Characterization and sources of carbonaceous aerosol in ambient PM1 in Qingdao, a coastal megacity of northern China from 2017 to 2022

Abstract

Organic carbon (OC) and elemental carbon (EC) are major chemical constituents of ambient submicron particles (PM1) and have substantial implications for air quality, climate dynamics, and human health. Long-term observations of daily mean mass concentrations of OC and EC in PM1 were conducted in Qingdao, a typical coastal megacity in northern China, in autumn and winter from Nov. 2017 to Jan. 2023. The variety in OC and EC concentrations under the active emission reduction policies of long-term carbon reduction in China, combined with the impact of the COVID-19 pandemic, were analyzed. OC and EC concentrations decreased noticeably from 8.28 ± 4.59 μg m−3 and 2.00 ± 1.17 μg m−3 during pre-COVID-19 pandemic to 6.34 ± 3.82 μg m−3 and 1.87 ± 1.01 μg m−3 during post-COVID-19 pandemic, respectively. The XGBoost-SHAP model indicated that emission sources had the most significant effect on OC and EC concentrations, followed by meteorological factors. Unfavorable meteorological conditions and a substantial increase in emissions are responsible for the increase of OC and EC concentration in winter. Potential source contribution function results indicated that the southern, eastern, and central Shandong regions were the primary source areas for transporting high concentrations of carbonaceous components. Positive matrix factorization analysis suggested that carbonaceous aerosols in Qingdao predominantly originated from coal/biomass combustion (54.75%–81.78%) and local vehicle emissions (8.72%–28.73%). Compared with that before COVID-19, coal/biomass combustion's contribution to OC and EC decreased by 19% after the COVID-19 pandemic. The contribution of vehicles increased by 110%, possibly due to the increase in motor vehicles and the rapid recovery in diesel consumption in freight transportation. Prohibiting biomass burning, such as open burning of straw, and measures such as promoting low-carbon and clean production of coal-fired industrial furnaces might have played a key role in reducing OC and EC levels. These results contribute to a deeper understanding of the concentration levels and sources of carbonaceous components in PM1 and provide theoretical guidance for environmental management.