Divergent Evolution of Carbonaceous Aerosols during Dispersal of East Asian Haze

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.

Dual‐Isotope Constraints on Seasonally Resolved Source Fingerprinting of Black Carbon Aerosols in Sites of the Four Emission Hot Spot Regions of China

“…Previous studies reported that for urban environments in China, the daily average PM 2.5 (particulate matter with aerodynamic diameter ≤ 2.5 μm) levels for January both of 2013 and 2014 were observed to be 10 times higher than the recommended daily maximum level (25 μg/m 3 ) of the World Health Organization (e.g., Andersson et al, ; Fang et al, ; Sheehan et al, ; World Health Organization ). The daily values during haze days are also much higher than China's new Ambient Air Quality Standards for daily PM 2.5 (35 and 75 μg m −3 for Category I and II zones, respectively; Chinese Ministry of Environmental Protection, ).…”

“…High BC emissions in China is a contributing factor to the very high concentrations of aerosols during severe haze events (e.g., Ding et al, ; Fang et al, ; Qin & Xie, ). However, bottom‐up technology‐based emission inventories (EIs) are acknowledged to carry an uncertainty by factors of 2–4 for BC, with the uncertainty stemming largely from variations in BC emission factors (EF, mass of BC emitted per mass fuel consumed, or product produced) but also from uncertainties in activity estimates (e.g., energy consumption data; e.g., Bond et al, ; Lu et al, ; Wang et al, ; Zhao et al, ).…”

“…However, bottom‐up technology‐based emission inventories (EIs) are acknowledged to carry an uncertainty by factors of 2–4 for BC, with the uncertainty stemming largely from variations in BC emission factors (EF, mass of BC emitted per mass fuel consumed, or product produced) but also from uncertainties in activity estimates (e.g., energy consumption data; e.g., Bond et al, ; Lu et al, ; Wang et al, ; Zhao et al, ). Observationally based studies are combining to demonstrate that the relative contributions of biomass burning versus fossil fuel combustion estimated by bottom‐up EIs are systematically inconsistent with observationally‐based (i.e., top‐down) diagnostic source apportionment of BC in East Asia based on the 14 C‐BC fingerprint (Andersson et al, ; Chen et al, ; Fang et al, ; Li et al, ; Liu, Mo, et al, ; Ni et al, ; Zhang et al, ). These 14 C‐based source apportionments of BC showed that fossil source is dominant in East Asian urban areas (e.g., Beijing, Shanghai, and Guangzhou) and ~50% in Himalayan‐Tibetan Plateau.…”

“…Recently, the application of dual‐carbon isotopes (radiocarbon 14 C/ 12 C and stable carbon isotope ratio 13 C/ 12 C) of BC (here refer to elemental carbon (EC), the commonly used mass analog isolate of BC) have proven the ability to quantitatively quantify the relative contribution from different combustion sources ― coal combustion, liquid fossil combustion (e.g., oil, diesel, and gasoline), and biomass burning (Andersson et al, ; Chen et al, ; Fang et al, ; Li et al, ; Winiger et al, ). The 14 C in fossil sources are completely depleted while the (modern) biomass sources has a distinct 14 C/ 12 C signature, allowing calculating the fraction of fossil versus biomass with high resolution.…”

Evidence of Rural and Suburban Sources of Urban Haze Formation in China: A Case Study From the Pearl River Delta Region

“…Radiocarbon ( 14 C, half-life = 5,730 years) is a state-of-the-art tracer that can directly and clearly separate OC and EC into fossil (e.g., coal and petroleum) and nonfossil (e.g., BB and biogenic emissions) sources based on the fact that the fraction of modern carbon (f m ) is very close to 1 in nonfossil materials while the f m value in fossil fuels is 0 (Szidat, 2009). There is a growing number of 14 C-based studies in China Chen et al, 2013;W. Fang et al, 2017;Huang et al, 2014;J.…”