石河子市大气NH_(3)污染特征及影响因素研究

CHARACTERISTICS AND INFLUENCING FACTORS OF ATMOSPHERIC NH_(3) POLLUTION IN SHIHEZI

大气氨(NH_(3))对二次气溶胶的形成有重要影响。为研究石河子市大气NH_(3)污染特征,于2020年12月—2021年11月对石河子市NH_(3)浓度进行了连续观测,结合大气NH_(3)排放特征和同期气象因素的变化特征分析了石河子市NH_(3)浓度水平、污染特征和影响因素。结果表明:石河子市大气ρ(NH_(3))年均为21.0μg/m^(3),ρ(NH_(3))季均分布为20.2~21.7μg/m^(3),季节变化幅度较小。农业源是石河子市大气NH_(3)的主要贡献源;而冬季大气NH_(3)主要来源于工业烟气脱硝过程中的氨逃逸,冬季持续的低边界层高度和低风速致使大气扩散条件转差,不利的扩散条件是冬季NH_(3)浓度累积升高的重要原因。冬季加大对烟气脱硝过程中氨逃逸的治理力度有利于降低石河子市冬季大气NH_(3)浓度。石河子市4个季节大气NH_(3)浓度均表现为白天高夜间低,且NH_(3)浓度在春季和冬季呈单峰日变化特征,峰值分别出现在12:00和16:00;在夏季和秋季呈多峰日变化特征,最大峰值分别出现在11:00和13:00。与国内其他城市相比,石河子市4个季节大气NH_(3)浓度日间峰值出现时间晚1~3 h。随机森林算法对大气NH_(3)浓度影响因素的定量评估表明,4个季节气象因素对NH_(3)浓度的影响分别达到了63.6%、58.8%、73.9%和64.5%,气象因素是大气NH_(3)浓度变化的主要影响因素。

Atmospheric ammonia(NH_3)has an important impact on the formation of secondary aerosols.To investigate the characteristics of atmospheric NH_(3)pollution in Shihezi,the atmospheric NH_(3)concentration was observed continuously from December 2020 to November 2021,and the magnitude level,variation characteristics,and influencing factors of atmospheric NH_(3)in Shihezi were analyzed,in combination with the characteristics of atmospheric NH_(3)emissions and the characteristics of concurrent meteorological parameters.The results show that the annual average concentration of atmospheric NH_(3)in Shihezi was 21.0μg/m^(3),the average concentration of atmospheric NH_(3)in the four seasons ranged from 20.2μg/m^(3)to 21.7μg/m^(3),with a small seasonal fluctuation.In winter,the main source of atmospheric NH_(3)in Shihezi was the escape of ammonia during the industrial flue gas denitrification process,and the continuous low boundary layer height and low wind speed in winter led to the deterioration of atmospheric diffusion conditions.The unfavorable diffusion conditions were an important reason for the accumulation of atmospheric NH_(3)concentration in winter.Increasing the control of ammonia escape during flue gas denitrification was beneficial to reducing the atmospheric NH_(3)concentration in Shihezi.The diurnal variation of atmospheric NH_(3)concentration showed a pattern of higher during the day and lower at night in Shihezi in all seasons,with the daily variation of atmospheric NH_(3)concentration being highest in spring and lowest in winter.The atmospheric NH_(3)concentrations in spring and winter showed a single-peak pattern,with dual peaks at 12:00 and 16:00,respectively,and summer and autumn atmospheric NH_(3)concentrations showed a multi-peak pattern,with maximum peaks at 11:00 and 13:00,respectively.Compared with other cities in China,the daytime peak of atmospheric NH_(3)concentration in Shihezi appeared 1 to 3 hours later.The quantitative evaluation of the influencing factors of atmospheric NH_(3)concentration by the random forest algorithm showed that the influence of meteorological factors on atmospheric NH_(3)in the four seasons reached 63.6%,58.8%,73.9%,and 64.5%,respectively,and meteorological factors were the main influencing factors of atmospheric NH_(3)concentration.