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大气PM2.5(细颗粒物)是指环境空气中空气动力学当量直径小于或等于2.5 µm的颗粒物,由于其能较长时间悬浮于空气中,对空气质量、人体健康具有重要影响[1-5]。PM2.5中主要包含OC(有机碳)、EC(元素碳)、水溶性离子、地壳元素和微量元素等,水溶性离子在PM2.5中占比可达60%以上,是其重要组成部分[6-7]。由于水溶性离子具有亲水性,对云的宏观特征[8]、大气能见度和降水酸碱度等具有重要影响[9-11],因此对水溶性离子的研究备受国内外学者重视[12]。
目前很多学者对水溶性离子特征展开了研究,其中四川盆地内针对PM2.5中水溶性离子的研究主要集中于成都市[6-7,13]:冬季水溶性离子质量浓度显著高于其他季节,且重污染期间移动源已成为水溶性离子的重要来源;水溶性离子中SNA为主要组分,占比达80%以上且主要经二次转化生成,大气整体呈富氨状态,二次离子存在形式主要为(NH4)2SO4和NH4NO3。此外,杨留明等[14]对郑州市水溶性离子分析发现二次离子主要以(NH4)2SO4和NH4NO3形式存在,且相对湿度对SOR影响较大,而温度对NOR影响较大。陶俊等[15]对广州夏季城区水溶性离子展开研究,发现较高温度和O3浓度有利于
${{\rm{SO}}_4^{2-} }$ 的生成,较高相对湿度利于${{\rm{NO}}_3^{-} }$ 生成,亲水性较强的SNA对散射系数和能见度影响较大。黄炯丽等[16]利用高分辨率MARGA分析了桂林市气象因素与水溶性离子间的影响,结果表明降雨对水溶性离子具有显著清除作用,能见度随二次离子质量浓度的增加呈幂指数递减规律。绵阳市区位独特,位于成都市、重庆市、西安市“西三角”的腹心地带,是成都平原城市群的重要节点城市。根据四川省环境公报数据显示,2015年至2018年绵阳市PM2.5浓度均超过环境空气质量标准二级限值,且冬季易出现持续性区域性污染,而目前针对绵阳市颗粒物化学组分方面的研究较少,本文对绵阳市PM2.5中水溶性离子特征及来源展开分析,以期为绵阳市后续大气污染防治工作提供科学依据。
绵阳市PM2.5中水溶性离子特征及来源分析
Characteristics and source analysis of water-soluble ions in PM2.5 in Mianyang
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摘要: 为研究绵阳市PM2.5中水溶性离子污染特征及来源,于2018年4月15日—2019年2月28日在绵阳市设置5个采样点位进行样品采集,利用Dionex ICS-2000离子色谱仪分析了9种离子(F−、Cl−、
${{\rm{NO}}_3^{-} }$ 、${{\rm{SO}}_4^{2-} } $ 、Na+、${{\rm{NH}}_4^{+} }$ 、K+、Mg2+、Ca2+),并通过SPSS进行来源解析。结果表明,绵阳市ρ(总水溶性离子)年均值为20.8 μg·m−3,在PM2.5中w(总水溶性离子)为46.6%。离子中质量浓度大小顺序依次为:$\rho \left( {{{\rm{NO}}_3^{-} } } \right) \gt \rho \left( {{{\rm{SO}}_4^{2-} } } \right) \gt \rho \left( {{\rm{NH}}_4^{+} } \right) \gt \rho \left( {{\rm{C}}{{\rm{a}}^{2 + }}} \right) \gt \rho \left( {{{\rm{K}}^ + }} \right) \gt \rho \left( {{\rm{C}}{{\rm{l}}^ - }} \right) \gt \rho \left( {{\rm{N}}{{\rm{a}}^ + }} \right) \gt \rho \left( {{\rm{M}}{{\rm{g}}^{2 + }}} \right) \gt \rho \left( {{{\rm{F}}^ - }} \right)$ ,其中SNA(二次离子$ {{\rm{NO}}_3^{-} } $ 、${{\rm{SO}}_4^{2-} } $ 、${{\rm{NH}}_4^{+} }$ )为水溶性离子主要组成部分,水溶性离子中w(SNA)为86.4%。水溶性离子质量浓度季节变化趋势为:冬季>秋季>春季>夏季,除Mg2+外其余离子质量浓度季节变化趋势与总离子浓度趋势一致,ρ(Mg2+)夏季与春季相当。SNA间具有较好的相关性,表明二次离子来源具有高度相似性,${{\rm{NH}}_4^{+} } $ 与$ {{\rm{SO}}_4^{2-} }$ 摩尔当量浓度线性拟合斜率大于0.75,表明绵阳市大气环境为富氨状态,二次离子主要以(NH4)2SO4和NH4NO3形式存在。污染天NO2、w(${{\rm{NO}}_3^{-} } $ )和NOR(氮氧化率)均增大,且污染水平越严重w($ {{\rm{NO}}_3^{-} } $ )增幅越大,而w(${{\rm{SO}}_4^{2-} } $ )和w($ {{\rm{NH}}_4^{+} } $ )基本不变,表明$ {{\rm{NO}}_3^{-} } $ 增加导致PM2.5浓度升高。四季SOR(硫氧化率)和NOR均大于0.1,表明$ {{\rm{NO}}_3^{-} } $ 、${{\rm{SO}}_4^{2-} } $ 主要来源于气态污染物二次转化,受温度和湿度影响,SOR值夏季最高,NOR值夏季最低冬季最高。SPSS来源解析结果显示绵阳市PM2.5中水溶性离子主要受二次转化、生物质燃烧以及扬尘源影响,三者合计贡献率为82.7%。Abstract: To study on the pollution characteristics of water-soluble ions, PM2.5 samples were collected at five locations in Mianyang from April 2018 to February 2019. Nine water-soluble ions (F−, Cl−,$ {{\rm{NO}}_3^{-} } $ ,$ {{\rm{SO}}_4^{2-} } $ , Na+,${{\rm{NH}}_4^{+} } $ , K+, Mg2+, Ca2+) were analyzed by Dionex ICS-2000, and the source analysis of these ions were determined by SPSS. The results showed that the annual average mass concentration of total water-soluble ions were 20.8 μg·m−3, accounting for 46.6% of PM2.5 mass. The mass concentration of these ions were in order of$\rho \left( {{{\rm{NO}}_3^{-} } } \right) \gt \rho\left( {{{\rm{SO}}_4^{2-} } } \right) \gt \rho\left( {{\rm{NH}}_4^{+} } \right) \gt \rho\left( {{\rm{C}}{{\rm{a}}^{2 + }}} \right) \gt \rho\left( {{{\rm{K}}^ + }} \right) \gt $ $\rho\left( {{\rm{C}}{{\rm{l}}^ - }} \right) \gt \rho\left( {{\rm{N}}{{\rm{a}}^ + }} \right) \gt \rho\left( {{\rm{M}}{{\rm{g}}^{2 + }}} \right) \gt \rho\left( {{{\rm{F}}^ - }} \right)$ . The water-soluble ions were mainly composed of secondary ions ($ {{\rm{NO}}_3^{-} } $ ,${{\rm{SO}}_4^{2-} } $ ,$ {{\rm{NH}}_4^{+} } $ ), accounting for 86.4% of total water-soluble ions. All water-soluble ions mass concentrations showed a seasonal variation with winter > autumn > spring > summer, but Mg2+ in summer was slightly higher than spring. The correlation of SNA were strong, indicating that the mechanism of evolution of SNA in the atmosphere were highly similar to each other. The correlation between${{\rm{NH}}_4^ + }$ and${{\rm{SO}}_4^{2-} } $ molar equivalent concentration was greater than 0.75, indicating that the atmospheric environment of Mianyang was in the rich of ammonia, so that SNA was mainly in the form of (NH4)2SO4 and NH4NO3. The NO2, w($ {{\rm{NO}}_3^{-} } $ ) and NOR went up with the increase of PM2.5 pollution levels, w(${{\rm{NO}}_3^{-} } $ ) particularly, while the w(${{\rm{SO}}_4^{2-} } $ ) and w(${{\rm{NH}}_4^{+} } $ ) remained largely unchanged, which indicated that the obvious increase of$ {{\rm{NO}}_3^{-} } $ led to the increase of PM2.5.The sulfur oxidation rate(SOR) and nitrogen oxidation rate(NOR) were greater than 0.1 in four seasons, suggesting that$ {{\rm{NO}}_3^{-} } $ and${{\rm{SO}}_4^{2-} } $ in PM2.5 were formed mainly through secondary transformation. SOR were the highest in summer while NOR were the highest in winter but lowest in summer which were both affected by temperature and humidity, respectively. The principal component analysis (PCA) analysis indicated that the major sources of water-soluble ions PM2.5 were secondary transformation, biomass burning and fugitive dust, accounting for 82.7%.-
Key words:
- water-soluble ions /
- PM2.5 /
- secondary transformation /
- Mianyang
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表 1 PM2.5中水溶性离子平均质量浓度及季节性变化 (μg·m−3)
Table 1. Seasonal variation of water-soluble ions in PM2.5 (μg·m−3)
F− Cl− ${{\rm{SO}}_4^{2-} } $ ${{\rm{NO}}_3^{-} } $ Na+ ${{\rm{NH}}_4^{+} } $ K+ Mg2+ Ca2+ SNA 离子合计 PM2.5 春季 0.0477 0.227 2.65 4.02 0.698 2.09 0.491 0.0851 0.803 8.76 11.1 36.6 夏季 0.0161 0.173 2.30 2.32 0.0936 1.99 0.283 0.0904 0.575 6.61 7.84 20.9 秋季 0.0168 0.544 4.08 5.86 0.321 2.78 0.384 0.129 0.675 12.7 14.8 30.5 冬季 0.150 0.822 6.04 10.4 0.189 5.93 0.774 0.277 1.41 22.3 26.0 59.6 年均 0.0971 0.575 5.07 8.70 0.317 4.20 0.588 0.193 1.07 18.0 20.8 44.6 表 2 水溶性离子相关系数矩阵
Table 2. The correlation of water-soluble ions
F− Cl− ${{\rm{SO}}_4^{2-} } $ ${{\rm{NO}}_3^{-} } $ Na+ ${{\rm{NH}}_4^{+} } $ K+ Mg2+ Ca2+ F− 1.00 Cl− 0.524 1.00 ${{\rm{SO}}_4^{2-} } $ 0.324** 0.421** 1.00 ${{\rm{NO}}_3^{-} } $ 0.526** 0.699** 0.653** 1.00 Na+ 0.287** 0.051 0.002 −0.186 1.00 ${{\rm{NH}}_4^{+} } $ 0.604** 0.615** 0.662** 0.826** −0.281** 1.00 K+ 0.611** 0.687** 0.625** 0.686** −0.0589 0.769** 1.00 Mg2+ 0.616** 0.413** 0.182** 0.298** −0.205** 0.461** 0.578** 1.00 Ca2+ 0.627** 0.382** 0.203** 0.282** −0.0851 0.439** 0.595** 0.914** 1.00 **表示在0.01水平上显著相关. 表 3 不同污染水平下二次离子、SO2、NO2浓度及二次离子在PM2.5中占比
Table 3. The mass concentration of SNA, SO2, NO2 and the ratio of SNA in PM2.5 at different pollution grade
水溶性离子
Water-soluble ions非污染天 Clean days 轻度污染 Lightly pollution 中度污染 Moderate pollution 质量浓度/(μg·m−3)
Concentration占比/%
Proportion质量浓度/(μg·m−3)
Concentration占比/%
Proportion质量浓度/(μg·m−3)
Concentration/占比/%
Proportion${{\rm{SO}}_4^{2-} } $ 4.00 9.41% 7.63 8.94% 10.53 8.69% ${{\rm{NO}}_3^{-} } $ 6.21 14.6% 13.45 15.7% 27.94 23.1% ${{\rm{NH}}_4^{+} } $ 3.60 8.48% 7.85 9.19% 9.32 7.70% SNA 13.80 32.5% 28.93 33.9% 47.79 39.5% SO2 5.23 — 7.22 — 6.33 — NO2 24.62 — 41.67 — 42.33 / 表 4 PM2.5中水溶性离子因子分析结果
Table 4. PCA result of water-soluble ions in PM2.5
项目 Project 因子1 Factor 1 因子2 Factor 2 因子3 Factor 3 F− 0.463 0.709 −0.258 Cl− 0.707 0.352 −0.064 ${{\rm{SO}}_4^{2-} } $ 0.801 0.045 0.163 ${{\rm{NO}}_3^{-} } $ 0.917 0.143 −0.121 Na+ −0.048 −0.096 0.974 ${{\rm{NH}}_4^{+} } $ 0.824 0.293 −0.249 K+ 0.739 0.552 −0.027 Mg2+ 0.159 0.945 −0.076 Ca2+ 0.180 0.943 −0.003 贡献率/% 55.6 15.9 11.2 特征值 5.00 1.43 1.00 -
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