太原地区大气氮湿沉降变化特征

为研究太原地区的大气氮湿沉降时空变化规律，于2016年1月～2017年12月采用雨量器对太原市市中、近郊和远郊三地大气氮湿沉降进行了为期2年的监测。得到市中、近郊、远郊的NO₃^--N平均浓度为12.9、18.4、1.3 mg/L，NH₄⁺-N平均浓度分别为3.6、2.3、1.6 mg/L。季节变化上看，NH₄⁺-N浓度值四季相对平均，春夏季稍高，而NO₃^--N浓度变化较大且冬春季浓度值较高。三个采样点大气氮湿沉降量（无机氮）年均沉降量分别为40.0、48.0、14.2 kg/hm²，以近郊的沉降量最高。市中、近郊、远郊的NH₄⁺-N沉降量分别为9.0、5.0、8.2 kg/hm²，占总无机氮湿沉降量的比重分别为22%、11%、57%，NO₃^--N沉降量分别是31.0、43.0、6.0 kg/hm²，占总无机氮湿沉降量的比重分别为78%、89%、43%。从上可知城市降水中主要以NO₃^--N沉降为主，农村则以NH₄⁺-N沉降为主。结合市中、近郊、远郊NH₄⁺-N/NO₃^--N浓度比值分别为0.54、0.30、1.31，充分表明市中和近郊大气氮湿沉降主要来自工业和交通运输源，远郊则来自农业源。另外，市中、近郊月氮湿沉降量与降雨量差异不显著，远郊则达到极显著水平，说明影响市区两点氮湿沉降的因素较为复杂。由以上数据看出市中和近郊氮污染情况比较严重，应根据各自沉降特点予以控制。

Characteristics of Atmospheric Nitrogen Wet Deposition Variations in the Taiyuan Area

A research on temporal and spatial variation of atmospheric nitrogen wet deposition was conducted using the rain gauge method at the downtown, suburb and outer suburbs of the Taiyuan City from January 2016 to December 2017. The concentrations of NO₃^--N and NH₄⁺-N averaged from1.3 mg/L to18.4 mg/L and from1.6 to 3.6 mg/L, respectively. The average concentrations of NH₄⁺-N were stable in all seasons, but average concentrations of NO₃^--N were higher in winter and spring seasons. The annual averaged wet depositions of inorganic N(IN) were 40.0, 48.0, 14.2 kg/hm², respectively, at three sampling sites (downtown, suburb and outer suburbs of Taiyuan). The wet deposition rates of NH₄⁺-N were 9.0, 5.0, 8.2 kg/hm² and accounted for 22%, 11%, 57% of the IN depositions, while wet deposition rates of NO₃^--N were 31.0, 43.0, 6.0 kg/hm²and accounted for 78%, 89%, 43% of IN depositions at three sampling sites, respectively. The average concentration ratios of NH₄⁺-N/NO₃^--N were 0.54, 0.30 and 1.31, respectively, at three sites. In addition, the difference between nitrogen wet deposition and rainfall in the downtown and suburban areas was not significant but reached a very significant level at outer suburbs, indicating that affecting factors of wet deposition at urban areas are more complicated than at the outer suburbs. These results might suggest that atmospheric nitrogen wet depositions were affected mainly by industry or/and transportation at downtown and suburb, while by agriculture activities at outer suburbs. In summary, to prevent high wet depositions of N in the Taiyuan area, different strategies should be applied according to different sites.