Process analysis of a regional air pollution episode over Pearl River Delta Region,China, using the MM5-CMAQ model

This study focuses on the influences of a warm high-pressure meteorological system on aerosol pollutants, employing the simulations by the Models-3/CMAQ system and the observations collected during October 10–12, 2004, over the Pearl River Delta (PRD) region. The results show that the spatial distributions of air pollutants are generally circular near Guangzhou and Foshan, which are cities with high emissions rates. The primary pollutant is particulate matter (PM) over the PRD. MM5 shows reasonable performance for major meteorological variables (i.e., temperature, relative humidity, wind direction) with normalized mean biases (NMB) of 4.5–38.8% and for their time series. CMAQ can capture one peak of all air pollutant concentrations on October 11, but misses other peaks. The CMAQ model systematically underpredicts the mass concentrations of all air pollutants. Compared with chemical observations, SO₂ and O₃ are predicted well with a correlation coefficient of 0.70 and 0.65. PM_2.5 and NO are significantly underpredicted with an NMB of 43% and 90%, respectively. The process analysis results show that the emission, dry deposition, horizontal transport, and vertical transport are four main processes affecting air pollutants. The contributions of each physical process are different for the various pollutants. The most important process for PM₁₀ is dry deposition, and for NO_x it is transport. The contributions of horizontal and vertical transport processes vary during the period, but these two processes mostly contribute to the removal of air pollutants at Guangzhou city, whose emissions are high. For this high-pressure case, the contributions of the various processes show high correlations in cities with the similar geographical attributes. According to the statistical results, cities in the PRD region are divided into four groups with different features. The contributions from local and nonlocal emission sources are discussed in different groups.

Implications: The characteristics of aerosol pollution episodes are intensively studied in this work using the high-resolution modeling system MM5/SMOKE/CMAQ, with special efforts on examining the contributions of different physical and chemical processes to air concentrations for each city over the PRD region by a process analysis method, so as to provide a scientific basis for understanding the formation mechanism of regional aerosol pollution under the high-pressure system over PRD.     

Source analysis of high particulate matter days in Hong Kong

This study identifies major contributing sources of high particulate matter (PM) days in Hong Kong and conducive meteorological conditions leading to high PM. The PM₁₀ chemical composition of 3393 ambient samples collected at ten monitoring stations in Hong Kong during 1998–2005 were used as input for positive matrix factorization (PMF) modeling to identify and quantify the aerosol sources in Hong Kong. Days with PM₁₀ levels exceeding 56 μg m^?3, the average plus one standard deviation of the mass concentration of all samples, are defined as high PM days. A total of 401 samples fell in the high PM category during the study period. Biomass burning, secondary sulfate and secondary nitrate were found to be the major contributors leading to high PM, responsible for 68–73% of PM₁₀ mass on high PM days. The contributions by these sources on high PM days were 140–180% higher than their respective average concentration contributions. These sources were identified to be regional sources on the grounds of little spatial variation in their concentrations among the monitoring stations and a temporal pattern of higher in the winter and lower in the summer. Sampling days of high PM in 2004 and 2005 were individually examined for weather charts and regional surface wind maps. Weak high pressures over mainland China were the most important synoptic event leading to high PM days in the fall and winter, while typhoon episodes were responsible for most summer cases. Approximately 80% of the high PM days were in the fall and winter months (September–February). Almost all the high PM days were associated with northwesterly, northerly or northeasterly regional transport. Anthropogenic primary sources (coal combustion, vehicular exhaust, and residue oil combustion) showed the highest contributions associated with northwesterly wind, indicating the strong influence of the more urbanized areas to the northwest of Hong Kong in the Pearl River Delta region.     

Ozone episodes in urban Hong Kong 1994–1999

Summer pollution episodes in Hong Kong are related to the passage of tropical storms close to the territory. Between 1994 and 1999, there were six territory-wide ozone episodes in Hong Kong during which the Hong Kong Air Quality Objective for ozone (240 μg m⁻³, 1 h) was violated. The maximum O₃ concentration for the period was 334 μg m⁻³ recorded in August 1999. Synoptically, tropical storms were in the vicinity on all the episode days. Northwesterly/westerly winds induced by the storms are believed to cause ozone precursor emissions from local power plants in the western part of Hong Kong to impact the territory, and at the same time allowing the import of emissions from upwind sources along the mainland coast. Other important meteorological factors that contribute to the occurrence of the episode events include: stable atmospheres, morning break-up of nocturnal inversions, low winds, strong solar radiation and high temperatures. Trajectory analysis of airflows at 850 hPa confirms the long-range pollutant transport. The strong correlation between non-sea-salt sulphate (NS-SO₄) and selenium for the summer of 1999 indicates that the main source of high levels of NS-SO₄ in summer in Hong Kong is coal combustion. The correlation between arsenic (As) and vanadium (V) for the summers of 1996–1999 suggests a concomitant influence of coal and residual oil combustion in the region.     

Analysis of regional and temporal characteristics of PM10 during an Asian dust episode in Korea

This study analyzes the regional and temporal distributions of PM10 concentrations observed in major metropolitan cities in Korea before, during and after a recent Asian dust episode in 2002. There were spatial and temporal variations in PM10 concentrations among the mid-western, the southwestern, the southeastern, and the southern parts of Korea during this Asian dust period due to the different air mass movement time and the different wind directions and speeds of prevailing winds in each city or region. The origins of the three-day Asian dust episode were identified by an analysis of two-day backward isentropic air trajectories. The different origins for each day also significantly contributed to the spatial and temporal variations in PM10 concentrations. A significant relationship was found between PM10 concentrations on the day preceding the first peak day and the first peak day of the Asian dust period but only in the mid-western areas. The concentrations of PM10 just after the Asian dust episode were much higher than those just before. There was a significant increase in a coarse fraction, having soil origins, of particles during the Asian dust episode. Concentrations of Mn, Fe, Ni and Cr extracted from the total suspended particulate (TSP) samples collected in 7 cities during the Asian dust episode were much higher when compared with other days in 2001. However, the Asian dust did not consistently increase the concentrations of lead, cadmium and copper as they are influenced by local sources such as local traffic or industrial emissions.     

Internally mixed sea salt, soot, and sulfates at Macao, a coastal city in South China

Direct observation of the mixing state of aerosol particles in a coastal urban city is critical to understand atmospheric processing and hygroscopic growth in humid air. Morphology, composition, and mixing state of individual aerosol particles from Macao, located south of the Pearl River Delta (PRD) and 100 km west of Hong Kong, were investigated using scanning electron microscopy (SEM) and transmission electron microscopy coupled with energy-dispersive X-ray spectrometry (TEM/EDX). SEM images show that soot and roughly spherical particles are prevalent in the samples. Based on the compositions of individual aerosol particles, aerosol particles with roughly spherical shape are classified into coarse Na-rich and fine S-rich particles. TEM/EDX indicates that each Na-rich particle consists of a Na-S core and NaNO3 shell. Even in the absence of heavy pollution, the marine sea salt particles were completely depleted in chloride, and Na-related sulfates and nitrates were enriched in Macao air. The reason could be that SO2 from the polluted PRD and ships in the South China Sea and NO2 from vehicles in the city sped up the chlorine depletion in sea salt through heterogeneous reactions. Fresh soot particles from vehicular emissions mainly occur near curbside. However, there are many aged soot particles in the sampling site surrounded by main roads 200 to 400 m away, suggesting that the fresh soot likely underwent a quick aging. Overall, secondary nitrates and sulfates internally mixed with soot and sea salt particles can totally change their surface hygroscopicity in coastal cities.     

Heavy metals and Pb isotopic composition of aerosols in urban and suburban areas of Hong Kong and Guangzhou,South China—Evidence of the long-range transport of air contaminants

Rapid urbanization and industrialization in South China has placed great strain on the environment and on human health. In the present study, the total suspended particulate matter (TSP) in the urban and suburban areas of Hong Kong and Guangzhou, the two largest urban centres in South China, was sampled from December 2003 to January 2005. The samples were analysed for the concentrations of major elements (Al, Fe, Mg and Mn) and trace metals (Cd, Cr, Cu, Pb, V and Zn), and for Pb isotopic composition. Elevated concentrations of metals, especially Cd, Pb, V and Zn, were observed in the urban and suburban areas of Guangzhou, showing significant atmospheric trace element pollution. Distinct seasonal patterns were observed in the heavy metal concentrations of aerosols in Hong Kong, with higher metal concentrations during the winter monsoon period, and lower concentrations during summertime. The seasonal variations in the metal concentrations of the aerosols in Guangzhou were less distinct, suggesting the dominance of local sources of pollution around the city. The Pb isotopic composition in the aerosols of Hong Kong had higher ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb ratios in winter, showing the influence of Pb from the northern inland areas of China and the Pearl River Delta (PRD) region, and lower ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb ratios in summer, indicating the influence of Pb from the South Asian region and from marine sources. The back trajectory analysis showed that the enrichment of heavy metals in Hong Kong and Guangzhou was closely associated with the air mass from the north and northeast that originated from northern China, reflecting the long-range transport of heavy metal contaminants from the northern inland areas of China to the South China coast.     

Indoor and outdoor air quality investigation at schools in Hong Kong

Five classrooms in Hong Kong (HK), air-conditioned or ceiling fans ventilated, were chosen for investigation of indoor and outdoor air quality. Parameters such as temperature, relative humidity (RH), carbon dioxide (CO2), sulphur dioxide (SO2), nitric oxide (NO), nitrogen dioxide (NO2), respirable particulate matter (PM10), formaldehyde (HCHO), and total bacteria counts were monitored indoors and outdoors simultaneously. The average respirable particulate matter concentrations were higher than the HK Objective, and the maximum indoor PM10 level exceeded 1000 microg/m3. Indoor CO2 concentrations often exceeded 1000 microl/l in air-conditioning and ceiling fan classrooms, indicating inadequate ventilation. Maximum indoor CO2 level reached 5900 microl/l during class at the classroom with cooling tower ventilation. Increasing the rate of ventilation or implementation of breaks between classes is recommended to alleviate the high CO2 level. Other pollution parameters measured in this study complied with the standards. The two most important classroom air quality problems in Hong Kong were PM10 and CO2 levels.     

Carbonyl sulfide,dimethyl sulfide and carbon disulfide in the Pearl River Delta of southern China: Impact of anthropogenic and biogenic sources

Reduced sulfur compounds (RSCs) such as carbonyl sulfide (OCS), dimethyl sulfide (DMS) and carbon disulfide (CS₂) impact radiative forcing, ozone depletion, and acid rain. Although Asia is a large source of these compounds, until now a long-term study of their emission patterns has not been carried out. Here we analyze 16 months of RSC data measured at a polluted rural/coastal site in the greater Pearl River Delta (PRD) of southern China. A total of 188 canister air samples were collected from August 2001 to December 2002. The OCS and CS₂ mixing ratios within these samples were higher in autumn/winter and lower in summer due to the influence of Asian monsoon circulations. Comparatively low DMS values observed in this coastal region suggest a relatively low biological productivity during summer months. The springtime OCS levels in the study region (574 ± 40 pptv) were 25% higher than those on other East Asia coasts such Japan, whereas the springtime CS₂ and DMS mixing ratios in the PRD (47 ± 38 pptv and 22 ± 5 pptv, respectively) were 3–30 times lower than elevated values that have been measured elsewhere in East Asia (Japan and Korea) at this time of year. Poor correlations were found among the three RSCs in the whole group of 188 samples, suggesting their complex and variable sources in the region. By means of backward Lagrangian particle release simulations, air samples originating from the inner PRD, urban Hong Kong and South China Sea were identified. The mean mixing ratio of OCS in the inner PRD was significantly higher than that in Hong Kong urban air and South China Sea marine air (p < 0.001), whereas no statistical differences were found for DMS and CS₂ among the three regions (p > 0.05). Using a linear regression method based on correlations with the urban tracer CO, the estimated OCS emission in inner PRD (49.6 ± 4.7 Gg yr^?1) was much higher than that in Hong Kong (0.32 ± 0.05 Gg yr^?1), whereas the estimated CS₂ and DMS emissions in the study region accounted for a very few percentage of the total CS₂ and DMS emission in China. These findings lay the foundation for better understanding sulfur chemistry in the greater PRD region of southern China.     

Extensive aerosol optical properties and aerosol mass related measurements during TRAMP/TexAQS 2006 – Implications for PM compliance and planning

Extensive aerosol optical properties, particle size distributions, and Aerodyne quadrupole aerosol mass spectrometer measurements collected during TRAMP/TexAQS 2006 were examined in light of collocated meteorological and chemical measurements. Much of the evident variability in the observed aerosol-related air quality is due to changing synoptic meteorological situations that direct emissions from various sources to the TRAMP site near the center of the Houston-Galveston-Brazoria (HGB) metropolitan area. In this study, five distinct long-term periods have been identified. During each of these periods, observed aerosol properties have implications that are of interest to environmental quality management agencies. During three of the periods, long range transport (LRT), both intra-continental and intercontinental, appears to have played an important role in producing the observed aerosol. During late August 2006, southerly winds brought super-micron Saharan dust and sea salt to the HGB area, adding mass to fine particulate matter (PM_2.5) measurements, but apparently not affecting secondary particle growth or gas-phase air pollution. A second type of LRT was associated with northerly winds in early September 2006 and with increased ozone and sub-micron particulate matter in the HGB area. Later in the study, LRT of emissions from wildfires appeared to increase the abundance of absorbing aerosols (and carbon monoxide and other chemical tracers) in the HGB area. However, the greatest impacts on Houston PM_2.5 air quality are caused by periods with low-wind-speed sea breeze circulation or winds that directly transport pollutants from major industrial areas, i.e., the Houston Ship Channel, into the city center.     

Effects of wind direction on coarse and fine particulate matter concentrations in southeast Kansas

Field data for coarse particulate matter ([PM] PM10) and fine particulate matter (PM2.5) were collected at selected sites in Southeast Kansas from March 1999 to October 2000, using portable MiniVol particulate samplers. The purpose was to assess the influence on air quality of four industrial facilities that burn hazardous waste in the area located in the communities of Chanute, Independence, Fredonia, and Coffeyville. Both spatial and temporal variation were observed in the data. Variation because of sampling site was found to be statistically significant for PM10 but not for PM2.5. PM10 concentrations were typically slightly higher at sites located within the four study communities than at background sites. Sampling sites were located north and south of the four targeted sources to provide upwind and downwind monitoring pairs. No statistically significant differences were found between upwind and downwind samples for either PM10 or PM2.5, indicating that the targeted sources did not contribute significantly to PM concentrations. Wind direction can frequently contribute to temporal variation in air pollutant concentrations and was investigated in this study. Sampling days were divided into four classifications: predominantly south winds, predominantly north winds, calm/variable winds, and winds from other directions. The effect of wind direction was found to be statistically significant for both PM10 and PM2.5. For both size ranges, PM concentrations were typically highest on days with predominantly south winds; days with calm/variable winds generally produced higher concentrations than did those with predominantly north winds or those with winds from "other" directions. The significant effect of wind direction suggests that regional sources may exert a large influence on PM concentrations in the area.     

Demolition of high-rise public housing increases particulate matter air pollution in communities of high-risk asthmatics

Public housing developments across the United States are being demolished, potentially increasing local concentrations of particulate matter (PM) in communities with high burdens of severe asthma. Little is known about the impact of demolition on local air quality. At three public housing developments in Chicago, IL, PM with an aerodynamic diameter < 10 microm (PM10) and < 2.5 microm were measured before and during high-rise demolition. Additionally, size-selective sampling and real-time monitoring were concurrently performed upwind and downwind of one demolition site. The concentration of particulates attributable to demolition was estimated after accounting for background urban air pollution. Particle microscopy was performed on a small number of samples. Substantial increases of PM10 occurred during demolition, with the magnitude of that increase varying based on sampler distance, wind direction, and averaging time. During structural demolition, local concentrations of PM10 42 m downwind of a demolition site increased 4- to 9-fold above upwind concentrations (6-hr averaging time). After adjusting for background PM10, the presence of dusty conditions was associated with a 74% increase in PM10 100 m downwind of demolition sites (24-hr averaging times). During structural demolition, short-term peaks in real-time PM10 (30-sec averaging time) occasionally exceeded 500 microg/m(3). The median particle size downwind of a demolition site (17.3 microm) was significantly larger than background (3 microm). Specific activities are associated with realtime particulate measures. Microscopy did not identify asbestos or high concentrations of mold spores. In conclusion, individuals living near sites of public housing demolition are at risk for exposure to high particulate concentrations. This increase is characterized by relatively large particles and high short-term peaks in PM concentration.     

Particulate matter source apportionment in a village situated in industrial region of Central Europe

The bilinear receptor model positive matrix factorization (PMF) was used to apportion particulate matter with an aerodynamic diameter of 1–10 μm (PM_1–10) sources in a village, B?ezno, situated in an industrial region of northern Bohemia in Central Europe. The receptor model analyzed the data sets of 90- and 60-min integrations of PM_1–10 mass concentrations and elemental composition for 27 elements. The 14-day sampling campaigns were conducted in the village in summer 2008 and winter 2010. Also, to ensure seasonal and regional representativeness of the data sets recorded in the village, the spatial-temporal variability of the 24-hr PM₁₀ and PM_1–10 within 2008–2010 in winter and summer across the multiple sites was evaluated. There were statistically significant interseasonal differences of the 24-hr PM data, but not intrasummer or intrawinter differences of the 24-hr PM_1–10 data across the multiple sites. PMF resolved seven sources of PM_1–10. They were high-temperature coal combustion; combustion in local heating boilers; marine aerosol; mineral dust; primary biological/wood burning; road dust, car brakes; and gypsum. The main summer factors were assigned to mineral dust (38.2%) and primary biological/wood burning (33.1%). In winter, combustion factors dominated (80%) contribution to PM_1–10. The conditional probability function (CPF) helped to identified local sources of PM_1–10. The source of marine aerosol from the North Sea and English Channel was indicated by the Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT).

Implications: This is the first application of PMF to highly time/size resolved PM data in Czech Republic. The coarse aerosol fraction, PM_1–10, was chosen with regard to industrial character of the region, sampling site near the coal strip mine and coal power stations. Contrary to expectation, source apportionment did not show dominance of emissions from the coal strip mine. The results will enable local authorities and state bodies responsible for air quality assessment to focus on sources most responsible for air pollution in this industrial region.

Supplemental Materials:?Supplemental materials are available for this paper. Go to the publisher's online edition of the Journal of the Air & Waste Management Association for (1) details of measurement campaigns; (2) CPF for each of the sources contributing to PM_1–10; (3) factors contribution to PM_1–10 resolved by PMF; (4) diurnal pattern of road dust, car brake factor in summer and winter; (5) trajectories during the marine aerosol episode in winter 2010; and (6) temporal temperature, concentration, and wind speed relationships during the summer 2008 campaign and winter 2010 campaign.     

The long-range transport of aerosols from northern China to Hong Kong – a multi-technique study

The results of the inorganic and organic analyses of aerosol samples collected on the east and west sides of Hong Kong during a dust episode (9–10 May 1996) are reported. The origin of the dust was traced to Northern China. The dust reached Hong Kong by way of the East China Sea. The characteristics of the inorganic elements and organic compounds were quite different from the non-episodic samples collected on 1–2 April 1996, EPD (Environmental Protection Department, Special Administrative Region, Hong Kong, China) results for April–May 1994, and our early studies (Zheng et al., 1997. Atmospheric Environment 31(2), 227–237.). Results from X-ray spectrometry showed pronounced increase in the relative abundance of Al, Fe, Ca, S and Cl in the dust samples compared to the non-episodic samples. The high abundance of Cl in the dust samples suggested the aerosols experienced long-range transport by way of the sea. ICP-MS analysis revealed higher concentrations of Fe, Ca, S and Pb in the episodic samples relative to the values measured during April–May 1994 by EPD. The high Ca content in the soil samples is a characteristic of northern Chinese crustal material (Liu et al., 1985). Hong Kong aerosols are characterized by high octadecenoic acid concentration due to heavy urbanization and Chinese-style stir-fry cooking. A much lower C_18:1/C_18:0 ratio was found in the episodic samples, however, suggesting the aerosols were transported from a long distance. The high ratio of ⩾C₂₀/<C₂₀ in n-alkanoic acids, the high input of n-alkanes and n-alkanols from plant waxes, and the unusually similar distribution of the organic compounds in the east and west samples suggested the existence of non-local sources on 9–10 May 1996. The compositions and distributions of lipids in the aerosol samples collected during the episode corresponded well with those of the eolian dust samples over the Atlantic and Pacific Oceans. Back trajectories and low altitude (<3 km) mesoscale flow modeling were performed, suggesting the existence of a mesoscale atmospheric structure off the east China coast, which could be responsible for the dust episode. Surface charts indicated the presence of suspended dust near Shanghai on 8 May 1996. Taiwan also experienced a similar episode on 8–9 May 1996. This integrated, multi-technique approach provides clear evidence that the 9–10 May episode was attributed to a consequence of Asian Dust. This is the first scientific report of Asian Dust in Hong Kong.     

Seasonal and spatial variation of solvent extractable organic compounds in fine suspended particulate matter in Hong Kong

The results of a 12-month study of more than 100 solvent extractable organic compounds (SEOC) in particulate matter (PM) less than or equal to 2.5 microm (PM2.5) collected at three air monitoring stations located at roadside, urban, and rural sites in Hong Kong are reported. The total yield of SEOC that accounts for approximately 8-18% of organic carbon (OC) determined by a thermal optical transmittance method was 125-2060 ng/m3, which included 14.6-128 ng/m3 resolved aliphatic hydrocarbons, 39.4-1380 ng/m3 unresolved complex mixtures, 0.6-17.2 ng/m3 polycyclic aromatic hydrocarbons, 41.6-520 ng/m3 fatty acids, and < 0.1-12.1 ng/m3 alkanols. Distinct seasonal variations (summer/winter differences) were observed with higher concentrations of the total and each class of SEOC in the winter and lower concentrations in the summer. Spatial variations are also obvious, with the roadside samples having the highest concentrations of SEOC and the rural samples having the lowest concentrations in all seasons. Characteristic ratios of petroleum hydrocarbons, such as carbon preference index, unresolved to resolved components, and carbon number with maximum concentration, suggest that PM2.5 carbon in Hong Kong originates from both biogenic and anthropogenic sources. The proportion of SEOC in PM2.5 from anthropogenic sources is estimated.     

Measurement of organic mass to organic carbon ratio in ambient aerosol samples using a gravimetric technique in combination with chemical analysis

Organic materials make up a significant fraction of ambient particulate mass. It is important to quantify their contributions to the total aerosol mass for the identification of aerosol sources and subsequently formulating effective control measures. The organic carbon (OC) mass can be determined by an aerosol carbon analyzer; however, there is no direct method for the determination of the mass of organic compounds, which also contain N, H, and O atoms in addition to C. The often-adopted approach is to estimate the organic mass (OM) from OC multiplying by a factor. However, this OC-to-OM multiplier was rarely measured for a lack of appropriate methods for OM. We report here a top-down approach to determine OM by coupling thermal gravimetric and chemical analyses. OM is taken to be the mass difference of a filter before and after heating at 550 °C in air for 4 h minus mass losses due to elemental carbon (EC), volatile inorganic compounds (e.g., NH₄NO₃), and loss of aerosol-associated water that arise from the heating treatment. The losses of EC and inorganic compounds are determined through chemical analysis of the filter before and after the heating treatment. We analyzed 37 ambient aerosol samples collected in Hong Kong during the winter of 2003, spring of 2004, and summer of 2005. A value of 2.1±0.3 was found to be the appropriate factor to convert OC to OM in these Hong Kong aerosol samples. If the dominant air mass is classified into two categories, then an OM-to-OC ratio of 2.2 was applicable to aerosols dominated by continent-originated air mass, and 1.9 was applicable to aerosols dominated by marine air mass.     

Size distributions of nano/micron dicarboxylic acids and inorganic ions in suburban PM episode and non-episodic aerosol

The distribution of nano/micron dicarboxylic acids and inorganic ions in size-segregated suburban aerosol of southern Taiwan was studied for a PM episode and a non-episodic pollution period, revealing for the first time the distribution of these nanoscale particles in suburban aerosols. Inorganic species, especially nitrate, were present in higher concentrations during the PM episode. A combination of gas-to-nuclei conversion of nitrate particles and accumulation of secondary photochemical products originating from traffic-related emissions was likely a crucial cause of the PM episode. Sulfate, ammonium, and oxalic acid were the dominant anion, cation, and dicarboxylic acid, respectively, accounting for a minimum of 49% of the total anion, cation or dicarboxylic acid mass. Peak concentrations of these species occurred at 0.54 μm in the droplet mode during both non-episodic and PM episode periods, indicating an association with cloud-processed particles. On average, sulfate concentration was 16–17 times that of oxalic acid. Oxalic acid was nevertheless the most abundant dicarboxylic acid during both periods, followed by succinic, malonic, maleic, malic and tartaric acid. The mass median aerodynamic diameter (MMAD) of oxalic acid was 0.77 μm with a bi-modal presence at 0.54 μm and 18 nm during non-episodic pollution and an MMAD of 0.67 μm with mono-modal presence at 0.54 μm in PM episode aerosol. The concomitant formation of malonic acid and oxalic acid was attributed to in-cloud processes. During the PM episode in the 5–100 nm nanoscale range, an oxalic acid/sulfate mass ratio of 40.2–82.3% suggested a stronger formation potential for oxalic acid than for sulfate in the nuclei mode. For total cations (TC), total inorganic anions (TIA) and total dicarboxylic acids (TDA), major contributing particles were in the droplet mode, with least in the nuclei mode. The ratio of TDA to TIA in the nuclei mode increased greatly from 8.40% during the non-episodic pollution period to 28.08% during the PM episode, favoring dicarboxylic acid formation in the nuclei mode. The evidence suggests stronger formation strength and contribution potential exists for dicarboxylic acids than for inorganic salts in nanoscale particles, especially in PM episode aerosol.     

Local and regional anthropogenic influence on PM2.5 elements in Hong Kong

Hong Kong's persistent unhealthy level of fine particulate matter is a current public health challenge, complicated by the city being located in the rapidly industrializing Pearl River Delta Region of China. While the sources of the region's fine particulate matter (PM_2.5) are still not well understood, this study provides new source information through ground measurements and statistical analysis of 24 elements associated with particulate matter collected on filters. Field measurements took place over 4 months (October 2002, December 2002, March 2003, and June 2003) at seven sites throughout the Pearl River Delta, with three sites located in Hong Kong and four sites in the neighboring province, Guangdong. The 4-month average element concentrations show significant variation throughout the region, with higher levels of nearly every species seen among the northern Guangdong sites in comparison to Hong Kong. The high correlation (Pearson r>0.8) and similar magnitudes of 11 species (Al, Si, S, K, Ca, Mn, Fe, Zn, Br, Rb, and Pb) at three contrasting sites in Hong Kong indicate that sources external to Hong Kong dominate the regional levels of these elements. Further correlative analysis compared Hong Kong against potential source areas in Guangdong Province (Shenzhen, Zhongshan, and Guangzhou). Moderate correlation of sulfur for all pairings of Hong Kong sites with three Guangdong sites in developed areas (average Pearson r of 0.52–0.94) supports the importance of long-distance transport impacting the region as a whole, although local sources also clearly impact observed concentrations. Varying correlative characteristics for zinc when Hong Kong sites are paired with Shenzhen (average r=0.86), Guangzhou (average r=−0.65) and Zhongshan (average r=0.45) points to a source area located south of Guangzhou and locally impacting Zhongshan. The concentration distribution and correlative characteristics of bromide point to sources located within the Pearl River Delta, but the specific location is yet inconclusive. Uniquely poor correlation of eight species (Al, Si, K, Ca, Mn, Fe, Rb, and Pb) for the pairing of Hong Kong sites with Guangzhou, in addition to the relatively higher concentrations measured at Guangzhou, indicates a significant regional impact due to land development and industrial activities in the Guangzhou vicinity.     

Regional contributions to airborne particulate matter in central California during a severe pollution episode

The externally-mixed source-oriented UCD/CIT air quality model was applied to determine the significance of inter-regional transport for primary and secondary particulate matter (PM) in California's Central Valley during a severe wintertime PM pollution episode from December 15, 2000 to January 7, 2001. The gases and primary PM emitted from eight different geographical sub-regions were tracked separately in a model simulation that included transport, physical and chemical transformation and deposition processes. The model results directly predict the contribution that each sub-region makes to PM concentrations throughout the entire model domain. The boundary layer was relatively stagnant during the simulated 3-week air quality episode, and no consistent transport pattern for primary PM was predicted. Several significant inter-regional transport events were identified that each lasted a few days. Each of these inter-regional events was characterized by transport of gas-phase precursors of nitrate that combined with local emissions of ammonia to produce particulate nitrate. Nitrate already in the particle phase was not transported efficiently due to higher dry deposition rates for particles relative to gas-phase nitrogen oxides. The distinctive pattern of transport for nitrate precursors reflects the relatively long timescales required to convert NO_x emissions to nitrate during winter conditions characterized by low temperatures, weak photolysis rates, and low oxidant concentrations. The equilibrium partitioning of nitrate and ammonia to the particle phase is relatively fast once the nitrate has been produced. The most-likely transport distance for nitrate during the current episode varied from 130–140 km for the northern portion of the Central Valley to 50–60 km in the southern portion of the Central Valley. Sub-regions further south in the Valley have smaller transport distances because of slower wind speeds and the greater abundance of ammonia in these areas, leading to faster conversion of gas-phase reactive nitrogen into particulate nitrate, which has a higher dry deposition rate than the gas-phase species. The most-likely transport distance for primary organic compounds (OC) was found to be less than that for nitrate, varying from 50 to 60 km for the northern portion of the Valley to 20–30 km for southern portion of the Valley. Overall, 68% of the particulate nitrate formed in the most polluted sub-regions of the Central Valley originates from emissions in those same sub-regions. Local emissions controls should therefore provide an effective strategy to reduce airborne particulate matter concentrations to acceptable levels.     

Effects of Wind Direction on Coarse and Fine Particulate Matter Concentrations in Southeast Kansas

Abstract

Field data for coarse particulate matter ([PM] PM₁₀) and fine particulate matter (PM_2.5) were collected at selected sites in Southeast Kansas from March 1999 to October 2000, using portable MiniVol particulate samplers. The purpose was to assess the influence on air quality of four industrial facilities that burn hazardous waste in the area located in the communities of Chanute, Independence, Fredonia, and Coffeyville. Both spatial and temporal variation were observed in the data. Variation because of sampling site was found to be statistically significant for PM₁₀ but not for PM_2.5. PM₁₀ concentrations were typically slightly higher at sites located within the four study communities than at background sites. Sampling sites were located north and south of the four targeted sources to provide upwind and downwind monitoring pairs. No statistically significant differences were found between upwind and downwind samples for either PM₁₀ or PM_2.5, indicating that the targeted sources did not contribute significantly to PM concentrations. Wind direction can frequently contribute to temporal variation in air pollutant concentrations and was investigated in this study. Sampling days were divided into four classifications: predominantly south winds, predominantly north winds, calm/variable winds, and winds from other directions. The effect of wind direction was found to be statistically significant for both PM₁₀ and PM_2.5. For both size ranges, PM concentrations were typically highest on days with predominantly south winds; days with calm/variable winds generally produced higher concentrations than did those with predominantly north winds or those with winds from “other” directions. The significant effect of wind direction suggests that regional sources may exert a large influence on PM concentrations in the area.     

Application of satellite remote-sensing data for source analysis of fine particulate matter transport events

Satellite sensors have provided new datasets for monitoring regional and urban air quality. Satellite sensors provide comprehensive geospatial information on air quality with both qualitative imagery and quantitative data, such as aerosol optical depth. Yet there has been limited application of these new datasets in the study of air pollutant sources relevant to public policy. One promising approach to more directly link satellite sensor data to air quality policy is to integrate satellite sensor data with air quality parameters and models. This paper presents a visualization technique to integrate satellite sensor data, ground-based data, and back trajectory analysis relevant to a new rule concerning the transport of particulate matter across state boundaries. Overlaying satellite aerosol optical depth data and back trajectories in the days leading up to a known fine particulate matter with an aerodynamic diameter of <2.5 microm (PM2.5) event may indicate whether transport or local sources appear to be most responsible for high PM2.5 levels in a certain location at a certain time. Events in five cities in the United States are presented as case studies. This type of analysis can be used to help understand the source locations of pollutants during specific events and to support regulatory compliance decisions in cases of long distance transport.