Tempo-spatial Variation Of PAHs And Its Long-range Transport Capability In Atmosphere Over Yanghe Watershed

Polycyclic Aromatic Hydrocarbons (PAHs), a class of persistent toxic compounds, is high toxic, persistent and bio-accumulated and can transport with air. As incomplete combustion products, some PAHs could adsorb on the particle surface. Dust, as a belt connecting the exchange of air and others environmental substances, can transport to remote areas with PAHs, and then fall to the earth by gravity. Aerosol was a kind of suspended particulate matter with diameter below 10 micron. This particulate matter could absorb large amount of PAHs, and have a serious impact on human health. PAHs, entering the environment with aerosol and dust by transport, not only have a potential threat to environment, but also have a potential threat to ecology of ground and surface water. Since watershed as source of industrial, agricultural and drink water is typically vulnerable, the research of PAHs in watershed is important and attracting a lot of academic attention.The Yanghe Watershed, situated to the upwind of Beijing, is not only an important old industrial base, but also an important water source area and ecologic protection barrier for Beijing. The Yanghe Watershed is a farming-pastoral transitional area and an ecologically vulnerable region, as well as the place applying for 2022 winter Olympic game. In order to reflect the pollution situation of atmospheric PAHs in Yanghe Watershed, the statistical data of industries, agriculture and residents living within the Yanghe Watershed were collected, and PAHs emission factors were estimated in the present study. Meanwhile, in order to analysis the PAHs emission, tempo-spatial variation and its capabilities of long-range transport in atmosphere, twenty samples sites, representing background areas, industrial areas, residential areas, water sources areas and Beijing city areas, were set in Yanghe Watershed and Beijing to collected PAHs in ambient air from November of 2013 to November of 2014. Results indicated that:(1) coal combustion was the main emission sources of PAHs in Yanghe Watershed.76% PAHs emission in air is from coal consumption. Coal consumption of industrial and home was 6.1×103t and 8.4×102t, respectively; PAHs emission was 1.8×102 t and 1.2x102t, respectively. Emission of coal burning was followed by straw burning.16% emission of PAHs in air is by straw burning. Others sources accounted for less than 10% in Yanghe Watershed. Xuanhua County had the greatest emission of PAHs, about 49t, due to rapid economic development and the extent of the coal-based energy structure, followed by Xinghe’s 29 t, related with transport and home cooking or heating. Wanquan County has the least emission of PAHs, about 15 t. For 16 isomers of PAHs, the emission of high molecular weight isomers containing 4-6 rings were approximate to that of low molecular weight isomers containing 2-3 rings. Nap accounted for 21% of the total PAHs emission, which may be related with heavy fuel oil, coal tar or metal smelting. Phe, Flu, Pyr and BaP accounted for 12%, 9.1%, 8.4% and 7.4%, respectively.(2) Experimental data indicated that the annual PAHs in aerosol from Yanghe Watershed was 655 - 1689ng/m3, mean ± standard deviation was 308±139ng/m3. The PAHs in aerosol were dominated by lower molecular weight, as lower molecular weight more than 1.3 times larger than higher molecular weight. The maximum concentration of Σ16PAHs was in winter and mineral concentration of Σ16PAHs was in summer. The concentration of Σ16PAHs in spring was approximate to that of in autumn. The lowest concentration of Σ16PAHs was in Xinghe and Tianzhen county. The highest concentration of Σ16PAHs was in Chanyao and Beijing city sample site. PAHs in aerosol showed significant spatial distribution due to geographical environment and energy structure and weather conditions. Industrial areas (1388 ng/m3)> Beijing City (1077 ng/m3)>residential areas (844ng/m3)> water source (708 ng/m3)> Background areas (374ng/m3).(3) The emission of PAHs in dust were 503-2593ng/m2, mean ± standard deviation were 308±139ng/m2. The temporal distribution of PAHs in dust was consist with that of in aerosol. The lowest concentration of Σ16PAHs was in Houbaihu sample site. The highest concentration of Σ16PAHs was in Chanyao sample site. Different function area has differences PAHs concentration. Industrial area (1729 ng/m2)> Background (1566ng/m2)> Beijing City (1389 ng/m2)> residential (1062ng/m2)> water source (172 ng/m2).(4) The range of dust concentration in Yanghe Watershed from 0.26-1.06g/m2, mean ± standard deviation was 0.49±0.22 g/m. The maximum dust concentration was in spring and mineral dust concentration was in winter. The highest dust concentration was in Fangjiazhuang, about 1.1 g/m2. The lowest dust concentration was in Batuwan and Dongbeixincun sample sites, about 0.27 g/m2. Industrial area (0.62g/m2)> Residential (0.58g/m2)> Water source (0.5g/m2)> Background (0.32g/m2).(5) Coal and petroleum combustion may be the main sources in Yanghe Watershed. It related with coal and biomass burning, combustion of diesel or petrol engine exhaust emissions. Additionally, heavy metal smelting, steel and other industrial production also contribute to high concentration of PAHs in study area.(6) Pyr, Chr and Flu could transport to downstream area, and has potential hazard to Beijing environment. The characteristic travel distance (CTD) of 16 PAHs through air were 13 km (DBA)-712 km (Flu). The shortest CTD were DBA and BghiP. The longest CTD was Flu. over all persistence (Pov) in air were 0.33 d (Acy)-907 d (BaP). Most of PAHs possess the characteristic of near-source pollution, that means PAHs has potentral hazard to Zhangjiakou city.