杭州秋冬季PM2.5污染特征分析

为研究杭州PM_2.5污染来源特征，利用2013—2019年杭州市PM_2.5监测数据和气象观测数据，分析了杭州市2013—2019年PM_2.5浓度变化，选取本地积累型和输入型2种PM_2.5污染过程，结合单颗粒气溶胶飞行时间质谱仪（SPAMS）和在线离子色谱数据，探讨杭州市PM_2.5化学组分和污染来源。结果表明：每年秋冬季（11月至次年3月）杭州以东北风、西北风及偏南风为主，风速低于4 m/s时，大气扩散条件差，受本地污染物积累影响，PM_2.5浓度容易出现超标；风速较大且为东北风和西北风时，受上游污染输入影响，易出现PM_2.5重度污染。本地积累型和输入型案例中，PM_2.5化学组分中占比最大的为NO₃^-、SO₄^2-和NH₄⁺；PM_2.5浓度上升过程中，二次NO₃^-和SO₄^2-转换率明显上升，其中NO₃^-上升更为显著，二次气溶胶污染严重。2次案例中，PM_2.5来源贡献占比前3位均为机动车尾气源、燃煤源和工业工艺源，其中本地积累型PM_2.5浓度上升阶段，机动车尾气源占比会明显上升；输入型案例中，输入阶段机动车尾气源占比显著上升，燃煤源贡献也小幅上升。

Analysis of Pollution Characteristics of PM2.5 in Hangzhou in Autumn and Winter

To investigate the pollution characteristics and sources apportionment of PM_2.5 in Hangzhou,the national environmental monitoring PM_2.5 data and meteorological data of Hangzhou during 2013-2019 were used to analyze the changes characteristics of PM_2.5 concentration in the past five years.And two typical PM_2.5 pollution processes,local origin and external input,were collected and analyzed for PM_2.5 chemical composition and pollution source by use a single particle aerosol mass spectrometer (SPAMS) and ion chromatography analyzer data.The results showed that high PM_2.5 episodes usually occurred in autumn and winter,during the period from November to the following March,because of the pollutants accumulation when the wind speed was lower than 4 m/s.If the wind speed was large and the wind direction was northeast or northwest,it was also prone to occur PM_2.5 heavy pollution due to pollutants transportation.In both of local accumulation and import cases,the largest proportions of PM_2.5 chemical components were NO₃^-,SO₄^2- and NH₄⁺.And the conversion rate of secondary NO₃^- and SO₄^2- increased significantly during the increase of PM_2.5 concentration.The increase of NO₃^- was more remarkable,and the secondary aerosol pollution was serious in Hangzhou.The source characteristics of PM_2.5 indicated that the top three pollution sources contributed by PM_2.5 in Hangzhou were vehicle exhaust,coal combustion and industrial process respectively.In the local accumulation case,the proportion of motor vehicle exhaust increased significantly when the PM_2.5 concentration rose;and in the imported case,the proportion of motor vehicle exhaust increased significantly,and the contribution of coal-fired sources also increased slightly.