Abstract
To study the impacts of emission controls on aerosol physical and chemical properties, real-time measurements of size-resolved aerosol number concentration and chemical composition were conducted in urban Beijing during the 2014 Asia-Pacific Economic Cooperation (APEC) summit, in a period that a series of measures, for example shutting down or halting production from factories and power plants, and restricting the number of vehicles on the roads were implemented in Beijing and surrounding regions. Significantly, reductions in particle mass concentration (55% for PM2.5 and 48% for PM10) were observed during the APEC summit. A clear decrease in secondary inorganic aerosols (SIA), such as sulphate, nitrate and ammonium, was found during APEC, with the reduction ranged from 65.7 to 72.2% for PM1, in which sulphate showed the largest decrease compared with periods before APEC. As a comparison, organics showed a much smaller decrease of 44.3% for PM1 during APEC. These changes were mainly caused by large reductions in accumulation mode particles, which decreased by 36% compared with 19% for Aitken mode particles. The results from the positive matrix factorization (PMF) of particle number concentration indicate that regionally transported aerosols showed significant decreases (70%), similar to those of SIA during APEC, whereas primary factors from traffic and local combustion sources presented much smaller decreases, with the reduction ranged from 4 to 40%. The elevated contributions of these sources indicated the presence of strong local source emissions. The changes in particle chemical composition, size distribution and sources during the evolution of pollution episodes with and without emission controls are further illustrated. Our results highlight the importance of regional atmospheric transport in the formation of severe pollution episodes in Beijing, indicating that reducing the precursors of secondary aerosol over regional scales represent the key steps to reduce the urban particulate pollution. However, stricter emission controls on local source emissions are needed to further mitigate air pollution in Beijing.
Highlights
Atmospheric aerosols, especially fine particles of particulate matter (PM) with aerodynamic diameters of less than 2.5 μm, have significant impacts on air quality and visibility (Watson, 2002; Molina and Molina, 2004) and are detrimental to human health (Liu et al, 2013)
A smaller diameter mode of organics was observed in EP5_P compared to that of organics in EP3_P (Fig. 8), suggesting the contribution of organics from ultrafine particles was increased in EP5_P. These results indicated that local sources probably contributed more to organics in the peak stage of pollution episode during Asia-Pacific Economic Cooperation (APEC), as ultrafine particles primarily originating from local emission sources in urban locations (Canagaratna et al, 2004; Zhang et al, 2005)
We present a detailed investigation of the impacts of emission controls on changes in mass and number concentration, chemical composition and sources of fine particles
Summary
Atmospheric aerosols, especially fine particles of particulate matter (PM) with aerodynamic diameters of less than 2.5 μm, have significant impacts on air quality and visibility (Watson, 2002; Molina and Molina, 2004) and are detrimental to human health (Liu et al, 2013). Close relationship between particle number concentration and cardiovascular mortality has been reported in recent studies (Breitner et al, 2011; Leitte et al, 2011). All of these observations show that particle number concentration warrants equal or greater attention than mass concentration
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