Abstract
Abstract. Severe wintertime haze events with exceedingly high levels of aerosols have occurred frequently in China in recent years, impacting human health, weather, and the climate. A better knowledge of the formation mechanism and aerosol properties during haze events is helpful for the development of effective mitigation policies. In this study, we present field measurements of aerosol properties at an urban site in Beijing during January and February 2015. A suite of aerosol instruments were deployed to measure a comprehensive set of aerosol chemical and physical properties. The evolution of haze events in winter, dependent on meteorological conditions, consistently involves new particle formation during the clean period and subsequently continuous growth from the nucleation mode particles to submicron particles over the course of multiple days. Particulate organic matter is 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 hygroscopic parameter (κ) of ambient particles are approximately 1.37 g cm−3 and 0.25 during the clean period and increase to 1.42 g cm−3 and 0.4 during the polluted period, indicating the formation of secondary inorganic species from the continuous growth of nucleation mode particles. Our results corroborate that the periodic cycles of severe haze formation in Beijing during winter are attributed to the efficient nucleation and secondary aerosol growth under high gaseous precursor concentrations and the stagnant air conditions, highlighting that reductions in emissions of aerosol precursor gases are critical for remedying secondary aerosol formation and thereby mitigating haze pollution.
Highlights
Three decades of rapid industrialization have made China the second largest economy in the world
The first haze event began with a new particle formation (NPF) event (Zhang et al, 2004), which was followed by the continuous particle growth over 3 d (Fig. 1a)
We have evaluated the influence of meteorology, local emissions, and aerosol processes on severe haze events in Beijing during winter by conducting comprehensive aerosol properties measurements
Summary
Three decades of rapid industrialization have made China the second largest economy in the world. This rapid economic development has resulted in a deterioration of the quality of air, water, land, and ecosystems (Chang et al, 2009; Su et al, 2012; Wang et al, 2008; WHO et al, 2006). Huang et al (2014) demonstrated that severe PM2.5 pollution in four megacities in China (i.e., Beijing, Shanghai, Guangzhou, and Xi’an) was driven to a large extent by the secondary aerosol formation. Guo et al (2014) elucidated that the formation of severe urban haze in Bei- To elucidate the mechanism of severe PM2.5 pollution, considerable efforts have been made in the past few years. Huang et al (2014) demonstrated that severe PM2.5 pollution in four megacities in China (i.e., Beijing, Shanghai, Guangzhou, and Xi’an) was driven to a large extent by the secondary aerosol formation. Guo et al (2014) elucidated that the formation of severe urban haze in Bei-
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