Abstract: Using monitoring concentration data of PM_2.5, O₃, NO, NO_x, CO and SO₂ from 2011 to 2013 at national weather station of Chaoyang district of Beijing, variation of concentrations of 6 air pollutants in different time scales were analyzed.The results show that PM_2.5 concentration is of a significantly increasing trend and the number of days with heavy pollution grade is also increasing.There is no significant trend for annual average concentration of the other five gaseous pollutants.However, they have obviously seasonal variations.The O₃ concentration is high in summer and low in winter, while it is opposite to concentrations of PM_2.5, NO_x, CO and SO₂.The latter is related to the increase of pollutant emission in heating period of winter.The curve of diurnal variation for concentrations of pollutants is bimodal except O₃ (unimodal), which may be related to human activities and weather conditions.The diurnal variations of pollutants' concentrations at Chaoyang district differ significantly from those at Baolian, Shunyi and Shangdianzi stations which represent urban area, inner and outer suburbs of Beijing respectively.Among them, difference of PM_2.5 concentration is the most significant.The diurnal variation of PM_2.5 concentration is bimodal at Chaoyang station, three peaks at Baolian station, and unimodal at Changping and Shangdianzi stations.The single peak occurs at night in the latter two stations.Urbanization development in different regions differs each other, which leads to significant differences in local pollutants' concentrations.

Key words: PM_2.5, Gaseous pollutants, Urbanization