Abstract：In order to study the effects of relative humidity (RH) and aerosol fine particles (PM2.5 and PM10) on visibility, visibility, RH, PM2.5 and PM10 during 11th December, 2008~27th August, 2009 in Guangzhou, and 14th July~17th September, 2008 in Beijing were measured, respectively. PM2.5 and RH were the main factors on effecting visibility. When the RH was lower than 70% and between 80% and 90%, the effects of PM2.5 on visibility in Guangzhou and Beijing were different. However, a good correlation between visibility and PM2.5 was found both in Guangzhou and Beijing when RH was between 70% and 80%. A division was found in 0.05mg/m3 from the fitting curve. The visibility did not vary obviously with the PM2.5 concentration reduction when the concentration of PM2.5 was higher than 0.05mg/m3. However, a rapid improving in visibility was observed with decreasing of the PM2.5 concentration when the concentration of PM2.5 was lower than 0.05mg/m3. Therefore, the reduction on PM2.5 did not show obvious improving in visibility at the early time of controlling PM2.5, whereas the visibility could be remarkably improved when the concentration of PM2.5 reduced to a certain value.
