Seasonal variation of the size distribution of urban particulate matter and associated organic pollutants in the ambient air

Size-segregated samples of urban particulate matter (<0.95, 0.95–1.5, 1.5–3.0, 3.0–7.5, >7.5 μm) were collected in Thessaloniki, northern Greece, during winter and summer of 2007–2008, in order to study the size distribution of organic compounds such as polycyclic aromatic hydrocarbons (PAHs), aliphatic hydrocarbons (AHs) including n-alkanes and the isoprenoids pristane and phytane, organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs). All organic compounds were accumulated in the particle size fraction <0.95 μm particularly in the cold season. Particulate matter displayed a bimodal normalized distribution in both seasons with a stable coarse mode located at 3.0–7.5 μm and a fine mode shifting from 0.95–1.5 μm in winter to <0.95 μm in summer. Unimodal normalized distributions, predominant at 0.95–1.5 μm size range, were found for most organic compounds in both seasons, suggesting gas-to-particle transformation after emission. A second minor mode at larger particles (3.0–7.5 μm) was observed for C₁₉ and certain OCPs suggesting redistribution due to volatilization and condensation.     

Source contributions to fine particulate matter in an urban atmosphere

This paper proposes a practical method for estimating source attribution by using a three-step methodology. The main objective of this study is to explore the use of the three-step methodology for quantifying the source impacts of 24-h PM2.5 particles at an urban site in Seoul, Korea. 12-h PM2.5 samples were collected and analyzed for their elemental composition by ICP-AES/ICP-MS/AAS to generate the source composition profiles. In order to assess the daily average PM2.5 source impacts, 24-h PM2.5 and polycyclic aromatic hydrocarbons (PAH) ambient samples were simultaneously collected at the same site. The PM2.5 particle samples were then analyzed for trace elements. Ionic and carbonaceous species concentrations were measured by ICP-AES/ICP-MS/AAS, IC, and a selective thermal MnO2 oxidation method. The 12-h PM2.5 chemical data was used to estimate possible source signatures using the principal component analysis (PCA) and the absolute principal component scores method followed by the multiple linear regression analysis. The 24-h PM2.5 source categories were extracted with a combination of PM2.5 and some PAH chemical data using the PCA, and their quantitative source contributions were estimated by chemical mass balance (CMB) receptor model using the estimated source profiles and those in the literature. The results of PM2.5 source apportionment using the 12-h derived source composition profiles show that the CMB performance indices; chi2, R2, and percent of mass accounted for are 2.3%, 0.97%, and 100.7%, which are within the target range specified. According to the average PM2.5 source contribution estimate results, motor vehicle exhaust was the major contributor at the sampling site, contributing 26% on average of measured PM2.5 mass (41.8 microg m-3), followed by secondary sulfate (23%) and nitrate (16%), refuse incineration (15%), soil dust (13%), field burning (4%), oil combustion (2.7%), and marine aerosol (1.3%). It can be concluded that quantitative source attribution to PM2.5 in an urban area where source profiles have not been developed can be estimated using the proposed three-step methodology approach.     

Size distribution and source identification of total suspended particulate matter and associated heavy metals in the urban atmosphere of Delhi

A study of the atmospheric particulate size distribution of total suspended particulate matter (TSPM) and associated heavy metal concentrations has been carried out for the city of Delhi. Urban particles were collected using a five-stage impactor at six sites in three different seasons, viz. winter, summer and monsoon in the year 2001. Five samples from each site in each season were collected. Each sample (filter paper) was extracted with a mixture of nitric acid, hydrochloric acid and hydrofluoric acid. The acid solutions of the samples were analysed in five-particle fractions by atomic absorption spectrometry (AAS). The impactor stage fractionation of particles shows that a major portion of TSPM concentration is in the form of PM0.7 (i.e. <0.7microm). Similarly, the most of the metal mass viz. Mn, Cr, Cd, Pb, Ni, and Fe are also concentrated in the PM0.7 mode. The only exceptions are size distributions pertaining to Cu and Ca. Though, Cu is more in PM0.7 mode, its presence in size intervals 5.4-1.6microm and 1.6-0.7microm is also significant, whilst in case of Ca there is no definite pattern in its distribution with size of particles. The average PM10.9 (i.e. <10.9microm) concentrations are approximately 90.2%+/-4.5%, 81.4%+/-1.4% and 86.4%+/-9.6% of TSPM for winter, summer and monsoon seasons, respectively. Source apportionment reveals that there are two sources of TSPM and PM10.9, while three and four sources were observed for PM1.6 (i.e. <1.6microm) and PM0.7, respectively. Results of regression analyses show definite correlations between PM10.9 and other fine size fractions, suggesting PM10.9 may adequately act as a surrogate for both PM1.6 and PM0.7, while PM1.6 may adequately act as a surrogate for PM0.7.     

Characteristics of inhalable particulate matter concentration and size distribution from power plants in China

In this investigation, the collection efficiency of particulate emission control devices (PECDs), particulate matter (PM) emissions, and PM size distribution were determined experimentally at the inlet and outlet of PECDs at five coal-fired power plants. Different boilers, coals, and PECDs are used in these power plants. Measurement in situ was performed by an electrical low-pressure impactor with a sampling system, which consisted of an isokinetic sampler probe, precut cyclone, and two-stage dilution system with a sample line to the instruments. The size distribution was measured over a range from 0.03 to 10 microm. Before and after all of the PECDs, the particle number size distributions display a bimodal distribution. The PM2.5 fraction emitted to atmosphere includes a significant amount of the mass from the coarse particle mode. The controlled and uncontrolled emission factors of total PM, inhalable PM (PM10), and fine PM P(M2.5) were obtained. Electrostatic precipitator (ESP) and baghouse total collection efficiencies are 96.38-99.89% and 99.94%, respectively. The minimum collection efficiency of the ESP and the baghouse both appear in the particle size range of 0.1-1 microm. In this size range, ESP and baghouse collection efficiencies are 85.79-98.6% and 99.54%. Real-time measurement shows that the mass and number concentration of PM10 will be greatly affected by the operating conditions of the PECDs. The number of emitted particles increases with increasing boiler load level because of higher combustion temperature. During test run periods, the data reproducibility is satisfactory.     

Size distribution of airborne particulate matter and associated heavy metals in the roadside environment

The size distributions of airborne particulate matter (PM) and associated heavy metals Pb, Cd, Ni, Cr, V, Mn, Cu and Fe in different inhalable fractions (< 0.8 microm, 0.8-1.3 microm, 1.3-2.7 microm, 2.7-6.7 microm and > 6.7 microm) were determined at a traffic-orientated urban site in the city of Thessaloniki, northern Greece. The airborne PM displayed a bimodal distribution with most of the mass (52%) contained in the submicron size range (< 0.8 microm) and an additional minor mode (20%) in the coarse size fraction (> 6.7 microm). Characteristic size distributions of heavy metals allowed identification of three main behavioral types: (a) metals whose mass was resided mainly within the accumulation mode (Pb,Cd), (b) those which were distributed between fine, intermediate and coarse modes (Ni,Cu,Mn), and (c) those which were mainly found within particles larger than 2.7 microm in diameter (Fe). The mean mass median aerodynamic diameter (MMAD) of PM was found at 0.85+/-0.71 microm, while the mean MMADs of heavy metals followed the order Pb (0.96 +/- 0.71 microm) < Cd (1.14 +/- 0.82 microm) < V (1.38 +/- 0.63 microm) < Ni (1.45 +/- 0.88 microm) < Cu (2.04 +/- 0.77 microm) < Mn (2.61 +/- 1.23 microm) < Cr (2.91 +/- 1.40 microm) < Fe (3.82 +/- 0.88 microm). The measured distributions are believed to result from a combination of processes including local anthropogenic and natural sources, such as traffic, industrial emissions and resuspension of road dust.     

Spatial and temporal variability in urban fine particulate matter concentrations

Identification of hot spots for urban fine particulate matter (PM(2.5)) concentrations is complicated by the significant contributions from regional atmospheric transport and the dependence of spatial and temporal variability on averaging time. We focus on PM(2.5) patterns in New York City, which includes significant local sources, street canyons, and upwind contributions to concentrations. A literature synthesis demonstrates that long-term (e.g., one-year) average PM(2.5) concentrations at a small number of widely-distributed monitoring sites would not show substantial variability, whereas short-term (e.g., 1-h) average measurements with high spatial density would show significant variability. Statistical analyses of ambient monitoring data as a function of wind speed and direction reinforce the significance of regional transport but show evidence of local contributions. We conclude that current monitor siting may not adequately capture PM(2.5) variability in an urban area, especially in a mega-city, reinforcing the necessity of dispersion modeling and methods for analyzing high-resolution monitoring observations.     

Seasonal and spatial differences in mass concentration levels and particle size distribution of aerosols over an urban area

Data on mass concentration levels and particle size distribution based on samples simultaneously collected at three different areas of a city in winter and in summer were analysed and compared. In summer concentrations were consistent at all three sites, while in winter significantly higher concentrations were recorded in a densely populated city centre with traditional space heating. The investigated correlations and regression equations indicate that the city centre acts as a major source of particulate pollution in the winter time and that it influences air pollution in other parts of the town, especially in the south in the direction of prevalent NE winds. All concentration levels were within the limits established by Whitby and Liu in American cities.The particle size distribution was bimodal and very consistent for the three sites but there was a significant shift towards smaller particles in winter.     

Concentration and size distribution of particulate matter in a new aviary system for laying hens in China

ABSTRACT

Particulate matter (PM) from poultry production facilities may strongly affect the health of animals and workers in the houses, and PM emitted to the ambient air is an important pollution source to the surrounding areas. Aviary system is considered as a welfare friendly production system for laying hens. However, its air quality is typically worse as compared with conventional cage systems, because of the higher PM concentration of indoor air and other airborne contaminants. Furthermore, PM’s physical property, which has a direct impact on the penetration depth into the lungs of the birds and humans, is largely unknown for the aviary system. Therefore, a systematic method was utilized to investigate the characteristics of particles in the aviary house with large cage aviary unit system (LCAU) in Beijing, China. For the field measurements, three measuring locations were selected with two inside and one outside the house with LCAU to continuously monitor PM concentrations and collect the samples for particle size distribution (PSD) analysis. Results showed that PM_2.5, PM₁₀, and total suspended particulate (TSP) concentrations averaged at 0.037 ± 0.025 mg/m³, 0.42 ± 0.10 mg/m³, and 1.92 ± 1.91 mg/m³, respectively. Particle concentrations increased from October to December due to less ventilation as the weather got colder, and were generally affected by stocking density, ventilation rate, birds’ activities, and housing system. Meanwhile, indoor PM_2.5 concentration was easily impacted by the ambient air quality. Mass median diameter (MMD) and mass geometric standard deviation (MGSD) of the TSP during the measurement were 18.92 ± 7.08 μm and 3.11 ± 0.31, respectively. Count median diameter (CMD) and count geometric standard deviation (CGSD) were 1.94 ± 0.14 μm and 1.48 ± 0.08, respectively. Results indicated that the aviary system can attain a good indoor condition by suitable system design and environment control strategy.

Implications: Indoor PM_2.5 concentration of the layer house can be significantly affected by ambient air quality when the air quality index (AQI) was larger than 100. PM_2.5 and PM₁₀ concentrations of the layer house with a LCAU system were comparable to the cage system. TSP concentration was higher, and PM size was larger than most of the cage system. System design, larger space volume, and higher ventilation rate were the main influence factors. Good indoor environment of the aviary system can be achieved through the reasonable design of the production system and appropriate environment control strategy.     

A multi-approach monitoring of particulate matter, metals and PAHs in an urban street canyon

For the first time until now, the results from a prediction model (Atmospheric Dispersion Modelling System (ADMS)-Road) of pollutant dispersion in a street canyon were compared to the results obtained from biomonitors. In particular, the instrumental monitoring of particulate matter (PM10) and the biomonitoring of 14 polycyclic aromatic hydrocarbons (PAHs) and 11 metals by Quercus ilex leaves and Hypnum cupressiforme moss bags, acting as long- and short-term accumulators, respectively, were carried out. For both PAHs and metals, similar bioaccumulation trends were observed, with higher concentrations in biomonitors exposed at the leeward canyon side, affected by primary air vortex. The major pollutant accumulation at the leeward side was also predicted by the ADMS-Road model, on the basis of the prevailing wind direction that determines different exposure of the street canyon sides to pollutants emitted by vehicular traffic. A clear vertical (3, 6 and 9 m) distribution gradient of pollutants was not observed, so that both the model and biomonitoring results suggested that local air turbulences in the street canyon could contribute to uniform pollutant distribution at different heights.     

The impact of a building implosion on airborne particulate matter in an urban community

In response to community concerns, the air quality impact of imploding a 22-story building in east Baltimore, MD, was studied. Time- and space-resolved concentrations of indoor and outdoor particulate matter (PM) (nominally 0.5-10 microm) were measured using a portable nephelometer at seven and four locations, respectively. PM10 levels varied in time and space; there was no measurable effect observed upwind of the implosion. The downwind peak PM10 levels varied with distance (54,000-589 microg/m3) exceeding pre-implosion levels for sites 100 and 1130 m 3000- and 20-fold, respectively. Estimated outdoor 24-hr integrated mass concentrations varied from 15 to 72 microg/m3. The implosion did not result in the U.S. Environmental Protection Agency (EPA) National Ambient Air Quality Standard (NAAQS) for PM10 being exceeded. X-ray fluorescence analysis indicated that the elemental composition was dominated by crustal elements: calcium (57%), silicon (23%), aluminum (7.6%), and iron (6.1%). Lead was above background but at a low level (0.17 microg/m3). Peak PM10 concentrations were short-lived; most sites returned to background within 15 min. No increase in indoor PM10 was observed even at the most proximate 250 m location. These results demonstrate that a building implosion can have a severe but short-lived impact on community air quality. Effective protection is offered by being indoors or upwind.     

Spatial variability of different fractions of particulate matter within an urban environment and between urban and rural sites

The spatial variability of different fractions of particulate matter (PM) was investigated in the city of Basel, Switzerland, based on measurements performed throughout 1997 with a mobile monitoring station at six sites and permanently recorded measurements from a fixed site. Additionally, PM10 measurements from the following year, which were concurrently recorded at two urban and two rural sites, were compared. Generally, the spatial variability of PM4, PM10, and total suspended particulates (TSP) within this Swiss urban environment (area = 36 km2) was rather limited. With the exception of one site in a street canyon next to a traffic light, traffic density had only a weak tendency to increase the levels of PM. Mean PM10 concentration at six sites with different traffic densities was in the range of less than +/- 10% of the mean urban PM10 level. However, comparing the mean PM levels on workdays to that on weekends indicated that the impact of human activities, including traffic, on ambient PM levels may be considerable. Differences in the daily PM10 concentrations between urban and more elevated rural sites were strongly influenced by the stability of the atmosphere. In summer, when no persistent surface inversions exist, differences between urban and rural sites were rather small. It can therefore be concluded that spatial variability of annual mean PM concentration between urban and rural sites in the Basel area may more likely be caused by varying altitude than by distance to the city center.     

Respirable particulate matter at an urban and nearby industrial location: concentrations and variability and synoptic weather conditions during high pollution episodes

Continuous data of the concentration measurements of respirable suspended particulates (PM10, particles with aerodynamic diameter smaller than or equal to 10 pm) were analyzed. These measurements were carried out at an urban and nearby industrial location in northern Greece for the 5-year period 1996-2000. The time series concentration trend was examined, the seasonal and diurnal variations were identified, and the lognormality of the daily mean concentration data sets was tested. Over the 5-year data-gathering period, the days on which the U.S. Environmental Protection Agency (EPA) 24-hr PM10 standard was exceeded (episode days) were identified and their relation to prevailing synoptic-scale meteorological conditions was studied. The analysis led to useful information concerning the air quality levels, the contribution of the main pollution sources in this area, as well as some of the mechanisms that influence the PM10 concentrations. It also was proved that the measured PM10 concentrations are a result of a combination of processes including local anthropogenic sources, mesoscale transport, and resuspension. A complex system of sources and meteorological conditions modulate the heavy particulate pollution in the area of interest.     

A comparison of air particulate matter and associated polycyclic aromatic hydrocarbons in some tropical and temperate urban environments

A 12 month study of urban concentrations of total suspended particulates (TSP) and 20 polycyclic aromatic hydrocarbons (PAH) was carried out in Seoul (South Korea), Hong Kong, Bangkok (Thailand), Jakarta (Indonesia) and Melbourne (Australia). Concentrations of particulate matter in the atmosphere varied widely between the cities over the course of the study, ranging from a low of 24.1 μg m⁻³ in Melbourne during the winter to a high of 376.2 μg m⁻³ in Jakarta during the dry season. Seasonal variations in both TSP and PAH were observed in the tropical cities in the study with higher concentrations during the dry season and lower concentrations during the wet season. TSP and PAH concentrations are correlated with each other in these cities, suggesting that they have related sources and sinks for these cities. In the temperate cities of Melbourne and Seoul, PAH concentrations were higher during the cold winter season and lower during the warm summer. However, TSP was quite variable over the years in these latter cities and no clear seasonal trend was observed. A number of factors have been investigated which could be contributing to seasonal variations in pollutant levels. In the temperate climates, increased emissions due to the use of fossil fuels for heating in the winter is evident. However, an interrogation of the database with respect to the other factors such as (1) increased photolytic degradation during the summer, (2) transport of pollutants from other sources, (3) removal of PAH via wet deposition and in-cloud scavenging mechanisms and (4) volatilisation of lower molecular weight species during periods of high temperature indicates the importance of multiple processes. Even though there are clearly much lower levels of both particulates and PAH in the wet season of the tropical climates, no statistically significant correlations have been observed between rainfall levels and pollutant concentrations.     

Relationships between fine particulate species,gaseous pollutants and meteorological parameters in detroit

During June, July and August 1981, General Motors Research Laboratories operated a comprehensive air-quality monitoring site in Detroit. Parameters monitored included the criteria pollutants, meteorological variables and the organic carbon, elemental carbon and sulfate content of the fine and coarse fractions of inhalable particulates (diameter ⩽ 15 μm). In addition, air parcel trajectories were used to compute the length of time air parcels spent in various upwind emission-source areas before arriving in Detroit. The data were analyzed using varimax-rotated principal component analysis. The results show that midwestern sources upwind of southeastern (SE) Michigan are responsible for most of the observed sulfate, which accounted for about 50% of the fine particle fraction. Significant amounts of ozone, particulate organic carbon and sulfur dioxide are also transported in from upwind sources. Local emissions dominate the concentrations of coarse particulate mass, elemental carbon, carbon monoxide and non-methane hydrocarbons. Important local sources exist for nitrogen oxides, sulfur dioxide and particulate organic carbon.     

The Steubenville comprehensive air monitoring program (SCAMP): associations among fine particulate matter, co-pollutants, and meteorological conditions

We determined 24-hr average ambient concentrations of PM2.5 and its ionic and carbonaceous components in Steubenville, OH, between May 2000 and May 2002. We also determined daily average gaseous co-pollutant concentrations, meteorological conditions, and pollen and mold spore counts. Data were analyzed graphically and by linear regression and time series models. Multiple-day episodes of elevated fine particulate matter (PM2.5) concentrations often occurred during periods of locally high temperature (especially during summer), high pressure, or low wind speed (especially during winter) and generally ended with the passage of a frontal system. After removing autocorrelation, we observed statistically significant positive associations between concentrations of PM2.5 and concentrations of CO, NOx, and SO2. Associations with NOx and CO exhibited significant seasonal dependencies, with the strongest correlations during fall and winter. NOx, CO, SO2, O3, temperature, relative humidity, and wind speed were all significant predictors of PM2.5 concentration in a time-series model with external regressors, which successfully accounted for 79% of the variance in log-transformed daily PM2.5 concentrations. Coefficient estimates for NOx and temperature varied significantly by season. The results provide insight that may be useful in the development of future PM2.5 reduction strategies for Steubenville. Additionally, they demonstrate the need for PM epidemiology studies in Steubenville (and elsewhere) to carefully consider the potential confounding effects of gaseous co-pollutants, such as CO and NOx, and their seasonally dependent associations with PM2.5.     

Statistical distributions of particulate matter and the error associated with sampling frequency

The distribution of particulate matter (PM) concentrations has an impact on human health effects and the setting of PM regulations. Since PM is commonly sampled on less than daily schedules, the magnitude of sampling errors needs to be determined. Daily PM data from Spokane, Washington were resampled to simulate common sampling schedules and the sampling error was computed for regulatory and distribution statistics. Probability density functions (pdf's) were fit to the annual daily data to determine the shape of the PM_2.5 and PM₈ concentration distributions and they were also fit to the less than daily sampling to determine if pdf's could be used to predict the daily high-concentration percentiles. There is an error when using a less than daily sampling schedule for all statistics. The error expressed as a percentage difference from the everyday sampling for the PM_2.5 mean was as large as 1.7, 3.4 and 7.7% and the 98th percentile error was as great as 8.8, 18 and 67% for 1-in-2 day, 1-in-3 day and 1-in-6 day sampling, respectively. For PM₈ the error in the mean was 2.5, 4.7 and 8.6% for and the error in the 99th percentile was 27, 18 and 46% for 1-in-2 day, 1-in-3 day, and 1-in-6 day sampling, respectively. The PM_2.5 and PM₈ concentration data were best fit by a three-parameter lognormal distribution and a generalized extreme value distribution, respectively. For PM_2.5 and PM₈, as the annual mean increased the mode concentration increased, but for PM₈ the shape of the distribution also flattened. Predicting the daily high percentiles from pdf's that were fit to the less than daily sampled data produced mixed results. For PM₈, the pdf's predicted high concentrations were closer to the daily percentiles than the actual less-than-daily sampling percentile while for PM_2.5 they were not.     

Aryl hydrocarbon receptor-mediated activity of atmospheric particulate matter from an urban and a rural site in Switzerland

Atmospheric particulate matter (PM) is an air-suspended mixture of solid and liquid particles that vary in size, shape, and chemical composition. Long-term exposure to elevated concentrations of fine atmospheric particles is considered to pose a health threat to humans and animals. In this context, it has been hypothesized that toxic chemicals such as polycyclic aromatic hydrocarbons (PAHs) play an important role. Some PAHs are known to be carcinogenic and it has been shown that carcinogenic effects of PAHs are mediated by the aryl hydrocarbon receptor (AhR). In this study, PM1 was collected at a rural and an urban traffic site during an intense winter smog period, in which concentration of PM1 often exceeded 50 μg m^?3. We applied an in vitro reporter gene assay (DR-CALUX) to detect and quantify PM1-associated chemicals that induce AhR-mediated gene expression. This activity was expressed as CALUX equivalents of 2,3,7,8-tetrachlorodibenzodioxin (PM-TCDD-CEQs). In addition, concentrations of PAHs in the PM1 extracts were determined using gas chromatography/high-resolution mass spectrometry. Concentrations of PM-TCDD-CEQs ranged from 10 to 85 pg m^?3 and from 19 to 87 pg m^?3 at the urban and rural site, respectively. By the use of known relative potency factors, the measured concentration of a PAH was converted into a PAH-TCDD-CEQ concentration. ΣPAH-TCDD-CEQ and PM-TCDD-CEQ were highly correlated at both sites (r² = 0.90 and 0.69). The calculated ΣPAH-TCDD-CEQs explain between 2% and 20% of the measured PM-TCDD-CEQs. Benzo[k]fluoranthene was the most important PAH causing approximately 60% of the total ΣPAH-TCDD-CEQ activity. In contrast to NO, CO, PM10, and PM1, the concentration of PM-TCDD-CEQs showed no significant difference between the two sites. No indications were found that road traffic emissions caused elevated concentrations of PM-TCDD-CEQs at the urban traffic site.     

Emission factors and particulate matter size distribution of polycyclic aromatic hydrocarbons from residential coal combustions in rural Northern China

Coal consumption is one important contributor to energy production, and is regarded as one of the most important sources of air pollutants that have considerable impacts on human health and climate change. Emissions of polycyclic aromatic hydrocarbons (PAHs) from coal combustion were studied in a typical stove. Emission factors (EFs) of 16 EPA priority PAHs from tested coals ranged from 6.25 ± 1.16 mg kg^?1 (anthracite) to 253 ± 170 mg kg^?1 (bituminous), with NAP and PHE dominated in gaseous and particulate phases, respectively. Size distributions of particulate phase PAHs from tested coals showed that they were mostly associated with particulate matter (PM) with size either between 0.7 and 2.1 μm or less than 0.4 μm (PM_0.4). In the latter category, not only were more PAHs present in PM_0.4, but also contained higher fractions of high molecular weight PAHs. Generally, there were more than 89% of total particulate phase PAHs associated with PM_2.5. Gas-particle partitioning of freshly emitted PAHs from residential coal combustions were thought to be mainly controlled by absorption rather than adsorption, which is similar to those from other sources. Besides, the influence of fuel properties and combustion conditions was further investigated by using stepwise regression analysis, which indicated that almost 57 ± 10% of total variations in PAH EFs can be accounted for by moisture and volatile matter content of coal in residential combustion.     

某高密度街区大气颗粒物质量浓度分布特征实测研究

为研究城市高密度街区大气颗粒物浓度分布特征,2019年秋季对上海市某高密度街区道路大气颗粒物浓度、空气温度、相对湿度、地理位置、车辆与道路图像视频信息进行了同步移动在线监测,并结合街区内固定站数据和后向轨迹模拟结果,总结了影响街区大气颗粒物浓度变化的主要因素。结果表明:城市大气颗粒物背景拟合值处于较低水平时,街区内的大气颗粒物浓度变化和影响因素易被识别;机动车污染源对大气颗粒物浓度贡献大,其中大型机动车的影响明显;户外施工和道路清扫会引起大气颗粒物浓度上升,其中PM₁₀上升更明显;交通密度大的十字路口大气颗粒物浓度通常较高;城市高架的盖状结构会阻碍大气颗粒物在垂直方向上的扩散,引起局部大气颗粒物浓度上升;街区内高大浓密的乔木对近地面的大气颗粒物屏蔽效果不理想,甚至有助于颗粒物累积;早晚高峰时段大气颗粒物浓度较非高峰时段高。