Abstract:To understand the characteristics of horizontal visibility and correlation with air pollution in winter in Tianjin, the observational data of PM10 and PM25 mass concentrations, reactive gas bulk concentrations, and horizontal visibility in December of 2008 and January of 2009 are studied. The results indicate that the average horizontal visibility value was 1159 km, and the diurnal variation exhibited a singlepeak pattern with the maximum in the afternoon, which were affected strongly by aerosol mass concentrations and relative humidity. The occurrence frequency of haze approached 50%, which, being an important symbol of the poor air quality, resulted in low horizontal visibility. The observational data of PM10 and PM25 mass concentrations can be used to reflect the horizontal visibility approximately by using different nonlinear regression equations in winter. There was a negative correlation between horizontal visibility and aerosol mass concentration, and PM25 has greater effect on visibility than PM10 does. Under the high humidity condition, there existed better correlation between visibility and aerosol mass concentration.