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随着中国经济快速发展,霾现象成为近年来国内热点话题,PM2.5作为霾的主要成分之一,更是备受关注。PM2.5是指空气动力学直径≤2.5 μm的大气细颗粒物[1],它不仅直接影响人体健康,容易诱发呼吸道和心血管疾病,还会降低能见度,妨碍正常生产生活,对气候变化也会产生重要影响[2-4]。其中水溶性无机离子约占PM2.5总质量分数的40%—80%[5-6],可以很好地表征空气质量状况,也被认为是引起霾污染的重要化学组分[7-8]。因此,研究水溶性离子的化学组分对于了解PM2.5的污染机理及来源解析具有重要意义。
许多国内学者对PM2.5中水溶性无机离子污染特征和来源情况开展相关研究工作。冯炎鹏等[9]发现,夏季光化学反应和液相反应共同作用生成
${\rm{SO}}_4^{2-} $ ,冬季高浓度NOx和低温环境使得${\rm{NO}}_3^{-} $ 大量形成且稳定存在。Zhang等[10]解析后发现,硫酸盐、硝酸盐、铵盐是南京大气中无机水溶性离子的主要成分。丁新航等[11]通过计算SOR和NOR的值,发现太原市采暖季存在明显的气溶胶二次转化过程,且温度和相对湿度对硫氧化率和氮氧化率均有一定影响。吕青等[12]研究发现,昆山市PM2.5的主要来源是二次气粒转化、建筑扬尘、生物质燃烧和燃煤。我国的研究学者开展PM2.5的观测研究主要集中在京津冀[13-15]、长三角[16-17]和珠三角地区[18-19],但对于污染问题同样严峻的东北地区缺乏研究。2019年辽宁省环境状况公报显示,沈阳市环境空气质量优、良天数为284 d,占全年总天数的77.8%,低于生态环境部公布该年全国平均优、良天数比例(82.0%)。吴丹等[20]通过对沈阳市多个采样点PM2.5均值进行比较,发现采暖季PM2.5值远高于非采暖季,且均高于《环境空气质量标准》(GB 3095—2012)二级标准限值。王国祯等[21]对沈阳市PM2.5中水溶性离子进行相关性分析,得出沈阳市冬季大气PM2.5的主要贡献组分为SNA和Cl−。田莎莎等[22]计算了沈阳市不同季节的
${\rm{NO}}_3^{-} $ 与${\rm{SO}}_4^{2-} $ 的比值,发现秋季机动车尾气的排放对大气污染贡献较大,冬季燃煤等固定源对大气污染的贡献较大。但上述研究工作存在时间久远、数据不连续、缺乏实时在线监测以及季节变化研究等问题。本研究使用在线气溶胶和气体离子监测仪对沈阳市进行为期1年的逐小时观测工作,通过分析PM2.5中水溶性离子的季节差异、日变化趋势和来源情况等,以期为沈阳市精准和科学治霾提供科学依据。
沈阳市大气PM2.5中水溶性离子的季节变化特征
Seasonal variation of water soluble ions in PM2.5 in Shenyang
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摘要: 为研究沈阳市大气中PM2.5及其水溶性离子的污染特征、季节差异和来源情况,使用URG-9000D在线监测系统对沈阳市2019年大气颗粒物进行连续的采样分析,并利用正交矩阵因子分析法(PMF)进行污染物的来源解析。结果表明,2019年沈阳市秋冬季节PM2.5质量浓度变化受相对湿度影响较大,冬季PM2.5平均质量浓度达到85.76 μg·m−3,细粒子污染较为严重。沈阳市大气PM2.5中SNA(
${{\rm{SO}}_4^{2-} }$ 、${{\rm{NO}}_3^{-} }$ 和${{\rm{NH}}_4^{+} }$ )所占比重表现为春季最高秋季最低;夏季${{\rm{SO}}_4^{2-} }$ 和${{\rm{NH}}_4^{+} }$ 浓度较高,而${{\rm{NO}}_3^{-} }$ 浓度较低。${{\rm{SO}}_4^{2-} }$ 在夏季呈单峰型日变化,与${{\rm{NO}}_3^{-} }$ 变化趋势相反。春夏秋三季${{\rm{NH}}_4^{+} }$ 与${{\rm{SO}}_4^{2-} }$ 、${{\rm{NO}}_3^{-} }$ 主要结合为(NH4)2SO4和NH4NO3,冬季${{\rm{NH}}_4^{+} }$ 主要以(NH4)2SO4和NH4HSO4的形式存在。沈阳市存在较强的SO2和NOx二次转化现象,且各季节中SO2的转化率均高于NO2。PMF源解析结果表明,二次源对沈阳市大气污染贡献最大,夏秋季生物质燃烧和冬季燃煤源贡献同样不可忽视。Abstract: In order to study the pollution characteristics, seasonal differences and sources of water-soluble ions in PM2.5 in Shenyang, the samples of atmospheric particulate matter were analyzed by the URG-9000D online monitoring system. The source of pollutants was analyzed using the orthogonal matrix factor analysis (PMF). The results showed that relative humidity had a great influence on the mass concentration of PM2.5 during autumn and winter of 2019 in Shenyang. The average PM2.5 mass concentration in winter reached 85.76 μg·m−3, and fine particle pollution was serious. The proportion of SNA (${\rm{SO}}_4^{2-} $ ,${\rm{NO}}_3^{-} $ and${\rm{NH}}_4^{+} $ ) in PM2.5 was the highest in spring and the lowest in autumn. In summer, the concentration of${\rm{SO}}_4^{2-} $ and${\rm{NH}}_4^{+} $ was higher, while the concentration of${\rm{NO}}_3^{-} $ was lower. In summer, the diurnal variation of${\rm{SO}}_4^{2-} $ showed uni-modal trend, which was contrary to that of${\rm{NO}}_3^{-} $ . The formation of (NH4)2SO4 and NH4NO3 existed in spring, summer and autumn, while those of (NH4)2SO4 and NH4HSO4 in winter. There were strong secondary conversion of SO2 and NOx in Shenyang, and the conversion rate of SO2 was higher than that of NO2 in the four seasons. PMF showed that secondary sources were the largest contributor to air pollution in Shenyang, and biomass combustion in summer and autumn and coal combustion in winter could not be ignored.-
Key words:
- pollution characteristics /
- seasonal variation /
- diurnal variation /
- source apportionment /
- Shenyang
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表 1 沈阳市四季PM2.5及其水溶性无机离子质量浓度(μg·m−3)
Table 1. Mass concentrations of water-soluble inorganic ions in PM2.5 of four reasons in Shenyang(μg·m−3)
季节
SeasonCa2+ Mg2+ K+ ${\rm{NH}}_4^{+} $ Na+ ${\rm{SO}}_4^{2-} $ ${\rm{NO}}_3^{-} $ Cl− 总离子
Total ionsPM2.5 总离子/ PM2.5
Total ions/ PM2.5春季 0.30 0.05 0.61 4.40 0.39 4.87 5.81 1.22 17.64 46.01 38.34% 夏季 0.11 0.05 6.25 6.91 0.17 7.69 3.01 0.25 24.76 35.48 69.79% 秋季 0.44 0.07 6.74 3.79 0.39 5.32 6.05 1.62 24.39 47.41 51.44% 冬季 0.31 0.09 1.43 4.69 0.46 7.46 7.72 3.83 25.83 85.76 30.12% 表 2 水溶性离子相关性分析矩阵
Table 2. Correlation analysis matrix of water soluble ions
季节Season Ca2+ Mg2+ K+ ${\rm{NH}}_4^{+} $ Na+ ${\rm{SO}}_4^{2-} $ ${\rm{NO}}_3^{-} $ Cl− 春季 Ca2+ 1.000 Mg2+ 0.277** 1.000 K+ 0.264** 0.194** 1.000 ${\rm{NH}}_4^{+} $ 0.025 0.187** 0.432** 1.000 Na+ 0.352** 0.262** 0.201** 0.301** 1.000 ${\rm{SO}}_4^{2-} $ 0.061 0.178** 0.382** 0.891** 0.296** 1.000 ${\rm{NO}}_3^{-} $ 0.054 0.195** 0.297** 0.906** 0.312** 0.717** 1.000 Cl− 0.135** 0.220** 0.745** 0.478** 0.412** 0.418** 0.321** 1.000 夏季 Ca2+ 1.000 Mg2+ 0.027 1.000 K+ 0.138** 0.098** 1.000 ${\rm{NH}}_4^{+} $ 0.018 0.015 0.098** 1.000 夏季 Na+ 0.586** 0.282** 0.044 0.013 1.000 ${\rm{SO}}_4^{2-} $ 0.009 0.068 0.124 0.870** 0.046 1.000 ${\rm{NO}}_3^{-} $ 0.057 0.121** -0.025 0.800** 0.035 0.505** 1.000 Cl− 0.440** 0.209 -0.023 0.358** 0.491** 0.213** 0.495** 1.000 秋季 Ca2+ 1.000 Mg2+ 0.371** 1.000 K+ 0.349** 0.266** 1.000 ${\rm{NH}}_4^{+} $ 0.030 0.319** 0.289** 1.000 Na+ 0.301** 0.413** 0.302** 0.411** 1.000 ${\rm{SO}}_4^{2-} $ 0.007 0.176** 0.146** 0.768** 0.379** 1.000 ${\rm{NO}}_3^{-} $ 0.003 0.225** 0.341** 0.878** 0.346** 0.642** 1.000 Cl− 0.191** 0.386** 0.383** 0.441** 0.408** 0.219** 0.301** 1.000 冬季 Ca2+ 1.000 Mg2+ 0.257** 1.000 K+ 0.249** 0.273** 1.000 ${\rm{NH}}_4^{+} $ 0.133** 0.238** 0.580** 1.000 Na+ 0.241** 0.423** 0.699** 0.525** 1.000 ${\rm{SO}}_4^{2-} $ 0.090* 0.158** 0.601** 0.514** 0.657** 1.000 ${\rm{NO}}_3^{-} $ 0.076 0.198** 0.567** 0.312** 0.611** 0.837** 1.000 Cl− 0.177** 0.242** 0.910** 0.545** 0.694** 0.522** 0.450** 1.000 1) *表示P<0.05,**表示P<0.01. -
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