| Atmospheric fine particulate matters (PM2.5) which are crucial factors resulting in haze, have significant effect on human health and climate change and have become the most serious atmospheric environmental problems in China at present. In this research, PM2.5 samples were collected at environmental monitoring station in Hongshan district, Wuhan, and chemical components and source of water soluble ions and polycyclic aromatic hydrocarbons were analysed in different seasons. The pollution process of atmospheric PM2.5 were discussed, as well as the atmospheric transport of PM2.5.The monitoring campaign was divided into 4 periods:Mar.2014-Apr.2014, Jun.2014-Jul.2014, Oct.2014-Nov.2014, Dec.2014-Jan.2015. Indicators of PM2.5 mass concentration, water soluble ions (including NH4+, NO3-, NO2-, SO42-,Cl-,K+, Na+, Ca2+, Mg2+), meteorological data provided by environmental monitoring station in Hongshan district and polycyclic aromatic hydrocarbons (including Nap, Any, Ace, Flu, Phe, Ant, Flt, Pyr, BaA, Chr, BbF, BkF, BaP, IcdP, DBA, BghiP) were analysed.The average mass concentration of atmospheric PM2.5 in Hongshan district,Wuhan during spring, summer, autumn and winter were 101.34±32.49 μg/m3,97.38±49.15 μg/m3, 108.77±43.48 μg/m3,116.47±41.50 μg/m3, the exceeding criteria rate were 81.82%,59.26%, 76.67%,84.00%; the average concentration of water soluble ions were 58.97±11.76 μg/m3, 37.31±22.71 μg/m3,55.47±23.88 μg/m3,68.38±26.66 μg/m3, accounted for 58.18%,38.31%, 51.00%,60.01% of PM2.5 mass concentration, respectively, the predominant ions were NH4+, SO42-, NO3-; the average concentration of polycyclic aromatic hydrocarbons were 20.38±6.75 ng/m3,10.52±8.76 ng/m3,23.48±9.64 ng/m3,49.46±29.40 ng/m3, accounted for 0.02%,0.01%, 0.02%,0.04% of PM2.5 mass concentration, respectively, the BbF had the highest concentration. The annual mean concentration of atmospheric PM2.5 was 105.99 μg/m3, the seasonal change trend of PM2.5:highest in winter, lowest in summer, spring and autumn is close, suggesting that the pollution of atmospheric PM2.5 in winter was more serious than summer. The seasonal concentrations of atmospheric PM2.5 were significantly correlated with the concentrations of water soluble ions and polycyclic aromatic hydrocarbons, especially for water soluble ions. The meteorological parameters of spring and autumn had no correlations with the concentration of atmospheric PM2.5, the concentration of atmospheric PM2.5 in summer was significantly correlated negatively with wind speed, it confirmed that the greater the wind speed, the lower the concentration of PM22.5, the concentration of atmospheric PM2.5 in winter had significantly correlations with relative humidity and temperature.The annual mean concentration of water soluble ions was 55.03 μg/m3, and its seasonal change trend was similar with atmospheric PM2.5. In addition to NO3-, SO42- and NH4+, the content of biomass combustion tracer K+ was higher in autumn and winter than summer and spring, this may be due to burning straw surrounding countryside during autumn in Wuhan, and coal combustion to keeping warm in winter. The content of crust element Ca2+ and Mg2+ also was higher in autumn and winter, this may be due to dry weather and less rainfall. The ratio of NO3-/SO42- was 1.84 in winter, a little less than 1 in spring and autumn,0.59 in summer, the seasonal ratio of NO3-/SO42- was 1.01, suggesting PM2.5 contribution of stationary emission like coal-fired power plant and mobile emission as vehicle exhaust were similar.The annual mean concentration of polycyclic aromatic hydrocarbons was 25.84 ng/m3, and its seasonal change trend was also similar with atmospheric PM2.5. The 4 rings PAHs had the highest concentration and the high concentration concentrated 3 to 6 rings PAHs. According to the diagnostic ratios analysis of Flt/(Flt+Pyr) and IcdP/(IcdP+BghiP) in different seasons, the source of PAHs in the atmospheric PM2.5 is relatively single in autumn, traffic emissions was the main source; the pollution of summer was the most light, but the pollution source was the most complex and mixed; traffic emissions and coal combustion were the dominant sources in spring; traffic emissions, biomass and coal combustion were the dominant sources of winter.Take autumn as an example, the pollution process of atmospheric PM2.5 could be affected by increase of the pollution sources and atmospheric transmission over a long distance.Factor analysis showed that secondary pollution caused by human activities, such as vehicle emissions and coal combustion, and soil dust were the major sources in atmospheric PM2.5 of water-soluble inorganic ion. The polycyclic aromatic hydrocarbons attached to the surface of atmospheric PM2.5 particles, which mainly comes from the traffic emission, coal combustion, coal carbonization, low temperature combustion and the volatilization and leak of petroleum. Therefore, traffic emission, coal combustion, soil dust, coal carbonization, low temperature combustion and the volatilization and leak of petroleum were the main sources of atmospheric PM2.5 in Hongshan district, Wuhan.As the air trajectory analysis showed, the period which the daily concentration of atmospheric PM2.5 exceeded 75 μg/m3, the local transport air mass from the northeast had a higher frenquency made a significant contribution to weighted concentrations of PM2.5 during spring and autumn. The air mass transmitted over a long distance from the northeast which had a higher frenquency made a significant contribution to weighted concentrations of PM2.5 during summer. The local air mass from the southwest and then through the west and southwest and the air mass transmitted over a long distance from the northeast which had a higher frenquency made a significant contribution to weighted concentrations of PM2.5 during winter.This study introduced the characteristics of water soluble ions and polycyclic aromatic hydrocarbons of PM2.5 in Hongshan district, Wuhan comprehensively, analysed the influence of different air masses, and had significant importance for researching the form transformation and transpot rules of air pollutants in city. |
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