Atmospheric Environment (v.39, #34)

The dry deposition of 12 polycyclic aromatic hydrocarbons (PAHs) was measured at an urban (Kozani), an adjacent coastal (Vegoritis) and a continental background site (Petrana) located in the Eordea basin, western Greece. Mean dry deposition fluxes of 3917, 3346 and 5648 ng m−2 month−1 (0.13, 0.11 and 0.19 μg m−2  day−1) were found in Petrana, Vegoritis and Kozani, respectively. Differences among sites were attributed to their different impact from emission sources and to differences in prevailing meteorological conditions. The correlation of dry deposition fluxes with particle- and gas-phase PAH concentrations determined at the three sites during the same sampling periods was investigated. Dry deposition velocities (V d) were calculated by dividing deposition fluxes with the corresponding average ambient PAH concentrations. The low V d values obtained suggest that gas phase PAHs and fine particle associated PAHs dominate their dry deposition. The influence of air mass movements to dry deposition and atmospheric concentrations of PAHs in the area was also investigated.
Keywords: PAHs; Dry deposition; Deposition velocities;

For the determination of effects of contaminated crude soil on the content of trace elements in the atmospheric aerosol, trace elements in crude soil samples from within the area of influence of local resuspension were analysed. The obtained results were used for determining the contribution of local resuspension on contents of trace elements in the atmospheric aerosol using the enrichment factors (EF) method. The content of trace elements in a crude soil could arise from the geochemical background of the soil or from anthropogenic contributions. Analysis of the quantile showed that Cd, Se and Ni originate from local emission sources. PCA showed that four groups of sources contributed to the content of trace elements in PM in part of the receptor. Using EF, it was ascertained that local resuspension of crude soil particles had a dominant influence on the content of Fe, Mn and Ti in the atmospheric aerosol, and that local resuspension had no influence on the content of Se in the atmospheric aerosol. Dust originating from deserts of North Africa and Middle East, through long-range transport and through resuspension of settled dust particles, significantly contributes to the content of Fe, Mn and Ti in the atmospheric aerosol. Cd originated from contaminated crude soil. The other investigated elements originated partly from crude soil but also from some other emission sources in the region.
Keywords: Mediterranean region; Trace elements; Particulate matter; Source contributions; Statistical models; EF;

Pollutant dispersion simulation for low wind speed condition by the ILS method by Jonas C. Carvalho; Marco Túllio M.B. de Vilhena (6282-6288).
A semi-analytical Lagrangian particle model to simulate the pollutant dispersion during low wind speed conditions is presented and tested. The method relies to a stochastic integral equation whose solution is obtained using ILS method, which consists in the iterative solution of Langevin equation by the Picard's iteration method. To consider the low wind speed effect, the solution for the horizontal components of the turbulent velocity takes account the Eulerian autocorrelation function as suggested by Frenkiel [1953. Advances in Applied Mechanics 3, 61–107]. The model results are shown to agree very well with the field tracer data collected during stable conditions at Idaho National Engineering Laboratory (INEL) and during convective conditions from the series of field experiments at Indian Institute of Technology (IIT). A statistical analysis reveals that the model simulates very well the experimental data and presents results comparable or even better than ones obtained with other models used as comparison. The analytical feature of the ILS method and the inclusion of the Eulerian autocorrelation function suggested by Frenkiel (1953) allow generating more accurate results.
Keywords: Low wind speed condition; Air pollution modeling; Lagrangian particle model; Picard iterative method; Autocorrelation function; Model evaluation;

Near-source atmospheric pollutant dispersion using the new GILTT method by D.M. Moreira; M.T. Vilhena; T. Tirabassi; D. Buske; R. Cotta (6289-6294).
In this work we present the GILTT method for the solution of the advection–diffusion equation utilizing an eddy diffusivity depending on source distance. With this new approach, where no approximation is made along the solution derivation so that it is an exact solution except for the round-off error due to the stepwise approximation of the eddy diffusivity in the x variable, it is possible to simulate the pollutant dispersion in the Planetary Boundary Layer. The present study reinforces that the inclusion of the memory effect, important in near regions from an elevated continuous point source, improves the description of the turbulent transport process of atmospheric pollutants.
Keywords: GILTT; Laplace transform; Atmospheric dispersion; Analytical solution; Advection–diffusion equation; Planetary boundary layer;

Plants and environmental variables are of importance for methane (CH4) emission from soils to the atmosphere. To understand the key factors controlling CH4 emission in temperate wetlands, we performed field measurements in the Inner Mongolia marshes to compare the diurnal CH4 fluxes between summer and winter, between a sandy site and an organic site, and between the wet meadow and the waterlogged habitat of each site. (i) In the summer, we found apparent diurnal patterns in CH4 emission with unique peaks. For the sandy site, temperatures and water table were mediated to some degree by solar radiation, and thus their overall effect was noted in a diurnal cycle of CH4 flux. Plant photosynthesis greatly affected the mechanisms of CH4 production, oxidation and transport, resulting in a diurnal variation of CH4 emission with a peak in the late afternoon and the lowest value immediately prior to sunrise of the next day. In the organic site, plant-mediated CH4 transport, together with the absence of a significant relationship between CH4 flux and environmental variables, indicated that diurnal CH4 flux was determined by vascular plants. (ii) In the winter, we found slight double peaks in CH4 emissions in the sandy site but no diurnal variation rhythm in the organic site. The slight double peaks coincided with the maximal temperatures.
Keywords: Diurnal dynamics; CH4 flux; Vegetation; Temperature; Wetland;

226Ra, 232Th and 40K analysis has been carried out in soil samples collected from some areas of Himachal Pradesh, India using γ-ray spectrometry. The measured activity in soil ranges from 42.09 to 79.63 Bq kg−1, 52.83 to 105.81 Bq kg−1 and 95.33 to 160.30 Bq kg−1 for 226Ra, 232Th and 40K with the mean values of 57.34, 82.22 and 135.75 Bq kg−1, respectively. The measured activity concentration of 226Ra and 232Th in soil samples collected from these areas is higher and for 40K is lower than the world average. The radium equivalent activity in all the soil samples is lower than the safe limit set in the OECD report (370 Bq kg−1). The value of the external exposure dose has been determined from the content of these radionuclides in soil. It has been observed that on the average, the outdoor terrestrial gamma air absorbed dose rate is about 83.28 nGy h−1. The study yields an annual effective dose in the range of 0.07–0.13 mSv. The average value of annual effective dose lies in the global range of outdoor radiation exposure given in United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) [(2000). Effects and risks of ionizing radiations. UN, NY]. The activity concentration of 238U has also been determined using fission track technique and the values range from 3.26 to 7.71 mg kg−1 with a mean value of 4.38 mg kg−1.
Keywords: Fission track technique; Raeq activities; Annual effective dose; External hazard index;

Ozonolysis of monoterpenes in mechanical ventilation systems by Jerker Fick; Linda Pommer; Anders Åstrand; Ronny Östin; Calle Nilsson; Barbro Andersson (6315-6325).
In this investigation the ozonolysis of of three monoterpenes (α-pinene, Δ 3-carene and limonene) was studied was studied in authentic mechanical ventilation systems, that included either a cross flow or a rotary heat exchanger. The effects of varying three experimental parameters were investigated: the level of ozone (25 and 75 ppb), the reaction time (25 and 75 s), and the surface area in the ventilation duct (14.8 and 29.5 m2). The initial concentration of each of the monoterpenes was 20 ppb in every experiment, and 1–16% of the α-pinene, <0.5–13% of the Δ 3-carene, and <0.5–16% of the limonene reacted. The effects of humidity (g m−3) and temperature of the outdoor and supply air, and water losses in the ventilation duct, were also evaluated. Experiments were based on a chemometric statistical design. Comparison of the results to theoretically calculated values showed that theoretical calculations underestimated the amounts that reacted in the ventilation systems by factors of 2–13, depending on the monoterpene and experimental settings.
Keywords: Relative humidity; Surface chemistry; Heat exchanger; Ventilation duct;

This paper reports on a preliminary study of the forecast and evaluation of transport-related air pollution dispersion in urban areas. Some modifications of the traditional Gauss dispersion models are provided, and especially a crossroad model is built, which considers the great variation of vehicle emission attributed to different driving patterns at the crossroad. The above models are combined with a self-developed geographic information system (GIS) platform, and a simulative system with graphical interfaces is built. The system aims at visually describing the influences on the urban environment by urban traffic characteristics and therefore gives a reference to the improvement of urban air quality. Due to the introduction of a self-developed GIS platform and a creative crossroad model, the system is more effective, flexible and accurate. Finally, a comparison of the simulated (predicted) and observed hourly concentration is given, which indicates a good simulation.
Keywords: Vehicle emissions; Dispersion model; Crossroad; Geographic information system;

Trace gas emissions from Melbourne, Australia, based on AGAGE observations at Cape Grim, Tasmania, 1995–2000 by B.L. Dunse; L.P. Steele; S.R. Wilson; P.J. Fraser; P.B. Krummel (6334-6344).
Atmospheric observations of ten atmospheric gases have been used to estimate total emissions of nine of these ten trace gases from Melbourne, Australia. The ten trace gases measured as part of the AGAGE program at the Cape Grim Baseline Air Pollution Station in Tasmania are: CFC-11 (CCl3F), CFC-12 (CCl2F2), CFC-113 (CCl2FCClF2), methane (CH4), nitrous oxide (N2O), carbon monoxide (CO), hydrogen (H2), chloroform (CHCl3), methyl chloroform (CH3CCl3) and carbon tetrachloride (CCl4). The process of estimating emissions involved first identifying pollution episodes in the Cape Grim record that were attributed to air masses that passed over the Melbourne region before travelling across Bass Strait to Cape Grim. Correlations between the trace species and an estimate of CO emissions from Melbourne were used to deduce the mass of the Melbourne emissions. Where possible, comparisons of these estimates have been made with estimates from established inventory techniques. In particular, comparisons have been made with Australia's National Greenhouse Gas Inventory. Results from this study showed emission estimates of CFC-12 and CFC-11 ranging from 30–52% and 30–55%, respectively, of the inventory estimates. These results may indicate a more rapid phase-out of these CFCs than industrial inventory models predicted. The emission estimates of CH4 ranged from 53% to 87% of inventory estimates over the years 1995–2000. Emission estimates of N2O exceed inventory estimates by more than 200% over the years 1995–2000.
Keywords: AGAGE; Cape Grim Baseline Air Pollution Station; Emissions; Pollution episodes; Trace gases;

Prediction of transient turbulent dispersion by CFD–statistical hybrid modeling method by Michael K.H. Leung; Chun-Ho Liu; Alan H.S. Chan; Dennis Y.C. Leung; W.C. Yam; S.P. Ng; Lilian L.P. Vrijmoed (6345-6351).
The transient turbulent dispersion of a gaseous contaminant due to accidental leakage or similar critical situation can be studied by computational fluid dynamics (CFD). However, the transient CFD calculation is extremely computationally expensive because highly refined spatial and temporal resolutions are required for accurate results. In this investigation, a CFD–statistical hybrid modeling method was developed to solve the transient turbulent dispersion problem with a substantial computation time-saving. The computational domain of this modeling problem consists of a point source emitting gaseous contaminant and a fixed-point receptor susceptible to the contaminant dispersed in a steady-state turbulent flow field. In the modeling method, CFD is utilized to obtain the transport behavior of an emitted ultra-fine particle that conceptually represents a “microscopic” molecule of a vapor emission. In turn, the principles of statistics are employed to determine the most probable “macroscopic” time-dependent contaminant concentration at the receptor for a given time-varying point-source emission profile. In a case study, the results predicted by the CFD–statistical model agreed reasonably well with published k–ε modeling results and experimental data. The computation time was successfully reduced by one order of magnitude.
Keywords: Computational fluid dynamics (CFD); Statistical method; Transient turbulent dispersion; k–ε turbulence model; Particle transport;

A simple photochemical module implemented in RAMS for tropospheric ozone concentration forecast in the metropolitan area of São Paulo, Brazil: Coupling and validation by Edmilson Dias de Freitas; Leila Droprinchinski Martins; Pedro Leite da Silva Dias; Maria de Fátima Andrade (6352-6361).
An in-line simplified photochemical module was coupled with RAMS, an atmopsheric mesoscale model, to produce an operational forecast of ozone and other constituent concentration for the Metropolitan Area of São Paulo (MASP), Brazil. Comparisons between surface pollutants concentrations data, provided by automatic network stations for air quality monitoring and modeled values, show good agreement, with correlation coefficients greater than 0.7 for all stations considered. Mean values over all analyzed stations have an index of agreement higher than 0.8. An important feature observed during the simulations was the ability of the model to simulate nocturnal concentrations of ozone over MASP which are usually observed as a result of transport of this pollutant from other regions and from higher levels of the atmosphere, representing the close coupling between the micro scale process and the chemical reactions, although these nocturnal maximums are overestimated by the model in some cases. The computational efficiency of the model shows that it can be considered for operational procedures with relatively small PC-based clusters and used as a tool for emission control strategies by environmental agencies concerned with the improvement of air quality.
Keywords: Urban air pollution; Tropospheric ozone concentration forecast; RAMS; Photochemical pollution; Numerical modeling;

Urban thermal situation is thought to have a great influence on the air quality in urban areas. In recent years, the urban thermal environment has become worse, such as the days on which the temperature goes above 30 °C, the sultry nights and heat stroke increase due to changes in terrestrial cover and increased anthropogenic heat emission accompanied by urbanization. Therefore, the urban thermal environment should be carefully investigated and accurately analyzed for a better study of the air quality. Here, in order to study the urban thermal environment in summer, (1) the actual status of an urban thermal environment in a complex urban area covering a large district heating and cooling (DHC) system in Tokyo is investigated using field measurements, and (2) a numerical simulation program which can be adapted to complex urban areas coupled with convection, radiation and conduction is developed and used to predict the urban thermal environment. Wind velocity, temperature and humidity are obtained from the simulation, which shows good agreement with results of the field measurement. The spatial distribution of the standard effective temperature (SET*), the comprehensive index of human thermal comfort, is also calculated using the above results, to estimate the thermal comfort at the pedestrian level. This urban thermal numerical simulation can be coupled with air pollution dispersion and chemical processes to provide a more precise air quality prediction in complex urban areas.
Keywords: Urban thermal environment; Numerical simulation; Complex urban area;

Concentrations of elements and ions measured in aerosol samples collected from March 1992 to the end of December 1993 were investigated to identify source regions affecting chemical composition of aerosols in the eastern Mediterranean atmosphere. Collected samples were analyzed for approximately 40 elements and ions using a combination of atomic absorption spectrometry, instrumental neutron activation analysis, ion chromatography and colorimetry. Statistical techniques, such as enrichment factors and a non-parametric bootstrapped potential source contribution function, were applied on the data set to determine main source types and source regions of anthropogenic particles in the eastern Mediterranean basin. Source regions of two previously defined anthropogenic components, namely a long-range transported component and a local pollution component, were identified. The main source areas for pollutants reaching the eastern Mediterranean basin were determined as southern and western parts of Turkey, central and eastern regions of Ukraine, east of Belarus, Greece, Georgia, Romania, coastal areas along France and Spain and coastal areas around the Black Sea, Russia. More distant source regions in the South of UK and Sweden, the central part of Algeria, the northeastern part of Turkey, Russia, Germany, Hungary, Czech Republic, Bosnia and Herzegovina, and coastal areas of Egypt, Israel and Italy do affect aerosol composition in the eastern Mediterranean, but transport from these regions cannot account for the highest 20% of the measured pollutant concentrations.
Keywords: Eastern Mediterranean aerosols; Back trajectories; Potential source contribution function; Bootstrap; Source area;

Chemometric characterization of the quality of the atmospheric environment in Hong Kong by Fan Gong; Bo-Tang Wang; Ying-Sing Fung; Foo-Tim Chau (6388-6397).
In this paper, chemometric approaches based on correlative analysis, hierarchical clustering, classical and robust principal component analysis were investigated to characterize the quality of the atmospheric environment in Hong Kong. Since the weather behaved quite atypically as concerns both the rains and temperature during the sampling period, it is difficult to clarify the relationship between the chemical species, weather and the environmental quality with the raw data directly. However, with the help of suitable chemometric methods, the correlationship between samples or variables could be investigated. Moreover, pattern recognition based on hierarchical clustering, classical and robust principal component analysis could provide a visual aid for identifying the homogeneity and/or differences of the samples under study. The successful applications to 55 coarse and fine particulate observations from the atmospheric environment in Hong Kong showed that chemometric approaches could develop a clear picture concerning the correlation between samples or variables and especially the linkage of the chemical components, weather and the environmental quality for the atmospheric system with much complexity.
Keywords: Atmospheric environment; Quality assessment; Correlative analysis; Hierarchical clustering; Principal component analysis;

Ceiling dusts, the particulate matters accumulated on the ceiling surface of vehicular tunnels, collected from Cross-Harbor Tunnel in Hong Kong and Pear River Tunnel in Guangzhou, were analyzed for their organic compositions. Although the overall results revealed that most of the organic compounds of the ceiling dusts of both tunnels are directly derived from vehicular emission, there are significant differences in the organic content and compositions and distribution of hydrocarbon components in the ceiling dusts from these two tunnels. The ceiling dusts from the tunnel of Hong Kong were characterized by high content of organic carbon and unresolved complex matter compared to the much lower numbers in the ceiling dusts of Guangzhou. The distribution of molecular markers from CHT exhibited a 17α (H)-21β (H)-30-nor hopane (C29H) predominance (C29H>C30H) and the relative abundance of regular steranes is in an order of C27>C29>C28, whereas for the ceiling dusts from PRT, the hopanes displayed a 17α (H)-21β (H)-hopane (C30H) dominance (C29H<C30H) and the regular steranes are in the order of C29>C27>C28. It was also found that there was significant difference in the organic content in the ceiling dusts between the south- and northbound tubes of both CHT and PRT and the reasons for this require further investigation.
Keywords: Vehicular tunnels; Ceiling dusts; Organic matter; Composition and distribution of hydrocarbon compounds;

Almadén has a >2000y mining history and an unprecedented legacy of mercury contamination. Resuspended airborne particles were extracted from mine waste (Las Cuevas), retort site soil (Almadenejos), and urban car park dust (Almadén), separated into fine (PM10) and coarse (PM>10 μm) fractions, analysed for mercury using ICP-MS, and individual HgPM characterised using SEM. Cold extractable mercury concentrations in PM10 range from 100 to 150 μg g−1 (car parks), to nearly 6000 μg g−1 (mine waste), reaching a world record of 95,000 μg g−1 above the abandoned retort at Almadenejos where ultrafine HgPM have pervaded the brickwork and soil and entered the food chain: edible wild asparagus stem material from here contains 35–65 μg g−1 Hg, and pig hair from animals living, inhaling and ingesting HgPM10 at the site yielded 8–10 μg g−1. The PM10 fraction (dusts easily wind transported and deeply inhaled) contains much more mercury than the coarser fraction. The contribution of HgPM10 to ecosystem contamination and potential human health effects around old mercury mines has been underestimated.
Keywords: Almadén; Mercury aerosol contamination; PM10;

Variations in atmospheric trace elements in Dome C (East Antarctica) ice over the last two climatic cycles by Paolo Gabrielli; Carlo Barbante; Claude Boutron; Giulio Cozzi; Vania Gaspari; Frédéric Planchon; Christophe Ferrari; Clara Turetta; Sungmin Hong; Paolo Cescon (6420-6429).
Concentrations of Li, Mg, Cr, Mn, Co, Cu, As, Rb, Cd, Ba and Bi have been determined by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) in various sections of the new Dome C EPICA Antarctic ice core, down to the depth of 2193 m, covering a time period of two climatic cycles. The time resolution of these records is at least twice as good as previously published ultra trace elements profiles obtained from the Vostok ice core. During the ∼217 kyr period spanned by this record, a high variability in concentrations is observed for most elements, with low values during warm periods and high values during cold periods. The highest concentrations are recorded at the times of the last two glacial maxima (∼20 and ∼140 kyr BP). The timing and the amplitude of the main concentration peaks match remarkably well the insoluble dust concentration profile. It confirms that dust was the main carrier of atmospheric trace elements to East Antarctica during the cold periods. For Ba, Co, Cu and Rb the crustal contribution was also dominant during warm periods. For other elements the situation is more complex during interglacial periods, when other sources such as volcanic quiescent emissions, became possibly significant for several trace elements such as Cd and Bi. Peculiarly high concentration values are observed for Cd and Bi for a short depth interval dated at ∼18 kyr BP. It is the same depth interval in which elevated F values were previously observed. These very high concentrations are attributed to fallout from major local volcanic emissions at that time.
Keywords: Trace elements; Antarctica; Ice; Climatic cycles;

Total suspended particle mass concentrations (TSP) were determined in the Kozani-Ptolemais-Florina basin (western Macedonia, Greece), an area with intensive lignite burning for power generation. The study was conducted over a 1-year period (November 2000–November 2001) at 10 receptor sites located at variable distances from the power plants. Ambient TSP samples were analyzed for 27 major, minor and trace elements. Particulate emissions were also collected from a variety of sources including fly ash, lignite dust, automobile traffic, domestic heating, and open-air burning of agricultural biomass and refuse, and analyzed for the same chemical components. Ambient and source chemical profiles were used for source identification and apportionment of TSP by employing a chemical mass balance (CMB) receptor model. Diesel burning in vehicular traffic and in the power plants for generator start up was found to be the major contributor to ambient TSP levels at all 10 sites. Other sources with significant contributions were domestic coal burning, vegetative burning (wood combustion and agricultural burns) and refuse open-air burning. Fly ash escaping the electrostatic precipitators of the power plants was a minor contributor to ambient TSP.
Keywords: Atmospheric particulate matter; Chemical mass balance; Fly ash; Power generation; Receptor models; Source profiles; Trace elements;

A review of intraurban variations in particulate air pollution: Implications for epidemiological research by J. Gaines Wilson; Simon Kingham; Jamie Pearce; Andrew P. Sturman (6444-6462).
Epidemiological studies typically utilise one or few central monitoring stations as a proxy for personal exposure to particulate matter air pollution. However, recent research indicates that central monitoring sites may not accurately characterize the spatial complexities of the particulate field across an urban area. Consequently, intraurban assessment of exposure to air pollution has become a priority area of study. This paper reviews particulate air pollution exposure studies with a focus on monitored-data studies at the intraurban spatial scale. Portions of the literature provide contradictory conclusions as to the homogeneity of intraurban particulate concentrations, due in part to local conditions such as source composition, meteorology, locations of monitoring sites and topography, but which may also be a result of the methods and definitions used to quantify relative and absolute spatial concentration variations. Comparative analyses of the literature by particle size fraction, method of determining heterogeneity, and sampling characteristics were performed. We find that particular attention should be given to local conditions and methods when using one or few monitoring sites to characterise wider population exposures. The utilisation of absolute and relative measures of homogeneity such as the coefficient of divergence which are based on data from several monitoring sites (e.g., n > 4 ) in combination with an appropriate sample size (e.g., n ⩾ 50 ) may reduce the possibility of misclassification based on incorrect assumptions about heterogeneity. The errors in exposure misclassification based on these assumptions about intraurban concentration variations are especially critical in long-term cohort epidemiological analyses that assess the effects of exposure variations in air pollution upon health.
Keywords: Intraurban uniformity; Particulate matter; Air pollution; Exposure misclassification;

The Pearl River Delta (PRD) is a fast developing region in China that has experienced serious air pollution. In this study, we present the measurement results of fine particulate matter (PM2.5) mass, major ions, and carbonaceous concentrations at a rural site in southern PRD during November to December 2002. The aims of this study are to characterize the temporal variation of PM2.5 mass and chemical composition in winter, which is typically a season of high pollution, and to estimate the contribution of sources from PRD inland and coastal cities (Hong Kong and Shenzhen) on the levels of fine particles observed in the downwind area. The average concentration of 24-h PM2.5 filter samples (N=24) was 41.3 (±17.1) μg m−3 (±standard deviation), with the concentration of individual samples ranging from 10.1 to 89.9 μg m−3. Particulate organic matter (POM) and non-sea-salt sulfate (nss-SO4 2−) were the major components of PM2.5 accounting for 42% and 25% of the total mass, respectively. Examination of the ratio of secondary organic carbon to total organic carbon suggests that approximately 34% of organic carbon was of secondary origin. The temporal variations of PM2.5 concentrations were strongly influenced by synoptic wind flow. The regional outflows from PRD inland and coastal cities made significant contributions to the ambient concentrations in the study site, which accounted for 48–57% for PM2.5, 66–72% for POM, and 18–20% for nss-SO4 2−, respectively. An application of a formula developed in the IMPROVE study showed that POM accounted for 44%, 42% and 22% of the light extinction under northeasterly, northerly, and easterly winds, respectively, whereas ammonium sulfate contributed 45%, 47%, and 70%, respectively. This highlights the significance of fine sulfate in visibility impairment in region with humid climates.
Keywords: PM2.5; Pearl River Delta; Outflow; Particulate organic matter; Visibility;