Abstract: From January to May 2004, continuous measurements of mass concentration for atmospheric PM₁₀, PM_2.5, PM₁ and TSP, visibility and surface meteorological factors were carried out at a site in central urban Beijing. It was found thatfiner particles are at a higher ratio during the Spring Festival, namely, ρ(PM₁)/ρ(PM_2.5) is 0.81, ρ(PM₁₀₎/ρ(TSP)0.61; contrasted by those of 0.55 and 0.28 for a sandstorm time. The diurnal variations of concentrations for the above sized particles all showed a stronger peak at night than in morning rush hour. Visibility data was transformed into light extinction coefficients for both the atmosphere and particles using empirical equations. There are statistically strongpositive correlations between the PM concentration and the extinction coefficient of particles. Furthermore, the ratio of particle mass concentration to extinction coefficient (CE_P) was defined to study particle pollution properties.The result reveals that when CE_P is small (CE_P<103), PM mass concentration is low and fine particles are in the majority, which represents a favorable meteorological condition; while when CE_P become larger (CE_P>167), PM mass concentrations arehigh, ρ(PM_2.5)/ρ(PM₁₀₎is 0.5～0.7, and RH 20%～50%, which represents an unfavorable condition.