Comparison of characteristics of aerosol during rainy weather and cold air-dust weather in Guangzhou in late March 2012

Using the data on aerosol observed hourly by Marga ADI 2080 and Grimm 180, we compared the characteristics of aerosol during rainy weather and cold air-dust weather in Guangzhou in late March 2012. The mass concentration of aerosol appeared distinct between the two weather processes. During rainy weather, the mass concentration of PM and total water-soluble components decreased obviously. During cold air-dust weather, the cleaning effect of cold air occurred much more suddenly and about a half day earlier than the dust effect. As a result, the mass concentration of PM and total water-soluble components first dropped dramatically to a below-normal level and then rose gradually to an above-normal level. The ratio of PM₂.₅/PM₁₀ and PM₁/PM₁₀ decreased, suggesting that dust-storm weather mainly brought in coarse particles. The proportion of Ca²⁺ in the total water-soluble components significantly increased to as high as 50 % because of the effect of dust weather. We further analysed the ionic equilibrium during rainy and cold air-dust weather, and compared it with that during hazy weather during the same period. The aerosol during rainy weather was slightly acidic, whereas that during hazy weather and cold air-dust weather was obviously alkaline, with that during cold air-dust weather being significantly more alkaline. Most of the anions, including SO₄ ²⁻ and NO₃ ⁻, were neutralised by NH₄ ⁺ during rainy and hazy weather, and by Ca²⁺ during cold air-dust weather.