VILNIUS GEDIMINAS TECHNICAL UNIVERSITY

Vaida ŠEREVIČIENĖ

RESEARCH AND DEVELOPMENT OF NITROGEN DIOXIDE DIFFUSIVE SAMPLERS SUMMARY OF DOCTORAL DISSERTATION TECHNOLOGICAL SCIENCES, ENVIRONMENTAL ENGINEERING (04T)

Vilnius 2012

Doctoral dissertation was prepared at Vilnius Gediminas Technical University in 2008–2012. Scientific Supervisor

Assoc Prof Dr Dainius PALIULIS (Vilnius Gediminas Technical University, Technological Sciences, Environmental Engineering – 04T).

The dissertation is being defended at the Council of Scientific Field of Environmental Engineering at Vilnius Gediminas Technical University: Chairman

Prof Dr Saulius VASAREVIČIUS (Vilnius Gediminas Technical University, Technological Sciences, Environmental Engineering – 04T).

Members: Assoc Prof Dr Raimondas Leopoldas IDZELIS (Vilnius Gediminas Technical University, Technological Sciences, Environmental Engineering – 04T), Dr Dainius MARTUZEVIČIUS (Kaunas University of Technology, Technological Sciences, Environmental Engineering – 04T), Assoc Prof Dr Egidijus PETRAITIS (Vilnius Gediminas Technical University, Technological Sciences, Environmental Engineering – 04T), Prof Dr Habil Vida STRAVINSKIENĖ (Vytautas Magnus University, Biomedical Sciences, Ecology and Environmental – 03B).

Opponents: Dr Steigvilė BYČENKIENĖ (State Research Institute Center for Physical Sciences and Technology, Physical Sciences, Physics – 02P), Prof Dr Aloyzas GIRGŽDYS (Vilnius Gediminas Technical University, Technological Sciences, Environmental Engineering – 04T).

The dissertation will be defended at the public meeting of the Council of Scientific Field of Environmental Engineering in the Senate Hall of Vilnius Gediminas Technical University at 1 p. m. on 8 June 2012. Address: Saulėtekio al. 11, LT-10223 Vilnius, Lithuania. Tel.: +370 5 274 4952, +370 5 274 4956; fax +370 5 270 0112; e-mail: doktor@vgtu.lt The summary of the doctoral dissertation was distributed on 7 May 2012. A copy of the doctoral dissertation is available for review at the Library of Vilnius Gediminas Technical University (Saulėtekio al. 14, LT-10223 Vilnius, Lithuania).

© Vaida Šerevičienė, 2012

VILNIAUS GEDIMINO TECHNIKOS UNIVERSITETAS

Vaida ŠEREVIČIENĖ

AZOTO DIOKSIDO DIFUZINIŲ ĖMIKLIŲ TYRIMAI IR TOBULINIMAS DAKTARO DISERTACIJOS SANTRAUKA TECHNOLOGIJOS MOKSLAI, APLINKOS INŽINERIJA IR KRAŠTOTVARKA (04T)

Vilnius 2012

Disertacija rengta 2008–2012 metais Vilniaus Gedimino technikos universitete. Mokslinis vadovas doc. dr. Dainius PALIULIS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, aplinkos inžinerija ir kraštotvarka – 04T).

Disertacija ginama Vilniaus Gedimino technikos universiteto Aplinkos inžinerijos ir kraštotvarkos mokslo krypties taryboje: Pirmininkas

prof. dr. Saulius VASAREVIČIUS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, aplinkos inžinerija ir kraštotvarka – 04T).

Nariai: doc. dr. Raimondas Leopoldas IDZELIS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, aplinkos inžinerija ir kraštotvarka – 04T), dr. Dainius MARTUZEVIČIUS (Kauno technologijos universitetas, technologijos mokslai, aplinkos inžinerija ir kraštotvarka – 04T), doc. dr. Egidijus PETRAITIS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, aplinkos inžinerija ir kraštotvarka – 04T), prof. habil. dr. Vida STRAVINSKIENĖ (Vytauto Didžiojo universitetas, biomedicinos mokslai, ekologija ir aplinkotyra – 03B). Oponentai: dr. Steigvilė BYČENKIENĖ (Valstybinis mokslinių tyrimų institutas Fizinių ir technologijos mokslų centras, fiziniai mokslai, fizika – 02P), prof. dr. Aloyzas GIRGŽDYS (Vilniaus Gedimino technikos universitetas, technologijos mokslai, aplinkos inžinerija ir kraštotvarka – 04T). Disertacija bus ginama viešame Aplinkos inžinerijos ir kraštotvarkos mokslo

krypties tarybos posėdyje 2012 m. birželio 8 d. 13 val. Vilniaus Gedimino technikos universiteto senato posėdžių salėje. Adresas: Saulėtekio al. 11, LT-10223 Vilnius, Lietuva. Tel.: (8 5) 274 4952, (8 5) 274 4956; faksas (8 5) 270 0112; el. paštas doktor@vgtu.lt Disertacijos santrauka išsiuntinėta 2012 m. gegužės 7 d. Disertaciją galima peržiūrėti Vilniaus Gedimino technikos universiteto bibliotekoje (Saulėtekio al. 14, LT-10223 Vilnius, Lietuva). VGTU leidyklos „Technika“ 2002-M mokslo literatūros knyga.

© Vaida Šerevičienė, 2012

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Introduction Topicality of the problem In the second half of the 20th century there was looking for a different

ways to reduce industrial pollution by harmonizing the culture of consumption and environment and public health demands. Most of inorganic pollutants are emitted into the air from the facilities of industry and energy sector, as well as vehicles. One of the most dangerous inorganic air pollutants is nitrogen dioxide (NO2), which is formed during the combustion process. The coupling process of nitrogen dioxide with water vapor results is the formation of acid rain in the atmosphere. One of the main source of nitrogen oxides is motor transport which produces about half of nitrogen oxides emissions to the environment of Europe. Both wet and dry sedimentations of NO2 are harmful: they destroy vegetation, cause deterioration of soil, building materials and water quality. To mitigate the negative effects on environmental components it is important to monitor the concentration levels of the main pollutants in the ambient air of the most polluteed areas, to evaluate the gained results and to take measures to reduce them.

Measurements of nitrogen dioxide in ambient air is relevant problem not only in Lithuania, but also in Europe, as well as in other countries around the world. NO2 concentrations in ambient air is limited under directive 2008/50/EC of the European Parliament and of the Council. The reference method for the measurement of nitrogen dioxide and oxides of nitrogen is chemiluminescence method under this Directive. Accurate and reliable devices are used in air monitoring stations, but they are expensive and heavy. Installation and maintenance of these devices are quite complicated, therefore only in larger cities there are equipped with air quality monitoring stations. Air quality in Lithuania is continuously measured with reference methods in 14 automated urban and 3 integrated air monitoring stations. Many years ago equipped with stationary stations in present, during expansion of urban infrastructure, do not demonstrate the real impact of actually polluters to the air quality of the city.

Popularity of diffusive samplers increases in recent decades. Passive sampling system can be used for air monitoring of remote and limited access areas, such as forests.

Research of ambient air quality using diffusive samplers is one of the way to assess air quality in areas where continuous measurements aren’t carried out, especially when evaluating level of pollutant concentration over a longer period of time and indentifying areas that reach a specific pollutant. Diffusive samplers are a good tool to assess urban air quality and used to create air pollution maps.

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The inventor of diffusive samplers, an American scientist Edward Danelly Palmes (1976) described the diffusion tube sampler used during the working environment measurements. This type of diffusion samplers is still being used for the researches of higher pollutant concentrations. Swedish scientist Martin Ferm (1991) modified the original Palmes’ sampler by reducing its length – in order to increase sensitivity. Gregory Ayers (1995) and his colleagues used the membrane at the end of sampler, for the reduction of the influence of turbulent air movement.

Although since 1973, when these samplers were introduced, a large number of different modifications were developed. Different absorbent solutions were proposed, and various impregnation bases were applied. Often, during the modification, one parameter is optimized – the length of diffusive samplers, base, absorbent solution, etc., but there is no evaluation of all factors affecting the determination of nitrogen dioxide. Standard procedures for the preparation of diffusive samplers are not defined, different methods of determination influence measurement accuracy. Preparation and application of sampler is the mainly factor influencing the determination of NO2 concentrations.

Object of the work – diffusive sampler used during the researches of nitrogen dioxide concentration in the air.

Aim and tasks of the work. Aim of this work is to investigate main factors influencing accuracy of diffusive samplers. According to obtained experimental results to improve diffusive samplers and determine their sensitivity and uncertainty.

To reach the aim set in the thesis, it is necessary to tackle the following tasks:

1. To investigate the effect of diffusive sampler length and basis on the accuracy of determination of NO2 concentration. 2. To investigate the impact of aqueous triethanolamine solution on the determination of NO2 concentration by diffusive samplers. 3. To study the influence of meteorological factors (air temperature and relative humidity) on the operating efficiency of diffusion samplers.

4. To assess the dispersion of nitrogen dioxide in ambient air using numerical simulation and compare the results received with experimental ones.

Methodology of research includes passive and chemiluminescent methods for the determination of concentrations of nitrogen dioxide. ADMS-Urban

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software package has been used for the simulation of the dispersion of nitrogen dioxide in the ambient air.

Scientific novelty. Complex researches on measuring accuracy of determination of nitrogen dioxide applying different composition diffusive samplers and evaluation of influence of meteorological factors on their measuring uncertainty.

Practical value. On the grounds of the results of researches, it is possible to evaluate peculiarities of the application of diffusive samplers for the determination of nitrogen dioxide concentrations. Considering the researches results of field and laboratory chamber experimental studies, diffusive samplers of improved construction can be applied for the observation of ambient air.

Defended propositions 1. The lowest total indeterminacy for the evaluation of NO2 concentrations is obtained after the optimization of the body length of

diffusive sampler and the concentration of triethanolamine aqueous absorbent solution and exposure time by using a stainless steel grid as a base.

2. The detection limit of NO2 concentration with modified 3.4 cm long diffusive sampler with 10% absorbing TEA aqueous solution on stainless steel mesh when exposure time 336 hours is 2.2 µg/m3.

3. The air temperature has greater impact to the uncertainty of determination of nitrogen dioxide than relative humidity.

The scope of the scientific work. The scientific work consists of introduction, 5 chapters, common conclusions and recommendation, list of references and list of author’s publications. The total scope of the dissertation is 148 pages, 64 pictures, 22 tables, 44 formulas and 1 addendum. The dissertation author used 213 literary sources.

1. Research of nitrogen dioxide applying passive method Literary review presents the analysis of the formation of nitrogen dioxide in

the atmosphere and consistent patterns of their dispersion in the environment. It gives a brief consideration of NO2 impact on a person and environment. Diversity of diffusive samplers, principle of their effect, advantages and disadvantages is given in detail. Diffusive samplers of different structure and geometric parameters are used for the determination of inorganic pollutants in the air. However, they can be applied only under specific conditions (for the evaluation of different

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concentrations, outdoor and indoor air quality). Absorbent solutions used and their specificity are analyzed at length. Scientific literature gives inconsistent data on the influence of impregnating solution of triethanolamine concentration used in diffusive samplers for the determination of nitrogen dioxide under the method of passive accumulation. Meteorological factors influencing the result of diffusive samplers are analyzed. When using diffusive samplers in outdoor researches, they are strongly influenced by meteorological factors (temperature, relative humidity, wind speed). End of the chapter briefly discusses the possibility of simulation of nitrogen dioxide concentrations and dissemination using mathematical models through the use of simulation programmes.

The analysis of the scientific-technical literature showed that only few detailed purposeful researches, covering the researches on all the influencing factors and sampler structures have been carried out. Therefore it was decided that this dissertation shall cover the performance of complex studies of diffusive samplers, involving experimental studies in laboratory and under natural conditions through the examination of diffusive sampler structures, absorbent solutions and meteorological factors, as well as to evaluate the diffusion of nitrogen dioxide near motor roads through the application of diffusive samplers and mathematical simulation.

2. Experimental laboratory researches of diffusive samplers This chapter describes experimental studies of diffusive samplers during which

diffusive samplers of different lengths were analyzed in laboratory chamber. In order to increase the absorption rate of diffusive sampler, geometric parameters of diffusive sampler were changed. During laboratory experimental studies, diffusive sampler in diameter of 21 mm was examined, two variable parameters: length of diffusive sampler (2, 3.4 and 7 cm) and base (glass fibre filter (GFF) and stainless steel grid (SSM)). Greater relative errors of diffusive samplers with GFF (19%) than with SSM (11%) were determined.

According to the research data, it was determined that the sampler length is a significant factor for the result of the modified diffusive sampler (p<0.05), i.e. for relative error. Influence of different bases on the sampler performance was analyzed. Like in the case of sampler length, significant influence of different base (p<0.05) on the performance efficiency of diffusive samplers was determined through the assessment of relative error. Interaction of factors is not significant (p> 0.05), so the length of sampler can be interpreted irrespective of the base used. The relative error is on average higher using GFF base. Independent of the base, the lowest average relative error is of 3.4 cm long diffusive sampler, and the largest of 2 cm in length.

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The evidence of interaction of factors can be noticed since the difference between the relative error using the GFF and the SSM diffusive samplers of 3.4 cm in length is less than using the bodies of 2 or 7 cm in length. Diffusive samplers of different lengths were analyzed during the studies carried out by Kirby (et al. 2001): 4 cm and 5.5 cm, 7 cm and 12 cm. Average concentrations of NO2 measured using diffusive samplers of different lengths during the experimental studies ranged as follows: 4 cm ≥ 12 cm ≥ 7.1 cm ≥ 5.5 cm. Kirby said that the reason for the increase in NO2 concentrations applying diffusive sampler of 4 cm in length can be turbulent diffusion at the open end of sampler. Studies were carried out under natural conditions by through the display of samplers without protective hoods. This effect can be reduced by placing diffusive samplers in protective hoods.

Diffusive samplers are used for the measurement of ambient air quality. Exposure time of samplers can vary from several hours to several weeks. During experimental studies, dependence of the result of diffusive samplers on the exposure time was examined. Diffusive samplers of 3.4 cm and 7 cm in length, absorbent solution – TEA aqueous solution of 20%, impregnation base – stainless steel grid were chosen for the study. Diffusive samplers were displayed for 24, 168, 336, 504 and 672 hours at the same time.

During the display of 3.4 cm long diffusive samplers, lower NO2 concentrations, compared with the NOx analyzer were determined in all cases. Relative error ranged from 6.7 to 15.9%. Minimum error was determined after the exposure of diffusive samplers for 336 and 504 hours, i.e. for 2 and 3 weeks (Fig. 1).

24 168 336 504 672

Exponation time, h

-35

-30

-25

-20

-15

-10

-5

0

5

Relat

ive hu

midit

y, %

3.4 cm diffusive sampler lenght 7.0 cm diffusive sampler lenght

Fig. 1. Average relative errors of diffusive samplers of 3.4 cm and 7 cm length at different exposure time

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During experimental studies, when longer (7 cm) diffusive samplers were displayed during different period of time, the longer exposure time was, the shorter relative error value became (Fig. 1). Relative error ranged from 3.1 to 25.7%. The lowest error was determined during the exposure of 7 cm long diffusive sampler for four weeks.

According to research data, it was determined that exposure time of diffusive sampler was a significant factor for the result of modified diffusive sampler (p <0.05) (Fig. 1). The least significant difference between the diffusive samplers of different lengths exposing them for 504 hours was determined.

Solution absorbing nitrogen dioxide and used most commonly is triethanolamine (TEA). Since TEA is viscous enough at room temperature, so it is diluted with various solvents on purpose to be used on the impregnation base of diffusive sampler. NO2 accumulated after exposure is extracted into an aqueous solution as nitrite ions, and their content is determined. Palmes (1976), Glasius (et al. 1999), Kirby (et al. 2000) and Martin (et al. 2001) suggested using absorbent solution of a different composition. The test of absorbent solution of diffusive sampler was carried out in laboratory chamber of experimental studies. During initial experimental laboratory study, samplers impregnated with TEA aqueous solutions with (GFF) of 5%, 10%, 20%, 30% and 50% (v/v) concentrations were examined. The obtained results showed that samplers impregnated with 30% and 50% aqueous solutions of TEA contain much lower concentration of nitrogen dioxide; the relative error was 68% and 83%, respectively. The lowest relative error of 8.1% was seen in diffusive samplers impregnated with solutions of TEA on GFF of 5% and 10%.

During experimental chamber studies, diffusive samplers where SSM was used as impregnation base were evaluated. The highest average relative error in diffusive samplers impregnated with TEA aqueous solutions of 50% was 11% (Fig. 2.). In case of other absorbent solutions, set relative errors ranged from 3 to 8%.

5 % 10 % 20 % 30 % 50 %

Concentration of TEA aqua solution

-20-16-12-8-4048

12

Relat

ive er

ror, %

Mean Mean±SE

Fig. 2. Relative error of diffusive samplers impregnated with various TEA aqueous solutions

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It was found that the results of SSM-based diffusive samplers impregnated with absorbent solution of 10%, 20% and 30% varied slightly, i. e. there were no significant differences statistically (p>0.05).

During field investigations, it is difficult to identify which environmental parameter most influences performance of diffusive sampler, because all the time air temperature and humidity changes, as well as variable and wind speed. It was evaluated results of diffusive samplers compared with the NOx analyser when air temperature changing from 20 to 35 °C and humidity from 30 to 80 %. It was determined lower relative error at 20–30 °C temperature. The relative error increased when relative humidity reached 80 % in laboratory chamber (Fig. 3).

Relative humidity 30 % 50 % 80 %

20 30 35Temperature, °C

-20-10

01020

Relat

ive er

ror, %

Fig. 3. Average relative error of diffusive samplers when environment temperature ranging from 20 to 35°C, relative humidity 30 to 80 %

Investigating the effect of the ambient temperature and relative humidity on diffusive sampler performance, it was found the significant effect (p<0.05) of these factors at 35 °C temperature and 80% relative humidity.

3. Experimental field research of diffusive samplers This chapter describes natural experimental studies of diffusive samplers.

The aim of experimental studies was to determine the efficiency of diffusive samplers during their use in natural studies, using different absorbent solutions and impregnation bases. Laboratory studies allow evaluation of each influencing factor separately. During natural studies, indication of diffusive samplers is observed when influencing factors act as a whole.

Natural experiments were carried out on the municipal territory of Mažeikiai district. 6 areas for exposure of diffusive samplers reflecting different concentrations of nitrogen dioxide – from 3 to 30 mg/m3 – were chosen.

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Research was carried out in 2009–2010. Samplers were exhibited for four seasons, by 2 weeks per season. In order to protect the samplers from the impact of meteorological factors and minimize the effects of wind, the samplers were mounted in special hoods at measurement site during the measurements when using diffusive samplers outdoors (Fig. 4).

In order to evaluate the potential influence of meteorological factors, the experimental studies were carried out at different seasons of the year. All the results of modified diffusion samplers were compared with the control samplers of company Passam ag (Fig. 4).

Fig. 4. Scheme of protective shield of diffusive sampler

Em = 0.61 + 0.85*Ek; r = 0.89; p = 0.000; r2 = 0.79

0 10 20 30 40 50NO2 concentration (control samplers), µg/m3

0

10

20

30

40

50

NO2 c

oncen

tratio

n(m

odifie

d sam

plers)

, µg/m

3

Fig. 5. Comparison of NO2 concentrations measured with modified and control diffusive samplers

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Statistically significant (p<0.05) strong positive correlation was determined, correlation coefficient r = 0.89. Regression equations describing the experimental data are presented in Figure 5, where Em – concentration of NO2 measured with modified diffusive samplers, Ek– concentration of NO2 measured with control diffusive samplers.

Mesh Filter

Base

-20

0

20

40

60

80

Relat

ive er

ror, %

10 % TEA solution 20 % TEA solution Fig. 6. Comparison of NO2 concentrations measured with modified and control diffusive

samplers

Although the correlation link is strong enough, but the result shows a mismatch, therefore it is necessary to analyze all the factors influencing the results of diffusive sampler. The results obtained during each season are analyzed and evaluated in detail. To assess the influence of meteorological factors, their change during each different period of studies was analyzed. Meteorological data of air monitoring station of Mažeikiai town were used.

During the first experimental studies (spring season), two impregnation bases (stainless steel grid (SSM) and glass fibre filter (GFF)) and two TEA aqueous absorbent solutions of 10% and 20% were used. When analyzing and comparing the indication of modified samplers with the control ones, change of indications was observed at 3–24 µg/m3 NO2 concentrations. When comparing the results of diffusive samplers with SPF with the control samplers, statistically significant (p<0.05) positive correlation was determined, where correlation coefficient is r = 0.93. Results of diffusive samplers with SSM also statistically significantly (p<0.05) correlate with indications of control samplers, r = 0.97.

During two-factor dispersive analysis, the influence of diffusion sampler base and TEA solution used on the result of diffusion sampler was evaluated. Research data showed that the base has a significant impact on the result of diffusion sampler (p<0.05), while the use of TEA solutions of two

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concentrations do not have a significant impact (p>0.05). In case of both solutions, greater errors were determined using glass fibre filter of diffusion-based sampler.

Diffusive samplers with NPT impregnated with TEA aqueous solutions of 5%, 10%, 20%, 30% and 50% were exhibited during the summer season at the same measurement sites. Dispersive analysis was carried out, and the hypothesis was checked that the TEA solution has a significant impact on the result of diffusive sampler at different concentrations of NO2 (measurements at different sites). In case of small concentrations (3–4 µg/m3) significant influence was determined (p = 0.036 and p = 0.007, respectively), i.e. the results of diffusive samplers impregnated with TEA solutions of 5% and 10% concentrations differed significantly from the samplers impregnated with solutions of 30% and 50%. In cases of other concentrations, significant differences were not observed (Fig. 7a).

Mean Mean ± SE

5% 10% 20% 30% 50%

Concentration of TEA solution

-30

-20

-10

0

10

20

30

40

Relat

ive er

ror, %

Mean Mean ± SE

5% 10% 20% 30% 50%

Concentration of TEA solution

-50

-40

-30

-20

-10

0

10

Relat

ive er

ror, %

Fig. 7. Average relative error of diffusive samplers impregnated with different aqueous

TEA solutions During the autumn season, diffusive samplers impregnated with different

absorbent solutions were exhibited. Figure 7 shows relative errors of diffusive samplers with TEA solutions of 5%, 10%, 20%, 30% and 50% concentrations. The maximum error of 5% was determined in case of TEA solution – 27.8%, the average errors of all other solutions were 15% (Fig. 7b).

4. Simulation of nitrogen dioxide dispersion NO2 concentration was measured by exposing them with diffusive samplers on street lighting poles at 25 sites of Žirmūnai catchment area in Vilnius city for two weeks. TEA aqueous solution and a stainless steel grid

a) b)

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were used in diffusive samplers. Data of diffusive samplers were compared to NO2 concentrations recorded at the nearby air monitoring station using chemiluminescent method. NO2 concentration measured with diffusive samplers was slightly different from the results obtained at air monitoring station using a chemiluminescent analyzer for measurement of nitrogen oxides. A two-week average nitrogen dioxide concentration recorded at the station was 37.5 µg/m3; while average concentration of NO2 measured with diffusive samplers was 39.2 µg/m3. The relative error between the two methods of nitrogen dioxide measurements was 4.3%.

The evaluation of the results of diffusive samplers show that higher NO2 concentrations were measured at the streets with intensive traffic: Kareivių and Žirmūnų streets. NO2 concentrations recorded at the sites of measurements of the following streets averaged 39.0 µg/m3 (Fig. 8a).

Fig. 8. Comparison of simulation and investigation results in Žirmūnai district. NO2 concentrations a) measured with diffusive samplers; b) modelled with ADMS-

Urban programme

NO2 µg/m3

a) b)

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NO2 concentrations measured at the measurement points located farther from the streets, in the yards of blocks of flats, were 2.2 times lower (17.7 µg/m3) (Fig. 8a). Air quality in Žirmūnai catchment was also evaluated, and the simulation using ADMS-Urban programme of nitrogen dioxide diffusion released by motor transport was carried out. The maximum NO2 concentration calculated applying the simulation for the evaluation of traffic flows is in north-western part of Žirmūnai: at the crossroad of Kareivių, Kalvarijų and Ozo streets (Fig. 8b). At the following crossroad, the NO2 concentration was 60 µg/m3. The lowest NO2 concentrations (20 mg/m3) were determined farther from the main source of pollution – traffic streets of motor transport.

A positive correlation link of statistically significant moderate strength was found between the indications of diffusive samplers and simulation results, correlation coefficient r = 0.64. After the comparison of nitrogen dioxide concentrations in ambient air of Žirmūnai catchment obtained by measuring with diffusive samplers with the results obtained using the ADMS-Urban simulation software package, the error ranged from 2.5 to 35.8%. The concentrations obtained during the measurements differed from the ADMS-Urban simulation programme results at an average of 13.9%. Simulation data is within the limits of indeterminacy set by the Directive 2008/50/EC for the determination of nitrogen dioxide concentration by means of simulation. The main factors influencing the non-compliance of simulation and experimental studies are: the change of motor transport characteristics (traffic intensity, vehicle type, age, speed) during the study; and incomplete compliance of mathematical model applied by ADMS-Urban programme for the dispersion of pollutants in the air with real conditions.

5. Engineering solutions This chapter describes the structure of new modified diffusive sampler.

The invention includes several tools – solution “all in one”. The base of sampler is divided into two parts, allowing the simultaneous determination of two air pollutants – nitrogen dioxide and other pollutants (sulphur dioxide or ozone) (Fig. 9).

The prototype of modified diffusive sampler allows the determination of only one air pollutant by one sampler. Sampler length can be changed, allowing it to be exhibited for a shorter or longer time, and determining the concentrations of inorganic air pollutants (nitrogen oxides and sulphur dioxide or ozone), which expands the scope of the use of diffusive samplers and allows their use both in ambient air and working environment researches. The prototype of modified diffusion sampler is of invariable length.

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Diffusive sampler in the description of the prototype chosen is very simple, it allows the evaluation of only one inorganic air pollutant by one sampler, and is not intended to be exhibited during different time. Deficiencies of the prototype – it is possible to determine only one air pollutant using one sampler. Another deficiency of the prototype chosen is limited options to adapt it for a longer or shorter exposure time.

Fig. 9. Modified diffusion sampler scheme: 1 – diffusive sampler body; diffusive

sampler body extension; 3 – impregnated base divided into two parts; 4 – supporting ring; 5 – cap

The proposed invention can be used for the monitoring of ambient air. It allows the reduction of research costs, because only one sampler can be used instead of two diffusive samplers, and it is more versatile because it is suitable for shorter and longer exposure time.

General conclusions

1. The analysis of the scientific literature showed that only few detailed

purposeful complex researches, covering researches in laboratory and under natural conditions during the examination of structures of diffusive samplers, absorbent solutions and meteorological factors have been carried out.

2. Investigation of three length of diffusive samplers (2, 3.4 and 7 cm) showed that using the optimal structure of a modified diffusive sampler – stainless steel grid and 3.4 cm long sampler, the lowest relative errors

5

4

3

2

1

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of 7–16% for the determination of concentrations of nitrogen dioxide were obtained.

3. Sensitivity of modified diffusive samplers for determination of NO2 in ambient air using TEA aqueous solution of 10% for the impregnation of base, when exposure time 2 weeks was 2.2 µg/m3.

4. Investigating the effect of the ambient temperature and relative humidity on diffusive sampler performance, it was found the significant effect (p<0.05) of these factors over 35 °C temperature and over 80% relative humidity.

5. Using the diffusive samplers of modified optimal structure for the measurement of nitrogen dioxide concentration, when the concentration of TEA aqueous solution is 10% and 20%, the average indeterminacy is within the value limits of indicator method of 25% set by the Directive 2008/50/EC.

6. Average relative error of nitrogen dioxide concentrations simulated with ADMS-Urban software in ambient air of Žirmūnai catchment does not exceed the value of 30% for the simulation method set by the Directive 2008/50/EC and is equal 14% compared with NO2 concentration measured with the diffusive samplers.

Recommendation It is recommended to use a made-up diffusive sampler with split base for the determination of two inorganic air pollutants (nitrogen dioxide and other inorganic contaminants) in ambient air.

List of published works on the topic of the dissertation In the reviewed scientific journals Valuntaitė, V.; Šerevičienė, V.; Girgždienė, R., Paliulis, D. 2012. Relative humidity and temperature impact to ozone and nitrogen oxides removal rate in the experimental chamber. Journal of environmental engineering and landscape management. Vilnius: Technika. ISSN 1648-6897 (print), ISSN 1822-4199 (online). 20(1): 35–41 (Thomson ISI Web of Science). IF = 1,333 (2010). Šerevičienė, V.; Paliulis, D. 2011. Assessment of air quality using diffusive sampler and ADMS-Urban. Ekologija.Vilnius: Lietuvos mokslų akademija. ISSN 0235-7224 (print), ISSN 2029-0586 (online). 57(3): 129–136 (Thomson ISI Master Journal List). Šerevičienė, V.; Valuntaitė, V.; Paliulis, D. 2010. Impregnuojančio tirpalo įtakos difuzi-nių kaupiklių efektyvumui eksperimentiniai tyrimai. Mokslas – Lietuvos ateitis = Science – future of Lithuania: Aplinkos apsaugos inžinerija. Vilnius: Technika. ISSN 2029-2341(print), ISSN 2029-2252 (online). 2(5): 103–108 (Index Copernicus).

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Valuntaitė, V.; Šerevičienė, V.; Girgždienė, R. 2009. Ozone concentrations variations near high-voltage transmission lines. Journal of environmental engineering and landscape management. Vilnius: Technika. ISSN 1648-6897 (print), ISSN 1822-4199 (online). 17(1): 28–35 (Thomson ISI Web of Science). IF=1,508 (2009). In the other editions Šerevičienė, V.; Paliulis, D.; Valuntaitė, V. 2011. Laboratory and field testing of new design nitrogen dioxide diffusive samplers. The 8th International conference "Environ-mental engineering" selected papers, May 19–20, 2011 Vilnius, Lithuania. Vilnius: Technika, ISBN 978-9955-28-826-8. 1: 347–351. Šerevičienė, V.; Paliulis, D. 2009. Difuzinių kaupiklių taikymas aplinkosauginiuose ty-rimuose. Aplinkos apsaugos inžinerija, 12-osios Lietuvos jaunųjų mokslininkų konferencijos "Mokslas – Lietuvos ateitis" pranešimų medžiaga. Vilnius: Technika. 1–6. Šerevičienė,V.; Valuntaitė, V.; Girgždienė, R. 2008. Pasyviųjų kaupiklių taikymas ozono koncentracijai tirti. Bioinžinerija ir bioinformatika, fizika ir fizinė kompiuterija, 11-osios Lietuvos jaunųjų mokslininkų konferencijos "Mokslas – Lietuvos ateitis" straipsnių rinkinys. Vilnius: Technika. ISBN 978-9955-28-301-0. 145–152. Prepared application of patent Paliulis, D.; Šerevičienė, V. 2012. Difuzinis ėmiklis, [Difusive sampler]. No. 2012 027. About the author

Vaida Šerevičienė was born in Vilnius on 16 May 1984. In 2006 she acquired Bachelor’s degree in Bioengineering at Faculty of Fundamental Sciences at Vilnius Gediminas Technical University. In 2008, she received a Master’s of Science degree in Environmental and Ecology with honours at Faculty of Fundamental Sciences at Vilnius Gediminas Technical University. Since 2008 – she is phD student at Vilnius Gediminas Technical University. Since 2007 she is working as a head of training laboratory at the Department of Environmental Protection at Vilnius Gediminas Technical University.

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AZOTO DIOKSIDO DIFUZINIŲ ĖMIKLIŲ TYRIMAI IR TOBULINIMAS

Mokslo problemos aktualumas XX a. antrojoje pusėje stengiantis suderinti vartojimo kultūrą bei

gamtosaugos ir visuomenės sveikatos poreikius, pradėta ieškoti pramonės taršos sumažinimo būdų. Iš energetikos ir pramonės sektoriaus objektų bei transporto priemonių į aplinkos orą išmetama didžioji dalis neorganinių teršalų. Tarp jų vienas iš pavojingiausių yra azoto dioksidas (NO2), dažniausiai susidarantis vykstant degimo procesams. Azoto dioksidui jungiantis su vandens garais, atmosferoje susidaro rūgštūs lietūs. Vienas iš pagrindinių azoto oksidų šaltinių – autotransportas, į aplinką išmetantis apie pusę azoto oksidų kiekio Europoje. Ir šlapieji, ir sausieji NO2 nusėdimai yra kenksmingi: naikina augaliją, kenkia dirvožemio, statybinių medžiagų ir vandens telkinių kokybei. Neigiamo poveikio aplinkos komponentams sušvelninimui būtina stebėti pagrindinių teršalų koncentraciją aplinkos ore labiausiai užterštose vietose, vertinti gautus rezultatus ir imtis priemonių oro taršai mažinti.

Azoto dioksido matavimai aplinkos ore yra svarbūs ne tik Lietuvoje, bet ir visoje Europoje, taip pat ir kitose pasaulio šalyse. NO2 koncentracija aplinkos ore ribojama pagal 2008/50/EB Europos Parlamento ir Tarybos direktyvą. Pagal šią direktyvą, azoto dioksido ir kitų azoto oksidų koncentracijai nustatyti naudojamas pamatinis chemiliuminiscencinis metodas. Oro monitoringo stotyse yra naudojami tikslūs ir patikimi prietaisai, tačiau jie brangūs ir sunkūs, o jų įrengimas ir techninė priežiūra sudėtinga, todėl oro kokybės matavimų stotys įrengtos tik didesniuosiuose miestuose. Lietuvoje oro kokybė nuolatos vertinama 14 automatinių miesto ir 3 integruoto monitoringo stotyse, taikant pamatinius koncentracijos nustatymo metodus. Plečiantis miestų infrastruktūrai prieš daugelį metų įrengtos stacionarios stotys neparodo tikrųjų taršos objektų įtakos miesto oro kokybei.

Pastaraisiais dešimtmečiais vis populiaresni tampa difuziniai ėmikliai. Pasyviojo mėginio ėmimo sistema gali būti naudojama tolimųjų ir sunkiau prieinamų vietovių, tokių kaip miškai, oro stebėsenai.

Teritorijose, kuriose neatliekami nuolatiniai matavimai, aplinkos oro kokybės įvertinimui gali būti pritaikyti difuziniai ėmikliai. Ypatingai svarbus jų panaudojimas, kai reikia įvertinti ilgesnio laikotarpio teršalo koncentracijos lygį arba nustatyti vietoves, kurias pasiekia konkretus teršalas. Difuziniai ėmikliai yra veiksminga priemonė, vertinant miesto oro kokybę bei sudarant oro taršos žemėlapius.

Difuzinių ėmiklių išradėjas amerikiečių mokslininkas Edvardas Danielis Palmesas (1976) yra aprašęs vamzdelio formos difuzinį ėmiklį, kurį panaudojo

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darbo aplinkos kokybės įvertinimui. Tokio tipo difuziniai ėmikliai ir dabar naudojami didesnių teršalo koncentracijų tyrimams. Švedų mokslininkas Martinas Fermas (1991) sumažino Palmeso ėmiklio ilgį jautrumui padidinti. Gregas Ayersas su kolegomis (1995) panaudojo membraną atmosferos turbulentinio judėjimo įtakai mažinti.

Nors nuo 1973 metų, kai šie ėmikliai buvo pradėti naudoti, atlikta daug jų tobulinimų. Buvo siūlomi įvairūs sugeriantieji tirpalai ir jų paruošimo būdai, naudojami skirtingi ėmiklių pagrindai. Dažnai optimizuojamas vienas difuzinių ėmiklių parametras – difuzinių ėmiklių ilgis, pagrindas, impregnavimo tirpalas ir kt., bet trūksta visų azoto dioksido nustatymą lemiančių veiksnių įtakos įvertinimo. Šiuo metu nėra standartinės NO2 koncentracijos nustatymo difuziniais ėmikliais metodikos, todėl skirtingi nustatymo būdai įtakoja rezultatų tikslumą. Ėmiklio paruošimas ir taikymas – viena iš pagrindinių NO2 koncentracijos nustatymo neapibrėžčių.

Tyrimų objektas – difuzinis ėmiklis, naudojamas azoto dioksido

koncentracijai ore nustatyti. Darbo tikslas ir uždaviniai. Tikslas – ištirti svarbiausius veiksnius

darančius įtaką difuzinio ėmiklio matavimo tikslumui. Remiantis atliktų eksperimentinių tyrimų rezultatais patobulinti difuzinius ėmiklius ir nustatyti jų jautrį bei neapibrėžtį.

Darbo tikslui pasiekti darbe reikia spręsti šiuos uždavinius: 1. Išanalizuoti difuzinio ėmiklio ilgio ir pagrindo įtaką azoto dioksido

koncentracijos nustatymo tikslumui. 2. Ištirti trietanolamino vandeninio tirpalo koncentracijos įtaką azoto

dioksido kiekio ore įvertinimui difuziniais ėmikliais. 3. Ištirti meteorologinių veiksnių (oro temperatūros ir santykinio drėgnio)

įtaką azoto dioksido koncentracijos nustatymo neapibrėžčiai naudojant difuzinius ėmiklius.

4. Įvertinti azoto dioksido sklaidą aplinkos ore naudojant skaitinį modeliavimą ir gautuosius rezultatus palyginti su eksperimentiniais.

Tyrimų metodika. Darbe taikyti azoto dioksido koncentracijos pasyvusis ir chemiliuminiscencinis nustatymo metodai. Azoto dioksido sklaidai aplinkos ore modeliuoti naudotas ADMS-Urban programinės įrangos paketas.

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Mokslinis darbo naujumas Kompleksiniai skirtingos sudėties difuzinių ėmiklių azoto dioksido nustatymo tikslumo tyrimai bei meteorologinių veiksnių įtakos matavimo neapibrėžčiai įvertinimas.

Praktinė reikšmė. Remiantis atliktų tyrimų rezultatais, galima įvertinti

difuzinių ėmiklių taikymo azoto dioksido koncentracijai nustatyti ypatumus. Atsižvelgiant į gautus natūrinių ir laboratorinių eksperimentinių tyrimų rezultatus, patobulintos konstrukcijos difuziniai ėmikliai gali būti naudojami aplinkos oro stebėsenai.

Ginamieji teiginiai 1. Mažiausia suminė azoto dioksido koncentracijos nustatymo

neapibrėžtis gaunama optimizavus difuzinio ėmiklio korpuso ilgį, sugeriančiojo trietanolamino vandeninio tirpalo koncentraciją, bei eksponavimo laiką, kai difuzinio ėmiklio pagrindas – nerūdijančio plieno tinklelis.

2. Modifikuoto 3,4 cm ilgio difuzinio ėmiklio su nerūdijančio plieno tinklelio pagrindu, kai sugeriančio vandeninio tirpalo koncentracija – 10 % ir eksponavimo laikas – 336 valandos, azoto dioksido koncentracijos nustatymo riba – 2,2 µg/m3.

3. Azoto dioksido koncentracijos nustatymo neapibrėžčiai temperatūra daro didesnę įtaką negu santykinis drėgnis.

Darbo apimtis. Disertaciją sudaro įvadas, penki skyriai, bendrosios

išvados ir rekomendacijos, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai. Darbo apimtis yra 148 puslapiai, tekste panaudotos 44 numeruotos formulės, 64 paveikslai, 22 lentelė ir 1 priedas. Rašant disertaciją buvo panaudota 213 literatūros šaltinių.

Pirmajame skyriuje išanalizuotas azoto dioksido susidarymas ir sklaida aplinkos ore, išnagrinėti difuziniai ėmikliai ir jų veikimo ir konstrukcijų ypatumai, detalizuoti selektyvūs sugeriamieji tirpalai ir jų veikimui turintys įtakos aplinkos veiksniai. Taip pat išanalizuoti programiniai paketai, skirti azoto dioksido sklaidai aplinkos ore modeliuoti. Skyriaus pabaigoje suformuluotos išvados ir iškelti tolesnių mokslinių tyrimų uždaviniai. Antrajame skyriuje pristatyta difuzinių ėmiklių laboratorinių tyrimų metodika ir pateikta gautųjų rezultatų analizė bei išvados. Trečiajame skyriuje atskleista natūrinių eksperimentų tyrimų metodika. Įvertintas skirtingos sudėties difuzinių ėmiklių matavimo tikslumas eksponuojant juos Mažeikių rajono teritorijoje. Detalizuota rezultatų analizė ir išvados. Ketvirtajame skyriuje pristatyta modeliavimo metodika, pateiktas azoto dioksido

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sklaidos Vilniaus miesto Žirmūnų mikrorajono aplinkos ore modeliavimo ir tyrimų metu gautų rezultatų palyginimas, suformuluotos išvados. Penktajame skyriuje aprašytas inžinerinis sprendimas leidžiantis vienu metu matuoti dviejų neorganinių teršalų koncentraciją ore.

Bendrosios išvados 1. Išanalizavus mokslinę literatūrą, nustatyta, kad nepakankamai atlikta

kryptingų kompleksinių laboratorinių ir natūrinių tyrimų, kuriuose analizuojamos difuzinių ėmiklių konstrukcijos, azoto dioksido sugeriantieji tirpalai ir meteorologinių veiksnių įtaka NO2 koncentracijos nustatymo neapibrėžčiai.

2. Ištyrus trijų ilgių difuzinius ėmiklius (2, 3,4 ir 7 cm) nustatyta, kad naudojant optimalią modifikuoto difuzinio ėmiklio konstrukciją – nerūdijančio plieno tinklelį ir 3,4 cm ilgio ėmiklį, gautos mažiausios azoto dioksido koncentracijos nustatymo santykinės paklaidos 7–16 %.

3. Modifikuotų difuzinių ėmiklių, naudojant nerūdijančio plieno tinklelio pagrindo padengimui 10 % trietanolamino vandeninį tirpalą, kai eksponavimo laikas 2 savaitės, azoto dioksido koncentracijos apatinė nustatymo riba – 2,2 µg/m3.

4. Tiriant aplinkos temperatūros ir santykinio drėgnio įtaką azoto dioksido koncentracijos nustatymo difuziniais ėmikliais tikslumui, nustatyta šių aplinkos veiksnių reikšminga (p<0,05) įtaka, esant >35 °C temperatūrai ir >80 % santykiniam drėgniui.

5. Naudojant azoto dioksido koncentracijos matavimui natūrinėmis sąlygomis modifikuotus optimalios konstrukcijos difuzinius ėmiklius, kai trietanolamino vandeninio tirpalo koncentracija – 10 % ir 20 %, vidutinė neapibrėžtis neviršija 2008/50/EB direktyvoje indikatoriniam metodui nurodytos 25 % vertės.

6. ADMS-Urban programa sumodeliuotų azoto dioksido koncentracijų Vilniaus miesto Žirmūnų mikrorajono aplinkos ore vidutinė santykinė paklaida neviršija 2008/50/EB direktyvoje modeliavimo metodui nurodytos 30 % vertės ir yra lygi 14 %, lyginant su difuziniais ėmikliais išmatuota NO2 koncentracija.

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Rekomendacija Siekiant vienu metu nustatyti dviejų neorganinių oro teršalų koncentraciją (azoto dioksido ir kito neorganinio teršalo) aplinkos ore, siūlome naudoti sukurtą perskirto pagrindo difuzinį ėmiklį.

Trumpos žinios apie autorių Vaida Šerevičienė gimė 1984 m. gegužės 16 d. Vilniuje. 2006 m. įgijo bioinžinerijos bakalauro laipsnį Vilniaus Gedimino

technikos universiteto Fundamentinių mokslų fakultete. 2008 m. baigė aplinkotyros ir ekologijos magistro studijas su pagyrimu Vilniaus Gedimino technikos universiteto Fundamentinių mokslų fakultete. 2008–2012 m. – Vilniaus Gedimino technikos universiteto doktorantė. Nuo 2007 m. dirba Aplinkos chemijos mokomosios laboratorijos vedėja Vilniaus Gedimino technikos universiteto Aplinkos apsaugos katedroje.