Intra-regional transport of black carbon between the south edge of the North China Plain and central China during winter haze episodes

Abstract

Abstract. Black carbon (BC), which is formed from the incomplete combustion of fuel sources (mainly fossil fuel, biofuel and open biomass burning), is a chemically inert optical absorber in the atmosphere. It has significant impacts on global climate, regional air quality and human health. During transportation, its physical and chemical characteristics as well as its sources change dramatically. To investigate the properties of BC (i.e., mass concentration, sources and optical properties) during intra-regional transport between the southern edge of the North China Plain (SE-NCP) and central China (CC), simultaneous BC observations were conducted in a megacity (Wuhan – WH) in CC, in three borderline cities (Xiangyang – XY, Suixian – SX and Hong'an – HA; from west to east) between the SE-NCP and CC, and in a city (Luohe – LH) in the SE-NCP during typical winter haze episodes. Using an Aethalometer, the highest equivalent BC (eBC) mass concentrations and the highest aerosol absorption coefficients (σabs) were found in LH in the SE-NCP, followed by the borderline cities (XY, SX and HA) and WH. The levels, sources, optical properties (i.e., σabs and absorption Ångström exponent, AAE) and geographic origins of eBC were different between clean and polluted periods. Compared with clean days, higher eBC levels (26.4 %–163 % higher) and σabs (18.2 %–236 % higher) were found during pollution episodes due to the increased combustion of fossil fuels (increased by 51.1 %–277 %), which was supported by the decreased AAE values (decreased by 7.40 %–12.7 %). The conditional bivariate probability function (CBPF) and concentration-weighted trajectory (CWT) results showed that the geographic origins of biomass burning (BCbb) and fossil fuel (BCff) combustion-derived BC were different. Air parcels from the south dominated for border sites during clean days, with contributions of 46.0 %–58.2 %, whereas trajectories from the northeast showed higher contributions (37.5 %–51.2 %) during pollution episodes. At the SE-NCP site (LH), transboundary influences from the south (CC) exhibited a more frequent impact (with air parcels from this direction comprising 47.8 % of all parcels) on the ambient eBC levels during pollution episodes. At WH, eBC was mainly from the northeast transport route throughout the observation period. Two transportation cases showed that the mass concentrations of eBC, BCff and σabs all increased, from upwind to downwind, whereas AAE decreased. This study highlights that intra-regional prevention and control for dominant sources at each specific site should be considered in order to improve the regional air quality.

Heavy air pollution with a unique “non-stagnant” atmospheric boundary layer in the Yangtze River middle basin aggravated by regional transport of PM<sub>2.5</sub> over China

“…Due to the specialized location of the YRMB as a regional air pollutant transport hub with subbasin topography (Fig. 1b), the regional transport of air pollutants driven by the cold air flows of the East Asian winter monsoon over the CEC can create a special source-receptor relationship between the source regions of haze pollution in the upstream and the downwind YRMB region (Zhong et al, 2019). However, there are unresolved questions regarding the meteorological processes involved in the regional transport of air pollutants and the patterns of regional transport over CEC that may contribute to the air pollution changes observed in the YRMB area.…”

Effectiveness of emission control to reduce PM<sub>2.5</sub> pollution of Central China during winter haze episodes under various potential synoptic controls

“…1). As a regional pollutant transport hub with sub basin topography, Central China is a region of transportation-pollution characteristics affected by two reported transport pathways from the vast flatland in central eastern China (Yu et al, 2020) and from the NCP region (Zheng et al, 2019a). In combination with high anthropogenic emissions and secondary aerosol formation (Huang et al, 2020), Central China often suffers severe pollution episodes in winter caused by PM 2.5 (Gong et al, 2015;Xu et al, 2017).…”

Optical source apportionment and radiative forcing of light-absorbing carbonaceous aerosol at a tropical marine monsoon climate zone: the importance of ship emissions

“…This method can typically explain two different types of sources (e.g., fossil fuel versus biomass burning) that contribute to LAC light absorption, and the results are highly relied on the source-specific absorption Ångström exponent (AAE) used in models. However, owing to the lack of access to obtaining these AAE data, most studies applied empirical values reported in other literatures (e.g., Healy et al, 2017;Küpper et al, 2018;Zheng et al, 2019). This may lead to a large uncertainty to the results, because the source-specific AAEs are site-dependent variables and varies with fuel types and their burning efficiencies (Tian et al, 2019).…”