Distinct Ultrafine‐ and Accumulation‐Mode Particle Properties in Clean and Polluted Urban Environments

• Published in: Geophysical research letters 2019-10, Vol.46 (19), p.10918-10925
• Main Authors: Wang, Yuying, Li, Zhanqing, Zhang, Renyi, Jin, Xiaoai, Xu, Weiqi, Fan, Xinxin, Wu, Hao, Zhang, Fang, Sun, Yele, Wang, Qiuyan, Cribb, Maureen, Hu, Dawei
• Format: Article
• Language: English
• Subjects: Accumulation; Aerosol concentrations; aerosol formation process; aerosol hygroscopicity; aerosol properties; Aerosols; Cascade chemical reactions; Chemical composition; Chemical reactions; Emissions; Hygroscopicity; H‐TDMA; Instruments; Measuring instruments; Mobility; Nucleation; Organic chemistry; Properties; Properties (attributes); Ultrafines; Urban environments
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2019GL084047

In this study, we report the phenomenon of fast changes in aerosol hygroscopicity between clean and polluted periods observed frequently in urban Beijing during winter using a hygroscopicity tandem mobility analyzer. The cause of this phenomenon and the formation process of particles in different modes are discussed. During clean periods, ultrafine‐mode particles (i.e., nucleation and Aitken modes) stem mainly from nucleation events with subsequent growth. During heavily polluted periods, ultrafine‐mode particles originate chiefly from primary emissions. Larger‐mode particles like accumulation‐mode particles are mainly from primary emissions during clean periods and aqueous reactions during polluted periods. This finding based on hygroscopicity tandem mobility analyzer measurements can make up the deficiency of mass‐dependent instruments in analyzing sources and chemical processes of ultrafine‐mode particles. Plain Language Summary The mass concentration of ultrafine‐mode particles in the atmosphere is extremely low, and their properties are rarely investigated using instruments specialized in measuring such things. The hygroscopicity tandem mobility analyzer makes it possible to study sources and chemical processes of ultrafine‐mode particles. They were measured in terms of aerosol number concentration, and aerosol hygroscopicity indirectly reflects aerosol chemical compositions. The properties of ultrafine‐ and accumulation‐mode particles differed considerably between clean and polluted urban environments. Investigated were their different formation processes. Key Points Aerosol hygroscopicity changes quickly between clean and polluted periods in Beijing Ultrafine‐mode particles stem chiefly from nucleation in clean environments and from primary emissions in polluted environments Ultrafine‐ and accumulation‐mode particles have distinct properties in urban environments