|其他摘要||Air pollution is one of the most serious environmental problems in China, and inhalable particulate matter smaller than 10 μm (PM10), fine particulate matter smaller than 2.5 μm (PM2.5) and atmospheric reactive nitrogen species such as NH3 and NOx are important atmospheric pollutants. PM10 and PM2.5 and atmospheric reactive nitrogen will be harmful to human health and ecological environment. Due to the special natural environment, Xinjiang consists of three major ecological zones of mountains, oasis and deserts. In order to reflect pollution status of particulate matter (mainly PM10 and secondary aerosols such as PM2.5) and reactive nitrogen in the whole Xinjiang region, grassland, farmland, urban, desert, desert and oasis ecotone and forest ecosystems must be selected. Therefore, based on field experimental stations in the Chinese Academy of sciences and through multi-year and multi-sampling and analysis of influencing factors, we revealed the spatial and temporal variation of atmospheric particulate matter in different ecosystems. And we also clarified the fluxes of atmospheric reactive nitrogen dry and wet deposition and the influence of atmospheric reactive nitrogen emissions to the atmosphere of particulate matter pollution. This study can provide systematic data for understanding atmospheric particles and atmospheric reactive nitrogen pollution in the typical region of Xinjiang. It also can provide theoretical basis for Xinjiang government to make the effective control measures for atmospheric particles and atmospheric reactive nitrogen pollution. The main results are summarized as follows:
1. The annual average concentrations of PM10 were 26.1, 36.0, 208, 359, 443 and 454 μg m-3 at monitoring sites in grassland, forest, urban, farmland, desert oasis ecotone and desert ecosystems, respectively. There was no significant difference in the annual concentration of PM10 in the long-term sampling sites. PM10 concentrations had an obvious seasonal variation in different ecosystems. PM10 concentrations were higher in spring and summer and lower in autumn and winter in grassland, forest, farmland, desert and oasis ecotone and desert ecosystems. And PM10 concentrations were highest in winter and lowest in summer in urban ecosystem. There was a significant positive correlation between PM10 concentration and wind speed in the south of Xinjiang (South of Tianshan Mountains), however, significant negative correlations were observed between PM10 concentration and temperature and PM10 concentration and wind speed in the north of Xinjiang (North of Tianshan Mountains). The concentrations of ions and metal elements in PM10 had significant spatio-temporal variations in the different ecosystems.
2. The annual mean concentrations of PM2.5 were 152, 171 and 87 μg m-3 in 2010, 2011 and 2012 in Urumqi, which were 4.34, 4.89 and 2.48 times higher than the Chinese second class Ambient Air Quality Standard (annual mean concentrations of 35 μg m-3). PM2.5 concentrations had significant (p<0.05) seasonal variation, which were highest in winter and lowest in summer. The concentrations of PM2.5 were 114, 84.8, 118 and 323 μg m-3 in spring, summer, autumn and winter, respectively. The concentration of water soluble ions (NO3- , NH4+, SO42-, Cl-, Na+, K+, Mg2+ and Ca2+) in PM2.5 also had significant (p<0.05) seasonal variation. The concentrations of NO3- , NH4+, SO42-, Cl-, Na+, K+ and Mg2+ were higher in winter than in other three seasons. However, Ca2+ concentration was highest in spring. The mass concentrations of secondary particles and its proportion in PM2.5 were highest in winter and lowest in summer. The proportion of secondary particles in PM2.5 had two turning points which rapidly decreased after the annual mid-April and increased rapidly after the annual mid-October.
Further research showed that the action of “shifting from coal to natural gas” in winter could significantly reduce concentrations of PM2.5 in Urumqi. Compared with the same period in 2011 and 2012 (mean concentration of 322.5 μg m-3), PM2.5 concentrations in January 2013 (120 μg m-3) and in January 2014 (78.9 μg m-3) were decreased 63% and 76%, respectively. This was resulted from the effects of the action of “shifting from coal to natural gas”, which was initially and totally completed in January 2013 and 2014. Meanwhile, “Shifting from coal to natural gas” also significantly reduced the concentrations of water soluble ions (NH4+, NO3-, SO42-, Cl-, Na+, Mg2+ and Ca2+) and metal elements (As, Cr, Mn, Ni, Cu, Cd, Pb and Al).
3. PM10 deposition fluxes were ranged from 36.9 to 1316 kg ha-1 yr-1 at all the thirteen sampling sites in the typical region of Xinjiang. PM10 deposition fluxes were 36.9, 49.9, 288, 486, 614 and 629 kg ha-1 yr-1 in grassland, forest, urban, farmland, desert and oasis and desert ecosystems, respectively. Cl-, Na+, K+, SO42-, Mg2+ and Ca2+ had low deposition fluxes in grassland and forest ecosystems. Cl-, Na+, SO42-, Mg2+ and Ca2+ had highest deposition fluxes in desert ecosystem. However, K+ had highest deposition fluxes in urban ecosystem. The deposition fluxes of As, Ni, Zn, Cd and Al in PM10 were highest in urban ecosystem. The deposition fluxes of Mn, Li, Cr, Cu and Pb were relative higher in urban ecosystem. The deposition fluxes of Mn and Li in urban ecosystem were lower than in desert ecosystem. The deposition fluxes of Cr, Cu and Pb in urban ecosystem were lower than in desert oasis ecotone ecosystem.
4. In different ecosystems, NH3 concentrations were orderly: grassland ecosystem (2.23 μg m-3) |