A novel method for distinguishing fog and haze based on PM2.5, visibility, and relative humidity

Haze and fog are both low visibility events, but with different physical properties. Haze is caused by the increase of aerosol loading or the hygroscopic growth of aerosol at high relative humidity, whereas visibility degradation in fog is due to the light scattering of fog droplets, which are transited from aerosols via activation. Based on the difference of physical properties between haze and fog, this study presents a novel method to distinguish haze and fog using real time measurements of PM2.5, visibility, and relative humidity. In this method, a criterion can be developed based on the local historical data of particle number size distributions and aerosol hygroscopicity. Low visibility events can be classified into haze and fog according to this criterion.