舟山市大气PM2.5中SO42-、NO3-、Cl-和NH4+浓度分析

Concentrations of SO42-,NO3-,Cl- and NH4+ in atmospheric PM2.5 in Zhoushan

目的了解舟山市大气PM2.5中SO4^2-、NO3^-、Cl^-和NH4+4种水溶性非金属离子浓度及来源,为控制PM2.5污染和制定有效的环保措施提供依据。方法在舟山市新城区域设立监测点,于2015—2016年每月10—16日和雾霾天气(空气质量指数>200)时连续进行大气PM2.5采样,采用称重法测定PM2.5质量浓度,采用离子色谱法检测PM2.5中SO4^2-、NO3^-、Cl^-和NH4^+含量并分析。结果2015—2016年舟山市监测点日均PM2.5浓度为(40.91±27.39)μg/m^3;4种水溶性非金属离子浓度为3.56~103.03μg/m^3,平均浓度为(23.06±20.00)μg/m^3,占PM2.5含量的56.64%。SO4^2-月平均浓度最高,为(10.35±6.48)μg/m^3;Cl-月平均浓度最低,为(0.49±0.73)μg/m^3。冬季4种离子总浓度最高,为(37.56±27.74)μg/m^3;夏季最低,为(12.32±5.88)μg/m^3;不同季节4种离子浓度差异有统计学意义(P<0.05)。冬季NO3-浓度最高,为(14.48±13.28)μg/m^3,NO3^-与SO42-浓度比值为0~2.58,平均0.55;大于1共有28 d,占14.74%,其中22 d在冬季。结论舟山市大气PM2.5中的水溶性非金属离子以SO42-浓度最高,Cl^-浓度最低;4种离子浓度均以冬季最高,其中NO3^-平均浓度在冬季大于SO4^2-,提示机动车尾气排放可能是冬季大气PM2.5污染的主要来源。

Objective To understand the concentrations and source of SO4^2-,NO3^-,Cl^-and NH4^+in atmospheric PM2.5 in Zhoushan,and to provide reference for controlling PM2.5 and formulating effective environmental protection measures.Methods Monitoring sites in new districts of Zhoushan were set up to continuously collect PM2.5 from 10th to 16th of each month and under the hazy weather during 2015-2016(AQI>200).The mass concentration of PM2.5 was measured by weighing method,and the concentrations of SO4^2-,NO3^-,Cl^-and NH4^+in PM2.5 components was detected by ion chromatography.Results The average daily concentration of PM2.5 in Zhoushan from 2015 to 2016 was(40.91±27.39)μg/m^3.The concentration of the four water-soluble non-metal ions in PM2.5 components was 3.56-103.03μg/m^3,with an average of(23.06±20.00)μg/m^3,accounting for about 56.64%of PM2.5 contents.The average monthly concentration of SO4^2-was the highest[(10.35±6.48)μg/m^3],while the average monthly concentration of Cl^-was the lowest[(0.49±0.73)μg/m^3].The concentration of the four ions was the highest in winter[(37.56±27.74)μg/m^3]and the lowest in summer[(12.32±5.88)μg/m^3].The differences between different seasons was statistically significant(P<0.05).The highest concentration of NO3^-occurred in winter,which was(14.48±13.28)μg/m^3.The concentration ratio of NO3^-to SO4^2-ranged from 0 to 2.58,with an average of 0.55.There were 28 days(14.74%)with the ratio greater than one,22 days of which was in winter.Conclusion The concentration of SO4^2-was the highest and Cl^-was the lowest in atmospheric PM2.5 in Zhoushan.The highest concentration of the four ions occurred in winter.The concentration of NO3^-in winter was higher than that of SO4^2-,suggesting that motor vehicle exhaust might be the main source of PM2.5 in winter.