Fossil and Non-fossil Fuel Sources of Organic and Elemental Carbonaceous Aerosol in Beijing, Shanghai, and Guangzhou: Seasonal Carbon Source Variation

Di Liu,Yanlin Zhang,Jun Li,Matthias Vonwiller,Guangcai Zhong,Yinjun Chen,Junwen Liu,Gan Zhang,Chongguo Tian,Pingqing Fu,Zhineng Cheng,Sönke Szidat

doi:10.4209/aaqr.2019.12.0642

Abstract

ABSTRACT We measured the radiocarbon isotope signals in various fractions of carbonaceous aerosols sampled across four seasons (Oct 2013–Jul 2014) in three megacities of China, viz., Beijing, Shanghai, and Guangzhou. The contributions of fossil fuel (FF) and non-fossil fuel (NF) to the carbonaceous aerosol were estimated based on the radiocarbon content in the organic carbon (OC), water-soluble organic carbon (WSOC), water-insoluble organic carbon (WIOC), and elemental carbon (EC). Although NF generated the primary share (> 55%) during autumn in all of the cities, the seasonal contributions of the sources differed by location during the rest of the year. During winter, FF emissions constituted the majority of the carbonaceous pollution (64%) in Beijing, probably as a result of increased coal combustion for heating. On average, the EC, WSOC, and WIOC generated by FF composed ~10%, 35%, and 19% of the total carbon (TC). Overall, NF was identified as the largest source of carbonaceous aerosol in Guangzhou (63%), whereas FF was the largest source, contributing slightly more than NF, in Shanghai (54%). During spring and summer, FF played a greater role than NF in Beijing (~55%) and Guangzhou (~63%); additionally, based on our limited number of samples, it contributed 71% in Shanghai during the latter season, with a significant portion due to fuel combustion (i.e., industrial, vehicular, fishing-boat, and large-vessel emissions).

Highlights

Large-scale pollution of fine particles occurs frequently, impacting air quality in the megacities of China due to massive and intensive pollutant emissions combined with unfavorable meteorological conditions
The pattern in Beijing was similar to those in Shanghai and Guangzhou, but the trend shifted to the opposite of those in Shanghai and Guangzhou when the winter samples were included. These results suggest that the fossil fuel secondary OC (SOC) in Beijing is sourced mainly from residential coal combustion during winter and from vehicle exhaust or industrial emissions during other seasons
Emissions arising from fossil fuel (FF) combustion dominated the elemental carbon (EC) (> 72%), whereas those derived from NF accounted for a slightly higher proportion of the organic carbon (OC) (50–55%)

Summary

Introduction

Large-scale pollution of fine particles (aerodynamic diameter ≤ 2.5 μm; PM2.5) occurs frequently, impacting air quality in the megacities of China due to massive and intensive pollutant emissions combined with unfavorable meteorological conditions. Using a recently developed method, source apportionment can be determined by measuring the radiocarbon (14C) content of OC and EC separately, which enables unambiguous differentiation between FF and non-FF (NF) sources (Liu et al, 2013; Liu et al, 2014; Zhang et al, 2015a; Liu et al, 2016; Zong et al, 2016; Liu et al, 2017c) This differentiation is possible because 14C is completely decayed in FF sources (i.e., diesel exhaust, gasoline exhaust and coal combustion), whereas NF sources (i.e., BB, cooking and biogenic emissions) exhibit contemporary 14C levels (Szidat et al, 2009). Even more precise 14C-based source apportionment can be obtained by dividing OC into WSOC and WIOC (Liu et al, 201; Zong et al, 20166; Zhang et al, 2017)

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Results

Conclusion