Abstract
Abstract. To ensure good air quality for the 2014 Asia-Pacific Economic Cooperation (APEC) summit, stringent emission controls were implemented in Beijing and its surrounding regions, leading to a significant reduction in PM2.5 loadings. To investigate the impact of the emission controls on aerosol chemistry, high-volume PM2.5 samples were collected in Beijing from 8 October to 24 November 2014 and determined for secondary inorganic aerosols (SIA, i.e., SO42−, NO3−, and NH4+), dicarboxylic acids, keto-carboxylic acid, and α-dicarbonyls, as well as stable carbon isotope composition of oxalic acid (C2). Our results showed that SIA, C2, and related secondary organic aerosols in PM2.5 during APEC were 2–4 times lower than those before APEC, which is firstly ascribed to the strict emission control measures and secondly attributed to the relatively colder and drier conditions during the event that are unfavorable for secondary aerosol production.C2 in the polluted air masses, which mostly occurred before APEC, are abundant and enriched in 13C. On the contrary, C2 in the clean air masses, which mostly occurred during APEC, is much less abundant but still enriched in 13C. In the mixed type of clean and polluted air masses, which mostly occurred after APEC, C2 is lower than that before APEC but higher than that during APEC and enriched in lighter 12C. A comparison on chemical composition of fine particles and δ13C values of C2 in two events that are characterized by high loadings of PM2.5 further showed that after APEC SIA and the total detected organic compounds (TDOC) are much less abundant and fine aerosols are enriched with primary organics and relatively fresh, compared with those before APEC.
Highlights
Atmospheric aerosols profoundly impact the global climate directly by scattering and absorbing solar radiation and indirectly by affecting cloud formation and distribution via acting as cloud condensation nuclei (CCN) and ice nuclei (IN)
The mass ratio of NO−3 / SO24− in PM2.5 during the whole study time is 1.8 ± 1.9 (Table 1), which is in agreement with the ratio (1.6– 2.4) for PM1 observed during the same time by using aerosol mass spectrometry (AMS; Sun et al, 2016)
Temporal variations in molecular distribution of SIA, dicarboxylic acids, ketoacids, α-dicarbonyl, and stable carbon isotopic composition (δ13C) of C2 in PM2.5 collected in Beijing before, during and after the 2014 Asia-Pacific Economic Cooperation (APEC) were investigated
Summary
Atmospheric aerosols profoundly impact the global climate directly by scattering and absorbing solar radiation and indirectly by affecting cloud formation and distribution via acting as cloud condensation nuclei (CCN) and ice nuclei (IN). To ensure good air quality for the summit, a joint strict emission control program was conducted from 3 November 2014 in Beijing and its neighboring provinces including Inner Mongolia, Shanxi, Hebei, and Shandong provinces During this period thousands of factories and power plants with high emissions were shut down and/or halted, all the construction activities were stopped, and the numbers of on-road vehicles were reduced. 2015) and a term of “APEC blue” being created to refer to the good air quality Such strong artificial intervening reduced PM2.5 and its precursors’ loadings in Beijing and its surrounding areas and affected the composition and formation mechanisms of the fine particles (Sun et al, 2016)
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