南京市一次霾污染过程中水溶性离子分布特征

使用MARGA离子在线分析仪ADI 2080对2017年12月27日~2018年1月5日南京市PM_2.5化学组分进行连续采样分析，结合气象要素和大气环境监测数据，探讨了霾污染过程中水溶性离子的时间分布特征及其来源特征.结果表明：霾日中南京水溶性离子浓度为121.41μg/m³，是洁净日的3.2倍.霾污染过程中水溶性离子平均浓度大小顺序为NO₃^- > SO₄^2- > NH₄⁺ > Cl^- > K⁺ > Ca²⁺ > Mg²⁺，SNA离子占总水溶性离子浓度的91.97%.霾日中水溶性离子日变化均为三峰型，洁净日中Cl^-、SO₄^2-和NH₄⁺的日变化为单峰型，Ca²⁺为双峰型，K⁺、Mg²⁺为三峰型.随着空气污染状况的加重，总水溶性离子在PM_2.5中的占比不断减少，空气质量为优时占比95.93%，严重污染时为63.25%.霾日中随着污染加重，NH₄⁺占总离子的比例稳定在23%左右，SO₄^2-占比缓慢减小，NO₃^-占比不断增大.NOR、SOR的日变化在霾日呈双峰型分布，洁净日则较为平稳.观测期间的水溶性离子主要来源有二次转化、煤烟尘、扬尘以及生物质燃烧.

Distribution characteristics of water-soluble ions during a haze pollution process in Nanjing

The composition of PM_2.5 was monitored online continuously by using MARGA 1S Analyzer ADI 2080 in Nanjing from December 27, 2017 to January 5, 2018. Combined with meteorological elements and atmospheric environmental monitoring data, the time distribution and source characteristics of water-soluble ions in haze pollution process was investigated. The mass concentration of water-soluble ions in Nanjing during the haze pollution was 121.41μg/m³, 3.2 times of the level in clean days. The order of the average mass concentration of water-soluble ions in the haze pollution process was NO₃^- > SO₄^2- > NH₄⁺ > Cl^- > K⁺ > Ca²⁺ > Mg²⁺. SO₄^2-, NO₃^- and NH₄⁺ accounted for 91.97% of the total water-soluble ions concentration. The diurnal variations of water-soluble ions in haze days were all trimodal, while in clean days, Cl^-, SO₄^2- and NH₄^- were unimodal, Ca²⁺ was bimodal, K⁺ and Mg²⁺ were trimodal. With the aggravation of the air pollution, the proportion of total water-soluble ions in PM_2.5 was decreasing. When the air quality was excellent, the proportion was 95.93%, while it was 63.25% when serious pollution occurred. With the increase of pollution in haze days, the proportion of NH₄⁺ to total water-soluble ions was stable at around 23%, the proportion of SO₄^2- decreased slowly, and the proportion of NO₃^- increased continuously. The diurnal variations of NOR and SOR were bimodal in haze days, while in clear days, they were relatively stable. During the observation period, water-soluble ions were derived mainly from secondary conversion, coal ash, dust, and biomass combustion.