Insight into the composition of organic compounds ( ≥  C₆) in PM_2.5 in wintertime in Beijing, China

Abstract

Abstract. Organic matter is a major component of PM2.5 in megacities. In order to understand the detailed characteristics of organic compounds (≥ C6) at a molecular level on non-haze and haze days, we determined more than 300 organic compounds in the PM2.5 from an urban area of Beijing collected in November–December 2016 using two-dimensional gas chromatography coupled to time-of-flight mass spectrometry (GC × GC-ToF-MS). The identified organic compounds have been classified into groups, and quantitative methods were used to calculate their concentrations. Primary emission sources make significant contributions to the atmospheric organic compounds, and six groups (including n-alkanes, polycyclic aromatic hydrocarbons – PAHs, levoglucosan, branched alkanes, n-alkenes and alkyl-benzenes) account for 66 % of total identified organic compound mass. In addition, PAHs and oxygenated PAHs (O-PAHs) were abundant amongst the atmospheric organic compounds on both haze and non-haze days. The most abundant hydrocarbon groups were observed with a carbon atom range of C19–C28. In addition, the total concentration of unidentified compounds present in the chromatogram was estimated in the present study. The total identified compounds account for approximately 47 % of total organic compounds (≥ C6) in the chromatogram on both the non-haze and haze days. The total mass concentrations of organic compounds (≥ C6) in the chromatogram were 4.0 and 7.4 µg m−3 on the non-haze and haze days, respectively, accounting for 26.4 % and 18.5 % of organic matter, respectively, on those days estimated from the total organic carbon concentration. Ratios of individual compound concentrations between haze and non-haze days do not give a clear indication of the degree of oxidation, but the overall distribution of organic compounds in the chromatogram provides strong evidence that the organic aerosol is less GC volatile and hence more highly oxidized on haze days.

Role of black carbon in the formation of primary organic aerosols: Insights from molecular dynamics simulations

“…This selectivity of adsorption suggests that molecules with planar structures could form more stable and larger aggregates when interacting with BC in atmosphere. This is in keeping with previously reported correlations between the concentrations of aromatic compounds and aerosol PM, notably those of polycyclic aromatic hydrocarbons (PAHs) which could have been formed from small aromatic molecules (Haritash and Kaushik, 2009;Mu et al, 2017;Lyu et al, 2019;Richter and Howard, 2000;Marr et al, 2006;Elzein et al, 2019;Lv et al, 2016;Polidori et al, 2008).…”

Trans‐Regional Transport of Haze Particles From the North China Plain to Yangtze River Delta During Winter

“…As a result, air pollutants in haze events in the NCP are rapidly transported to downwind regions such as the YRD (Kang et al, 2019) or East China Sea (F. Wang et al, 2016). To date, most of studies have focused on physicochemical characteristics of aerosol particles and regional haze formation in the NCP or the YRD as two isolated regions (Cheng et al, 2013;Ge et al, 2018;Herrmann et al, 2014;Lyu et al, 2019;Wang, An, et al, 2014;S. Zhai et al, 2018).…”

Differences in the composition of organic aerosols between winter and summer in Beijing: a study by direct-infusion ultrahigh-resolution mass spectrometry

“…This unusually low concentration compared to the cited studies might be due to the fact that our campaign was conducted earlier in summer than the others. Studies have also shown that the formation rate of SO 2− 4 is particularly high during haze episodes, with a strong contribution from heterogeneous oxidation within haze droplets (Ma et al, 2018;Wang et al, S. S. Steimer et al: Differences in the composition of organic aerosols in Beijing 2006), leading to high maximum concentrations of sulfate during haze events, of which several strong ones occurred in winter during our campaign. While organosulfate formation has been primarily understood to be a secondary process, a recent direct-infusion UHRMS study of coal combustion by Song et al (2019) found 5 %-25 % of formulae in the methanol-extracted fraction to contain sulfur, indicating the potential importance of direct organosulfate emissions.…”