Mist Cannon Trucks Can Exacerbate Secondary Organic Aerosol Formation and PM_2.5 Pollution in the Road Environment

Abstract. Mist cannon trucks have been widely applied in megacities in China to reduce the road dust. Their practical effect on controlling the formation of secondary organic aerosol and fine particles remains unknown. We characterized the chemical composition variations in PM2.5 collected on the road sides with the simulated operations of mist cannon truck and traditional sprinkling truck via Fourier transform ion cyclotron resonance mass spectrometry and ion chromatography. The mass concentrations of water-soluble organic carbon in PM2.5 showed a significant increase (62–70 %) after air spraying. Further, we found that secondary organic aerosols, particularly organic nitrates, increased significantly via the interactions of reactive gas-phase organics, atmospheric oxidants, and aerosol liquid water after air spraying, although the air spraying had a better effect on suppressing road dust than the ground aspersion. Moreover, the formation of PM2.5 in the road segment where the mist cannon truck passed was promoted, with an increase of up to 13 % in mass concentration after 25–35 minutes, on average. The application of mist cannon trucks undoubtedly worsens the road atmospheric environment and causes health hazards to walking residents. The overall results provide not only valuable insights to the formation processes of secondary organic aerosols associated with aerosol liquid water in the road environment but also management strategies to regulate the mist cannon truck operation in China.