Aerosol composition, sources and processes during wintertime in Beijing, China

Abstract

Air pollution is a major environmental concern during all seasons in the megacity of Beijing, China. Here we present the results from a winter study that was conducted from 21 November 2011 to 20 January 2012 with an Aerodyne Aerosol Chemical Speciation Monitor (ACSM) and various collocated instruments. The non-refractory submicron aerosol (NR-PM₁) species vary dramatically with clean periods and pollution episodes alternating frequently. Compared to summer, wintertime submicron aerosols show much enhanced organics and chloride, which on average account for 52% and 5%, respectively, of the total NR-PM₁ mass. All NR-PM₁ species show quite different diurnal behaviors between summer and winter. For example, the wintertime nitrate presents a gradual increase during daytime and correlates well with secondary organic aerosol (OA), indicating a dominant role of photochemical production over gas–particle partitioning. Positive matrix factorization was performed on ACSM OA mass spectra, and identified three primary OA (POA) factors, i.e., hydrocarbon-like OA (HOA), cooking OA (COA), and coal combustion OA (CCOA), and one secondary factor, i.e., oxygenated OA (OOA). The POA dominates OA during wintertime, contributing 69%, with the other 31% being SOA. Further, all POA components show pronounced diurnal cycles with the highest concentrations occurring at nighttime. CCOA is the largest primary source during the heating season, on average accounting for 33% of OA and 17% of NR-PM₁. CCOA also plays a significant role in chemically resolved particulate matter (PM) pollution as its mass contribution increases linearly as a function of NR-PM₁ mass loadings. The SOA, however, presents a reverse trend, which might indicate the limited SOA formation during high PM pollution episodes in winter. The effects of meteorology on PM pollution and aerosol processing were also explored. In particular, the sulfate mass is largely enhanced during periods with high humidity because of fog processing of high concentration of precursor SO₂. In addition, the increased traffic-related HOA emission at low temperature is also highlighted

Persistent sulfate formation from London Fog to Chinese haze

“…2A). Hence, SO 4 2− and NO 3 − in fine PM are completely neutralized, because of the presence of high levels of gaseous ammonia (17)(18)(19)(20)(21)(22)(23) , and Cl − ) is also near unity (Fig. 2B and SI Appendix, Fig.…”

“…Hence, the acidity, hygroscopicity, and RH represent the key factors for sulfate formation on fine PM, explaining the differences in the various ambient measurements (14,(20)(21)(22)(23)(24)(25). For example, the acidity effect on fine aerosols is effectively overcome by NH 3 neutralization in Xi'an and Beijing (Fig.…”

“…A model simulation of dissolution of NO 2 in cloud droplets under NO x -rich environments has shown enhanced regional wintertime sulfate by up to 20%, resulting in better agreement between simulations and observations (13). Also, atmospheric measurements have revealed high sulfate production during severe haze events in China (21)(22)(23)(24)(25), which cannot be explained by current atmospheric models and suggests missing sulfur oxidation mechanisms (14). Typically, high sulfate levels during haze events in China occurred with concurrently elevated RH, NO x , and NH 3 (24,25), implicating an aqueous sulfur oxidation pathway.…”

Nitrogen dioxide measurement by cavity attenuated phase shift spectroscopy (CAPS) and implications in ozone production efficiency and nitrate formation in Beijing, China

“…The detailed descriptions of ACSM measurements can be found in Sun et al [2012Sun et al [ , 2013. In addition, all the data in this study are reported at Beijing local time which equals Coordinated Universal Time (UTC) plus 8 h.…”

Numerical Investigation of the Diffusion Feature of Aerosol

“…Large plenty of researches have been conducted for the purpose of understanding the size distribution and components [7,8] , optical characteristics [9,10] , and physicochemical properties of aerosol particles [2,11] . The transportation and diffusion of aerosol is vital for the prediction of affected area and the exploration of the emission source.…”