Measurement of aerosol properties during wintertime in Beijing
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Abstract. Severe haze events with exceedingly high-levels of aerosols have occurred frequently in China in recent years, threatening human health and affecting regional and global radiative budget. A better knowledge of aerosol properties during haze events, particularly for those occurring during wintertime, will be helpful for elucidating the haze formation mechanism. In this study, we conducted a field measurement at an urban site in Beijing during January and February of 2015. A suite of aerosol instruments was deployed to measure a comprehensive set of aerosol chemical and physical properties. The haze events in winter, regulated by meteorological conditions, typically start with a new particle formation event and progress in terms of the subsequently continuous growth of the nucleation mode particles to submicron particles over the following multiple days. Particulate organic matters are primarily responsible for producing the nucleation mode particles, while secondary organic and inorganic components jointly contribute to the high aerosol mass observed during haze events. The average effective density and kappa value of ambient particles are approximately 1.37gcm3 and 0.25 during the clean days, and 1.42gcm3 and 0.4 during the severe haze episodes, respectively, indicating the formation of secondary inorganic species during the development of the severe haze events. Our results reveal that the periodic cycles of severe haze formation in Beijing during wintertime are attributed to the fast secondary aerosol formation due to the high gaseous precursor concentrations and the stagnant air mass, which are analogous to the severe haze events observed during autumn.
