深圳大气PM2.5化学组成的长期变化特征

为分析深圳市大气细颗粒物（PM_2.5）浓度长期持续下降的原因，进而明确PM_2.5下一步减排潜力和精细化管理方向，本研究基于2019年在深圳市西乡点位采集的PM_2.5样品，分析了西乡PM_2.5的化学组成及季节分布特征.结果表明，2019年西乡点位PM_2.5年均浓度为29.4μg/m³，总体上呈现夏低冬高的季节特征，有机物（OM）和硫酸根（SO₄^2-）仍是主要的组分，分别占总质量的42.3%和17.6%.对2009、2014、2019年典型月份PM_2.5的组分进行对比，PM_2.5全年质量浓度从42.3μg/m³（2009年）下降至24.6μg/m^3.（2019年），OM、SO₄^2-、硝酸根（NO₃^-）、铵根（NH₄⁺）和元素碳（EC）等都有明显的下降趋势.矿物质元素（Al、Ca）是地面扬尘和建筑尘的标识组分，近年来Al、Ca浓度的增加趋势表明宝安区西乡扬尘的影响在逐渐扩大.2009、2014、2019年OC/EC的值逐渐扩大，说明了一次燃烧源排放的影响逐渐减小，但二次有机物（SOC）的贡献逐渐凸显.通过分析2004、2009、2014、2019年夏、冬季PM_2.5中6种主要组分变化趋势，表明6种主要组分夏冬两季皆有下降趋势，但由于气象因素导致冬季污染物受到区域传输的影响较大，夏季各组分浓度的下降幅度普遍高于冬季.总体来说深圳市PM_2.5浓度持续下降的原因是深圳市对机动车、工业VOC （挥发性有机物）、远洋船舶以及一次燃烧源的管控和减排.

Long-term variational characteristics of the chemical composition of PM2.5 in Shenzhen.

This work was aimed to analyze the long-term variational characteristics of PM_2.5 (particulate matter with aerodynamic diameter less than 2.5μm) and chemical species and investigate their reasons in Shenzhen. To this end, PM_2.5 was sampled and chemical compositions were analyzed at Xixiang site in the four seasons in 2019, and the results were compared with that in 2004, 2009, and 2014. The results showed that the annual average concentration of PM_2.5 was 29.4μg/m³ in Xixiang in 2019, with obvious seasonal variation that high levels in summer and low levels winter. OM and SO₄^2- were still the main components, accounting for 42.3% and 17.6% of the PM_2.5 mass, respectively. Comparison with PM_2.5 and chemical species in 2009, 2014, and 2019, the annual average PM_2.5 concentration dropped from 42.3μg/m³ in 2009 to 24.6μg/m³ in 2019. Organic matter, sulfate, nitrate, ammonium salt, and carbon and other elements also obtained obvious decreasing trend. However, Al and Ca, the tracers of fugitive dust and construction dust, exhibited the increasing trend in recent years, indicating the increasing impact of dust on PM_2.5 in Xixiang, Baoan District. The value of OC/EC gradually increased from 2009, 2014 to 2019, indicating that the impact of primary combustion source gradually decreased while the contribution of secondary organic matter became prominent. This work also investigated the seasonal (summer and winter) trends of six components of PM_2.5 in 2004, 2009, 2014, and 2019. The results suggested that the six components obtained larger decrements in summer than that in winter due to unfavorable meteorological conditions in winter. In summary, the reasons for the continuous decrease of PM_2.5 concentration were the emission reductions of motor vehicles, industrial emissions (VOCs), shipping emissions and other primary combustion sources in Shenzhen.