|其他摘要||Since the industrial revolution, anthropogenic reactive nitrogen (N) emissions have been greatly increased mainly by over-fertilization, fossil fuel use and intensive animal husbandry and they lead to a continual increase in atmospheric N deposition worldwide. Nitrogen deposition can cause a series of serious ecological and environemntal problems, such as eutrophication in water bodies, biodiversity decline, soil acidification and forest degradation. This study aimed to quantify atmospheric reactive N concentration, wet and dry N deposition as well as the primary characteristics of 15N stable isotopes of gaseous N in Urumqi city and its surrounding areas in order to obtain basic information on evaluating the present atmospheric reactive N pollution status in Urumqi. The main results are summarized as follows:
1. Mean concentrations of ammonia (NH3), nitrogen dioxide (NO2), particulate ammonium (pNH4+) and nitrate (pNO3-) varied greatly across different regions. The highest NH3 concentration was 405.8 g m-3 at a swine farm site, the lowest NH3 concentrations was 8.22 µg m-3 at Nanshan (NS) forest site; the highest NO2 concentration was 63.3 µg m-3 at a traffic site in downtown of Urumqi. Atmospheric reactive N concentrations showed obvious seasonal variations in the study area. These results suggest that atmospheric reactive N concentrations are closely related to anthropogenic reactive N emissions (including emissions from animal husbandry and traffic vehicles).
2. Ammonia concentration showed negative correlation with pNH4+ at the sampling sites. The NO2 concentration had a significant positive correlation with pNO3- except for the farm site (Anningqu) during the study period. Particulate NH4+ showed high positive correlation with pNO3-.
3. The main water-soluble ions in particulate matter at sampling sites included K+, Na+, NH4+, Ca2+, Mg2+, Cl-, NO3- and SO42-. The NH4+, NO3- and SO42- were major water-soluble ions, which were mainly in the forms of secondary aerosols such as (NH4)2SO4, NH4HSO4 and NH4NO3 through the correlation analysis. The ratios of NO3-/SO42- ranged from 0.22 to 0.48 and the mean value was 0.36 in Urumqi, indicating that the fixed source (containing sulfur fuel combustion) is still the main source of secondary aerosols in the atmosphere in Urumqi.
4. Atmospheic dry N deposition, measured by the inferential method was 15.7, 22.0, 7.48 kg N ha-1 yr-1 at downtown of Urumqi, Anningqu, NS, respectively. Reduced N (NH3 and pNH4+) deposition is the main form at the sampling sites. Highest dry deposition was found from late autumn to early spring next year at downtown of Urumqi and Anningqu sites. The opposite trend of dry deposition was observed at NS site. Total annual inorganic N deposition (wet plus dry) was approximately 21.0 kg N ha-1, with 76% as dry N deposition in Urumqi.
5. The δ15N values of NH3 at sites around all sources were negative; while the δ15N values of NO2 were mostly positive at the sampling sites. Averaged δ15N values of NH3 followed by the sequences of NS forest site (-4.20‰) > cropland site (-7.04‰) and traffic site (-7.89‰) > swine farm site (-19.2‰). The mean δ15N values of NO2 ranked by the order of thermal powerplant site (31.1‰) > industrial source site (23.6‰) > traffic site (7.97‰), respectively.|