Exploring the Change in PM2.5 and Ozone Concentrations Caused by Aerosol-Radiation Interactions and Aerosol-Cloud Interactions and the Relationship with Meteorological Factors

Aerosols can interact with other meteorological variables in the air via aerosol-radiation or aerosol-cloud interactions (ARIs/ACIs), thus affecting the concentrations of particle pollutants and ozone. The online-coupled model WRF-Chem was applied to simulate the changes in the PM2.5 (particulate matter less than 2.5 mu m in aerodynamic diameter) and ozone concentrations that are caused by these mechanisms in China by conducting three parallel sensitivity tests. In each case, availabilities of aerosol-radiation interactions and aerosol-cloud interactions were set differently in order to distinguish each pathway. Partial correlation coefficients were also analyzed using statistical tools. As suggested by the results, the ARIs reduced ground air temperature, wind speed, and planetary boundary height while increasing relative humidity in most places. Consequently, the ozone concentration in the corresponding region declined by 4%, with a rise in the local annual mean PM2.5 concentration by approximately 12 mu m/m(3). The positive feedback of the PM2.5 concentration via ACIs was also found in some city clusters across China, despite the overall enhancement value via ACIs being merely around a quarter to half that via ARIs. The change in ozone concentration via ACIs exhibited different trends. The ozone concentration level increased via ACIs, which can be attributed to the drier air in the south and the diminished solar radiation that is received in central and northern China. The correlation coefficient suggests that the suppression in the planetary boundary layer is the most significant factor for the increase in PM2.5 followed by the rise in moisture required for hygroscopic growth. Ozone showed a significant correlation with NO2, while oxidation rates and radiation variance were also shown to be vitally important.

Automated summary

The study shows that aerosols interact with meteorological variables, affecting particulate matter and ozone concentrations in China. Aerosol-radiation interactions reduce air temperature and wind speed while increasing humidity, leading to a rise in PM2.5 and a decline in ozone concentrations. Aerosol-cloud interactions contribute to a positive feedback on PM2.5 concentration in some city clusters.