbonic acid, but unpolluted rain also contains other chemicals. – H2O (l) + CO2 (g) → H2CO3 (aq)

• Carbonic acid then can ionize in water forming low concentrations of hydronium and carbonate ions: – 2 H2O (l) + H2CO3 (aq) → CO3

2− (aq) + 2 H3O+ (aq)

• Acid deposition as an environmental issue would include additional acids to H2CO3.

• Sulfuric acid and nitric acid, sulfates and nitrates.

• Acidic precursors are able being transported to thousand kilometers, across boundaries

Acid rain was mainly in southern-central China.

However:

2006 2007

2008

Air pollution and air pollutants

London Smog

Los Angeles Smog

Acid rain

Ozone layer depletion

Sandstorms

Asian Brown Cloud

Fine particulate matter

Coal burning

type

Photochemical smog

NOx and HCs

O3, PAN, Aldehydes

Rain water pH value

Smaller than 5.6

CFCs

PM2.5,

sulfates/nitrates

A special air pollution in China:

“Grey” haze

Haze in Beijing

美刊：老外对中国城市污染很无奈 2011年05月29日 09:53:19 来源： 新华国际

• 在罕见的蓝天下，我们向来华看望我们的朋友抱怨中国污染太重。他们会说：“这儿的空气看起来还好嘛!”我们的回答是：“你再住几天看看就知道了。”

• 然后还有这种心理和情绪上的影响。很多常驻中国的老外都会经历和我一样的心路历程，慢慢适应。先是诧异：怎么会这样？这儿的人怎么生活啊？接下来，诧异被一种近乎绝望的焦虑所代替：这会对我们的身体产生什么影响？然后是听之任之：我们不能老想着污染。在中国呆了三年以后，我们达到了这样的境界——我们知道自己最终会回国。

• 如果你是一个老外而非土生土长的本地人，那么在谈论一个国家不好的地方时，你必须谨慎小心。我在美国的时候，每当听到来访者批评这个国家的某些东西，我都会异乎寻常地涌起爱国主义情怀，为自己的国家辩护。所以我在中国的时候，对批评污染问题也非常小心。

• 在那些雾蒙蒙的天气里，我和附近洗衣店熨衣服的工人、市场里卖蔬菜的小贩、出租车司机或是在人行道上卖烤红薯的人打招呼的第一句话往往是：“天气不好！”这似乎是一句通用的问候语，也是“哎呀，今天空气污染真严重！”的委婉说法。

美国大西洋月刊26日发表题为“天气不好：在污染地区生活的侨民指南”文章

• 我的意思大家都明白。中国人清楚地意识到他们的污染问题。2008年皮尤世界民情项目调查说，有四分之三的中国人认为空气污染是个大问题。

• 官方的用语是“污染”，但在对话中用到这个词似乎有些太过强烈。我用“天气不好”来描述污染问题，一方面是为了礼貌，另一方面这么说也符合汉语的表达习惯。

• 中国人对许多常用的形容词往往不那么讲究。就像他们用“好吃” 来形容各种美食一样，在污染问题上，他们常常用“天气不好”来描述糟糕的空气质量。

• 我想在污染面前调整心态的最高境界就是忽视它——就像我们忽视纽约州布法罗的积雪和华盛顿三伏天的潮湿那样。某个夏日，我和一位中国朋友行至北京市中心的—座天桥，桥下车来车往。向远方眺望，我突然再次被震惊：空气是如此糟糕边，以至于我忍不住向身边的朋友抱怨：“污染太可怕了，你怎么忍受得了？”

• 她回答说自己没有注意到污染问题。我问她有什么诀窍。她说，“我总是这么忙，只有时间注意眼前的事情。”她的解释似乎完全合理。中国是一个忙碌的地方，只关注你眼前的东西能让你忘掉更大的危机。（作者德博拉·法洛斯）

Grey Haze in China

• Dust suspension by construction or road?

• Sand storms?

• Photo chemical smog because of the increasing numbers of vehicles?

• The consequence of burning huge amount of

coal?

• SO2 is a short lived pollutant, but how is the

impact of sulfates?

“Grey” Haze • Wikipedia: “Haze is traditionally an atmospheric

phenomenon where dust, smoke and other dry particles obscure the clarity of the sky. The World Meteorological Organization manual of codes includes a classification of horizontal obscuration into categories of fog, ice fog, steam fog, mist, haze, smoke, volcanic ash, dust, sand and snow. Sources for haze particles include farming (ploughing in dry weather), traffic, industry, and wildfires. ”

• http://en.wikipedia.org/wiki/Haze

• Fine particles are only a fraction of the size of a human hair.

How Fine is Fine?

Fine Particles

(2.5 mm)

Cross section of a human hair (magnified to 60 mm)

Coarse Particles

(10 mm)

Terms

• Particulate: extremely small fragments of solids or liquid droplets suspended in air.

• Dust(粉尘): suspended solids roughly 1 to 100μm in size

– From material handling activities or mechanical operation, including grinding

• Smoke(黑烟): smaller suspended solids less than 1 μm

– Common product of incomplete combustion

– Mostly carbonaceous material

– Soot(煤烟): visible clusters of carbon particles

Terms

• Fume(烟): size less than 1 μm, consisting

of very small metallic oxide particles

• Mist(雾): A suspension of liquid particles

between 0.1 and 10 μm in size

• Spray: consists of liquid particles greater

then 10 μm in size

• Aerosol(气溶胶): quantity of any small

particles, liquid or solid, suspended in air

Haze in Los

Angeles, Jan

15, 2010

Haze at Kuala Lumbur, Aug 11, 2005

Haze in Mosque, Nov 26, 2008

Grey haze and its control

• A phenomenon of air pollution meteorology

• High concentration of “wet” aerosols with favorable meteorological conditions: humidity, stagnation

• Obscure visibility: < 10 km

• Sulfuric acid and sulfates are the major “wet” aerosols;

• Coal combustion is the main cause;

• Vehicular emission is the second place

• Vehicular induced air pollution, e.g., NO2 and photochemical smog (O3) must be controlled for urban air quality, but for grey haze, the main efforts should be put on SO2 emissions, and pollutant sources of larger areas should be taken into account.

Current air pollution problems

• In China ? • In Shanghai ?

Coal burning

PM10

SO2

Acid rain

Automobile related air

pollution in large cities

Sandstorms

PM10, PM2.5

NO2

Automobile related air

pollution

Visibility,

photochemical smog

Indoor

Acid rain

Future air pollution problems: CO2, accidental release

To establish ambient air quality standards:

• Physical/chemical/biological analysis

• Animal experiments

• Short-term exposure of human volunteers

(observe measurable, irreversible short-term or

long-term effects)

• Epidemiology

Air Quality Standards and

Air Pollution Index (API)

Pollutant Average period Concentration

First class Second class Third class Unit

Sulfur dioxide SO2

annually

daily

hourly

0.02

0.05

0.15

0.06

0.15

0.50

0.10

0.25

0.70

Total suspended

particulates TSP

annually

daily

0.08

0.12

0.20

0.30

0.30

0.50

Respirable

particulates PM10

annually

daily

0.04

0.05

0.10

0.15

0.15

0.25

Nitrogen oxides

NOx

annually

daily

hourly

0.05

0.10

0.15

0.05

0.10

0.15

0.10

0.15

0.30

mg/m3

(Standard state)

Nitrogen dioxide

NO2

annually

daily

hourly

0.04

0.08

0.12

0.04

0.08

0.12

0.08

0.12

0.24

Carbon oxide CO daily

hourly

4.00

10.00

4.00

10.00

6.00

20.00

Ozone O3 hourly 0.12 0.16 0.20

Lead Pb seasonally

annually

1.50

1.00

3,4-Benzopyrene daily 0.01 μg/m3

(Standard state)

Fluorides daily

hourly

7①

20①

F monthly

Plant growing seas.

1.8②

1.2②

3.0③

2.0③ μg/(dm2·d)

National Ambient Air Quality Standards (GB 3095－1996 )

Air Pollution Index (API)

• Air Pollution Index (API) was introduced by US as Pollutant Standard Index (PSI) in 1972, and currently is referred to as Air Quality Index (AQI).

• In China, API weekly report started in 1997, daily report in 1999, for TSP, SO2 and NOx. From June 2000, the index pollutants were changed to PM10, SO2, and NO2.

• There are now 86 cities reporting daily APIs on MoEP website

• API forecasting

• API

calculation

API system of Shanghai

Class I II III IV V

API Range 0-50 51-100 101-200 201-300 >300

Description Good Fair Lightly

polluted

Polluted Heavily

polluted

The API system in China

Before June 2000Air quality

ClassAPI

SO2 NOX TSP

Ⅰ 0-50 0.000-0.050 0.000-0.050 0.000-0.120

Ⅱ 50-100 0.050-0.150 0.050-0.100 0.120-0.300

Ⅲ 100-200 0.150-0.250 0.100-0.150 0.300-0.500

Ⅳ 200-300 0.250-1.600 0.150-0.565 0.500-0.625

Ⅴ 300-400 1.600-2.100 0.565-0.750 0.625-0.875

400-500 2.100-2.620 0.750-0.940 0.875-1.000

After June 2000Air quality

ClassAPI

SO2 NO2 PM10

Ⅰ 0-50 0.000-0.050 0.000-0.080 0.000-0.050

Ⅱ 50-100 0.050-0.150 0.080-0.120 0.050-0.150

Ⅲ 100-200 0.150-0.800 0.120-0.280 0.150-0.350

Ⅳ 200-300 0.800-1.600 0.280-0.565 0.350-0.425

Ⅴ 300-400 1.600-2.100 0.565-0.750 0.420-0.500

400-500 2.100-2.620 0.750-0.940 0.500-0.600

Shown in API curves, with great efforts, the air quality of Chinese cities is improving.

Controlling Air Pollution through

Regulations • Economic activity, population growth, meteorological

conditions, and regulatory efforts to control emissions, all

influence the trends in air pollution.

• The Clean Air Act of 1970 mandated the setting of

standards for four of the primary pollutants—

– particulates,

– sulfur dioxide,

– carbon monoxide, and

– Nitrogen

– as well as the secondary pollutant ozone.

Have Regulations Helped? • In 1997, the emissions of the five major primary

pollutants in the United States were about 31 percent lower than 1970.

• In 1990, Congress passed the Clean Air Act Amendments, which further tightened controls on air quality.

• Regulations and standards regarding the provisions of the Clean Air Act Amendments of 1990 are periodically established and revised.