运城市2020—2021年采暖季PM_(2.5)污染成因分析

Cause of PM_(2.5) pollution during the 2020—2021 heating season in Yuncheng

科学分析采暖季PM_(2.5)污染特征和成因,有助于制定更精准有效的减排措施,为本地污染管控与城市联防联控提供准确、全面的依据.本研究采用1 h分辨率在线仪器对运城市2020年采暖季PM_(2.5)中水溶性离子和碳质组分进行同步测量,并采用正定矩阵因子分析(PMF)模型结合在线数据对PM_(2.5)污染源进行精细化解析.结果表明:①随着污染程度的加重,二次无机离子中的SNA(SO_(4)^(2-)、NO_(3)^(-)、NH_(4)^(+))对PM_(2.5)的贡献占比逐渐降低,有机碳(OC)和元素碳(EC)占比升高,OC/EC质量比表明PM_(2.5)受燃煤排放影响较大;②RH是影响SO_(4)^(2-)形成的关键因素,光化学反应更有利于NO_(3)^(-)的生成,在贫铵条件下NO_(3)^(-)的形成主要受夜间N_(2)O_(5)吸收系数的限制,非均相反应占主导地位;③PMF模型识别出5类PM_(2.5)的来源,分别为燃煤和工业排放源(32.2%)、二次源(30.5%)、移动源(27.8%)、扬尘源(6.1%)和生物质燃烧源(3.4%);污染天PM_(2.5)主要排放源为煤炭燃烧和工业排放源和二次源,优良天则主要为移动源和扬尘源;煤炭燃烧和工业排放源和二次源促进了雾霾事件的形成与演变.

Scientific analysis of the characteristics and causes of PM_(2.5) pollution during the heating season can help formulate more accurate and effective emission reduction measures and provide an accurate and comprehensive basis for local pollution control and urban joint prevention and control.This study used online instruments with a 1-hour resolution to synchronously measure water-soluble ions and carbonaceous components in PM_(2.5) during the 2020 heating season in Yuncheng City.Based on the online data,the positive matrix factorization(PMF)model was used to analyze the sources of PM_(2.5) pollution finely.The results showed that:①with the increase in pollution level,the contribution of secondary inorganic ions(SNA,i.e.,SO_(4)^(2-)+NO_(3)^(-)+NH_(4)^(+))to PM_(2.5) gradually decreased,while the proportion of organic carbon(OC)and elemental carbon(EC)increased.The mass ratio of OC/EC indicated that PM_(2.5) was greatly affected by coal combustion emissions;②relative humidity(RH)was the critical factor affecting the formation of SO_(4)^(2-),and photochemical reactions were more favourable for the generation of NO_(3)^(-).Under the condition of poor ammonium,the formation of NO_(3)^(-)was mainly limited by the absorption coefficient of N_(2)O_(5) at night,and heterogeneous reactions dominated;③the PMF model identified five sources of PM_(2.5),namely coal and industrial emission sources(32.2%),secondary sources(30.5%),mobile sources(27.8%),dust sources(6.1%),and biomass burning sources(3.4%).Coal combustion,industrial emissions,and secondary sources were the main emission sources of PM_(2.5) on polluted days,while mobile and dust sources were the primary sources on clean days.Coal combustion,industrial emissions,and secondary sources promoted the formation and evolution of haze events.