京津冀城市群冬季二次PM2.5的时空分布特征

二次组分是造成京津冀城市群冬季PM_2.5污染的重要因素.采用CO示踪法，估算2017～2021年冬季京津冀城市群二次PM_2.5浓度，并分析其时空分布特征，探讨区域二次PM_2.5的影响因素.结果表明，2017～2021年冬季京津冀区域PM_2.5浓度下降趋势明显，河北中南部一次PM_2.5下降幅度最大，二次PM_2.5浓度年际波动平稳，北京和天津二次PM_2.5占比明显高于其他城市.随着污染程度加剧，一次PM_2.5和二次PM_2.5质量浓度均有不同程度的增加，二次PM_2.5占比呈显著增大趋势.与直接测量结果相比，CO示踪法获得的结果偏低，与冬季CO浓度较高，一次PM_2.5浓度高估有关，选取合适的一次气溶胶基准值是改进该方法，获取合理估算值的关键.

Spatio-temporal Distribution Characteristics of Secondary Aerosol in Beijing-Tianjin-Hebei Urban Agglomeration in Winter

The secondary component is an important factor causing PM_2.5 pollution in the Beijing-Tianjin-Hebei urban agglomeration in winter. In this study, the CO tracer method was used to estimate the secondary PM_2.5 concentration of the Beijing-Tianjin-Hebei urban agglomeration in the winter of 2017-2021. The temporal and spatial distribution characteristics were analyzed, and the influencing factors of regional secondary PM_2.5 were discussed. The results showed that the decreasing trend of PM_2.5 concentration in the Beijing-Tianjin-Hebei Region in the winter of 2017-2021 was obvious, and the cities with the largest decline were located in the central and southern part of Hebei Province, mainly contributed by primary PM_2.5. There was a good correlation between secondary PM_2.5 and PM_2.5 in all cities of the Beijing-Tianjin-Hebei urban agglomeration, and the proportion of secondary PM_2.5 in Beijing and Tianjin was significantly higher than that in other cities. With the aggravation of pollution degree, the mass concentration of primary PM_2.5 and secondary PM_2.5 increased in varying degrees, and the proportion of secondary PM_2.5 increased significantly. Compared with the direct measurement results, the estimated value obtained by this method was lower as a whole. The selection of appropriate primary aerosol reference value was the key to improving this method and estimating the secondary PM_2.5 concentration.