215 / 2023-04-02 15:27:18

Aging of mineral dust in the polluted environment and its role in scavenging anthropogenic aerosols

Mineral dust; anthropogenic aerosols; particle depolarization ratio; backscattering Ångström exponent

Aging of mineral dust in anthropogenic polluted environment was investigated in this work based on comprehensive observations of a long durative dust event from March 15 to 18, 2021 over northern China. The morphology and size of dust particles in dust event were analyzed by parameters of particle depolarization ratio (PDR) and backscattering Ångström exponent (BAE), respectively, which were calculated on observations of a Raman-depolarization lidar (355nm, 387 nm) and a micro-pulse lidar (532 nm). The BAE of dust particles increased in dust event, indicating that the averdaged size of dust particles decreased due to high deposition velocities of coarse particles. Moreover, the PDR of dust particles decreased in dust event, e.g., from 0.24 at 09:00 on March 15 to 0.12 at 00:00 on March 18, indicating that dust particles become more spherical in a polluted environment likely due to mixing with anthropogenic aerosols. The vertical profile of the PDR shows that the averaged PDR in the 0-500 m layer was smaller than that in the 500-3000 m layer, which confirmed the mixing of mineral dust with anthropogenic aerosols was enhanced in the polluted low layer. A sharp decrease in anthropogenic aerosol in PM_2.5 during dust event, especially for inorganic components, supports above viewpoint. The mass concentration of anthropogenic aerosol in PM_2.5 decreased by 78% in dust event though its precursors NO_x and SO₂ increased by 13% and 28%. Further analyses suggest that such a decrease of anthropogenic aerosol in PM_2.5 is caused by the coating of fine anthropogenic aerosols on coarse dust particles, rather than weakened chemical reactions. Dust particles own high deposition velocity due to their coarse size. Hence, dust particles enhance the scavenging of anthropogenic aerosols.