Long-term Source Apportionment of Black Carbon in Beijing and Changes during the COVID-19 Period in Urban and Plateau Region in China

Abstract:

Black carbon (BC) plays an important role in climate change, air quality and human health. Due to high emissions of BC in China, BC in both urban and plateau region in China has received great attention. In this study, high time resolution measurement (1 min) of BC was conducted for four years in Beijing and for one year in the Tibetan Plateau including the COVID-19 pandemic period (from January to March 2020). Our objective is to examine the trend and changes of BC sources in the past few years in Beijing and the impacts of emission reduction and meteorology during the COVID-19 period in two different regions (Beijing and the Tibet Plateau). BC measured by the 7-wavelength Aethalometer (AE-33), along with other chemical components including organic carbon by a Sunset instrument, multiple metals by the Xact 625, and ions by the IGAC (in-situ Gas and Aerosol Compositions monitor) were combined to identify sources of BC by the receptor model in Beijing while Aethalometer model was conducted in Tibet. Our findings include that (1) BC concentration in Beijing has significantly decreased from 2016 to 2019, (2) traffic source was the predominant source for BC in non-haze periods while the contribution of coal combustion and biomass burning sources increased during haze periods in Beijing, (3) under the policy control and emission reduction in 2017, it could be seen that Beijing has an effective control of coal combustion source as the contribution of coal combustion to BC decreased the most in 2017 by about 80%. However, at the same time, there is an increased importance of traffic source to BC in Beijing with the relative contribution increased to 44% in 2017, and (4) during our study period of the COVID-19 pandemic, BC in Tibetan Plateau decreased by over 80% while it increased in Beijing due to a few heavy pollution episodes experienced in Beijing in February 2020.