Composition and mixing state of water soluble inorganic ions during hazy days in a background region of North China

Knowledge of haze particles in background areas of North China is limited, although they have been studied well in urban settings. Atmospheric aerosol particles were collected at a background site in the North China Plain during 16–31 January, 2011. Water soluble inorganic ions of PM2.5 and physicochemical characteristics of individual particles on hazy and clean days were measured by Ion Chromatography(IC) and Transmission Electron Microscopy(TEM), respectively. Average PM2.5 mass concentration was 50.4±29.9 μg m?3 with 62.5±26.8 μg m?3 on hazy days and 19.9±11.5 μg m?3 on clean days. SO42?, NO3?, and NH4+ with a combined mass concentration of 19.0±11.5 μg m?3 accounted for 69.8%–89.4% of the total water soluble inorganic ions. Size distributions of SO42? and NH4+ showed one unimodal peak at 0.56–1.8 μm on hazy days, whereas NO3? appeared as bimodal peaks at 0.56–1.8 and 5.6–10 μm, respectively. Individual particle analyses showed that the dominant aerosols were a mixture of sulfate, nitrate, and carbonaceous species, which together determine their mixing states. 48-h air mass back trajectories on hazy days suggested that air masses crossed the polluted continental areas(such as Jing-jin-ji region and Shandong province) and entrained ground air pollutants 11–19 hours before reaching the background area. During long-range transport particles undergo ageing and tend to be internally mixed mainly due to condensation in the background atmosphere. Our results suggest that hygroscopic and optical properties of these aerosol particles in the background area differ substantially from those in urban areas.

Chemical compositions of PM_(2.5) aerosol during haze periods in the mountainous city of Yong'an, China

Haze phenomena were found to have an increasing tendency in recent years in Yong＇an, a mountainous industrial city located in the center part of Fujian Province, China. Atmospheric fine particles （PM2.5） in the urban area during haze periods in three seasons （spring, autumn and winter） from 2007 to 2008 were collected, and the mass concentrations and chemical compositions （seventeen elements, water soluble inorganic ions （WSIIs） and carbonaceous species） of PM2.5 were determined. PM2.5 mass concentrations did not show a distinct difference among the three seasons. The carbonaceous species organic carbon （OC） and elemental carbon （EC） constituted up to 19.2%-30.4% of the PM2.5 mass during sampling periods, while WSIIs made up 25.3%-52.5% of the PM2.5 mass. The major ions in PM2.5 were SO42-, NO3- and NH4~, while the major elements were Si, K, Pb, Zn, Ca and A1. The experimental results （from data based on three haze periods with a 10-day sampling length for each period） showed that the crustal element species was the most abundant component of PM2.5 in spring, and the secondary ions species （SO42-, NO3-, NH4＋, etc.） was the most abundant component in PM2.5 in autumn and winter. This indicated that dust was the primary pollution source for PM2.5 in spring and combustion and traffic emissions could be the main pollution sources for PM2.5 in autumn and winter. Generally, coal combustion and traffic emissions were considered to be the most prominent pollution sources for this city on haze days.

Chemical characteristics and source apportionment of PM_(2.5) between heavily polluted days and other days in Zhengzhou, China

PM（2.5） samples were collected in Zhengzhou during 3 years of observation, and chemical characteristics and source contribution were analyzed. Approximately 96% of the daily PM（2.5） concentrations and annual average values exceeded the Chinese National Ambient Air Quality Daily and Annual Standards, indicating serious PM（2.5） pollution. The average concentration of water-soluble inorganic ions was 2.4 times higher in heavily polluted days（daily PM32.5 concentrations ＆gt; 250 μg/mand visibility ＆lt; 3 km） than that in other days, with sulfate, nitrate, and ammonium as major ions. According to the ratio of NO-3/SO2-4,stationary sources are still the dominant source of PM（2.5） and vehicle emission could not be ignored. The ratio of secondary organic carbon to organic carbon indicated that photochemical reactivity in heavily polluted days was more intense than in other days.Crustal elements were the most abundant elements, accounting for more than 60% of 23 elements. Chemical Mass Balance results indicated that the contributions of major sources（i.e., nitrate, sulfate, biomass, carbon and refractory material, coal combustion, soil dust,vehicle, and industry） of PM（2.5） were 13%, 16%, 12%, 2%, 14%, 8%, 7%, and 8% in heavily polluted days and 20%, 18%, 9%, 2%, 27%, 14%, 15%, and 9% in other days, respectively.Extensive combustion activities were the main sources of polycyclic aromatic hydrocarbons during the episode（Jan 1-9, 2015） and the total benzo[a]pyrene equivalency concentrations in heavily polluted days present significant health threat. Because of the effect of regional transport, the pollution level of PM（2.5） in the study area was aggravated.

Chemical characteristics of PM_(2.5) during haze episodes in the urban of Fuzhou,China

Atmospheric fine particles （PM2.5） were collected in this study with middle volume samplers in Fuzhou, China, during both normal days and haze days in summer （September 2007） and winter （january 2008）. The concentrations, distributions, and sources of polycyclic aromatic hydrocarbons （PAHs）, organic carbon （OC）, elemental carbon （EC）, and water soluble inorganic ions （WSIls） were determinated. The results showed that the concentrations of PM2.s, PAHs, OC, EC, and WSIIs were in the orders of haze 〉 normal and winter〉 summer. The dominant PAHs of PM2.s in Fuzhou were Fluo, Pyr, Chr, BbF, BkF, BaP, BghiP, and IcdP, which represented about 80.0% of the total PAHs during different sampling periods. The BaPeq concentrations of ^-~PAHs were 0.78, 0.99, 1.22, and 2.43 ng/m3 in summer normal, summer haze, winter normal, and winter haze, respectively. Secondary pollutants （SO42 , NO3 , NH4＊, and OC） were the major chemical compositions of PM2.5, accounting for 69.0%, 55.1%, 63.4%, and 64.9% of PM2.s mass in summer normal, summer haze, winter normal, and winter haze, respectively. Correspondingly, secondary organic carbon （SOC） in Fuzhou accounted for 20.1%, 48.6%, 24.5%, and 50.5% of OC. The average values of nitrogen oxidation ratio （NOR） and sulfur oxidation ratio （SOR） were higher in haze days （0.08 and 0.27） than in normal days （0.05 and 0.22）. Higher OC/EC ratios were also found in haze days （5.0） than in normal days （3.3）. Correlation analysis demonstrated that visibility had positive correlations with wind speed, and neg- ative correlations with relative humidity and major air pollutants. Overall, the enrichments of PM2.5, OC, EC, SO42 ,andNO3 promoted haze formation. Furthermore, the diagnostic ratios of IcdP/（IcdP ＋ BghiP）, lcdP/BghiP, OC/EC, and NO3 /SO42 indicated that vehicle exhaust and coal consumption were the main sources of pollutants in Fuzhou.