Characteristics of visibility-impairing aerosol observed during the routine monitoring periods in Gwangju, Korea

Aerosol chemistry measurements were performed during the routine monitoring periods in the urban atmosphere of Gwangju, Korea. Routine aerosol monitoring was carried out every sixth day in order to investigate the dependence of domestic sources and air mass transport characteristics on physicochemical and optical properties of atmospheric aerosol. Aerosol optical properties; atmospheric extinction and scattering coefficients were also measured continuously with a transmissometer and a nephelometer, respectively in order to investigate the causes of visibility impairment. Prevailing atmospheric condition was classified into four categories; one affected by stagnant condition (D), one affected by continental and domestic aerosols (CD), one affected by marine and domestic aerosols (MD), and one affected by continental, marine and domestic aerosols (CMD). Atmospheric condition type was further classified into thirteen sub-categories with the occurrences of episodic events such as Asian dust storm, biomass burning, and airborne pollen. The air mass types of D, CD, MD, and CMD were observed to be 11, 18, 43, and 78 events out of total 150 events, respectively. The fine mass concentration increased under continental air mass types. The average fine mass concentration of 23.0 ± 8.6 μg m⁻³ for CD type was slightly larger than that of 20.7 ± 5.2 μg m⁻³ for CMD type. Both of them were higher than that for D (18.9 ± 4.5 μg m⁻³) type. Increments of the fine mass concentrations for Asian dust storm (A) and Biomass-burning (B) events ranged from 141 to 151% and from 152 to 160% compared to those for D and CD types, respectively. The increments in the mass concentrations of nitrate, OC, EC, and BC for CD and CMD types in comparison with D air mass type were calculated to be approximately 17, 6, 8, and 22%, respectively. The mean mass extinction efficiency of PM10 was relatively higher in D (3.6 ± 1.6 m² g⁻¹) type and B events (4.1 ± 1.5 m² g⁻¹), but it was the lowest in MD air mass type. The aerosols observed in Gwangju were found to be influenced by the continental aerosol during the A events. Aerosol of CMD air mass type caused mainly poor visibility. The visibility reduction of Gwangju was influenced by the increase of carbonaceous particles under both domestically stagnant condition and air mass pathway from the continent. And ammonium sulfates and ammonium nitrates contributed the largest in CMD air mass type.