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随着城市化以及工业化进程的快速推进,空气污染也随之加重并且成为人民日益关注的热点之一[1]。大气细颗粒物作为《环境空气质量标准》(GB3095—2012)中6项污染物指标之一,从《大气污染防治行动计划》到《蓝天保卫战三年行动计划》,大气细颗粒物污染治理更是国家这几年大气污染防治的工作重点[2]。大气颗粒物通过吸收或散射太阳辐射进而对地-气系统的辐射平衡产生直接影响,另一方面也可以通过影响云凝结核的活化特性,间接改变云反照率并影响气候系统变化[3-4],细颗粒物比表面积较大,粒径较小,活性强,易富集有毒有害物质,长期暴露在颗粒物污染环境下会对人的身体健康产生巨大伤害[5-6]。颗粒物的粒径、组分以及混合态各存特征,因其来源、反应环境及过程不同而发生变化,故研究单颗粒的组分及粒径分布具有重要意义。
传统的颗粒物组分研究主要依靠对颗粒物进行离线采样及实验室分析,该种方法处理时间周期较长,不能连续真实地反映污染实况[7],因此,实时在线测量大气颗粒物组分可以了解大气颗粒物污染特征。这对分析颗粒物来源及其成因有着重要作用,同时能够对大气污染防治提供精准科技支撑。近年来合肥市二、三产业发展较快,2017年合肥市生产总值第一产业占比3.8%,第二产业占比50.5%,第三产业占比45.7%[8]。目前在合肥地区对颗粒物组分研究内容较少,主要利用离线实验室分析方法研究,如刘可可等[9]利用X射线荧光光谱法(XRF)对合肥市重污染和非污染天气下大气颗粒物中元素组成进行差异性分析;汪洋等[10]对合肥大气PM2.5中重金属元素的含量、富集系数和可能来源展开研究;施学美等[11]用热/光碳分析仪测定合肥春季大气PM10和PM2.5中有机碳、元素碳的含量,并对其来源进行初步解析。相比于离线采样分析,单颗粒气溶胶质谱仪具有时间分辨率高,灵敏度高,信息量大等优点,填补了传统方法的不足,相比其他在线分析仪器如Marga等,SPAMS侧重从单颗粒尺度获取组分特征,能更全面地解析单个颗粒物来源及混合状态等,有利于定性分析,已被国内广泛应用于颗粒物的研究[12-19]。
本文选取一次重污染天气为研究对象,在不同污染天气内测定颗粒物的粒径分布、化学组成和变化规律,并对颗粒物进行分类,通过进一步分析不同污染天气内各类颗粒物的来源和污染特征,以期为进一步开展大气细颗粒物源解析研究提供基础数据,为环境管理和污染防治对策提供科学依据。
合肥市一次重污染过程细颗粒物化学组分特征及成因分析
Analysis of fine particles chemical characteristics and causes during a heavy pollution period in Hefei
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摘要: 使用单颗粒质谱仪(SPAMS)研究了合肥市2018年1月重污染过程空气细颗粒物化学组分特征,研究结果表明,重污染期间,EC、HM、MD及RK颗粒占比显著,分别占74.9%、10.0%、5.0%和6.8%,本次重污染主要污染物为元素碳类型颗粒物;进入污染消散期间后,细颗粒物平均峰值粒径减小0.1 μm,含元素碳的各类颗粒峰值粒径分别下降0.04、0.02、0.36、0.22 μm,MD颗粒增大0.08 μm,OC和Lev颗粒峰值粒径未改变。重污染过程来临前,扩散条件较差,加之本地源排放加剧,导致重污染天气形成,化学组分分析显示,EC占比最高,22日中午出现污染反弹,午后,北方清洁气团入境,扩散条件好转,污染消散。EC、HM、RK颗粒之间存在强相关性,且分别与风速呈现强负相关,说明该次重污染主要是不利气象造成汽车尾气长时间积累而造成。Abstract: The single particle mass spectrometer (SPAMS) was used to study the chemical component characteristics of fine particle during heavy pollution in Hefei in January 2018. The analysis shows that EC, HM, MD and RK particles accounted for 74.9 % , 10.0 % , 5.0 % and 6.8 % respectively, with significant proportion during heavy pollution, particles containing elemental carbon was the dominant pollutant. During the period of pollution dissipation, the peak diameters of carbon-containing particles decreased by 0.04, 0.02, 0.36, 0.22 μm, while the peak diameters of MD rose by 0.08 μm, OC and Lev remained unchanged. Before the heavy pollution, the unfavorable diffusion conditions, coupled with the aggravation of local emissions, led to the formation of heavy pollution. The composition analysis showed that EC accounted for the highest proportion. On the noon of the 22nd, the pollution rebounded again. In the afternoon, the diffusion intensified and the pollution dissolve due to the arrival of clean air mass. The strong correlations among EC, HM and RK particles, and a strong negative correlation with wind speed, shows that long-time accumulation of automobile exhaust caused by unfavorable weather condition contributed most to the heavy pollution process.
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Key words:
- fine particles /
- SPAMS /
- chemical composition /
- cause
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表 1 颗粒物组分间相关性分析
Table 1. The pearson coorelation between the components of PM2.5
EC ECOC HM HOC K Lev Na OC Other MD EC 1 0.378** 0.926** 0.367** 0.924** −0.455** −0.577** −0.546** −0.336** 0.770** ECOC 1 0.441** 0.494** 0.395** 0.299** −0.212** 0.407** −0.058 0.333** HM 1 0.352** 0.829** −0.413** −0.479** −0.479** −0.280** 0.863** HOC 1 0.296** 0.391** −0.13 0.199** −0.139 0.215** K 1 −0.457** −0.669** −0.451** −0.300** 0.754** Lev 1 0.416** 0.760** 0.258** −0.420** Na 1 0.356** 0.277** −0.312** OC 1 0.394** −0.398** Other 1 −0.235** MD 1 ** P<0.01. 表 2 颗粒物组分与气象要素之间的相关性分析
Table 2. The pearson coorelation between the meteorological parameters and the components of PM2.5
EC ECOC HM HOC K Lev Na OC Other MD 数浓度
Number
concentration质量浓度
Mass
concentration风速 0.796** −0.14 0.727** 0.304** 0.757** 0.452** 0.553** 0.615** 0.339** 0.599** −0781** −0.724** 能见度 0.498** −0.122 0.481** −0.14 0.428** 0.271** 0.353** 0.443** 0.217** 0.347** −0.486** −0.426** 温度 0.829** 0.113 0.741** 0.314** 0.809** 0.475** 0.610** 0.558** 0.256** 0.617** 0.821** 0.794** 相对湿度 0.411** 0.273** 0.447** 0.024 0.352** 0.246** 0.247** 0.336** 0.273** 0.324** 0.383** 0.389** ** P<0.01. -
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