Abstract
Wintertime East Asia is plagued by severe haze episodes, characterized by large contributions of carbonaceous aerosols. However, the sources and atmospheric transformations of these major components are poorly constrained, hindering development of efficient mitigation strategies and detailed modelling of effects. Here we present dual carbon isotope (δ13C and Δ14C) signatures for black carbon (BC), organic carbon (OC) and water-soluble organic carbon (WSOC) aerosols collected in urban (Beijing and BC for Shanghai) and regional receptors (e.g., Korea Climate Observatory at Gosan) during January 2014. Fossil sources (>50%) dominate BC at all sites with most stemming from coal combustion, except for Shanghai, where liquid fossil source is largest. During source-to-receptor transport, the δ13C fingerprint becomes enriched for WSOC but depleted for water-insoluble OC (WIOC). This reveals that the atmospheric processing of these two major pools are fundamentally different. The photochemical aging (e.g., photodissociation, photooxidation) during formation and transport can release CO2/CO or short-chain VOCs with lighter carbon, whereas the remaining WSOC becomes increasingly enriched in δ13C. On the other hand, several processes, e.g., secondary formation, rearrangement reaction in the particle phase, and photooxidation can influence WIOC. Taken together, this study highlights high fossil contributions for all carbonaceous aerosol sub-compartments in East Asia, and suggests different transformation pathways for different classes of carbonaceous aerosols.
Highlights
Carbonaceous aerosols (CA) – including black carbon (BC, or elemental carbon, EC) and organic carbon (OC) – are large components (35‒50%) of PM2.51 in East Asia[8]
Technology-based emission inventories (EI) estimate that anthropogenic BC and OC emissions from East Asia contribute more than 20% of current global emissions[8, 10, 11]
Contributions, implying potentially factors of 2–4 uncertainties in BC and OC EIs10–12. This is reflected in the relative contributions from fossil fuel combustion being systematically under-predicted by EI models relative to atmospheric-observational 14C-based diagnostic source apportionment of BC, for both South Asia and East Asia[3, 10, 13,14,15,16]
Summary
Wenzheng Fang[1], August Andersson[1], Mei Zheng[2], Meehye Lee[3], Henry Holmstrand[1], Sang-Woo Kim[4], Ke Du 5 & Örjan Gustafsson[1]. The Chinese Government has issued far-reaching policies to combat air pollution such as the ‘Action Plan for Air Pollution Prevention and Control (2013‒2017)’ and ‘Coordinated Development of Ecological Environment Protection Plan in Beijing-Tianjin-Hebei area’ (2015); with the latter plan including a mandatory 40% reduction in annual average concentrations of PM2.5 by 2020 in Beijing compared to 20136, 7 Achieving such ambitious goals remains a challenge in part due to large uncertainties concerning the contributions from different emission sources and complex atmospheric processes. Contributions (from technology-based emission inventory databases), implying potentially factors of 2–4 uncertainties in BC and OC EIs10–12 This is reflected in the relative contributions from fossil fuel combustion (versus biomass burning) being systematically under-predicted by EI models relative to atmospheric-observational 14C-based diagnostic source apportionment of BC, for both South Asia and East Asia[3, 10, 13,14,15,16]. Knowledge about the sources and processing of carbonaceous aerosol components from this study facilitate an improved estimate of aerosol-induced climate and health impacts, and a scientific underpinning for developing a regionally-tailored mitigation strategy for different areas and source profiles in East Asia
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