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随着我国国民经济的快速发展,对美好环境的需求日益增长,然而快速城市化带来污染排放问题依然严峻,PM2.5已成为我国大部分地区大气环境的首要污染物[1],目前大气颗粒物污染呈现出区域复合性污染特征,大气颗粒物主要由含碳化合物(煤、飞灰及有机物),可溶性无机离子(硫酸盐、硝酸盐以及铵盐等)和几乎不溶的无机物(元素氧化物)等3部分组成[2]其中,水溶性无机离子是大气颗粒物中重要的组分,对大气消光系数具有较高的贡献率,二次离子SNA(
${\rm{SO}}_4^{2-} $ 、${\rm{NO}}_3^{-} $ 和${\rm{NH}}_4^{+} $ )是重污染期间能见度低的重要原因[3],且对人类呼吸系统及心脏系统等生命系统有严重伤害[4],严重影响人们的身体健康,所以研究大气中PM2.5中水溶性离子的组成对客观认识PM2.5的污染特征及环境影响具有重要的现实意义。目前国内外诸多学者都已对水溶性离子污染特征进行了深入分析。有学者分别研究了兰州市、安阳市大气PM2.5中水溶性离子污染特征及来源解析[5-6],结果表明硝酸根及硫酸根均占比较大,水溶性离子来源大多与二次生成、燃煤、生物质燃烧和扬尘息息相关。前人还对霾不同污染阶段下水溶性离子变化特征进行了分析[7-8],结果表明雾霾天多种水溶性离子浓度是干净天数倍,说明划分采暖季及非采暖季或污染天及清洁天研究水溶性离子污染特征尤其重要。
京津冀作为我国空气污染问题突出的地区之一,大气污染治理一直备受关注,2017年4月,中共中央、国务院决定设立河北雄安新区,涉及保定市雄县、容城、安新等3县及周边部分区域,故对保定市污染治理要求日益迫切。本文通过对保定市细颗粒物进行采样分析,有针对性的研究保定市大气气溶胶中PM2.5水溶性无机离子污染特征及来源,并对成因进行识别和判定,可以为保定市科学治霾提供技术支撑及科学依据。
保定市PM2.5中水溶性离子污染特征及来源分析
The pollution pattern and source analysis of water-soluble ions of PM2.5 in Baoding City
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摘要: 为研究保定市PM2.5中水溶性离子污染特征及来源,利用中流量采样器采集保定市2017年秋、冬季10月—2017年12月污染天的PM2.5样品(40个),进行水溶性离子组分分析,并辅以保定市同期气象数据及空气质量数据进行成因探讨。计算离子间相关性,采用离子平衡法衡量大气酸碱度,并对保定市日夜不同时段PM2.5中水溶性离子污染特征进行细节分析,并利用主成分分析法分析PM2.5中水溶性离子来源,且对二次离子来源及气象条件影响进行了深入分析。根据离子之间相关性,推测保定市K+和
${{\rm{NO}}_3^{-} }$ 、Cl−具有同源性,主要源于生物质燃烧;${{\rm{NH}}_4^{+} }$ 在大气中主要以NH4NO3、(NH4)2SO4及NH4HSO4等形式存在;推测${{\rm{NO}}_3^{-} }$ 及${{\rm{SO}}_4^{2-} }$ 两离子主要来源均为工业排放污染物的化学转化;保定市非采暖期大气颗粒物呈酸性,采暖期大气颗粒物呈现碱性。多数水溶性离子含量均呈现夜间高于白天的现象,这一现象可能与气象变化及周围环境影响等诸多因素有关;污染天和清洁天大气PM2.5中二次离子主要来源于移动源;二次离子与湿度均呈正相关趋势,而${{\rm{SO}}_4^{2-} }$ 与温度呈负相关趋势;水溶性离子浓度高低依次为${{\rm{NO}}_3^{-}} $ >Na+>${{\rm{SO}}_4^{2-} }$ >Cl−>${{\rm{NH}}_4^{+} }$ >${{\rm{NO}}_2^{-}} $ >Ca2+>K+>F−>Mg2+,10—12月PM2.5中多数水溶性离子含量均呈现夜间高于白天的现象;采暖季SOR、NOR均低于非采暖季,二次污染物转化效率较低,这可能与采暖季煤燃烧释放污染物有关;保定市PM2.5水溶性离子主要来源为生物质燃烧、化石燃料燃烧及扬尘源及二次源。Abstract: A total of 40 samples of PM2.5 in Baoding city spanning from October 2017 to December 2017 were collected by using the flow sampler(TH-150C, Wuhan-Tianhong,Wuhan). Water-soluble ion groups of the PM2.5 samples were measured to study the pollution pattern and sources of water-soluble ions in PM2.5 in Baoding City. Combining with the meteorological data and air quality data obtained in the same period, the possible cause of the air pollutants were discussed. The correlations between various ions were calculated and analyzed, and the atmospheric acidity or alkalinity were estimated by using ionic equilibrium method. The pollution pattern of water-soluble ions in PM2.5 during the daytime and the night time were analyzed further in detail. The sources of water-soluble ions in PM2.5 were analyzed by principal component analysis (PCA), and the source of secondary ion and corresponding meteorological influences were also analyzed. The results showed that: based on correlation analysis, it was suggested that (1) K+ and${\rm{NO}}_3^{-} $ , Cl− in Baoding City were mainly from the same source: biomass combustion; (2)${\rm{NH}}_4^{+} $ mainly existed in the air in the form of NH4NO3、(NH4)2SO4 and NH4HSO4; (3) the main sources of${\rm{NO}}_3^{-} $ and${\rm{SO}}_4^{2-} $ ions were chemical transformation of the industrial pollutants; (4) the atmospheric particulate matter in Baoding City was acidic in the non-heating season and alkaline in the heating season. The water-soluble ion contents of most samples were higher at night than during the day, which may be related to various factors including meteorological conditions and environmental impacts. In both polluted and clean days, the secondary ions in PM2.5 mainly come from mobile sources. The mass concentration of secondary ions showed a positive correlation with humidity. Meanwhile,${\rm{SO}}_4^{2-} $ had a negative correlation with temperature. The concentration of water-soluble ions was in order of${\rm{NO}}_3^{-} $ >Na+>${\rm{SO}}_4^{2-} $ >Cl−>${\rm{NH}}_4^{+} $ >${\rm{NO}}_2^{-} $ >Ca2+>K+>F−>Mg2+. The content of most water-soluble ions in PM2.5 from October to December were higher at night; the SOR and NOR in the heating season were lower than those in the non-heating season, and the conversion efficiency of secondary pollutants was low, which may be related to the release of pollutants from coal combustion during the heating season. The main sources of water-soluble ions of PM2.5 in Baoding were biomass combustion, fossil fuel combustion, dust sources and secondary sources.-
Key words:
- PM2.5 /
- water-soluble ions /
- PCA /
- SNA /
- meteorological factors
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表 1 保定市水溶性离子质量浓度(μg·m−3)
Table 1. Water-soluble ions mass concentration in Baoding City(μg·m−3)
F− Cl− ${\rm{NO}}_2^{-} $ ${\rm{NO}}_3^{-} $ ${\rm{SO}}_4^{2-} $ Na+ ${\rm{NH}}_4^{+} $ K+ Mg2+ Ca2+ 清洁天 0.075 0.452 0.282 0.641 0.668 — — 0.160 0.114 0.106 轻度污染天 0.118 1.387 0.311 2.550 1.910 1.143 1.130 0.331 0.025 0.594 中度污染天 0.111 0.983 0.299 5.136 3.157 — 2.403 0.267 0.004 0.203 重度污染天 0.122 2.350 0.346 4.355 4.221 3.107 2.003 0.619 0.001 0.470 严重污染天 0.121 2.646 0.337 7.772 7.314 2.980 3.261 0.784 0.001 0.211 表 2 保定市水溶性离子相关矩阵
Table 2. Water-soluble ions correlation Matrix in Baoding City
F− Cl− ${\rm{NO}}_3^{-} $ ${\rm{SO}}_4^{2-} $ Na+ ${\rm{NH}}_4^{+} $ K+ Mg2+ Ca2+ F− 1 Cl− 0.335 1 ${\rm{NO}}_3^{-} $ −0.073 0.749** 1 ${\rm{SO}}_4^{2-} $ −0.118 0.684** 0.938** 1 Na+ −0.184 0.340 0.231 0.201 1 ${\rm{NH}}_4^{+} $ −0.045 0.782** 0.964** 0.957** 0.258 1 K+ −0.008 0.813** 0.854** 0.751** 0.344 0.845** 1 Mg2+ 0.275 −0.003 −0.134 −0.16 0.044 −0.147 −0.193 1 Ca2+ 0.292 0.419* −0.062 −0.016 0.229 −0.03 0.183 −0.165 1 “*” P<0.05, represents a significant correlation at 0.05 level (2-sided),“**” P<0.01, represents a significant correlation at 0.01 level (2-sided). 表 3 本研究与保定市其他年份水溶性离子浓度对比(μg·m−3)
Table 3. Comparison of concentration of water-soluble ions of Baoding between this study and other years(μg·m−3)
表 4 保定市水溶性离子浓度(μg·m−3)
Table 4. Water-soluble ions concentration in Baoding City(μg·m−3)
F− Cl− ${\rm{NO}}_2^{-} $ ${\rm{NO}}_3^{-} $ ${\rm{SO}}_4^{2-} $ Na+ ${\rm{NH}}_4^{+} $ K+ Mg2+ Ca2+ 日间 0.140 1.209 0.468 3.126 2.548 3.365 1.242 0.270 0.033 0.514 夜间 0.194 2.247 0.530 4.263 3.233 3.517 2.030 0.482 0.023 0.375 表 5 保定市水溶性离子与气象条件相关性
Table 5. Correlation between water-soluble ions and meteorological conditions in Baoding City
Cl− ${\rm{NO}}_2^{-} $ ${\rm{NO}}_3^{-} $ ${\rm{SO}}_4^{2-} $ Na+ ${\rm{NH}}_4^{+} $ K+ Mg2+ Ca2+ 温度 白天 −0.434** 0.039 0.603** 0.288 −0.953** 0.774** −0.269 0.438** −0.427** 晚上 −0.659** −0.393* 0.183 −0.145 −0.930** 0.176 −0.540** 0.487** −0.699** 能见度 白天 −0.318 0.013 0.187 0.052 −0.636** 0.443* −0.189 0.683** −0.332 晚上 −0.347* − 0.108 0.008 −0.476** 0.163 −0.236 0.280 −0.394* 阵风 白天 0.077 −0.031 −0.394* −0.186 0.550** −0.533** 0.002 −0.249 0.420* 晚上 0.065 −0.045 −0.245 −0.147 0.307 −0.179 0.065 −0.178 0.174 表 6 保定市昼夜气象数据
Table 6. Day and Night Meteorological Data of Baoding City
阵风/mph
Gustiness能见度/mile
Visibility温度/℃
Temperature/白天 261.3 13.2 −4.3 晚上 88.5 13.5 −4.2 表 7 大气PM2.5中SNA与气象条件相关性
Table 7. Correlation between SNA and meteorological conditions of PM2.5
${\rm{NO}}_3^{-} $ ${\rm{SO}}_4^{2-} $ ${\rm{NH}}_4^{+} $ SOR NOR 温度 0.461** −0.019 0.458** 0.233 0.367* 相对湿度 0.633** 0.291 0.650** 0.070 0.529** 风速 −0.455** −0.345* −0.471** −0.087 −0.532** 表 8 保定市采暖季与非采暖季SOR、NOR日均值
Table 8. Daily mean value of SOR,NOR in heating season and non-heating season in Baoding City
SOR NOR 非采暖季 日间 0.165 0.112 夜间 0.182 0.087 采暖季 日间 0.080 0.029 夜间 0.089 0.055 表 9 保定市水溶性离子主成分分析
Table 9. Principal component analysis of water-soluble Ions in Baoding City
离子名称
Ion name因子1
Component 1因子2
Component 2Cl— 0.918 0.235 ${\rm{NO}}_3^{-} $ −0.097 0.948 ${\rm{SO}}_4^{2-} $ 0.368 0.852 Na+ 0.852 −0.284 ${\rm{NH}}_4^{+} $ −0.133 0.959 K+ 0.808 0.440 Mg2+ −0.550 −0.045 Ca2+ 0.717 −0.162 贡献率/% 40.014 36.277 累计贡献率/% 40.014 76.291 特征值 3.415 2.688 来源分析 生物质燃烧、化石燃料燃烧及扬尘混合源 二次源 -
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