The relationship between PM2.5 pollution and aerosol radiative forcing in a heavy industrial city, Taiyuan, in China

Abstract Rapid economic development had an important impact on the concentration of air pollutants and the aerosol properties in Taiyuan City, one of China's most important energy and heavy industry bases. Therefore, the long-term measurements of the optical and radiation properties of aerosols and air pollutants monitored by several urban sites in Taiyuan from 2013 to 2019 were analyzed. During the observation period, the multi-year mean concentrations of PM2.5, PM10, SO2, NO2 and CO were 65 ± 7 μg/m3, 129 ± 14 μg/m3, 57 ± 21 μg/m3, 45 ± 6 μg/m3, 1.45 ± 0.31 mg/m3, respectively. The concentrations of various pollutants were highest in winter (PM2.5: 90 μg/m3; PM10: 149 μg/m3; SO2: 109 μg/m3; NO2: 49 μg/m3; CO: 2.03 mg/m3). After the implementation of air pollution control in 2013, the annual mean concentrations of PM2.5, PM10, SO2 and CO in 2019 had been reduced by 28%, 29%, 73% and 47% respectively compared with those in 2013. But aerosol optical depth (AOD) and radiative forcing had no remarkable downtrend. Annual mean of AOD at 500 nm varied from 0.43 to 0.60 with high single scattering albedo (SSA), all above 0.91. Multi-year average radiative forcing at the top of atmosphere (TOA), interior of atmosphere (ATM), and bottom of the atmosphere (SFC) were − 2.68 ± 2.12 W/m2, 45.02 ± 3.14 W/m2, and − 47.46 ± 3.72 W/m2, respectively. And radiative forcing effects were strongest in winter (TOA: -5.74 ± 3.20 W/m2; ATM: 49.15 ± 3.85 W/m2; SFC: -54.83 ± 5.31 W/m2) due to the stronger anthropogenic emissions. The increase in humidity would increase the concentration of particulate matter and the extinction of the atmosphere. The increase of absorbing aerosols and scattering aerosols during the heating period in winter increased the aerosol radiative forcing, which would warm atmosphere and cool surface and then increase the stability of the atmosphere. Pollutants were difficult to diffuse and gradually accumulated thereby, and the radiative forcing effect continued to increase, forming positive feedback and making continuous pollution.