Potential Source Contribution Function Results Research Articles

Temporal variation of speciated atmospheric Hg and characteristics of size-fractioned HgP at a suburban site in Shijiazhuang City, North China

Atmospheric mercury (Hg) species were determined at a suburban site near Shijiazhuang, China from May 2016 to January 2017 to ascertain their seasonal and diurnal patterns, to identify the relationship with other parameters, and furthermore to elucidate their potential sources areas. The gaseous elemental Hg (GEM) concentration (3.66 ± 2.62 ng m−3) was about 2 times higher than the background level in the Northern Hemisphere, and the fine particulate bound Hg (HgP2.5) concentration (92.4 ± 59.6 pg m−3) was comparable to those at urban sites, while the gaseous oxidized Hg (GOM) level was quite low (5.7 ± 5.6 pg m−3). GEM and HgP2.5 concentrations exhibit pronounced seasonal (January > May > October > August) and diurnal (nighttime > daytime) patterns. In contrast, the seasonal and diurnal patterns of GOM were just opposite to those of GEM and HgP2.5. The significant positive relationship among GEM, HgP, CO, SO2, and NO2 reveals that they have similar anthropogenic sources. Interestingly, the size distributions of HgP in PM10 were observed to be unimodal during the four study periods, and peaks were all located in the fine mode (0.7–2.1 μm), and fine HgP contributed ∼70% (38.2–81.5%) of HgP10, indicating that the fine mode was the dominant size. The potential source contribution function (PSCF) result suggests that GEM level at the sampling site was highly impacted by regional sources rather than the long-range transport, and the potential source areas were predominantly located in southern Hebei and western Shandong. The results of wind rose and cluster analyses were consistent with the PSCF results.

Fine particle-bound polycyclic aromatic hydrocarbons (PAHs) at an urban site of Wuhan, central China: Characteristics, potential sources and cancer risks apportionment

Levels, compositions, sources, and cancer risks of fine particle (PM2.5)-bound PAHs were investigated at an urban site of Wuhan, Central China. Totally 115 PM2.5 samples collected during four seasons from 2014 to 2015 were analyzed for 16 USEPA priority PAHs. The annual average of PM2.5 and total PAHs were 106 ± 41.7 μg m−3 and 25.1 ± 19.4 ng m−3, respectively. The seasonal levels of PM2.5 and PAHs varied in a similar trend, with the highest concentrations in winter and the lowest in summer. PM2.5-bound PAHs under different pollution level was discussed and the highest average PAH levels were found at a moderate (115–150 μg m−3) air quality level. Three sources including coal combustion and biomass burning, petrogenic source, and vehicle emissions were extracted and quantified by the positive matrix factorization (PMF) model, accounting for 22.7 ± 21.3%, 34.4 ± 29.0% and 42.9 ± 31.3% of the total PAHs, respectively. The potential source contribution function (PSCF) and the concentration-weighted trajectory (CWT) were combined to explore the geographic origins of PAHs. The spatial distributions of coal combustion and biomass burning, petrogenic source, and vehicle emissions were well correlated with medium molecular weight (MMW), low molecular weight (LMW) and high molecular weight (HMW) PAHs, respectively. Results of PSCF and CWT indicated that the long-distance transport form north of Wuhan as far as northern and eastern of China was higher than that from the southern China while the contribution of local areas was higher than those from the long-range transport. The overall lifetime lung cancer risk (LLCR) via inhalation exposure to PM2.5-bound PAHs was estimated as 3.03 × 10−4, with vehicle emissions contributed 57.1% (1.6 × 10−4) to the total risk on average, followed by coal combustion and biomass burning (31.0%, 9.6 × 10−5), and petrogenic source (11.9%, 3.6 × 10−5).

Temporal variations and potential sources of organophosphate esters in PM2.5 in Xinxiang, North China

We monitored the concentrations of 10 organophosphate esters (OPEs) in 52 fine particulate matter (PM2.5) samples in Xinxiang, Henan Province, North China, in 2015. During the sampling period, the OPE concentrations in most samples (n = 47) differed minimally and were relatively stable (mean: 2.02 ± 0.93 ng m−3), although several samples (n = 5) had high total OPE (Ʃ10OPE) concentrations (mean: 9.99 ± 5.69 ng m−3), which may have been influenced by high PM2.5 levels. Meanwhile, some samples had high PM2.5 concentrations but low Ʃ10OPE concentrations (i.e. low OPE/PM2.5 ratios) or low PM2.5 concentrations but high Ʃ10OPE concentrations, which might have been influenced by air mass sources. Therefore, we assessed air mass sources using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model and wind direction frequency data, and subsequently analysed PM2.5 and OPE sources using a potential source contribution function (PSCF) model. The results revealed that air mass sources couldn't represent the source of specific pollutants, including PM2.5 and OPEs. Generally, both PM2.5 and OPEs were from Henan and Shandong Provinces; however, the major source areas differed, which may have resulted from diverse pollution characteristics in various source areas. The principal component analysis and PSCF results revealed that the 10 OPEs could be segmented into three groups, which were associated with different source areas. These results suggested that pollution characteristics of contaminants in source areas should be considered in source apportionment.

Seasonal variations of transport pathways and potential sources of PM2.5 in Chengdu, China (2012–2013)

Seasonal pattern of transport pathways and potential sources of PM2.5 in Chengdu during 2012–2013 were investigated based on hourly PM2.5 data, backward trajectories, clustering analysis, potential source contribution function (PSCF), and concentration-weighted trajectory (CWT) method. The annual hourly mean PM2.5 concentration in Chengdu was 97.4 mg·m–3. 5, 5, 5 and 3 mean clusters were generated in four seasons, respectively. Short-distance air masses, which travelled within the Sichuan Basin with no specific source direction and relatively high PM2.5 loadings (>80 mg·m–3) appeared as important pathways in all seasons. These short pathways indicated that emissions from both local and surrounding regions of Chengdu contributed significantly to PM2.5 pollution. The cities in southern Chengdu were major potential sources with PSCF>0.6 and CWT>90 mg·m–3. The northeastern pathway prevailed throughout the year with higher frequency in autumn and winter and lower frequency in spring and summer. In spring, long-range transport from southern Xinjiang was a representative dust invasion path to Chengdu, and the CWT values along the path were 30-60 mg·m–3. Long-range transport was also observed in autumn from southeastern Xinjiang along a northwesterly pathway, and in winter from the Tibetan Plateau along a westerly pathway. In summer, the potential source regions of Chengdu were smaller than those in other seasons, and no long-range transport pathway was observed. Results of PSCF and CWT indicated that regions in Qinghai and Tibet contributed to PM2.5 pollution in Chengdu as well, and their CWT values increased to above 30 mg·m–3 in winter.

Characteristics of size-resolved atmospheric inorganic and carbonaceous aerosols in urban Shanghai

Size-segregated aerosol particles were collected with a 10-stage Micro-Orifice Uniform Deposit Impactor (MOUDI) at an urban site in Shanghai, China for four non-consecutive months representing four seasons from 2015 to 2016. Chemical composition, including water-soluble ions as well as organic carbon (OC), elemental carbon (EC) and secondary organic carbon (SOC) of size-resolved (0.056–18 μm) atmospheric aerosols in four seasons and in different polluted cases were studied. The size distributions of sulfate, nitrate and ammonium (SNA) and carbonaceous aerosol (OC, EC and SOC) were discussed and the potential sources of PM1.8-associated secondary species (SO42−, NO3−, SNA and SOC) in different seasons were identified by potential source contribution function (PSCF) model. Results showed that atmospheric ultrafine and fine particle pollution in Shanghai were very serious during the study period. Most of the water-soluble ions tended to be enriched in fine particles, especially being abundant in the droplet mode in polluted cases. Compared with sulfate, size distributions of nitrate and ammonium presented more significant seasonal variations and showed distinctive characteristics in polluted days. Abundant nitrate was concentrated in fine particles in cold seasons (spring and winter), whereas it was enriched in coarse mode during summer and autumn. The droplet mode sulfate with high concentration did not result in the aggravation of air pollution, while the nucleation mode sulfate may have made a great contribution to the air pollution in urban Shanghai. It was also found that the formation of air pollution in urban Shanghai had a significant link with nitrate and ammonium, especially with nitrate and ammonium in condensation mode and droplet mode, and the contribution of sulfate to the pollution formation in Shanghai would somehow be surpassed by the increasing nitrate and ammonium. OC and EC concentrations from spring to winter were found to be 11.10, 7.10, 12.30, 20.16, and 3.73, 2.84, 4.63, 7.10 μg m−3, respectively, distinctly presenting the summer minima and winter maxima in this study. The maximum OC/EC was in the droplet mode and the minimum was in the nucleation mode for both clean and polluted days. The great contribution of SOC to OC in droplet mode and the occurrence of PM pollution necessarily had an important bearing on the SOC formation in droplet mode particles. Particle acidity may play a key role in secondary organic aerosol formation and the particles with the size of 0.056–0.1 μm was the most sensitive particles to acid catalysis in SOA formation. The similar PSCF results of PM1.8-associated SOC to those of SO42−, NO3− and SNA indicated possible connections between the formation of SOC and secondary inorganic species in PM.

Chemical characteristics and source apportionment of PM2.5 using PCA/APCS, UNMIX, and PMF at an urban site of Delhi, India.

The present study investigated the comprehensive chemical composition [organic carbon (OC), elemental carbon (EC), water-soluble inorganic ionic components (WSICs), and major & trace elements] of particulate matter (PM2.5) and scrutinized their emission sources for urban region of Delhi. The 135 PM2.5 samples were collected from January 2013 to December 2014 and analyzed for chemical constituents for source apportionment study. The average concentration of PM2.5 was recorded as 121.9±93.2μgm-3 (range 25.1-429.8μgm-3), whereas the total concentration of trace elements (Na, Ca, Mg, Al, S, Cl, K, Cr, Si, Ti, As, Br, Pb, Fe, Zn, and Mn) was accounted for ∼17% of PM2.5. Strong seasonal variation was observed in PM2.5 mass concentration and its chemical composition with maxima during winter and minima during monsoon seasons. The chemical composition of the PM2.5 was reconstructed using IMPROVE equation, which was observed to be in good agreement with the gravimetric mass. Source apportionment of PM2.5 was carried out using the following three different receptor models: principal component analysis with absolute principal component scores (PCA/APCS), which identified five major sources; UNMIX which identified four major sources; and positive matrix factorization (PMF), which explored seven major sources. The applied models were able to identify the major sources contributing to the PM2.5 and re-confirmed that secondary aerosols (SAs), soil/road dust (SD), vehicular emissions (VEs), biomass burning (BB), fossil fuel combustion (FFC), and industrial emission (IE) were dominant contributors to PM2.5 in Delhi. The influences of local and regional sources were also explored using 5-day backward air mass trajectory analysis, cluster analysis, and potential source contribution function (PSCF). Cluster and PSCF results indicated that local as well as long-transported PM2.5 from the north-west India and Pakistan were mostly pertinent.

Long-range and regional transported size-resolved atmospheric aerosols during summertime in urban Shanghai.

In this study, the concentrations of water soluble ions (WSI), organic carbon (OC), and elemental carbon (EC) of size-resolved (0.056-18μm) atmospheric aerosols were measured in July and August 2015 in Shanghai, China. Backward trajectory model and potential source contribution function (PSCF) model were used to identify the potential source distributions of size-resolved particles and PM1.8-associated atmospheric inorganic and carbonaceous aerosols. The results showed that the average mass concentrations of PM0.1, PM1, and PM1.8 were 21.21, 82.90, and 100.1μgm-3 in July and 7.00, 29.21, and 35.10μgm-3 in August, respectively, indicating that the particulate matter pollution was more serious in July than in August in this study due to the strong dependence of the aerosol species on the air mass origins. The trajectory cluster analysis revealed that the air masses originated from heavily industrialized areas including the Pearl River Delta (PRD) region, the Yangtze River Delta (YRD) region and the Beijing-Tianjin region were characterised with high OC and SO42- loadings. The results of PSCF showed that the pollution in July was mainly influenced by long-range transport while it was mainly associated to local and intra-regional transport in August. Besides the contributions of anthropogenic sources from YRD and PRD region, ship emissions from the East China Sea also made a great contribution to the high loadings of PM1.8 and PM1.8-associated NO3-, NH4+, and EC in July. SO42- in Shanghai was dominantly ascribed to anthropogenic sources and the high PSCF values for PM1.8-associated SO42- observed in August was mainly due to the ship emissions of Shanghai port, such as Wusong port and Yangshan deep-water port. These results indicated that the particulate pollutants from long-range transported air masses and shipping made a significant contribution to Shanghai's air pollution.

Identification of long-range transport pathways and potential sources of PM2.5 and PM10 in Beijing from 2014 to 2015

Trajectory clustering, potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) methods were applied to investigate the transport pathways and identify potential sources of PM2.5 and PM10 in different seasons from June 2014 to May 2015 in Beijing. The cluster analyses showed that Beijing was affected by trajectories from the south and southeast in summer and autumn. In winter and spring, Beijing was not only affected by the trajectories from the south and southeast, but was also affected by trajectories from the north and northwest. In addition, the analyses of the pressure profile of backward trajectories showed that backward trajectories, which have important influence on Beijing, were mainly distributed above 970hPa in summer and autumn and below 950hPa in spring and winter. This indicates that PM2.5 and PM10 were strongly affected by the near surface air masses in summer and autumn and by high altitude air masses in winter and spring. Results of PSCF and CWT analyses showed that the largest potential source areas were identified in spring, followed by winter and autumn, then summer. In addition, potential source regions of PM10 were similar to those of PM2.5. There were a clear seasonal and spatial variation of the potential source areas of Beijing and the airflow in the horizontal and vertical directions. Therefore, more effective regional emission reduction measures in Beijing's surrounding provinces should be implemented to reduce emissions of regional sources in different seasons.

Ambient PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) in Changhua County, central Taiwan: Seasonal variation, source apportionment and cancer risk assessment

This study investigates PM2.5-bound PAHs for rural sites (Dacheng and Fangyuan) positioned close to heavy air-polluting industries in Changhua County, central Taiwan. A total of 113 PM2.5 samples with 22 PAHs collected from 2014 to 2015 were analyzed, and Positive Matrix Factorization (PMF) and diagnostic ratios of PAHs were applied to quantify potential PAH sources. The influences of local and regional sources were also explored using the conditional probability function (CPF) and potential source contribution function (PSCF) with PMF-modeled results, respectively. Annual mean concentrations of total PAHs were 2.91 ± 1.34 and 3.04 ± 1.40 ng/m3 for Dacheng and Fangyuan, respectively, and their corresponding BaPeq were measured at 0.534 ± 0.255 and 0.563 ± 0.273 ng/m3 in concentration. Seasonal variations with higher PAHs found for the winter than for the spring and summer were observed for both sites. The lifetime excess cancer risk (ECR) from inhalation exposure to PAHs was recorded as 4.7 × 10−5 overall. Potential sources of PM2.5-bound PAHs include unburned petroleum and traffic emissions (42%), steel industry and coal combustion (31%), and petroleum and oil burning (27%), and unburned petroleum and traffic emission could contribute the highest ECR (2.4 × 10−5). The CPF results show that directional apportionment patterns were consistent with the actual locations of local PAH sources. The PSCF results indicate that mainly northeastern regions of China have contributed elevated PM2.5-bound PAHs from long-range transports.

Combining AOT, Angstrom Exponent and PM concentration data, with PSCF model, to distinguish fine and coarse aerosol intrusions in Southern France

In this paper, a cluster analysis of backward air mass trajectories, arriving in Avignon (Southern France), was combined with a Potential Source Contribution Function (PSCF) model on a 0.5°×0.5° resolution grid, in order to indicate possible aerosol intrusions. A strict triple criterion was constructed from Aerosol Optical Thickness (AOT), Angstrom Exponent (AE), and PM (PM10 and PM2.5) concentration measurements, aiming to distinguish more effectively Episodes of Fine, Coarse and Overall Aerosols (FAE, CAE and OAE respectively). Large fractions of FAE (60.0%) and CAE (40.6%) were strongly attributed to the prevalence of Eastern and South–Southwest (S–SW) airflows respectively, whereas these distinct trajectory clusters also gathered large fractions of OAE (90.2% cumulatively). According to PSCF results, FAE events were strongly associated with the influence of air masses traveling over North Italy and Southern Germany, hence the impact of urban and industrial combustion was emerged. Main sources of coarse aerosols were principally isolated over the Mediterranean, thus the import of sea spray and dust from the Sahara desert is presumed. Satellite AOT observations were used for a more detailed identification of an intense 5-day intrusion of coarse aerosols. Short range slow moving air mass trajectories, were proven to be a clear marker of atmospheric stagnation, based on a wind speed analysis, triggering the accumulation of locally emitted anthropogenic aerosols (mainly PM2.5) and lack of city ventilation.

Identification of potential regional sources of atmospheric total gaseous mercury in Windsor, Ontario, Canada using hybrid receptor modeling

Abstract. Windsor (Ontario, Canada) experiences trans-boundary air pollution as it is located on the border immediately downwind of industrialized regions of the United States of America. A study was conducted in 2007 to identify the potential regional sources of total gaseous mercury (TGM) and investigate the effects of regional sources and other factors on seasonal variability of TGM concentrations in Windsor. TGM concentration was measured at the University of Windsor campus using a Tekran® 2537A Hg vapour analyzer. An annual mean of 2.02±1.63 ng/m3 was observed in 2007. The average TGM concentration was high in the summer (2.48±2.68 ng/m3) and winter (2.17±2.01 ng/m3), compared to spring (1.88±0.78 ng/m3) and fall (1.76±0.58 ng/m3). Hybrid receptor modeling potential source contribution function (PSCF) was used by incorporating 72-h backward trajectories and measurements of TGM in Windsor. The results of PSCF were analyzed in conjunction with the Hg emissions inventory of North America (by state/province) to identify regions affecting Windsor. In addition to annual modeling, seasonal PSCF modeling was also conducted. The potential source region was identified between 24–61° N and 51–143° W. Annual PSCF modeling identified major sources southwest of Windsor, stretching from Ohio to Texas. The emissions inventory also supported the findings, as Hg emissions were high in those regions. Results of seasonal PSCF modeling were analyzed to find the combined effects of regional sources, meteorological conditions, and surface re-emissions, on seasonal variability of Hg concentrations. It was found that the summer and winter highs of atmospheric Hg can be attributed to areas where large numbers of coal fired power plants are located in the USA. Weak atmospheric dispersion due to low winds and high re-emission from surfaces due to higher temperatures also contributed to high concentrations in the summer. In the winter, the atmospheric removal of Hg was slow, but strong winds led to more dispersion, resulting in lower concentrations than the summer. Future studies could use smaller grid sizes and refined emission inventories, for more accurate analysis of source-receptor relationship of atmospheric Hg.

Identification of Sources of Fine and Coarse Particulate Matter in Dhaka, Bangladesh

In Bangladesh, the ambient air within Dhaka city is highly polluted by motor vehicle and brick kiln emissions. In addition, meteorological conditions during the winter cause increases in the fine particulate matter concentrations by factors of 4 to 5 fold compared to the rainy season. To understand the contribution of possible pollution sources, compositional data for both the coarse and fine fractions samples collected between May 2001 and March 2005 have been analyzed using Positive Matrix Factorization (PMF). The results were compared with the previous source apportionment results. Conditional Probability Function (CPF) plots were developed for each source using local wind data to explore the directionality of local sources. Back trajectory ensemble methods were used to identify potential source regions and pathways of transboundary transport of PM2.2 apportioned sources. The Potential Source Contribution Function (PSCF) domain extended around the receptor site in Dhaka (23.77°N, 90.38°E) over the range from 1.5° to 42.5°N and 56.5° to 110.5°E. The PSCF results are compared to the conditional probability function (CPF) analyses that use 3 hour average local wind directional data to determine the likely directions for the sources. Both PSCF and CPF help to identify the potential source locations, but on different distance scales. These analyses demonstrate that coarse particles are dominated by local sources. However, local and regional source contributed to the elevated fine PM levels in Dhaka. Thus, regional control efforts will be required in addition to local initiatives to improve the air quality in mega cities in this region like Dhaka.

Source Apportionment of Airborne Particulate Matter for the Speciation Trends Network Site in Cleveland, OH

Aerosol composition data from the Speciation Trends Network (STN) site (East 14th Street) in Cleveland, OH, were analyzed by advanced receptor model methods for source apportionment as well as by the standard positive matrix factorization (PMF) using PMF2. These different models are used in combination to test model limitations. These data were 24-hr average mass concentrations and compositions obtained for samples taken every third day from 2001 to 2003. The Multilinear Engine (ME) was used to solve an expanded model to estimate the source profiles and source contributions and also to investigate the wind speed, wind direction, time-of-day, weekend/weekday, and seasonal effects. PMF2 was applied to the same data-set. Potential source contribution function (PSCF) and conditional probability function (CPF) analyses were used to locate the regional and local sources using the resolved source contributions and appropriate meteorological data. Very little difference was observed between the results of the expanded model and the PMF2 values for the profiles and source contribution time series. The identified sources were as ferrous smelter, secondary sulfate, secondary nitrate, soil/combustion mixture, steel mill, traffic, wood smoke, and coal burning. The CPF analysis was useful in helping to identify local sources, whereas the PSCF results were only useful for regional source areas. Both of these analyses were more useful than the wind directional factor derived from the expanded factor analysis. However, the expanded analysis provided direct information on seasonality and day-of-week behavior of the sources.

Source Identification and Trends in Concentrations of Gaseous and Fine Particulate Principal Species in Seoul, South Korea

Ambient measurements were made using two sets of annular denuder system during the four seasons (April 2001 to February 2002) and were then compared with the results during the period of 1996–1997 to estimate the trends and seasonal variations in concentrations of gaseous and fine particulate matter (PM2.5) principal species. Annual averages of gaseous HNO3 and NH3 increased by 11% and 6%, respectively, compared with those of the previous study, whereas HONO and SO2 decreased by 11% and 136%, respectively. The PM2.5 concentration decreased by ∼17%, 35% for SO4 2−, and 29% for NH4 +, whereas NO3 − increased by 21%. Organic carbon (OC) and elemental carbon (EC) were 12.8 and 5.98 μg/m-3, accounting for ∼26 and 12% of PM2.5 concentration, respectively. The species studied accounted for 84% of PM2.5 concentration, ranging from 76% in winter to 97% in summer. Potential source contribution function (PSCF) analysis was used to identify possible source areas affecting air pollution levels at a receptor site in Seoul. High possible source areas in concentrations of PM2.5, NO3 −, SO4 2−, NH4 +, and K+ were coastal cities of Liaoning province (possibly emissions from oil-fired boilers on ocean liners and fishing vessels and industrial emissions), inland areas of Heibei/Shandong provinces (the highest density areas of agricultural production and population) in China, and typical port cities (Mokpo, Yeosu, and Busan) of South Korea. In the PSCF map for OC, high possible source areas were also coastal cities of Liaoning province and inland areas of Heibei/Shandong provinces in China. In contrast, high possible source areas of EC were highlighted in the south of the Yellow Sea, indicating possible emissions from oil-fired boilers on large ships between South Korea and Southeast Asia. In summary, the PSCF results may suggest that air pollution levels in Seoul are affected considerably by long-range transport from external areas, such as the coastal zone in China and other cities in South Korea, as well as Seoul itself.

Comparison of hybrid receptor models to locate PCB sources in Chicago

Results of three hybrid receptor models, potential source contribution function (PSCF), concentration weighted trajectory (CWT), and residence time weighted concentration (RTWC), were compared for locating polychlorinated biphenyl (PCB) sources contributing to the atmospheric concentrations in Chicago. Variations of these models, including PSCF using mean and 75% criterion concentrations, joint probability PSCF (JP-PSCF), changes of point filters and grid cell sizes for RTWC, and PSCF using wind trajectories started at different altitudes, are also discussed. Modeling results were relatively consistent between models. However, no single model provided as complete information as was obtained by using all of them. CWT and 75% PSCF appears to be able to distinguish between larger sources and moderate ones. RTWC resolved high potential source areas. RTWC and JP-PSCF pooling data from all sampling sites removed the trailing effect often seen in PSCF modeling. PSCF results using average concentration criteria, appears to identify both moderate and major sources. Each model has advantages and disadvantages. However, used in combination, they provide information that is not available if only one of them is used. For short-range atmospheric transport, PSCF results were consistent when using wind trajectories starting at different heights. Based on the archived PCB data, the modeling results indicate there is a large potential source area between Joliet and Kankakee, IL, and two moderate sources to the northwest and south of Chicago. On the south side of Chicago in the neighborhood of Lake Calumet, several PCB sources were identified. Other unidentified potential source location(s) will require additional upwind/downwind field sampling to verify modeling results.

Receptor modeling for smoke of 1998 biomass burning in Central America

The potential source contribution function (PSCF) is a receptor modeling technique for identifying emission sources and transport pathways. This technique has been widely used in the determination of potential emission sources and preferred transport pathways of a variety of air pollutants for more than a decade. However, the model has not been objectively evaluated against well‐documented real‐world data and the performance of the model is virtually untested. In this study we verified the PSCF model and tested the model performance by taking the opportunity of the 1998 Central America smoke events that produced elevated levels of aerosols detected at the Southern Great Plains site operated by the U.S. Department of Energy's Atmospheric Radiation Measurement. Our results show that the PSCF model could correctly identify the emission source locations and transport pathways of the smoke particles. However, one cannot take the PSCF results for granted without further examination of back trajectories that are responsible for the transport. False positives could result from the tailing of the back trajectories that travel over the true source locations. Model performance analysis suggests that using the mean or median as the criterion value yielded satisfactory PSCF results. Use of a high criterion value (e.g., the 90th percentile) and a larger database could improve the resolution of PSCF source identification. Trajectory arrival height above the surface sampling station should be carefully chosen to be within the column mixing height to ensure an effective coupling of transport and surface measurement.

Source Apportionment Study of Nitrogen Species Measured in Southern California in 1987

A novel receptor-oriented methodology has been developed to apportion source contributions of the nitrogen species measured in the south coast air quality basin (SoCAB) in the 1987 southern California air quality study (SCAQS). This method begins by calculating a conditional probability field [potential source contribution function (PSCF)] relating the probability of a 5 km by 5 km area to observed high concentrations at a receptor site. Comparison of the locations of known sources with areas of high PSCF values indicates the power of the PSCF results. The source contribution of a grid cell (i.e., a source area) was then computed by multiplying the available emissions inventory emissions rate by the PSCF value and including the contributions from the species into which the emitted compounds could be transformed. The probability weighted emission rate can then be interpreted in terms of source contribution as observed at the receptor site. The estimated source contribution includes the atmospheric transport, removal, and transformation processes. The PSCF-constructed source apportionment map could be effective in the design of emission control strategies than emission inventory values, because the PSCF results indicate the actual impact of each grid source on the total amount of material received at the receptor site.

A receptor‐oriented methodology for determining source regions of particulate sulfate observed at Dorset, Ontario

A statistical receptor‐oriented model was developed for long‐range transport of atmospheric sulfate to Dorset (elevation 320 m, latitude 4513′26″ N and longitude of 7855′52″ W), Ontario. This model computes the potential for sources within 1 latitude by 1 longitude grid cells across North America that contribute to the airborne concentrations measured at the ground station at Dorset. Airborne concentration data and air parcel backward trajectories were incorporated explicitly in the model calculation to identify the geographical areas of potential contributing sources. The present model is qualitative in nature; however, it provides a reasonable receptor‐oriented approach to examine the long‐range transport of atmospheric species. In order to fully understand the methodology and in a hope to optimize it, several aspects of the PSCF methodology have been examined in detailed in this study. Results of this study are presented that suggest interpolation of trajectory endpoints to increase the counting statistics for the potential source contribution function (PSCF) values is not reliable. The average concentration provides a reasonable criterion value; however, using the fiftieth percentile value as the criterion point provides an opportunity for identifying source areas that cannot be previously found by using the average concentration. The fiftieth percentile value may be a better choice for the particulate sulfate data in this case since Dorset is a relatively clean background site. Using the seventy‐fifth percentile, which is generally larger than the average, may not be suitable because it reduces the number of degrees of freedom. This could render the model to behave like a regular trajectory analysis model that has been used commonly for analyzing episodic pollution events. Separation of data into summer and winter periods is useful to illustrate the effects of photochemistry and meteorology on the PSCF results. Invoking the total probability concept and examining the trajectory arrival at different heights directly above the sampling site, the total PSCF was computed. This resultant function thus provides a time‐integrated geographical map useful for identifying sources of airborne particulate sulfate in a receptor‐oriented manner.