资源环境科技发展态势分析平台

Due to the complexity of emission sources, a better understanding of aerosol optical properties is required to mitigate climate change in China. Here, an intensive real-time measurement campaign was conducted in an urban area of China before and during the COVID-19 lockdown in order to explore the impacts of anthropogenic activities on aerosol light extinction and the direct radiative effect (DRE). The mean light extinction coefficient (b_ext) decreased from 774.7 ± 298.1 Mm⁻¹ during the normal period to 544.3 ± 179.4 Mm⁻¹ during the lockdown period. A generalised additive model analysis indicated that the large decline in b_ext (29.7 %) was due to sharp reductions in anthropogenic emissions. Chemical calculation of b_ext based on a ridge regression analysis showed that organic aerosol (OA) was the largest contributor to b_ext in both periods (45.1 %–61.4 %), and the contributions of two oxygenated OAs to b_ext increased by 3.0 %–14.6 % during the lockdown. A hybrid environmental receptor model combined with chemical and optical variables identified six sources of b_ext. It was found that b_ext from traffic-related emissions, coal combustion, fugitive dust, the nitrate and secondary OA (SOA) source, and the sulfate and SOA source decreased by 21.4 %–97.9 % in the lockdown, whereas b_ext from biomass burning increased by 27.1 %, mainly driven by the undiminished need for residential cooking and heating. An atmospheric radiative transfer model was further used to illustrate that biomass burning, rather than traffic-related emissions, became the largest positive effect (10.0 ± 10.9 W m⁻²) on aerosol DRE in the atmosphere during the lockdown. Our study provides insights into aerosol b_ext and DRE from anthropogenic sources, and the results imply the importance of controlling biomass burning for tackling climate change in China in the future.