Identification of Visibility Reducing Weather Phenomena Due to Aerosols

Abstract

Visibility reduction is usually caused by hydrometeor and lithometeor such as precipitation, fog, mist, haze, and dust. Among these weather phenomena the distinction of mist, haze and Asian dust is very difficult for naked observers especially for the case of mist and damp haze. A method for the distinction of mist, haze and Asian dust has been developed using the synoptic surface weather reporting data and the size segregated aerosol data (PM₁, PM_2.5 and PM₁₀) monitored at six sites over South Korea for three years (2009 to 2011). It is found that mist can be identified from haze with the use of observed water vapor mixing ratio and its 15-day trend curve for the data exceeding the minimum PM₁₀ concentration that causes visibility reduction at each monitoring site; Asian dust events are identified with conditions of hourly mean PM₁₀ concentration exceeding 90 mg m^-3 and the ratio of PM₁₀/PM₁ ≥ 4. It is also found that the visibility reducing weather events (occurrence frequency) are haze (23 %), mist (19 %), precipitation (13 %), fog (9 %) and Asian dust (1.1 %) in order at the island site, while those events (occurrence frequency) are haze (29 %), mist (21 %), precipitation (13 %), Asian dust (2.1 %) and fog (0.3 %) in order at the inland site, indicating more frequent occurrence of fog events at the island site. However, haze and mist events are found to occur most frequently at both the island and the inland sites caused by anthropogenic aerosols.