深圳市大气颗粒物分粒径有效密度及影响因素

为探究深圳市大气颗粒物分粒径有效密度变化特征及其影响因素,本文将离心颗粒物质量分析仪(CPMA)与差分电迁移粒径分析仪(DMA)联用,通过粒径筛分测定了2020年9月~2021年2月粒径范围为50~500nm的深圳市大气颗粒物分粒径有效密度.结果表明:深圳市大气颗粒物的中值有效密度范围在1.29~1.53g/cm³,颗粒物有效密度均随颗粒物粒径增加而增大,秋季有效密度略低于冬季.清洁时期,有效密度较低且观察到双峰分布,低密度颗粒物中值有效密度在0.70~0.80g/cm³范围内,表明存在新鲜排放的黑碳颗粒物,高密度颗粒物中值有效密度在1.3~1.5g/cm³范围内,介于二次无机颗粒物和有机物的材料密度之间,推测为二者混合状态.污染时期,不同粒径有效密度值增加且呈现单峰分布,表明颗粒物呈现内混态.在新粒子生成事件中,气态硝酸凝结可能是大气颗粒物后续粒径增长和有效密度增加的主要原因.

Study on effective density of size-resolved particles and the influencing factors in Shenzhen

In order to identify the characteristics of the particle effective density in Shenzhen and the influencing factors, we used a centrifugal particle mass analyzer (CPMA) combined with a differential mobility analyzer (DMA) to simultaneously measure the size-resolved effective density of particles of 50to 500nm at an urban site from September 2020 to February 2021. The median effective density ranged from 1.29 to 1.53g/cm³, increasing with the particle diameter, and the effective density in autumn was slightly lower than that in winter. During the clean period, the effective density of particles was low and a bimodal distribution was observed. The median effective density of a low-density mode was in the range of 0.70~0.80g/cm³, indicating the presence of fresh soot particles. While the median effective density of a high-density mode was in the range of 1.3~1.5g/cm³, which was between the material densities of secondary inorganic particles and organic particles, indicating mixing of them. During the polluted period, the effective density at different particle sizes increased and showed a unimodal distribution, which was a result of internal mixing. In the event of new particle formation, nitrate condensation was found to be the main reason for the subsequent increase in particle size and effective density.