Samples of airborne PM2.5 particles were collected during Fall 2011 from Guangzhou urban area. The morphology and size distribution of individual particles were analyzed by a Scanning Electron Microscopy coupled with Energy Dispersive X-ray Spectrometer(SEM-EDX) and Image Analysis System. Based on the morphology, three typical particles(soot aggregates, minerals, and coal fly ash) and other unknown particles in PM2.5 were identified. Results showed that the number-size distribution of PM2.5, peaking in the range of 0.1~0.2 μm, was dominated by the condensing sub-mode within the accumulation mode where gas phase reaction products were distributed. Both number and volume contribution of three typical particles were on the order of mineral soot aggregate fly ash. Minerals were mainly distributed in range of 0.1~0.3 μm with 41.97% in number percentage. The percentage of minerals in range of 0.1~0.2 μm was as high as 26.42%, which was the major factor influencing the overall size distribution of PM2.5. Size distributions of PM2.5particles were fairly similar during different sampling period(morning, afternoon, evening) as well as before and after raining, but the proportions of particles having sizes less than 0.1 μm were significantly decreased in the evening and after raining.
Airborne particles in urban Beijing during haze days and normal days were collected and analyzed in the autumn and winter seasons to reveal the chemical characteristics variations of air pollution. The air quality in haze days was substantially worse than that in normal days. Both the relatively low wind speed and high relative humidity were in favor of the accumulation of pollution species and new formation of secondary PM2.5 in the atmosphere. Elevated concentrations of elements and water-soluble inorganic ions were found on haze days for both PM10 and PM2.5. Particularly, the crustal element, such as Fe, in both PM10 and PM2.5 were substantially higher in autumn normal days and winter haze days than those in autumn haze days and winter normal days, indicating that the abundance of Fe in autumn haze days mainly be originated from crustal dust while in winter haze days it might be primarily emitted from anthropogenic sources (iron and steel smelting) instead of road dust. Secondary ion species (SO42−, NO3−, NH4+) in particles were generated much more during haze episodes, and contributed a higher proportion in PM2.5 than in PM10 during the two sampling periods. Moreover, HYSPLIT model was used to explain the possible transport of airborne particles from distant sources. By comparing with south-type trajectory, west-type trajectory entrained larger amounts of primary crustal pollutants, while, south-type trajectory was comprised of a higher mass of anthropogenic pollution species. The results of back trajectory analysis indicated that the elevated concentration of aerosol and its chemical components during haze days might be caused by the integrated effects of accumulation under stagnant meteorological condition and the transport emissions of pollutants from anthropogenic sources surrounding Beijing city.
Characteristics and sources of particle-bound polycyclic aromatic hydrocarbons (PAHs) in PMin three typical transportation microenvironments were investigated, and the health risks were assessed. Fine particle exposure by pedestrians and commuters taking buses and subways were collected using personal exposure samplers in December 2011 in Beijing. Concentrations of multiple PAHs were measured by gas chromatography-mass spectrometry (GC-MS). Sources of PAHs were identified by distribution patterns and ratios of different PAHs. Health risk assessments associated with respiratory exposure to PAHs were conducted based on benzopyrene (BaP) equivalent concentrations (BEQ), BaP based equivalent carcinogenic power (BaPE) and inhalation cancer risk. The results showed that:1) The average exposure level of PAHs in roadside, buses, and subways were (120±119), (101±46.6), and (50.8±25.6) ng/m, respectively. 2) The similarity of PAHs distribution patterns in the three transportation microenvironments and the ratios of PAHs ρ(Flt)/[ρ(Flt)+ρ(Pyr)] and ρ(IcdP)/[ρ(IcdP)+ρ(BghiP)]>0.5, ρ(BaA)/[ρ(BaA)+ρ(Chr)]>0.35 suggested common sources in these environments, mainly from vehicle emissions and coal combustion. 3) Inhalation cancer risk (19.8×10 -6, California Environmental Protection Agency(CalEPA)-based method; 15.6×10 -4, World Health Organization (WHO)-based method) was found to be highest in the roadside environment, about 1.4 and 3.6 times those for buses and subways, respectively. 4) PAHs were more enriched under the roadside and bus environments. Exposure to PAHs and the health risks obviously increased in the roadside environment during days with elevated PMconcentrations.
Regional air pollution is complex and becomes increasingly important in China.Among many others,secondary organic aerosol(SOA) is one of the most important components of PM2.5.This paper discusses various methods for quantifying SOA in the atmosphere(including methods based on the EC tracer,WSOC,receptor model,the SOA tracers,and air quality model),presents the basic principle of each method and points out that 1) the EC-tracer method,the WSOC method and the receptor model method are relatively simple and convenient,but limited by the availability of local source profiles and some specific tracers;2) the SOA-tracer method is analytically challenging but can supply source-specific SOA information;and 3) the air quality model method can provide large scale spatial distribution of SOA.This paper also summarizes the most recent results of SOA research in China and abroad and indicates that SOA is important in organic aerosol,and anthropogenic VOCs play a significant role in SOA formation in China.The primary purpose of this review is to provide basic and integrated information and suggestion for future directions of SOA study in China.
For the first time, PM2.5 source apportionment methods and techniques previously and currently applied in China are summarized, including sampling preparation, sampler selection, chemical speciation analysis, and source apportionment tools. The research direction for PM2.5 source apportionment work in China is also suggested. This review is expected to provide a fundamental understanding of PM2.5 source apportionment methods and to serve as an important reference for future source apportionment studies to be widely conducted in China and regulations or law for PM2.5 abatement in China.
In January 2013, a severe regional haze occurred over the North China Plain. An online-coupled meteorology-chemistry model was employed to simulate the impacts of aerosol–meteorology interactions on fine particles (PM2.5) pollution during this haze episode. The response of PM2.5 to meteorology change constituted a feedback loop whereby planetary boundary layer (PBL) dynamics amplified the initial perturbation of PM2.5. High PM2.5concentrations caused a decrease of surface solar radiation. The maximal decrease in daily average solar radiation reached 53% in Beijing, thereby leading to a more stable PBL. The peak PBL height in Beijing decreased from 690 m to 590 m when the aerosol extinction was considered. Enhanced PBL stability suppressed the dispersion of air pollutants, and resulted in higher PM2.5 concentrations. The maximal increase of PM2.5 concentrations reached 140 μg m−3 in Beijing. During most PM2.5 episodes, primary and secondary particles increased simultaneously. These results imply that the aerosol–radiation interactions played an important role in the haze episode in January 2013.
Exposure to ultrafine particles poses a potential health risk to school children. While many studies have focused on measuring ultrafine particle (UFP) concentrations in environments where children are at risk of high exposure, few studies have examined the particle deposition in the respiratory tract of children. This study aims to examine the particle deposition in the respiratory tract of school children in different microenvironments. UFP size distribution data were collected in residential homes, school buses, school classrooms, and from school outdoor air in both rural and urban areas of South Texas. The size distribution data were input to the Multiple Path Particle Dosimetry model to calculate regional and total particle deposition fraction. A 24-hour-school-day exposure was simulated by adding the time children spend in each microenvironment. The maximum pulmonary deposition fraction occurs at a diameter ranging from 18 to 40 nm, depending on condition. Age mostly affected the pulmonary region and the total lung deposition with the highest deposition fraction observed for younger children. In addition, comparison of size-dependent regional deposition and particle concentration establishes an accurate depiction of children's exposure and dose profiles. While children only spend 4% of the day in the home source environment, that environment may account for up to 77% of total daily dose intake. Higher deposition fraction occurs at smaller particle size. Younger children show increased levels of particle deposition than older children. Exposure period does not correlate to daily percentage of dose intake. This research can be used to assess children's accumulative exposure to UFPs.