Exploring wintertime regional haze in northeast China: role of coal and biomass burning

Abstract

Abstract. As one of the intense anthropogenic emission regions across the relatively high-latitude (>40∘ N) areas on Earth, northeast China faces the serious problem of regional haze during the heating period of the year. Aerosols in polluted haze in northeast China are poorly understood compared with the haze in other regions of China such as the North China Plain. Here, we integrated bulk chemical measurements with single-particle analysis from transmission electron microscopy (TEM), nanoscale secondary ion mass spectrometry (NanoSIMS), and atomic force microscopy (AFM) to obtain morphology, size, composition, aging process, and sources of aerosol particles collected during two contrasting regional haze events (Haze-I and Haze-II) at an urban site and a mountain site in northeast China and further investigated the causes of regional haze formation. Haze-I evolved from moderate (average PM2.5: 76–108 µg m−3) to heavy pollution (151–154 µg m−3), with the dominant PM2.5 component changing from organic matter (OM) (39–45 µg m−3) to secondary inorganic ions (94–101 µg m−3). Similarly, TEM observations showed that S-rich particles internally mixed with OM (named S-OM) increased from 29 % to 60 % by number at an urban site and 64 % to 74 % at a mountain site from the moderate Haze-I to heavy Haze-I events, and 75 %–96 % of Haze-I particles included primary OM. We found that change of wind direction caused Haze-I to rapidly turn into Haze-II (185–223 µg m−3) with predominantly OM (98–133 µg m−3) and unexpectedly high K+ (3.8 µg m−3). TEM also showed that K-rich particles internally mixed with OM (named K-OM) increased from 4 %–5 % by number to 50 %–52 %. The results indicate that there were different sources of aerosol particles causing the Haze-I and Haze-II formation: Haze-I was mainly induced by accumulation of primary OM emitted from residential coal burning and further deteriorated by secondary aerosol formation via heterogeneous reactions; Haze-II was caused by long-range transport of agricultural biomass burning emissions. Moreover, abundant primary OM particles emitted from coal and biomass burning were considered to be one typical brown carbon, i.e., tar balls. Our study highlights that large numbers of light-absorbing tar balls significantly contribute to winter haze formation in northeast China and they should be further considered in climate models.

Spatiotemporal variations and reduction of air pollutants during the COVID-19 pandemic in a megacity of Yangtze River Delta in China

“…Concentration-weighted trajectory (CWT) analysis, which is based on the backward trajectory, can be employed to identify the transport event and estimate the contribution of air pollutants from different regions ( Zhang et al, 2020a ). In this study, 72-h air mass backward trajectories with one-hour resolution were calculated with an ending height of 500 m above ground level based on the meteorological data sets from the Nation Oceanic Atmospheric Administration (NOAA) ( ftp://arlftp.arlhq.noaa.gov/pub/archives/gdas1 ).…”

Measurement report: Comparison of wintertime individual particles at ground level and above the mixed layer in urban Beijing

“…Most of the OPs in our study were spherical or nearly spherical in shape according to the projected images, suggesting that they were formed through cooling process after the biomass or fossil fuel combustion pyrolysis products of volatile organic compounds were emitted into the atmosphere (Wang et al, 2015;Chen et al, 2017;Zhang et al, 2017). These spherical or near spherical OPs were considered to be brown carbon (Zhang et al, 2020). Brown carbon plays a significant role in atmospheric shortwave absorption and can cause warming of the atmosphere https://doi.org/10.5194/acp-2020-1031 Preprint.…”

Persistent residential burning-related primary organic particles during wintertime hazes in North China: insights into their aging and optical changes

“…Considering the adverse effects of residential coal and biomass burning on haze formation and climate change, we suggest that authorities should continue to implement "clean air actions" (Zhang and Geng, 2019) and especially encourage the use of clean energy such as electricity and natural gas for heating and cooking in rural areas of North China in winter.…”