光化学氧化对深圳市含黑碳气溶胶混合态和光吸收的影响

Effects of photochemical oxidation on the mixing state and light absorption of black carbon-containing aerosols in Shenzhen

于2021年2月在深圳开展了含黑碳气溶胶混合态和光学性质的测量,结合奇氧数(Ox)的同步分析,以探究光化学氧化对城市大气中含黑碳气溶胶包裹物、形貌与光吸收能力的影响.结果表明:观测期间黑碳颗粒群平均相对包裹物量(包裹物与黑碳核质量比,MR)平均值为4.3±0.7,有效密度平均值为(1.35±0.10)g/cm^(3),整体颗粒群形貌为球形的观测时段占比为70%,表明深圳城市点含黑碳气溶胶主要为中等不规则形貌的内部混合态颗粒.光化学氧化在含黑碳气溶胶混合态演变过程中起到重要作用.随着Ox的增加,颗粒群平均MR增幅约为38%,平均有效密度从1.32g/cm^(3)增至1.44g/cm^(3),动力学形状因子从1.05递减至1.00,表明光化学氧化过程促使非黑碳组分累积并使颗粒趋向于形成更致密的核壳球形.此外,Ox增加过程中,吸光增强(Eabs)增幅约为20%,增长速率为0.002/10-9,表明光化学氧化对城市点含黑碳气溶胶光吸收起到关键的驱动作用.

In February 2021,we conducted a study in Shenzhen to measure the mixing state and optical properties of black carbon(BC)-containing aerosols.Simultaneously,we analyzed odd oxygen(Ox)to explore the effects of photochemical oxidation on coating,morphology,and light absorption of BC-containing aerosols in an urban environment.The results show that,during the observation period,the mean bulk-averaged relative coating amounts(coating-to-core mass ratio,MR)over particle population was 4.3±0.7.The mean effective density was(1.35±0.10)g/cm^(3),and about 70%of the observed period exhibited spherical morphology,indicating that the BC-containing aerosols in Shenzhen were predominantly composed of internally mixed particles with moderately irregular shapes.Photochemical oxidation played an important role in the mixing state evolution of BC-containing aerosols.With rising Ox concentrations,the bulk-averaged MR increased by about 38%,the effective density increased from 1.32g/cm^(3) to 1.44g/cm^(3),and the dynamic shape factor decreased from 1.05 to 1.00,indicating that the photochemical oxidation process resulted in the accumulation of non-BC components and reshaped more compact spherical particles with core-shell structure.Additionally,as Ox concentrations increased,the light absorption enhancement(Eabs)exhibited an approximately 20%increase,with a growth rate of 0.002/ppbv,suggesting the key role of photochemical oxidation in enhancing light absorption of BC-containing aerosols in an urban site.