[Pollution Characteristics and Factors Influencing the Reduction in Ambient PM in Beijing from 2018 to 2020].

Air quality data from 33 environment sites and five regional sites from 2018 to 2020, as well as meteorological data, were used to research PM variation,spatial and temporal change, diurnal variation, and heavy pollutions in Beijing. The annual average mass concentrations of PM in Beijing were 51, 42, and 38 μg·m, which showed great progress in air quality improvement. However, the PM concentration in 2020 was still 8.6% above the national limit value despite a 30.9% decline since 2017. The PM south-north gradient in Beijing remained throughout the three years, but this pattern showed a less significant trend. The highest monthly mean PM concentrations in Beijing tended to occur in January-March, with the lowest in August-September. NO, CO, and PM concentrations were significantly higher in the heating season than in the non-heating season by 58.4%, 52.9%, and 27.5%, respectively. Diurnal variation showed that greater PM concentrations were observed at nighttime during the heating season and, conversely, at noontime during the non-heating season. Sixteen pollution episodes occurred in Beijing over the last three years, resulting in 25 heavy pollution days distributed in autumn-winter of 2018-2020. The regional heavy pollution characteristics of PM in Beijing were significant. Through analysis, a continuous pollution reduction was still the most important reason for the yearly decrease in PM. The concentrations of organic matter, elemental carbon, and crustal matter in the PM in Beijing decreased by 43.3%, 53.2%, and 51.5% since 2017, respectively, and nitrate, sulfate, and ammonium decreased by 34.2%, 52.2%, and 43.7%.The results showed that the control effect of PM in Beijing was obvious.