Despite recent efforts to investigate the distribution and fate of polycyclic aromatic hydrocarbons （PAHs） in air, water, and soil, very little is known about their temporal change in wet deposition. As a result of increased attention to public health, a large-scale survey on the deposition flux and distribution of PAH contamination in rainwater was urgently conducted in Shanghai, China. In this study, 163 rainwater samples were collected from six sites, and 15 PAH compounds were detected by the use of a simple solid phase microextraction （SPME） technique coupled with gas chromatography-mass spectrometry. The dominant PAH species monitored were naphthalene, phenanthrene, anthracene, and fluoranthene. The concentration of total PAHs per event was between 74 and 980 ng/L, with an average value of 481 ng/L, which is at the high end of worldwide figures. The annual deposition flux of PAHs in rainwater was estimated to be 4148 kg/yr in the Shanghai area, suggesting rainfall as a major possible pathway for removing PAHs from the atmosphere. Diagnostic analysis by the ratios of An/178 and Fl/Fl＋Py suggested that combustion of grass, wood, and coal was the major contributor to PAHs in the Shanghai region. Back trajectory analysis also indicated that the pollutant sources could be from the southern part of China.
Lili YanXiang LiJianmin ChenXinjun WangJianfei DuLin Ma
The hygroscopicity and optical properties of alkylaminium sulfates （AASs） were investigated using a hygroscopicity tandem differential mobility analyzer coupled to a cavity ring-down spectrometer and a nephelometer. AAS particles do not exhibit a deliquescence phenomenon and show a monotonic increase in diameter as the relative humidity （RH） ascends. Hygroscopic growth factors （GFs） for 40, 100 and 150 nm alkylaminium sulfate particles do not show an apparent Kelvin effect when RH is less than 45%, whereas GFs of the salt aerosols increase with initial particle size when RH is higher than 45%. Calculation using the Zdanovskii-Stokes-Robinson mixing rule suggests that hygroscopic growth of triethylaminium sulfate-ammonium sulfate mixtures is non-deliquescent, occurring at very low RH, implying that the displacement of ammonia by amine will significantly enhance the hygroscopicity of （NH4）2SO4 aerosols. In addition, light extinction of AAS particles is a combined effect of both scattering and absorption under dry conditions, but is dominated by scattering under wet conditions.
The semi-diurnal mean aerosol mass concentration, chemical composition, and optical properties of PM2.s were investigated in Shanghai during the spring of 2012. Slight pollution was observed during the study period. The average PM2.s concentration was 64.11± 22.83μg/m3. The mean coefficients of extinction, scattering, and absorption at 532 nm were 125.9 ± 78.5, 91.1 ± 56.3, and 34.9 ±23.6 Mm-1, respectively. A relatively low mean single scattering alhedo at 532 nm （0.73 ±0.04） and low level of elemental carbon （EC, 2.67± 1.96 μg/m3） suggested that the light absorption was enhanced due to the internal mixing of the EC. Sulfate contributed the most to aerosol light scattering in Shanghai. The chemical composition of PM2.5 was dominated by particulate organic matter, sulfate, nitrate, ammonium, and EC. Anthropogenic sources made a significant contribution to the emission and loading of the particulate pollutants. A relatively good correlation between the aerosol chemical composition and the cloud condensation nuclei （CCN） activation indicated that aerosol chemistry is an important factor that influences the saturated hygroscopicity and growth of the aerosol.
This paper explores the role of the secondary inorganic aerosol （SIA） species ammonium,NH4＋,nitrate,NO3-,and sulfate,SO24-,during haze and fog events using hourly mass concentrations of PM2.5 measured at a suburban site in Hangzhou,China.A total of 546 samples were collected between 1 April and 8 May 2012.The samples were analyzed and classified as clear,haze or fog depending on visibility and relative humidity （RH）.The contribution of SIA species to PM2.5 mass increased to ～50％ during haze and fog.The mass contribution of nitrate to PM2.5 increased from 11％ during clear to 20％ during haze episodes.Nitrate mass exceeded sulfate mass during haze,while near equal concentrations were observed during fog episodes.The role of RH on the correlation between concentrations of SIA and visibility was examined,with optimal correlation at 60％-70％ RH.The total acidity during clear,haze and fog periods was 42.38,48.38 and 45.51 nmol m-3,respectively,indicating that sulfate,nitrate and chloride were not neutralized by ammonium during any period.The nitrate to sulfate molar ratio,as a function of the ammonium to sulfate molar ratio,indicated that nitrate formation during fog started at a higher ammonium to sulfate molar ratio compared to clear and haze periods.During haze and fog,the nitrate oxidation ratio increased by a factor of 1.6-1.7,while the sulfur oxidation ratio increased by a factor of 1.2-1.5,indicating that both gaseous NO2 and SO2 were involved in the reduced visibility.
Roeland Cornelis JANSENSHI YangCHEN JianminHU YunJieXU ChangHONG ShengmaoLI JiaoZHANG Min
The aerosol number concentration and size distribution as well as size-resolved particle chemical composition were measured during haze and photochemical smog episodes in Shanghai in 2009. The number of haze days accounted for 43%, of which 30% was severe （visibility 〈 2 km） and moderate （2 km 〈 visibility 〈 3 km） haze, mainly distributed in winter and spring. The mean particle number concentration was about 17,000/cm3 in haze, more than 2 times that in clean days. The greatest increase of particle number concentration was in 0.5-1μm and 1-10 μm size fractions during haze events, about 17.78 times and 8.78 times those of clean days. The largest increase of particle number concentration was within 50-100 nm and 100-200 nm fractions during photochemical smog episodes, about 5.89 times and 4.29 times those of clean days. The particle volume concentration and surface concentration in haze, photochemical smog and clean days were 102, 49, 15 μm3/cm3 and 949, 649, 206 μm2/cm3, respectively. As haze events got more severe, the number concentration of particles smaller than 50 nm decreased, but the particles of 50-200 nm and 0.5-1μm increased. The diurnal variation of particle number concentration showed a bimodal pattern in haze days. All soluble ions were increased during haze events, of which NH4, SO24- and NO3 increased great/y, followed by Na＋, IC, Ca2＋ and CI-. These ions were very different in size-resolved particles during haze and photochemical smog episodes.
Xuemei WangJianmin ChenTiantao ChengRenyi ZhangXinming Wang
A set of micro pulse lidar （MPL） systems operating at 532 nm was used for ground-based observation of aerosols in Shanghai in 2011. Three typical particulate pollution events （e.g., haze） were examined to determine the evolution of aerosol vertical distribution and the planetary boundary layer （PBL） during these pollution episodes. The aerosol vertical extinction coefficient （VEC） at any given measured altitude was prominently larger during haze periods than that before or after the associated event. Aerosols originating from various source regions exerted forcing to some extent on aerosol loading and vertical layering, leading to different aerosol vertical distribution structures. Aerosol VECs were always maximized near the surface owing to the potential influence of local pollutant emissions. Several peaks in aerosol VECs were found at altitudes above 1 km during the dust- and bioburningoinfluenced haze events. Aerosol VECs decreased with increasing altitude during the local-polluted haze event, with a single maximum in the surface atmosphere. PM2.5 increased slowly while PBL and visibility decreased gradually in the early stages of haze events; subsequently, PM2.5 accumulated and was exacerbated until serious pollution bursts occurred in the middle and later stages. The results reveal that aerosols from different sources impact aerosol vertical distributions in the atmosphere and that the relationship between PBL and pollutant loadings may play an important role in the formation of pollution.
