Source apportionment of carbonaceous aerosols in Beijing with radiocarbon and organic tracers: insight into the differences between urban and rural sites

Abstract

Abstract. Carbonaceous aerosol is a dominant component of fine particles in Beijing. However, it is challenging to apportion its sources. Here, we applied a newly developed method which combined radiocarbon (14C) with organic tracers to apportion the sources of fine carbonaceous particles at an urban (IAP) and a rural (PG) site of Beijing. PM2.5 filter samples (24 h) were collected at both sites from 10 November to 11 December 2016 and from 22 May to 24 June 2017. 14C was determined in 25 aerosol samples (13 at IAP and 12 at PG) representing low pollution to haze conditions. Biomass burning tracers (levoglucosan, mannosan, and galactosan) in the samples were also determined using gas chromatography–mass spectrometry (GC-MS). Higher contributions of fossil-derived OC (OCf) were found at the urban site. The OCf / OC ratio decreased in the summer samples (IAP: 67.8 ± 4.0 % in winter and 54.2 ± 11.7 % in summer; PG: 59.3 ± 5.7 % in winter and 50.0 ± 9.0 % in summer) due to less consumption of coal in the warm season. A novel extended Gelencsér (EG) method incorporating the 14C and organic tracer data was developed to estimate the fossil and non-fossil sources of primary and secondary OC (POC and SOC). It showed that fossil-derived POC was the largest contributor to OC (35.8 ± 10.5 % and 34.1 ± 8.7 % in wintertime for IAP and PG, 28.9 ± 7.4 % and 29.1 ± 9.4 % in summer), regardless of season. SOC contributed 50.0 ± 12.3 % and 47.2 ± 15.5 % at IAP and 42.0 ± 11.7 % and 43.0 ± 13.4 % at PG in the winter and summer sampling periods, respectively, within which the fossil-derived SOC was predominant and contributed more in winter. The non-fossil fractions of SOC increased in summer due to a larger biogenic component. Concentrations of biomass burning OC (OCbb) are resolved by the extended Gelencsér method, with average contributions (to total OC) of 10.6 ± 1.7 % and 10.4 ± 1.5 % in winter at IAP and PG and 6.5 ± 5.2 % and 17.9 ± 3.5 % in summer, respectively. Correlations of water-insoluble OC (WINSOC) and water-soluble OC (WSOC) with POC and SOC showed that although WINSOC was the major contributor to POC, a non-negligible fraction of WINSOC was found in SOC for both fossil and non-fossil sources, especially during winter. In summer, a greater proportion of WSOC from non-fossil sources was found in SOC. Comparisons of the source apportionment results with those obtained from a chemical mass balance model were generally good, except for the cooking aerosol.

Fossil and Nonfossil Sources of Winter Organic Aerosols in the Regional Background Atmosphere of China

“…This method incorporates the mass concentrations of carbonaceous components and Levoglucosan (Lev), along with the estimated emission ratios and 14 C content of TC. This method was initially conceived for studies conducted in Europe and has been refined for applications in China. ,, The detailed methodology is presented as follows.…”

“…This method was initially conceived for studies conducted in Europe 30 and has been refined for applications in China. 13,19,31 The detailed methodology is presented as follows.…”

“…18 However, due to diverse emission sources and complex climatic conditions, the sources and concentrations of various carbonaceous aerosol components differ significantly within different regions of China. For example, in the winter of 2016, nonfossil sources contributed to 32% of TC in Beijing, 19 compared to 41% in Pinggu 19 and 48% in Nanjing. 16 Therefore, collecting CA that can represent regional atmospheric CA and determining their 14 C isotope signal can deepen our insight into the characteristics and sources of CA in different regions of China.…”

On the fossil and non-fossil fuel sources of carbonaceous aerosol with radiocarbon and AMS-PMF methods during winter hazy days in a rural area of North China plain

“…coal combustion and vehicle exhaust) and non-fossil sources (e.g. biomass burning, vegetation emission, cooking) (Hou et al, 2021;Minguillón et al, 2011;Sun et al, 2019).…”

“…biomass burning or biogenic emissions) contain contemporary 14 C (Heal, 2014;. Filter-based radiocarbon analyses apportioned the sources of fossil and non-fossil to particulate matter in China (Hou et al, 2021;Liu et al, 2017;Liu et al, 2020;Zhang et al, 2017a;Zhou et al, 2017). Positive matrix factorization (PMF) (Ulbrich et al, 2009) and a multilinear engine (ME-2) (Canonaco et al, 2013) modelling of high time resolution organic mass spectrometric data from aerosol mass spectrometer (AMS) have also been used to resolve organics into various OA factors, which correspond to different sources and processes.…”