Factors Influencing the Variability of SO2 Concentrations in Istanbul

ABSTRACT

The correlation between sulfur dioxide (SO₂) concentrations measured at the European and Asian sides of Istanbul and meteorological parameters is investigated using principal component analysis (PCA) and multiple regression analysis techniques. Several meteorological parameters are selected to represent the atmospheric conditions during two winter periods: 1993–1994 and 1994–1995. Six principal components are found to explain the majority of the observed meteorological variability. Surface pressure, 850-mb temperature, and surface zonal (east-west) and meridional (north-south) winds show high loadings on separate factors identified by PCA. We seek dominant meteorological parameters that control the SO₂ levels at each monitoring station. Several multiple regression analysis models are fitted to the data from each monitoring station using six principal components and previous day SO₂ concentrations as independent variables.

Results suggest that the most important parameters, highly correlated with SO₂ concentrations in the Istanbul metropolitan area, are atmospheric pressure and surface zonal and meridional winds. These components have more influence on the determination of the air pollution levels at the Asian side than at the European side.     

A New Method for Determining the Contribution of a Refinery to Local SO2 Levels in an Industrial Region

A new method was developed for determining the contribution of one pollutant source to the air quality in an industrialized region. Although the method is general, it is presented in reference to a 130,000 bbl/day petroleum refinery and its effect on ambient SO₂ concentrations in Sarnia, Ontario. The plumes from SO₂ emitters located upwind of the refinery were represented by a single hypothetical plume which influences monitoring stations located upwind as well as downwind from the refinery. However, the refinery emissions affect only the downwind stations. A simple equation was derived by means of which the concentration at the downwind station could be calculated from the concentration at the upwind station and the refinery emission. This equation contains two coefficients A and B which were evaluated such that the difference between the cumulative frequency distributions of the measured and calculated SO₂ concentrations at the downwind station was minimized. For the meteorological conditions and monitoring stations considered, it was found that the refinery contributed less than 4.5 pphm to ambient SO₂ concentrations over 1 hr periods. This result and the validity of the method are discussed.     

Assessing the impact of the acid deposition control program

A goal of the acidic deposition control program in the United States has been to link emissions control policies, such as those mandated under Title IV of the US Clean Air Act Amendments (CAAA) of 1990, to improvements in air and water quality. Recently, several researchers have reported trends in the time series of pollutant data in an effort to evaluate the effectiveness of the CAAA in reducing the acidic deposition problem. It is well known that pollutant concentrations are highly influenced by meteorological and climatic variations. Also, spatial and temporal inhomogeneities in time series of pollutant concentrations, induced by differences in the data collection, reduction, and reporting practices, can significantly affect the trend estimates. We present a method to discern breaks or discontinuities in the time series of pollutants stemming from emission reductions in the presence of meteorological and climatological variability. Using data from a few sites, this paper illustrates that linear trend estimates of concentrations of SO₂, aerosol SO₄²⁻, and precipitation-weighted SO₄²⁻ and NO₃⁻ can be biased because of such complex features embedded in pollutant time series.     

Contribution of transboundary air pollution to ionic concentrations in fog in the Kinki Region of Japan

To estimate the contribution of transboundary transported air pollutants from other Asian countries to Japan in ionic concentrations in fog water in March 2005, the Community Multiscale Air Quality (CMAQ) modeling system was utilized with meteorological fields produced by the 5th generation Mesoscale Model (MM5). For meteorological predictions, the model well reproduced the surface meteorological variables, particularly temperature and humidity, and generally captured fog occurrence. For chemical predictions, most of the model-predicted monthly mean concentrations were approximately within a factor of 2 of the observations, indicating that the model well simulated the long-range atmospheric transport from the Asian Continent to Japan. For SO₄^2?, NO₃^? and NH₄⁺, the contribution rates of the transboundary air pollution in the Kinki Region of Japan ranged from 69 to 82% for aerosols, from 47 to 87% for ionic concentrations in rain, and from 55 to 79% for ionic concentrations in fog. The study found that the transboundary air pollution also affected ionic concentrations in fog as well as aerosol concentrations and ionic concentrations in rain.     

Evaluation of aerosol sources at European high altitude background sites with trajectory statistical methods

This study has investigated the influence of synoptic weather patterns and long-range transport episodes on the concentrations of several compounds related to different aerosol sources (EC, OC, SO₄^2?, Ca²⁺, Na⁺, K⁺, ²¹⁰Pb, levoglucosan and dicarboxylic acids) registered in PM10 or PM2.5 aerosol samples collected at three remote background sites in central Europe. Air mass back-trajectories arriving at these sites have been analysed by statistical methods. Firstly, air mass back-trajectories have been grouped into clusters. Each cluster corresponds to specific meteorological scenarios, which were extracted and discussed. Finally, redistributed concentration fields have been computed to identify the main potential source regions of the different key aerosol components. A marked seasonal pattern is observed in the occurrence of the different clusters, with fast westerly and northerly Atlantic flows during winter and weak circulation flows in summer. Spring and fall were characterised by advection of moderate flows from northeastern and eastern Europe. Significant inter-cluster differences were observed for concentrations of receptor aerosol components, with the highest concentrations of EC, OC, SO₄^2?, K⁺ and ²¹⁰Pb associated with local and mesoscale aerosol sources located over central Europe related to enhanced photochemical processes. Emissions produced by fossil fuel and biomass burning processes from the Baltic countries, Byelorussia, western regions of Russia and Kazakhstan in spring and fall also contribute to elevated levels of EC, OC, SO₄^2?, K⁺ and ²¹⁰Pb. In the summer period long-range transport episodes of mineral dust from North-African deserts were also frequently detected, which caused elevated concentrations of coarse Ca²⁺ at sites. The baseline aerosol concentrations in central Europe at the high altitude background sites were registered in winter, with the exception of coarse Na⁺. While the relatively high concentrations of Na⁺ can be explained by sea salt advected from the Atlantic, the low levels of other aerosol components are caused by efficient aerosol scavenging associated to advections of Atlantic air masses, as well as lower emissions of these species over the Atlantic compared to those over the European continent and very limited vertical air mass exchange over the continent.     

Air pollution in the Krusne Hory region,Czech Republic during the 1990s

Emissions from the Black Triangle Region were considered to be the major source of air pollution problems in Europe during the 1990s. This discussion reviews the changes in emissions and pollution concentrations in the Krusne Hory Region (Czech Republic) in the winter half of the year during most of the past decade, and describes the relationships with meteorology. Sulfur dioxide (SO₂) is used as the example pollutant. The results show a decrease in pollution concentrations since 1996, as air pollution control and management strategies for important point sources take effect. The winter of 1995–1996 was especially harsh in the number of pollution episodes. Correlations between SO₂ and meteorological parameters are inconsistent. Wind direction provides the best relationship at monitoring stations along the Krusne Hory Plateau, with wind speed and temperature more variable depending on month and location. For the valley stations, higher SO₂ concentrations are strongly related to colder temperatures, higher relative humidities, and lower wind speeds. A case study during the winter of 1995–1996 (November 9–15) illustrated the importance of synoptic high pressure and a low-level inversion in minimizing plume dispersion from point sources. Specific sources of SO₂ affecting each station could thus be identified.     

Evaluation of a CMAQ simulation at high resolution over the UK for the calendar year 2003

A comprehensive ‘operational’ evaluation of the performance of the Community Multiscale Air Quality (CMAQ) modelling system version 4.6 was conducted in support of pollution assessment in the UK for the calendar year 2003. The model was run on multiple grids using one-way nests down to a horizontal resolution as fine as 5 km over the whole of the UK. The model performance was evaluated for pollutants with standards and limit values (e.g. O₃, PM₁₀) and species contributing to acidic and nitrogenous deposition (e.g. NH₃, SO₄^2–, NO₃^–, NH₄⁺) against data from operational national monitoring networks. The key performance characteristics of the modelling system were found to be variable according to acceptance criteria and to depend on the type (e.g. urban, rural) and location of the sites, as well as on the time of the year. As regards the techniques that were used for ‘operational’ evaluation, performance generally complied with expected levels and ranged from good (e.g. O₃, SO₄^2–) to moderate (e.g. PM₁₀, NO₃^–). At a few sites low correlations and large standard deviations for some species (e.g. SO₂) suggest that these sites are subject to local factors (e.g. topography, emission sources) that are not well described in the model. Overall, the model tends to over predict O₃ and under predict aerosol species (except SO₄^2–). Discrepancies between predicted and observed concentrations may be due to a variety of intertwined factors, which include inaccuracies in meteorological predictions, chemical boundary conditions, temporal variability in emissions, and uncertainties in the treatment of gas and aerosol chemistry. Further work is thus required to investigate the respective contributions of such factors on the predicted concentrations.     

meteorological program for limiting power plant stack emission

This paper is directed to those individuals concerned with preserving the local air quality in areas affected by power plant operations. A meteorological forecast and field measurement program has been developed by the Tennessee Valley Authority for limiting stack emissions at the Paradise Steam Plant to preserve the air quality during adverse atmospheric dispersion conditions. Meteorological and plume dispersion criteria, developed from analysis of prior experience, govern the program. The criteria values are designed for limiting surface sulfur dioxide (SO₂) concentrations below an established threshold level.

Daily forecasts of vertical wind and temperature distribution, maximum surface temperature, and sky condition are issued each afternoon by the National Oceanic and Atmospheric Administration National Weather Service, Knoxville, Tennessee. Through use of power plant computer facilities, the forecast data are processed to determine quantitative criteria values. If the values indicate that the threshold level may be exceeded, an Air Pollution Control Notice (APCN) is issued that afternoon for the period 0900–1400 CST the following day, which is the expected period of maximum SO₂, surface concentrations. The APCN specifies the allowable SO₂ emission rate, in terms of megawatt load generation, which should prevent surface SO₂ concentrations from exceeding the established threshold level. Confirmation or cancellation of the APCN is made the following morning, based on plant-site meteorological field measurements taken at 0700–0730 CST. If confirmed, plant load generation is reduced to the designated level by 0900 CST and is continued no later than 1400 CST during the expected period of maximum SO2 surface concentrations.

The APCN conditions identified with the newer and larger TV A power plants with high stacks are associated with one principal regional weather pattern—a large surface high-pressure system, with weak-to-moderate anticyclonic circulation and pronounced stability throughout the lowest few thousand meters. With the limited mixing layer, or sometimes referred to as trapping- or capping-type dispersion associated with this weather condition, relatively high surface concentrations may persist 2–5 hours between 0900–1400 CST.     

Influence of ship emissions on air quality and input of contaminants in southern Alaska National Parks and Wilderness Areas during the 2006 tourist season

The impact of ship emissions on air quality in Alaska National Parks and Wilderness Areas was investigated using the Weather Research and Forecasting model inline coupled with chemistry (WRF/Chem). The visibility and deposition of atmospheric contaminants was analyzed for the length of the 2006 tourist season. WRF/Chem reproduced the meteorological situation well. It seems to have captured the temporal behavior of aerosol concentrations when compared with the few data available. Air quality follows certain predetermined patterns associated with local meteorological conditions and ship emissions. Ship emissions have maximum impacts in Prince William Sound where topography and decaying lows trap pollutants. Along sea-lanes and adjacent coastal areas, NO_x, SO₂, O₃, PAN, HNO₃, and PM_2.5 increase up to 650 pptv, 325 pptv, 900 pptv, 18 pptv, 10 pptv, and 100 ng m^?3. Some of these increases are significant (95% confidence). Enhanced particulate matter concentrations from ship emissions reduce visibility up to 30% in Prince William Sound and 5–25% along sea-lanes.     

The Impact of Urban and Industrial Emissions on Mesoscale Precipitation Quality

Results from an acid rain field study around the city of Philadelphia are presented. The study involved the sampling of wet deposition at a network of 40 sites within a distance of 60 km from the Delaware River. Emphasis was placed on event-type rain sampling of frontal and primarily nonconvective storms which are responsible for most of the Northeast’s wet deposition. For most storms, meteorological conditions contributed to a predominant southeasterly transport. Since most of the area’s urban and industrial emissions occur along the Delaware River, the Pennsylvania sector of the network was identified as the downwind (target) region; the New Jersey sector was the upwind (control) region. Local emissions appear to impact the deposition of nitrate (NO₃?) which may register increases greater than 200%. It appears that this impact grows with distance from the river suggesting peaks beyond the 60 km boundary of the network. Comparisons with estimates of NO _x emissions reveal that a substantial fraction may be deposited as NO₃? on the mesoscale. The impact of local emissions on total sulfur is less striking; for some storms the sulfur excess is only in the form of dissolved SO₂. Storm-to-storm variabilities in meteorological conditions, emissions, and oxidant availabilities are probable causes of the variability in the magnitude of the local impact.     

Regional-scale impacts of Phase I of the Clean Air Act Amendments in the USA: the relation between emissions and concentrations,both wet and dry

A comparison of data records in the 1990s, both before (1991–1994) and after (1995–1997) implementation of Phase I of the Clean Air Act Amendments (CAAA) of 1990 for the eastern US, shows a significant reduction in SO₂ emissions for most states, except for Texas, North Carolina, Illinois, Florida, and Alabama. However, of the major NO_x emitting states, only two eastern states (New York and Pennsylvania) show significant declines in NO_x. A pattern of large declines in SO₂ emissions (>20%) after CAAA implementation, and large declines in precipitation SO₄²⁻ and H⁺, as well as air concentrations of SO₂ and SO₄²⁻ (components of dry deposition), exists for most regions of the eastern US. In most cases, the emission/concentration relations are close to 1 : 1 when the source region based on 15-h back trajectories is used for the New England region, and source regions based on 9-h back trajectories are used for the six other eastern US regions that were studied. The southern Appalachian Mountain region, an acid-sensitive area receiving high levels of acidic deposition, has not seen an appreciable improvement in precipitation acidity. This area has also shown the least improvement in wet and dry sulfur concentrations, of the areas examined. Precipitation base cations (Ca²⁺ and Mg²⁺) show a pattern of either increasing or level concentrations when comparing 1990–1994 to 1995–1998 data, for six of the seven regions examined. Ammonium concentrations have generally changed <10%, except for the Illinois and southern Appalachian Mtn. regions, which increased >15%.     

Significant geographic gradients in particulate sulfate over Japan determined from multiple-site measurements and a chemical transport model: Impacts of transboundary pollution from the Asian continent

We found a significant geographic gradient (longitudinal and latitudinal) in the sulfate (SO₄^2?) concentrations measured at multiple sites over the East Asian Pacific Rim region. Furthermore, the observed gradient was well reproduced by a regional chemical transport model. The observed and modeled SO₄^2? concentrations were higher at the sites closer to the Asian continent. The concentrations of SO₄^2? from China as calculated by the model also showed the fundamental features of the longitudinal/latitudinal gradient. The proportional contribution of Chinese SO₄^2? to the total in Japan throughout the year was above 50–70% in the control case, using data for Chinese sulfur dioxide (SO₂) emission from the Regional Emission Inventory in Asia (40–60% in the low Chinese emissions case, using Chinese SO₂ emissions data from the State Environmental Protection Administration of China), with a winter maximum of approximately 65–80%, although the actual concentrations of SO₄^2? from China were highest in summer. The multiple-site measurements and the model analysis strongly suggest that the SO₄^2? concentrations in Japan were influenced by the outflow from the Asian continent, and this influence was greatest in the areas closer to the Asian continent. In contrast, we found no longitudinal/latitudinal gradient in SO₂ concentrations; instead SO₂ concentrations were significantly correlated with local SO₂ emissions. Our results show that large amounts of particulate sulfate are transported over long distances from the East Asian Pacific Rim region, and consequently the SO₄^2? concentrations in Japan are controlled by the transboundary outflow from the Asian continent.     

Evaluating urban PM10 pollution benefit induced by street cleaning activities

Despite their burden in urban particulate air pollution, road traffic non-exhaust emissions are often uncontrolled and information about the effectiveness of mitigation measures on paved roads is still scarce. The present study is aimed to evaluate the effectiveness of mechanical sweeping/water flushing treatments in mitigating urban road dust resuspension and to quantify the real benefit in terms of ambient PM₁₀ concentrations. To this aim a specific campaign was carried out in a heavily trafficked central road of Barcelona (Spain), a Mediterranean city suffering from a traffic-related pollution, both for a high car density and a frequent lack of precipitation. Several street washings were performed by means of mechanical sweepers and pressure water during night in all traffic lanes and sidewalks. PM₁₀ levels were simultaneously compared with four reference urban background air quality stations to interpret any meteorological variability. At the downwind measurement site, PM₁₀ concentrations registered a mean daily decrease of 8.8 μg m^?3 during the 24 h after street washing treatments. However 3.7–4.9 μg m^?3 of such decrease were due to the meteorological variability detected at the upwind site, as well as at two of the reference sites. This reveals that an effective decrease of 4–5 μg m^?3 (7–10%) can be related to street washing efficiency. Mitigation of road dust resuspension was confirmed by investigating the chemical composition of airborne-PM₁₀ filters. Concentrations of Cu, Sb, Fe and mineral matter decrease significantly with respect to concentrations of elemental carbon, used as tracer for exhaust diesel emissions. High efficiency of street washing in reducing road dust loads was found by performing periodic samplings both on the treated and the untreated areas.     

Transport of SO2 and aerosol over the Yellow sea

Aircraft measurements of air pollutants were made to investigate the characteristic features of long-range transport of sulfur compounds over the Yellow Sea for the periods of 26–27 April and 7–10 November in 1998, and 9–11 April and 19 June in 1999, together with aerosol measurements at the Taean background station in Korea. The overall mean concentrations of SO₂, O₃ and aerosol number in the boundary layer for the observation period ranged 0.1–7.4 ppb 32.1–64.1 ppb and 1.0–143.6 cm⁻³, respectively. It was found that the air mass over the Yellow Sea had a character of both the polluted continental air and clean background air, and the sulfur transport was mainly confined in the atmospheric boundary layer. The median of SO₂ concentration within the boundary layer was about 0.1–2.2 ppb. However, on 8 November, 1998, the mean concentrations of SO₂ and aerosol number increased up to 7.4 ppb and 109.5 cm⁻³, respectively, in the boundary layer, whereas O₃ concentration decreased remarkably. This enhanced SO₂ concentration occurred in low level westerly air stream from China to Korea. Aerosol analyses at the downstream site of Taean in Korea showed 2–3 times higher sulfate concentration than that of other sampling days, indicating a significant amount of SO₂ conversion to non sea-salt sulfate during the long-range transport.     

PAH air pollution at a Portuguese urban area: carcinogenic risks and sources identification

This study aimed to characterize air pollution and the associated carcinogenic risks of polycyclic aromatic hydrocarbon (PAHs) at an urban site, to identify possible emission sources of PAHs using several statistical methodologies, and to analyze the influence of other air pollutants and meteorological variables on PAH concentrations.The air quality and meteorological data were collected in Oporto, the second largest city of Portugal. Eighteen PAHs (the 16 PAHs considered by United States Environment Protection Agency (USEPA) as priority pollutants, dibenzo[a,l]pyrene, and benzo[j]fluoranthene) were collected daily for 24 h in air (gas phase and in particles) during 40 consecutive days in November and December 2008 by constant low-flow samplers and using polytetrafluoroethylene (PTFE) membrane filters for particulate (PM₁₀ and PM_2.5 bound) PAHs and pre-cleaned polyurethane foam plugs for gaseous compounds. The other monitored air pollutants were SO₂, PM₁₀, NO₂, CO, and O₃; the meteorological variables were temperature, relative humidity, wind speed, total precipitation, and solar radiation. Benzo[a]pyrene reached a mean concentration of 2.02 ng?m^?3, surpassing the EU annual limit value. The target carcinogenic risks were equal than the health-based guideline level set by USEPA (10^?6) at the studied site, with the cancer risks of eight PAHs reaching senior levels of 9.98?×?10^?7 in PM₁₀ and 1.06?×?10^?6 in air. The applied statistical methods, correlation matrix, cluster analysis, and principal component analysis, were in agreement in the grouping of the PAHs. The groups were formed according to their chemical structure (number of rings), phase distribution, and emission sources. PAH diagnostic ratios were also calculated to evaluate the main emission sources. Diesel vehicular emissions were the major source of PAHs at the studied site. Besides that source, emissions from residential heating and oil refinery were identified to contribute to PAH levels at the respective area. Additionally, principal component regression indicated that SO₂, NO₂, PM₁₀, CO, and solar radiation had positive correlation with PAHs concentrations, while O₃, temperature, relative humidity, and wind speed were negatively correlated.     

NCAQ Report to Congress: Review and Response

Airborne measurements of gaseous and particulate sulfur and nitrogen pollutants were made in southwestern Kentucky on the afternoon of October 21, 1979. Back-trajectory analysis indicates that the sampled air parcel moved over northern Florida, Alabama, and western Tennessee during the two days prior to sampling. Before moving over Florida, the air parcel was over the Atlantic Ocean for at least five days. Analytical long-range transport (LRT) model predictions based on anthropogenic emissions account for only about 75% of the airborne measured concentrations of 14.7 μg m^?3 for SO₂ and 4.8 μg m^?3 for SO₄ ^2?. The remaining 25 % is thought to be due to biogenic sulfur emissions from the extensive wetland areas along the Gulf Coast.

Forward-trajectory analysis indicates that the air parcel moved to the Adirondack Mountains of New York State 24 hours after sampling. Model predictions indicate that SO₂ and SO₄ ^2? mean layer concentrations at the Adirondacks were 24 and 16 μg^?3, respectively. Almost half of this sulfur was estimated to come from emissions in the heavily industrialized region along the Ohio River Valley.

Further comparisons used a measurement data base obtained in southeastern Canada and the state of Arkansas during August 1976. An air parcel was tracked for seven days as it entered the north central United States, stagnated over the lower midwest, and then moved to eastern Canada. Model predictions were in substantial agreement with regional SO₄ ^2? concentrations measured at a number of ground-level sites. Average SO₄ ^2? concentrations measured in central Arkansas on August 10, 1976 were 20 μ m^?3 vs. a modeled value of 19 μ m^?3. Average SO₄ ^2? concentrations measured in Nova Scotia four days later were 22 μg^?3 vs. a modeled estimate of 24 μg^?3.     

Assessment of air quality benefits from national air pollution control policies in China. Part II: Evaluation of air quality predictions and air quality benefits assessment

Following the meteorological evaluation in Part I, this Part II paper presents the statistical evaluation of air quality predictions by the U.S. Environmental Protection Agency (U.S. EPA)’s Community Multi-Scale Air Quality (Models-3/CMAQ) model for the four simulated months in the base year 2005. The surface predictions were evaluated using the Air Pollution Index (API) data published by the China Ministry of Environmental Protection (MEP) for 31 capital cities and daily fine particulate matter (PM_2.5, particles with aerodiameter less than or equal to 2.5 μm) observations of an individual site in Tsinghua University (THU). To overcome the shortage in surface observations, satellite data are used to assess the column predictions including tropospheric nitrogen dioxide (NO₂) column abundance and aerosol optical depth (AOD). The result shows that CMAQ gives reasonably good predictions for the air quality.The air quality improvement that would result from the targeted sulfur dioxide (SO₂) and nitrogen oxides (NO_x) emission controls in China were assessed for the objective year 2010. The results show that the emission controls can lead to significant air quality benefits. SO₂ concentrations in highly polluted areas of East China in 2010 are estimated to be decreased by 30–60% compared to the levels in the 2010 Business-As-Usual (BAU) case. The annual PM_2.5 can also decline by 3–15 μg m^?3 (4–25%) due to the lower SO₂ and sulfate concentrations. If similar controls are implemented for NO_x emissions, NO_x concentrations are estimated to decrease by 30–60% as compared with the 2010 BAU scenario. The annual mean PM_2.5 concentrations will also decline by 2–14 μg m^?3 (3–12%). In addition, the number of ozone (O₃) non-attainment areas in the northern China is projected to be much lower, with the maximum 1-h average O₃ concentrations in the summer reduced by 8–30 ppb.     

Estimated long-term outdoor air pollution concentrations in a cohort study

Several recent studies associated long-term exposure to air pollution with increased mortality. An ongoing cohort study, the Netherlands Cohort Study on Diet and Cancer (NLCS), was used to study the association between long-term exposure to traffic-related air pollution and mortality. Following on a previous exposure assessment study in the NLCS, we improved the exposure assessment methods.Long-term exposure to nitrogen dioxide (NO₂), nitrogen oxide (NO), black smoke (BS), and sulphur dioxide (SO₂) was estimated. Exposure at each home address (N=21 868) was considered as a function of a regional, an urban and a local component. The regional component was estimated using inverse distance weighed interpolation of measurement data from regional background sites in a national monitoring network. Regression models with urban concentrations as dependent variables, and number of inhabitants in different buffers and land use variables, derived with a Geographic Information System (GIS), as predictor variables were used to estimate the urban component. The local component was assessed using a GIS and a digital road network with linked traffic intensities. Traffic intensity on the nearest road and on the nearest major road, and the sum of traffic intensity in a buffer of 100 m around each home address were assessed. Further, a quantitative estimate of the local component was estimated.The regression models to estimate the urban component explained 67%, 46%, 49% and 35% of the variances of NO₂, NO, BS, and SO₂ concentrations, respectively. Overall regression models which incorporated the regional, urban and local component explained 84%, 44%, 59% and 56% of the variability in concentrations for NO₂, NO, BS and SO₂, respectively.We were able to develop an exposure assessment model using GIS methods and traffic intensities that explained a large part of the variations in outdoor air pollution concentrations.     

Influence of NO2 and dissolved iron on the S(IV) oxidation in synthetic aqueous solution

The influence of dissolved NO₂ and iron on the oxidation rate of S(IV) species in the presence of dissolved oxygen is presented. To match the conditions in the real environment, the concentration of iron in the reaction solution and trace gases in the gas mixture was typical for a polluted atmosphere. The time dependence of HSO₃⁻, SO₄²⁻, NO₂⁻ and NO₃⁻ and the concentration ratio between Fe(II) and total dissolved iron were monitored. Sulphate formation was the most intensive in the presence of an SO₂/NO₂/air gas mixture and Fe(III) in solution. The highest contribution to the overall oxidation was from Fe-catalysed S(IV) autoxidation. The reaction rate in the presence of both components was equal to the sum of the reaction rates when NO₂ and Fe(III) were present separately, indicating that under selected experimental conditions there exist two systems: SO₂/NO₂/air and SO₂/NO₂/air/Fe(III), which are unlikely to interact with each other. The radical chain mechanism can be initiated via reactions Fe(III)–HSO₃⁻ and NO₂–SO₃²⁻/HSO₃⁻.