Abstract
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.
Highlights
AsGnudlefaaoteersomcsoaiesl spnritsoicflieacsrgsienlyg were enhanced during periods with highInhsutmruidmityebnetcaautisoe nof fog processing of high concentration ofMperetchurosodrsSOa2n.dIn addition, the increased traffic-related HODAaetmaisSsiyosntaet mlowstemperature is highlighted
Similar to the results observed in summer (Sun et al, 2012), the NR-PM1 mass measured by the Aerosol Chemical Speciation Monitor (ACSM) tracks well the PM2.5 measured by the TEOM (r2 = 0.77, Fig. S1)
One of the reasons is the evaporative loss of semi-volatile materials (SVM, e.g., ammonium nitrate and semi-volatile organics) for the TEOM measurements that were operated at 50 ◦C (Eatough et al, 2003)
Summary
The non-refractory submicron (NR-PM1) aerosol species including organics, sulfate, nitrate, ammonium, and chloride were measured in situ at the same location as Sun et al (2012), i.e., Institute of Atmospheric Physics (IAP), Chinese Academy of Sciences, located between the 3rd and 4th ring road in Beijing, from 21 November 2011 to 20 January 2012 with an ACSM. The aerosol sampling setup and the ACSM operations in this study were the same as those in Sun et al (2012). The meteorology data (wind speed, wind direction, relative humidity (RH), temperature, pressure, precipitation and solar radiation) during this study were obtained from the IAP tower that. Is approximately 30 m away and the ground meteorology station that is ∼ 20 m away
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