Atmospheric Environment (v.45, #3)
Editorial board (i).
Publisher’s Note by Bethan Keall (523).
Atmospheric amines – Part I. A review by Xinlei Ge; Anthony S. Wexler; Simon L. Clegg (524-546).
Amines are emitted by a wide range of sources and are ubiquitous atmospheric organic bases. Approximately 150 amines and about 30 amino acids have been identified in the atmosphere. We review the present knowledge of atmospherically relevant amines with respect to their sources, fluxes, and dynamics including gas-phase reactions, gas-to-particle conversion and deposition. The health effects of aliphatic and aromatic amines are briefly summarized as well as the atmospheric occurrence and reactivity of amino acids and urea.► 154 amines, 32 amino acids and urea have been identified in the atmosphere. ► Sources, fluxes, and dynamics of atmospheric amines and amino acids are reviewed. ► Health effects of aliphatic and aromatic amines are briefly summarized.
Keywords: Amines; Amino acids; Atmospheric chemistry; Gas/particle partitioning;
A re-assessment of aerosol size distributions from Masaya volcano (Nicaragua) by R.S. Martin; E. Ilyinskaya; G.M. Sawyer; V.I. Tsanev; C. Oppenheimer (547-560).
Cascade impactors were used to sample volcanic aerosol from Masaya (Nicaragua) in 2007, 2009 and 2010. Differences were found in the size distributions of volcanic aerosol between these recent campaigns and with a campaign in 2001: (1) SO4 2− showed modes in both the fine (<1 μm; with low Na+/K+) and coarse (>1 μm; with high Na+/K+) fractions in all of the recent campaigns despite being unimodal in 2001 (<1 μm); (2) The modal diameters for SO4 2− roughly doubled in 2009, compared to 2007 or 2010; (3) total Cl− was depleted in volcanic aerosol compared to background aerosol in all the more recent campaigns but was enriched in 2001. Other aspects of the volcanic aerosol appear to be persistent, such as a fine SO4 2−–H+–Na+–K+ mode, which was the most abundant mode in all campaigns, and a coarse Cl−–F−–Mg2+–Ca2+ mode of lower abundance. Water uptake and speciation in the aerosol were investigated using the equilibrium model, ISORROPIA II. Results show that the coarse SO4 2−-rich mode deliquesces at lower relative humidity (40% RH) than the fine SO4 2−-rich mode (50% RH) due to increased Na+/K+ in the former. The aerosol was predicted to be dry at ambient relative humidity in 2009 and dominated by NaHSO4, KHSO4, CaSO4 and MgSO4. In contrast, model results predict a liquid aerosol at ambient relative humidity in 2010. These results indicate that aerosol emissions from a volcano can vary in ionic composition and even more so in physical speciation (i.e., salts or solutions). These observations are set against a near-constant magmatic gas composition at Masaya, which highlights the significance of atmospheric and dynamic factors in the formation of volcanic aerosols.► <1 μm SO4 2−- and >1 μm Cl−-rich modes are persistent features of Masaya’s aerosol. ► New features of Masaya’s aerosol are identified, including a >1 μm SO4 2−-rich mode. ► Masaya’s aerosol is time-variable in ionic composition and physical speciation.
Keywords: Masaya; Volcanic; Aerosol; Cascade impactor;
Atmospheric amines – Part II. Thermodynamic properties and gas/particle partitioning by Xinlei Ge; Anthony S. Wexler; Simon L. Clegg (561-577).
► Thermodynamic data of amines that controls gas/particle partitioning are compiled. ► Data includes HLC, vapor pressure, activity coefficient and aqueous solubility. ► Partitioning of amines into aqueous aerosols is strongly dependent upon pH. ► Amines can partition into the aerosol, similar to or greater than that of ammonia.
Keywords: Amines; Amino acids; Vapor pressure; Dissociation constant; Thermodynamic model; Gas/particle partitioning;
Nationwide summer peaks of OC/EC ratios in the contiguous United States by Tao Zeng; Yuhang Wang (578-586).
The ratios of observed organic carbon (OC) to elemental carbon (EC) from the rural sites of the IMPROVE network are analyzed for the 5-year period from 2000 to 2004. Among these years, nationwide OC/EC peaks are observed most consistently in the summer of 2002. Several potential factors are analyzed, including biomass burning, secondary organic aerosols (SOA) formation from biogenic sources and in-cloud processing, long-range transport from East Asia, and meteorological conditions over the U.S. We find that biomass burning and SOA formation make the most significant contributions using the global GEOS-Chem model simulations. The effect of model estimated in-cloud SOA formation is significant compared to the estimate of (non-cloud) biogenic SOA. The impacts of Canadian and western U.S. fires are larger than fires in Russia or Mexico in summer. The dry meteorological condition of the summer of 2002 tends to promote higher OC/EC ratios by inducing larger fire emissions, SOA formation, and a longer OC lifetime.► Large-scale analysis of OC/EC peaks in the U.S. ► Biomass burning leads to regional OC/EC peaks. ► SOA formation leads to regional OC/EC peaks. ► Source apportionment based on OC/EC ratios.
Keywords: OC/EC ratio; Biomass burning; Summer burning; SOA; Model evaluation;
Contamination of Alpine snow and ice at Colle Gnifetti, Swiss/Italian Alps, from nuclear weapons tests by Jacopo Gabrieli; Giulio Cozzi; Paul Vallelonga; Margit Schwikowski; Michael Sigl; Jost Eickenberg; Lukas Wacker; Claude Boutron; Heinz Gäggeler; Paolo Cescon; Carlo Barbante (587-593).
Plutonium is present in the environment as a consequence of atmospheric nuclear tests, nuclear weapons production and industrial releases over the past 50 years. To study temporal trends, a high resolution Pu record was obtained by analyzing 52 discrete samples of an alpine firn/ice core from Colle Gnifetti (Monte Rosa, 4450 m a.s.l.), dating from 1945 to 1990. The 239Pu signal was recorded directly, without decontamination or preconcentration steps, using an Inductively Coupled Plasma – Sector Field Mass Spectrometer (ICP-SFMS) equipped with an high efficiency sample introduction system, thus requiring much less sample preparation than previously reported methods. The 239Pu profile reflects the three main periods of atmospheric nuclear weapons testing: the earliest peak lasted from 1954/55 to 1958 and was caused by the first testing period reaching a maximum in 1958. Despite a temporary halt of testing in 1959/60, the Pu concentration decreased only by half with respect to the 1958 peak due to long atmospheric residence times. In 1961/62 Pu concentrations rapidly increased reaching a maximum in 1963, which was about 40% more intense than the 1958 peak. After the signing of the “Limited Test Ban Treaty” between USA and USSR in 1964, Pu deposition decreased very sharply reaching a minimum in 1967. The third period (1967–1975) is characterized by irregular Pu concentrations with smaller peaks (about 20–30% of the 1964 peak) which might be related to the deposition of Saharan dust contaminated by the French nuclear tests of the 1960s. The data presented are in very good agreement with Pu profiles previously obtained from the Col du Dome ice core (by multi-collector ICP-MS) and Belukha ice core (by Accelerator Mass Spectrometry, AMS). Although a semi-quantitative method was employed here, the results are quantitatively comparable to previously published results.► High-resolution profile of atmospheric 239Pu deposition from Alpine ice core. ► Direct ICP-SFMS determination without preconcentration and purification. ► 239Pu profile reflects the three main periods of atmospheric nuclear weapons testing. ► The data presented are in very good agreement with 239Pu profiles previously obtained.
Keywords: Plutonium; Ice cores; Atmospheric pollution; Nuclear weapon tests; Colle Gnifetti;
Transport pathways and potential sources of PM10 in Beijing by Lei Zhu; Xin Huang; Hui Shi; Xuhui Cai; Yu Song (594-604).
Beijing has suffered from major air pollution in recent years from PM10. In this study, we investigated the transport pathways and potential sources of PM10 concentration based on backward trajectories and PM10 concentration records from 2003 to 2009. Four transport pathways of high PM10 existed. One was the northwest pathway, which had the most frequency of occurrence in spring and winter, and traveled over the southern Mongolia, western Inner Mongolia, and Loess plateaus. The second one was the south pathway, which mostly occurred during May and September, and passed from the south of Beijing. The third one was the V-shape southwest pathway, which occurred mostly during early autumn and passed over the west and south of Hebei. The highest PM10 concentration was found with the southwest pathway, which occurs mostly in April and October, and traveled over the Loess Plateau and the west and south of Hebei. Low concentrations of PM10 with the southwest and east pathways were possible due to intensive precipitation in summer. Characterizing with the lowest PM10 concentration, the north pathway was possible associated with strong winds that leaded to diffusion of air pollutants in Beijing. The contribution of PM10 from long transported was about 39.3 μg m−3, which accounted for about 26.0% of the PM10 concentrations in Beijing.► Transport pathways lead to different levels of PM10 in Beijing were identified. ► Transported pathways could be explained by typical synoptic patterns. ► Identified potential sources of PM10 matched with transport pathways.
Keywords: Transport pathway; Backward trajectory; Trajectory cluster; Trajectory sector analysis (TSA); Potential source contribution function (PSCF);
Emissions of mercury from the power sector in Poland by J. Zyśk; A. Wyrwa; M. Pluta (605-610).
Poland belongs to the European Union countries with the highest mercury emissions. This is mainly related to coal combustion. This paper presents estimates of mercury emissions from power sector in Poland. In this work, the bottom-up approach was applied and over 160 emission point sources were analysed. For each, the characteristics of the whole technological chain starting from fuel quality, boiler type as well as emission controls were taken into account. Our results show that emissions of mercury from brown coal power plants in 2005 were nearly four times greater than those of hard coal power plants. These estimates differ significantly from national statistics and some possible reasons are discussed. For the first time total mercury emissions from the Polish power sector were differentiated into its main atmospheric forms: gaseous elemental (GEM), reactive gaseous (RGM) and particulate-bound mercury. Information on emission source location and the likely vertical distribution of mercury emissions, which can be used in modelling of atmospheric dispersion of mercury is also provided.► Estimation of mercury emissions from the Polish power sector. ► First attempt to differentiate total mercury emissions into its three main forms. ► Comparison of results obtained with the bottom-up and top-down methodology.
Keywords: Mercury; Emission; Speciation; Bottom-up; Power sector; Poland;
Characteristics of airborne particles and the factors affecting them at bus stations by L. Wang; L. Morawska; E.R. Jayaratne; K. Mengersen; D. Heuff (611-620).
Measurements of airborne particle number size distributions, particle number and PM2.5 concentrations were conducted at two bus stations of different designs: open station and canyon station, operated according to the same timetables and fleet compositions, as well as at a reference point in Brisbane, Australia. Simultaneous traffic and meteorological parameters were also monitored, aiming to quantify particle characteristics and investigate the impact of station design and meteorological conditions on particle emissions at the two bus stations. It was found that there was no significant difference in average particle number concentrations in the size range 7–3000 nm (PN7–3000) between the two stations (fine days: p = 0.90 and rainy days: p = 0.80), and that PN50–120 contributed to the largest proportion of particle number concentrations. PN20–30 were observed to increase at the open station during all time periods, except 0:00–7:00, which is likely to be attributed to the lower average daily temperature at the open station (around 7 °C lower than at the canyon station). During precipitation, it was found that particle number concentration in the size range 25–250 nm decreased greatly, and the average daily reduction in PM2.5 concentration on rainy days compared to fine days was 44.2% and 22.6% at the open and canyon station, respectively. The effect of ambient wind speeds on particle number concentration was also examined, and no relationship was found between particle number concentration and wind speed for the entire measurement period. In addition, 33 pairs of average half-hourly PN7–3000 concentrations were calculated and identified at the two stations, during the same time of a day, and with the same ambient wind speeds and precipitation conditions. The results of a paired t-test showed that the average half-hourly PN7–3000 concentrations at the two stations were not significantly different at the 5% confidence level (t = 0.06, p = 0.96), which indicates that the different station designs were not a crucial factor for influencing PN7–3000 concentrations. This finding implies that the timescale of dispersion at the bus stations was comparatively long, and that the source contribution was more important compared to the atmospheric dispersions associated with different station designs.► PN concentration < 250 nm was unaffected by precipitation. ► Pollution at the bus stations took a relatively long time to disperse. ► Source contribution had a greater impact on pollution concentration than the dispersion patterns associated with different station designs.
Keywords: Bus station; Particle number concentration; PM2.5; Particle number size distribution; Precipitation; Meteorological parameters; Design;
Back-trajectory-based source apportionment of airborne sulfur and nitrogen concentrations at Rocky Mountain National Park, Colorado, USA by Kristi A. Gebhart; Bret A. Schichtel; William C. Malm; Michael G. Barna; Marco A. Rodriguez; Jeffrey L. Collett (621-633).
The Rocky Mountain Atmospheric Nitrogen and Sulfur Study (RoMANS), conducted during the spring and summer of 2006, was designed to assess the sources of nitrogen and sulfur species that contribute to wet and dry deposition and visibility impairment at Rocky Mountain National Park (RMNP), Colorado. Several source apportionment methods were utilized for RoMANS, including the Trajectory Mass Balance (TrMB) Model, a receptor-based method in which the hourly measured concentrations are the dependent variables and the residence times of back trajectories in several source regions are the independent variables. The regression coefficients are estimates of the mean emissions, dispersion, chemical transformation, and deposition between the source areas and the receptors. For RoMANS, a new ensemble technique was employed in which input parameters were varied to explore the range, variability, and model sensitivity of source attribution results and statistical measures of model fit over thousands of trials for each set of concentration measurements.Results showed that carefully chosen source regions dramatically improved the ability of TrMB to reproduce temporal patterns in the measured concentrations, and source attribution results were also very sensitive to source region choices. Conversely, attributions were relatively insensitive to trajectory start height, trajectory length, minimum endpoints per source area, and maximum endpoint height, as long as the trajectories were long enough to reach contributing source areas and were not overly restricted in height or horizontal location. Source attribution results estimated that more than half the ammonia and 30–45% of sulfur dioxide and other nitrogen-containing species at the RoMANS core site were from sources within the state of Colorado. Approximately a quarter to a third of the sulfate was from within Colorado.► New ensemble method for air quality source apportionment receptor model discussed. ► Trajectory Mass Balance used to attribute nitrogen and sulfur concentrations. ► Half ammonia at Rocky Mountain National Park, CO, USA estimated from within state. ► Third of sulfate at Rocky Mountain National Park, Colorado, USA from within state. ► Trajectory Mass Balance insensitive to many parameters if all sources included.
Keywords: Receptor modeling; Source attribution; Back trajectory analysis; Nitrogen; Sulfur; Rocky Mountain National Park; Air quality;
Spatial disaggregation of carbon dioxide emissions from road traffic based on multiple linear regression model by Yuqin Shu; Nina S.N. Lam (634-640).
Detailed estimates of carbon dioxide emissions at fine spatial scales are critical to both modelers and decision makers dealing with global warming and climate change. Globally, traffic-related emissions of carbon dioxide are growing rapidly. This paper presents a new method based on a multiple linear regression model to disaggregate traffic-related CO2 emission estimates from the parish-level scale to a 1 × 1 km grid scale. Considering the allocation factors (population density, urban area, income, road density) together, we used a correlation and regression analysis to determine the relationship between these factors and traffic-related CO2 emissions, and developed the best-fit model. The method was applied to downscale the traffic-related CO2 emission values by parish (i.e. county) for the State of Louisiana into 1-km2 grid cells. In the four highest parishes in traffic-related CO2 emissions, the biggest area that has above average CO2 emissions is found in East Baton Rouge, and the smallest area with no CO2 emissions is also in East Baton Rouge, but Orleans has the most CO2 emissions per unit area. The result reveals that high CO2 emissions are concentrated in dense road network of urban areas with high population density and low CO2 emissions are distributed in rural areas with low population density, sparse road network. The proposed method can be used to identify the emission “hot spots” at fine scale and is considered more accurate and less time-consuming than the previous methods.► Spatial disaggregation of traffic-related CO2 emissions from parish scale to 1-km2. ► Select allocation factors. ► Develop multiple linear regression model. ► Identify the emission “hot spots” at finer scale.
Keywords: Multiple linear regression model; Carbon dioxide emissions; Spatial disaggregation;
Summer 2009 wildfires in Portugal: Emission of trace gases and aerosol composition by Célia Alves; Ana Vicente; Teresa Nunes; Cátia Gonçalves; Ana Patrícia Fernandes; Fátima Mirante; Luís Tarelho; Ana M. Sánchez de la Campa; Xavier Querol; Alexandre Caseiro; Cristina Monteiro; Margarita Evtyugina; Casimiro Pio (641-649).
In summer 2009, emissions of trace gases and aerosols from several wildfires occurring in Portugal were sampled. A portable high-volume sampler was used to collect sequentially, on quartz fibre filters, coarse (PM2.5–10) and fine (PM2.5) smoke particles. Tedlar air sampling bags have been used for complementary chemical characterisation of the gaseous phase. The carbonaceous content (elemental and organic carbon, EC/OC) of particulate matter was analysed by a thermal-optical transmission technique. The levels of almost 50 elements were quantified by inductively coupled plasma-mass spectrometry. The water-soluble ions were obtained by ion chromatography. Emission factors of species that are favoured by the smouldering phase (e.g. CO) were above the values reported in the literature for biomass burning in other ecosystems. The CO emission factors were 231 ± 117 g kg−1 biomass (dry basis) burned. Emissions of compounds that are promoted in fresh plumes and during the flaming phase, such as CO2, were generally lower than those proposed for savannah and tropical forest fires. The CO2 emission factors ranged from about 1000 to 1700 g kg−1. Total hydrocarbons, PM2.5, PM10 and OC presented variable emissions, but in general substantially higher than values reported for wildfires in African and Amazonian biomes. The emission factors obtained in Portugal were as follows (in g kg−1 biomass, dry basis): 6–350 for total hydrocarbons, 0.5–42 for PM2.5, 1–60 for PM10, and 0.2–42 for OC (in PM10). The organic carbon-to-elemental carbon ratios measured in the present study largely exceeded those obtained by other researchers. The aerosol mass was dominated by organic matter (OC/PM2.5 = 50 ± 18%, OC/PM2.5–10 = 36 ± 18%). The metal elements represented, on average, 1.23 and 0.91%, while the measured water-soluble ions accounted for 2.6 and 2.1% of the PM2.5 and PM2.5–10 mass, respectively. Carbonates accounted for 0.15–3.1% (average = 0.83%) of PM2.5–10. The dominant elements were B, Ti, Mn, Cu, Zn, Zr and Ba.► Wildfires are a major contributor of trace gases and aerosol species. ►Emissions are a function of the vegetation type and combustion phase. ► Wildfire emissions in the Mediterranean area are not well-studied. ► Emission factors for CO, CO2 and hydrocarbons were determined. ► The chemical composition of smoke particles was characterised.
Keywords: Wildfires; Trace gases; Carbonaceous particles; Emission factors; Water-soluble ions; Metals;
Contrast in air pollution components between major streets and background locations: Particulate matter mass, black carbon, elemental composition, nitrogen oxide and ultrafine particle number by Hanna Boogaard; Gerard P.A. Kos; Ernie P. Weijers; Nicole A.H. Janssen; Paul H. Fischer; Saskia C. van der Zee; Jeroen J. de Hartog; Gerard Hoek (650-658).
Policies to reduce outdoor air pollution concentrations are often assessed on the basis of the regulated pollutants. Whether these are the most appropriate components to assess the potential health benefits is questionable, as other health-relevant pollutants may be more strongly related to traffic.The aim of this study is to compare the contrast in concentration between major roads and (sub)urban background for a large range of pollutants and to analyze the magnitude of the measured difference in the street – background for major streets with different street configurations.Measurements of PM10, PM2.5, particle number concentrations (PNC), black carbon (BC), elemental composition of PM10 and PM2.5 and NOx were conducted simultaneously in eight major streets and nine (sub)urban background locations in the Netherlands. Measurements were done six times for a week during a six month period in 2008.High contrasts between busy streets and background locations in the same city were found for chromium, copper and iron (factor 2–3). These elements were especially present in the coarse fraction of PM. In addition, high contrasts were found for BC and NOx (factor 1.8), typically indicators of direct combustion emissions. The contrast for PNC was similar to BC. NO2 contrast was lower (factor 1.5). The largest contrast was found for two street canyons and two streets with buildings at one side of the street only.The contrast between busy streets and urban background in NO2 was less than the contrast found for BC, PNC and elements indicative of non-exhaust emissions, adding evidence that NO2 is not representing (current) traffic well. The study supports a substantial role for non-exhaust emissions including brake- and tyre wear and road dust in addition to direct combustion emissions. Significant underestimation of disease burden may occur when relying too much on the regulated components.► High contrasts were found for chromium, copper and iron (factor 2–3). ► High contrasts were found for BC and NOx (factor 1.8). ► NO2 contrast was lower (factor 1.5), and is not representing (current) traffic well. ► Non-exhaust emissions are important in addition to exhaust emissions in urban areas.
Keywords: Air pollution; Elemental composition; Streets; Contrast; PM10; PM2.5; NO2; NOx; Black carbon; Chromium; Copper; Iron;
Using spatio-temporal modeling to predict long-term exposure to black smoke at fine spatial and temporal scale by Payam Dadvand; Stephen Rushton; Peter J. Diggle; Louis Goffe; Judith Rankin; Tanja Pless-Mulloli (659-664).
Whilst exposure to air pollution is linked to a wide range of adverse health outcomes, assessing levels of this exposure has remained a challenge. This study reports a modeling approach for the estimation of weekly levels of ambient black smoke (BS) at residential postcodes across Northeast England (2055 km2) over a 12 year period (1985–1996). A two-stage modeling strategy was developed using monitoring data on BS together with a range of covariates including data on traffic, population density, industrial activity, land cover (remote sensing), and meteorology. The first stage separates the temporal trend in BS for the region as a whole from within-region spatial variation and the second stage is a linear model which predicts BS levels at all locations in the region using spatially referenced covariate data as predictors and the regional predicted temporal trend as an offset. Traffic and land cover predictors were included in the final model, which predicted 70% of the spatio-temporal variation in BS across the study region over the study period. This modeling approach appears to provide a robust way of estimating exposure to BS at an inter-urban scale.► Using remote sensing, GIS, and statistical modeling to predict air pollution levels. ► A two-stage modeling to predict spatiotemporal variation in black smoke (BS) levels. ► First stage is a temporal model and the second stage is a spatiotemporal model. ► Predicting 70% of spatiotemporal variation in BS in Northern England, 1985–96. ► This modeling approach is efficient at both inter-urban and intra-urban levels.
Keywords: Spatiotemporal modeling; Exposure assessment; Geographical information system; GIS; Air pollution; Black smoke; Exposure modeling;
Impact of aerosol particles on cloud formation: Aircraft measurements in China by Qiang Zhang; Jiannong Quan; Xuexi Tie; Mengyu Huang; Xincheng Ma (665-672).
In-situ aircraft measurements of aerosols and clouds of 7 flights during the period from July to September of 2008 are analyzed in Beijing, China. The measured aerosol concentrations indicated that the Beijing region was highly polluted by aerosol particles. The impact of heavy aerosol particle loadings on cloud formation is studied. The microphysical characters of clouds (including number concentrations of cloud droplets (Nc), cloud droplet radius (Rc), liquid water content (LWC)), and number concentrations of aerosol particles (Na) were measured during the experiments. The aircraft measurements indicated that under high aerosol particle conditions, large number of cloud droplets was formed with small size of droplets. By contrast, under low aerosol particle conditions, the formation of cloud droplets was limited by the number of Na. In this case, small number of cloud droplets was formed with large size of droplets. The number concentrations of cloud droplets were sensitivity to LWC under high aerosol particle conditions. With low LWC value (<0.1 g m−3), the Nc was slowly increased with the Na. For example, the cloud droplets were increased from 200 to 300 cm−3, while aerosol particles were increased from 1000 to 6000 cm−3, indicating that a large amount of aerosol particles were unchanged under low LWC condition. By contrast, with high LWC value (>0.5 g m−3), the activation of aerosol particles to become cloud droplets was significantly enhanced. For example, the cloud droplets were increased from 700 to 1900 cm−3, while aerosol particles were increased from 1000 to 6000 cm−3, suggesting that a large amount of aerosol particles were converted to cloud droplets when there were enough LWC for supporting such conversions. This study also suggests that the Rc was also very sensitivity to the LWC values. The increase in the LWC values led to significant increase in the size of cloud droplets.► Under high aerosol particle conditions, large number of cloud droplets was formed with small size of droplets, while under low aerosol particle conditions, the formation of cloud droplets was limited by the number of Na. ► The number concentrations of cloud droplets were sensitivity to LWC under high aerosol particle conditions. With low LWC value (<0.1 g m−3), the Nc was slowly increased with the Na. However, with high LWC value (>0.5 g m−3), the activation of aerosol particles to become cloud droplets was significantly enhanced. ► The cloud radius (Rc) is very sensitivity to the LWC values. ► The increase in the LWC values led to significant increase in the size of cloud droplets.
Keywords: Heavy aerosol pollution; Aircraft measurements; Cloud formation; CCN and LWC; Beijing;
Canadian National Air Pollution Surveillance (NAPS) PM2.5 speciation program: Methodology and PM2.5 chemical composition for the years 2003–2008 by Ewa Dabek-Zlotorzynska; Tom F. Dann; P. Kalyani Martinelango; Valbona Celo; Jeffrey R. Brook; David Mathieu; Luyi Ding; Claire C. Austin (673-686).
The Canadian National Air Pollution Surveillance (NAPS) network, monitoring criteria gases (CO, O3, NOx, and SO2), PM2.5, PM10, volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs) and particle chemical mass and composition, has been in operation for over 40 years. Since 1984 both fine (<2.5 μm – PM2.5) and coarse (2.5–10 μm – PM10–2.5) particle mass measurements have been made at NAPS network sites using dichotomous samplers. In January 2003, the NAPS PM2.5 speciation program was initiated with the purpose of measuring all major components of PM2.5, including ammonium nitrate, ammonium sulphate, metals, and organic and elemental carbon. The present paper describes the improved sampling (e.g. Teflon/Nylon filter packs for nitrate loss, and an active blank for each and every sample in the determination of positive organic carbon artifacts), and analytical methods used in the Canadian NAPS PM2.5 speciation program. A detailed dataset was then analyzed for seasonal and geographical variations in the major components of 24-h time integrated PM2.5 samples collected at eight urban and three rural measurement sites across Canada (2003–2008). Chemical mass reconstruction was used for assessment of the adequacy of selected sampling and chemical parameters as well as for the determination of the relative contributions of different compound classes to PM2.5 mass. The highest frequency of PM2.5 episodes exceeding 30 μg m−3 were observed in Ontario and southern Quebec. In general, the most important contributions to PM2.5 mass were secondary aerosol sulphate and nitrate (38–63% for western sites and 3–44% for eastern sites), depending on the season. Organic matter (OM) was found to be the second most important component (21–45%), while particle-bound water (PBW) accounted for 6–12% of the PM2.5 mass. Golden B.C. was an exception, exhibiting high levels of OM (60–70%) and low levels of PBW (∼3%).► The Canadian NAPS PM2.5 Speciation program provides detailed PM2.5 composition data.► Major components of PM2.5 were secondary sulphate, nitrate, and organic matter.► Teflon/Nylon filter packs controlled for nitrate loss (summer ∼90%; winter ∼20%).► Active blanks for each sample accounted for positive organic carbon artefacts (34–61%).
Keywords: Canadian PM2.5 speciation program; Aerosol sampling; Chemical speciation; Mass reconstruction; Sampling artefact; Methods;
Adsorption sites, adsorption enthalpies and potential removal of terpenoids by atmospheric ice by Christian Czech; Sonja M. Hammer; Boris Bonn; Martin U. Schmidt (687-693).
Ice crystal formation and its effect on atmospheric trace gases are currently an important area of research because of its radiation and climate effects. However, the processes of adsorption of trace gases on ice surfaces and absorption into ice crystals are poorly understood. Both processes are investigated by lattice-energy minimisation for a selected number of atmospherically relevant volatile organic compounds, i.e. isoprene, methacrolein, acetone, methylbutenol, perillyl alcohol and 2,10-pinanediol, which can be considered as exemplary substances for similar structured compounds. Adsorption and absorption geometries and enthalpies are computed and the potential uptake strength is approximated. According to our calculations non-polar terpenes like isoprene are not significantly adsorbed by ice crystals. Oxidized terpenoids have stronger interactions with the ice surface (at least two hydrogen bonds) leading to larger adsorption enthalpies. Absorption into the ice crystal plays only a minor role. Correspondingly, in the atmosphere terpenoid compounds are increasingly adsorbed to ice surfaces with increasing oxygen numbers. Subsequently this process can contribute to the wet removal of terpenoids by ice, which is so far ignored in global transport models.► Interactions of terpenoids with atmospheric ice. ► Ad- and absorption sites and enthalpies calculated by lattice-energy minimisations. ► Increasing terpenoid adsorption with increasing oxidation degree. ► Adsorption of on ice surfaces terpenoids might be relevant for atmospheric removal. ► Absorption into ice crystals plays only a minor role.
Keywords: Adsorption; Absorption enthalpy; Ice phase; Volatile organic compounds; Terpenoids;
Source analysis of fine and coarse particulate matter from livestock houses by M. Cambra-López; A.G. Torres; A.J.A. Aarnink; N.W.M. Ogink (694-707).
The analyses of the different sources which can contribute to particulate matter (PM) emissions from livestock houses are essential to develop adequate reduction techniques. The aim of this study was to morphologically and chemically characterize several sources of PM from livestock houses. We collected known sources of PM from different housing systems for poultry and pigs, which were later aerosolized in a customized laboratory dust generator to collect fine and coarse PM samples. These samples were morphologically and chemically characterized using scanning electron microscopy with X-ray microanalysis to develop comprehensive morphological and chemical source profiles. Moreover, source particle-size distribution was determined. Results showed distinct and unique particle morphologies in collected sources from different housing systems for poultry and pigs. Although presence of N, Na, Mg, Al, Si, P, S, Cl, K, and Ca were identified in all sources, their relative element concentrations varied amongst sources and could be used to discriminate amongst them. Particle size and size distribution also varied amongst sources (size ranged from 2.1 μm to 18.1 μm projected area diameter), and mainly depended on its mineral or organic origin. The results from this work can be useful information for source identification and quantification in PM from livestock houses, improving the understanding of how PM is generated in such environments, and developing strategies for its reduction.► Individual particles in collected sources from different housing systems for poultry and pigs show distinct and unique particle morphologies. ► Similar elements are present in sources from poultry and pig houses, but their relative element concentrations vary amongst sources and can be used to discriminate amongst them. ► Particle size and size distribution varies amongst sources and mainly depends on its mineral or organic origin. ► This work provides useful information for source identification and quantification in PM from livestock houses, improving the understanding of how PM is generated in such environments, and developing strategies for its reduction.
Keywords: Characterization; Dust sources; Livestock housing; Source profile; SEM-EDX;
SOA formation in a photoreactor from a mixture of organic gases and HONO for different experimental conditions by Marta G. Vivanco; Manuel Santiago; Adela Martínez-Tarifa; Esther Borrás; Milagros Ródenas; Cristina García-Diego; Miguel Sánchez (708-715).
Smog chambers have been extensively used to investigate the chemical routes of oxidation reactions for several organic gases. In this study we present the results of a set of experiments performed in the EUPHORE photoreactor to analyze SOA formation from a mixture of four organic gases related to anthropogenic emissions (1,3,5-trimethylbenzene, o-xylene, octane and toluene) with an oxidant under different experimental conditions. The effect of the organic mixture and oxidant initial concentration and the effect of SO2 on SOA formation were analyzed. A mixture of three organic gases associated to biogenic emissions (isoprene, α-pinene and limonene) was also examined. An on-line analysis of the aerosol concentration and particle size distribution was performed by TEOM and SMPS. Two off-line techniques were also used: ion chromatography to quantify the inorganic fraction (sulfates and nitrates) and derivatization followed by GC–MS to analyse the hydroxyl-containing compounds. The experiment with the mixture of biogenic parent organic gases led to the highest organic aerosol yields and larger particles. High initial SO2 concentrations strongly increased aerosol yields for the anthropogenic mixture.
Keywords: SOA formation; Chamber experiments; Organic gases; Aerosols;
Satellite monitoring of the biomass-burning aerosols during the wildfires of August 2007 in Greece: Climate implications by D.G. Kaskaoutis; Shailesh Kumar Kharol; N. Sifakis; P.T. Nastos; Anu Rani Sharma; K.V.S. Badarinath; H.D. Kambezidis (716-726).
Biomass burning and associated emissions of aerosols into the atmosphere play a vital role in atmospheric composition and climate change. During summer of 2007, Greece faced the worst natural disaster recorded in recent decades in terms of human losses, number of fire outbreaks and extent of the estimated burned area (more than 12% of the total forested areas in Greece). The present study aims at analyzing the impact of these fire events in western Peloponnese on atmospheric aerosol concentrations using satellite data. MODIS-derived Aerosol Optical Depth (AOD), effective radius, Ångström exponent, mass concentration, cloud-condensation nuclei (CCN) and OMI Aerosol Index (AI), single scattering albedo, absorption and extinction optical depths were analyzed. MODIS data showed smoke plumes traversing thousands of kilometers southwards influencing the central Mediterranean as well as the north African coastal regions. These thick smoke plumes dramatically affected AOD and aerosol-mass concentrations over the region and altered the microphysical aerosol properties, such as the effective radius and absorption coefficient. Model calculations suggested that the shortwave radiation at the ground was reduced by ∼50 Wm2, while that at the top of the atmosphere was reduced by ∼20 Wm2 resulting in atmospheric heating of ∼30 Wm2 over the areas affected by the smoke plumes.
Keywords: Forest fires; Remote sensing; Biomass burning; Radiative forcing; Peloponnese; Greece;
Effects of convective parameterization schemes on estimation of the annual wet deposition over Northeast Asia by Hong-Rae Kim; Yun-Jong Kim; Cheol-Hee Kim (727-735).
This paper presents technique used to estimate annual total wet depositions of NO3 − and SO4 2−, and describes their sensitivities arising from various convective parameterization schemes over Northeast Asia. The representative synoptic meteorological conditions for the precipitation were identified by employing a cluster analysis technique, and four cumulus convective parameterization schemes, the Anthes–Kuo (AK), Betts–Miller (BM), Grell (GR), and Kain–Fritsch 2 (KF2) schemes, were applied to estimate annual wet deposition simulations. The four convective parameterization schemes were found to reproduce the overall observed precipitation band for each of the classified synoptic patterns. When cluster analysis was used with these four schemes, the estimated annual total wet depositions of SO4 2− and NO3 − over South Korea were found to reach 184–197 and 277–337 kton year−1, respectively, with the highest estimation found with the KF2 scheme. These estimates were higher than the results of the continuous full year-long simulations by three dimensional comprehensive acid deposition model, which found values of 130 kton year−1 for SO4 2− and 270 kton year−1 for NO3 −. There was a 15.2% variability in the annual total precipitation from the use of the different convective parameterizations of the four schemes, but the annual total wet depositions of the four cloud parameterization schemes were in good agreement, with estimated variabilities of approximately 9.1 and 8.8% for SO4 2− and NO3 −, respectively. At less than ∼10%, these variations were small and negligible in an estimation of the long-term depositions over the region of Korean Peninsula.
Keywords: Convective parameterizations; Precipitation; Wet deposition; Northeast Asia;
Physicochemical characterization and cytotoxicity of ambient coarse, fine, and ultrafine particulate matters in Shanghai atmosphere by Senlin Lu; Man Feng; Zhenkun Yao; An Jing; Zhong Yufang; Minghong Wu; Guoying Sheng; Jiamo Fu; Shinich Yonemochi; Jinping Zhang; Qingyue Wang; Ken Donaldson (736-744).
Epidemiological studies have demonstrated positive relationships between increases in air pollution and adverse health effects. Physicochemical characterization and toxicity of ambient coarse particles (1.8–10 μm diameter), fine particles (1.8–10 μm diameter) and ultrafine particles (<0.1 μm diameter) collected in Shanghai as major air pollutants were investigated. It was found that mass concentrations of different size ambient particles in Shanghai urban atmosphere were higher than those in suburban atmosphere. In addition, the mass concentrations among the different size particles were different. The coarse particles consisted of minerals, while the fine particles were mainly composed of soot aggregates and sulfates; ultrafine particles contained only small amounts of particulates. Crustal elements were mainly distributed in coarse particles, and the anthropogenic elements were mainly found in fine particles. Significant amounts of calcium and magnesium were found in ultrafine particles. Fine particles were found to generate more free radical than coarse and ultrafine particles. Moreover, the results of the cell proliferation assay indicated that ultrafine particles were more cytotoxic than fine and coarse particles. Further investigations are needed to study the mechanism of cytotoxic induced by the ambient particles.
Keywords: Shanghai; Ambient size-resolved particles; Physicochemical characterization; Free radicals; Toxicity;
A quantum chemical calculation of the potential energy surface in the formation of HOSO2 from OH + SO2 by Sanyasi Sitha; Linda L. Jewell; Stuart J. Piketh; Gerhard Fourie (745-754).
The formation of HOSO2 from OH and SO2 has been thoroughly investigated using several different methods (MP2=Full, MP2=FC, B3LYP, HF and composite G∗ methods) and basis sets (6–31G(d,p), 6–31++G(d,p), 6–31++G(2d,2p), 6–31++G(2df,2p) and aug-cc-pVnZ). We have found two different possible transition state structures, one of which is a true transition state since it has a higher energy than the reactants and products (MP2=Full, MP2=FC and HF), while the other is not a true transition state since it has an energy which lies between that of the reactants and products (B3LYP and B3LYP based methods). The transition state structure (from MP2) has a twist angle of the OH fragment relative to the SO bond of the SO2 fragment of −50.0°, whereas this angle is 26.7° in the product molecule. Examination of the displacement vectors confirms that this is a true transition state structure. The MP2=Full method with a larger basis set (MP2=Full/6–31++G(2df,2p)) predicts the enthalpy of reaction to be −112.8 kJ mol−1 which is close to the experimental value of −113.3 ± 6 kJ mol−1, and predicts a rather high barrier of 20.0 kJ mol−1. When the TS structure obtained by the MP2 method is used as the input for calculating the energetics using the QCISD/6–31++G(2df,2p) method, a barrier of 4.1 kJ mol−1 is obtained (ZPE corrected). The rate constant calculated from this barrier is 1.3 × 10−13 cm3 molecule−1 s−1. We conclude that while the MP2 methods correctly predict the TS from a structural point of view, higher level energy corrections are needed for estimation of exact barrier height.► Formation of HOSO2 has been investigated using various quantum chemical methods. ► MP2 based methods predict a true structural transition state. ► QCISD energy corrections predict a barrier height close to experimental value. ► The reaction OH+SO2 ˗ HOSO2 is not barrierless.
Keywords: Atmospheric H2SO4 formation; Quantum chemical calculations; HOSO2; SO2;
Radial diffusive samplers for determination of 8-h concentration of BTEX, acetone, ethanol and ozone in ambient air during a sea breeze event by Joelle Roukos; Nadine Locoge; Paolo Sacco; Hervé Plaisance (755-763).
The radial diffusive sampler Radiello® filled with Carbograph 4 was evaluated for monitoring BTEX, ethanol and acetone concentrations for 8-hour exposure time. The sampling rates were first evaluated in an exposure chamber under standard conditions. Benzene and toluene showed the highest sampling rates with satisfactory standard deviations. Ethylbenzene and xylenes showed medium sampling rates but higher standard deviations that can be attributed to a low affinity of these compounds with the adsorbent medium for short sampling time. Acetone has a fair result because of the increase of its partial pressure in the vicinity of the adsorbent surface in the course of sampling. The Carbograph 4 adsorbent does not seem to be suitable for sampling ethanol, likely because of its high volatility. The influences of three environmental factors (temperature (T), relative humidity (RH) and concentration level (C)) on the sampling rates were also evaluated, following a fractional factorial design at two factor levels (low and high). Results were only investigated on benzene, toluene and acetone. Temperature and relative humidity are found to be the most important factors leading to variability of the benzene and toluene sampling rates. The applicability of the sampler for 8-hour sampling was demonstrated by the results of a measurement campaign carried out during a sea breeze event. Mapping of benzene, toluene and acetone concentrations showed the highest concentrations in the industrial zone following the wind direction coming from the North. Nevertheless, the sea breeze tends to reduce the spread of the industrial plumes. On the contrary, the ozone map presents the lowest concentrations at the same industrial area indicating a net consumption of ozone. The highest ozone concentrations were found in the southeastern zone suggesting a local ozone formation.
Keywords: Oxygenated compounds; BTEX; Sea breeze; Passive sampling; Radial sampler; Design of experiment;
A comparative study of health risk of potentially toxic metals in urban and suburban road dust in the most populated city of China by Guitao Shi; Zhenlou Chen; Chunjuan Bi; Li Wang; Jiyan Teng; Yuansheng Li; Shiyuan Xu (764-771).
Urban and suburban road dust samples were collected in the most populated city of China, Shanghai. Size fractions of dust particles were analyzed; metal levels of the dust were also measured. Human exposure to individual toxic metals through road dust was assessed for both children and adults. The results showed that dust particles from urban and suburban road were presented similar size distribution pattern, with most particles in the range of 100–400 μm. Urban road dust consisted of higher proportions of inhalable, thoracic and respirable particles with increased risk of adverse effects to human. In general, mean grain sizes of urban road dust were smaller than suburban dust. Total organic carbon contents and levels of Pb, Cd, Cu, Zn, Ni, Cr in urban dust were higher than those of suburban dust. But the concentrations of As and Hg from suburban dust were higher, indicting a different main source. The exposure pathway which resulted in the highest level of risk for human exposed to road dust was ingestion of this material, which was followed by dermal contact. Except for some locations, risk values of both cancer and non-cancer obtained in this study were in the receivable range on the whole. Children had greater health risks than adults. The overall risks of non-cancer in urban area were higher than those in suburban area, but the values of cancer in the two areas were comparable. As for the aggregate noncarcinogenic risk, Pb was of most concern regarding the potential occurrence of health impacts. Of the three carcinogenic metals As, Cr and Cd, the only mean risk higher than 10−6 was Cr, accounting for a great percentage (95%) of the overall risk of cancer. Hence, potentially adverse health effects arising from Pb and Cr in road dust should arouse wide concern.
Keywords: Potentially toxic metals; Particle grain size; Road dust; Ingestion; Risk assessment;
Optimal redistribution of the background ozone monitoring stations over France by Lin Wu; Marc Bocquet (772-783).
Ozone is a harmful air pollutant at ground level, and its concentrations are routinely measured with monitoring networks. The network design problem aims at determining the optimal positioning of the monitoring stations. In this study, the background stations of the French routine pollution monitoring network (BDQA) are partially redistributed over France under a set of design objectives. These background stations report ozone variations at large spatial scale comparable with that of a chemistry-transport model (CTM). The design criterion needs to be defined on a regular grid that covers France, where in general no ozone observations are available for validation. Geostatistical ozone estimation methods are used to extrapolate concentrations to these grid nodes. The geostatistical criteria are introduced to minimize the theoretical error of those geostatistical extrapolations. A physical criterion is also introduced to measure the ability of a network to represent a physical ozone field retrieved from CTM simulations using geostatistical extrapolation methods. A third type of criteria of geometrical nature, e.g. a maximal coverage of the design domain, are based uniquely on the distance between the network stations. To complete the network design methodology, a stochastic optimization method, simulated annealing, is employed in the algorithm to select optimally the stations.Significant improvement with all the proposed criteria has been found for the optimally redistributed network against the original background BDQA network. For instance, the relative improvements in the physical criterion value range from 21% to 32% compared to randomly relocated networks. Different design criteria lead to different optimally relocated networks. The optimal networks under physical criteria are the most heterogeneously distributed. More background stations are displaced to the coast, frontiers, and large urban agglomerations, e.g. Paris and Marseilles. The ozone heterogeneous fields are not as well reconstructed from optimal networks under geostatistical or geometrical criteria as from the optimal network obtained with the physical criterion. The values of the physical criterion for the geostatistically and geometrically optimal networks show deteriorations of about 8% and 17% respectively compared to that of the physically optimal network.
Keywords: Air quality; Ozone monitoring; Network design;
An ensemble assessment of regional ozone model uncertainty with an explicit error representation by A. Boynard; M. Beekmann; G. Foret; A. Ung; S. Szopa; C. Schmechtig; A. Coman (784-793).
In this paper, we examine the extent to which an ensemble generated from a single air quality model correctly represents the global uncertainty of ozone simulations with a regional scale chemistry-transport model and whether it is suitable for ozone data assimilation. An ensemble of 30 members is constructed from a reference simulation in which the model parameters that are the most uncertain for determining ozone concentrations are randomly perturbed. Comparisons of the simulated ensemble using the model CHIMERE with observations are examined over the summer season both at the surface and higher in the troposphere. Although the ensemble overestimates vertical and horizontal correlation between errors, the average model error is well represented both at the surface and in the vertical dimension (after an adjustment for the latter). A variability of about 7–8 ppb is found. The results found in this study with respect to tropospheric ozone model errors and error correlation lengths both from ensemble simulations and model to observation comparisons are of particular interest for data assimilation when constructing model error covariance matrices.
Keywords: Ensemble method; Ozone; Modelling; Error covariance; Data assimilation;
Carbonaceous aerosol characteristics over a Pinus taeda plantation: Results from the CELTIC experiment by Chris Geron (794-801).
Carbonaceous particles smaller than 2.5 μm aerodynamic diameter (PM2.5) were collected in July, 2003 over a Loblolly Pine plantation at Duke Forest, NC during the Chemical Emission, Loss, Transformation and Interactions within Canopies (CELTIC) field study. Organic (OC) and elemental (EC) carbon in PM2.5 ranged from 1.4–6.3 and 0.08–0.41 μg C m−3, respectively, and concentrations measured above and below the pine canopy were in good agreement. Ambient OC was lower (<3 μg C m−3) during cooler periods (daytime maximum temperatures < 28 °C) and for periods following precipitation events, and was higher (>3 μg C m−3) during warm humid periods. Radiocarbon analysis indicates that on average 83% (range 78–91%) of the PM2.5 carbon was derived from contemporary (biogenic VOC and biomass burning) sources. This is higher than previous estimates from urban and suburban sites, and in good agreement with recently published data from other rural sites throughout the U.S. The estimates of contemporary PM2.5 carbon may represent a lower limit for this site since the sampler was located above the center of a 30 meter diameter plot fumigated with 200 ppm CO2 derived from fossil carbon sources. However, this effect is likely to be negligible. The regression relationship between OC/EC ratios and percent biogenic carbon in aerosol is very similar to those observed in recent summertime data from Tennessee and Florida. However, our values for both OC/EC and percent biogenic carbon are higher than those observed in the latter studies, likely due to the more rural character of the site. Simple box model estimates indicate that biogenic VOC (BVOC) emissions measured at the site provide sufficient reactive carbon sources to account for the observed levels of aerosol biogenic carbon. The magnitude and temporal pattern in the box model secondary organic aerosol estimates correlate well with the ambient aerosol carbon measurements. The model estimates of the relative contribution of isoprene, α-pinene, and β-caryophyllene oxidation to PM2.5 carbon are in reasonable agreement with a study recently conducted at a nearby site where aerosol tracers of these compounds were quantitatively analyzed in ambient PM2.5. Pinic acid concentrations in the below-canopy PM2.5 during CELTIC (from another recently published study) similarly suggest a significant contribution of α-pinene oxidation to PM2.5 carbon. The biomass burning tracers potassium and levoglucosan yielded fire contribution estimates to PM2.5 consistent with their respective published emission factors. These estimates indicate that biomass burning accounted for 1 to 5% (0.015 to 0.30 μg C m−3) of the PM2.5 carbon during CELTIC.
Keywords: CELTIC elemental carbon; Organic carbon; Radiocarbon; PM2.5; Ozone; Biogenic volatile organic compounds;
Implementation of resuspension from paved roads for the improvement of CALIOPE air quality system in Spain by María T. Pay; Pedro Jiménez-Guerrero; José M. Baldasano (802-807).
Emissions of resuspensed particles from paved roads (RPR) have received an increasing attention in air quality modeling, since chemistry transport models are generally unable to reproduce particulate levels near road traffic. However, among the models operated in the forecasting mode in Europe, there is a lack of systems including the contribution of RPR on an hourly basis. Therefore, this contribution describes the inclusion of the resuspension of particulate matter within HERMES emission model (operationally implemented in the CALIOPE forecasting system) and the improvements obtained in the simulations of the PM10 mass over a domain covering Spain for a whole year of simulation (2004). The results indicate a remarkable improvement of the PM10 predictions, reducing the biases and errors around 15–18% and 2.6 μg m−3 for the average bias in all Spain. The RPR emission have strong local effects on the modeled particle concentration in or near the largest urban zones (up to 7 μg m−3 as the annual average), albeit those positive effects are more limited in background areas, since the deposition mechanism was found to be a significant sink for RPR in the chemistry transport model. This approach is accurate and effective in order to improve the prediction of the PM10 mass and becomes essential to achieve the standards set in the regulations for modeling applications.
Keywords: Air quality; Forecasting; Emissions; Urban air quality;
Impact of emission control strategy on NO2 in urban areas of Korea by Zang-Ho Shon; Ki-Hyun Kim (808-812).
Long-term trend in nitrogen dioxide (NO2) levels was analyzed from 16 urban roadside (U-RS) locations in 7 major cities along with 5 reference background areas in Korea over an 11-year period (1998–2008). These NO2 data were examined after being grouped into periods I (1998–2000) and II (2001–2008) in light of the major emission control strategy such as the natural gas vehicle supply (NGVS) program initiated since June 2000. There were contrasting signals between Seoul (capital) and others. Although the long-term trends were dominantly toward decline from most stations (5 out of 7) in Seoul, an increasing trend was dominant in other cities (7 out of 9 stations). A line of evidence collected in this study indicated that NO2 levels and the emission ratio of NO2 to NO x (f(NO2)) in U-RS sites have gradually decreased over the years due to the combined effects of various control efforts (e.g., the implementation of NGVS and the use of low emission diesel engines).
Keywords: Nitrogen dioxide; Natural gas vehicle; Diesel; Long-term air quality; CNG; LPG;