An integrated modeling framework for PM2.5 source apportionment in the Yangtze River Delta using WRF-CMAQ and ISAM

With the increasing complexity of the PM_2.5 pollution problem and the diversity of emission sources, source apportionment analysis has become an important tool to better understand the nature of PM_2.5 pollution. In this study, the PM_2.5 emission sources in the Yangtze River Delta (YRD) urban agglomeration were analyzed using a two-layer nested the Weather Research and Forecasting (WRF) model and the Community Multiscale Air Quality (CMAQ) model, combined with the Integrated Source Apportionment Method (ISAM) pollution source analysis module. Based on a comprehensive analysis of sectoral PM_2.5 source data for the autumn and winter seasons, key characteristics emerged: Nanjing was dominated by industrial sources, Hangzhou was prominent in residential sources, Hefei had a relatively complex pollution composition, and Shanghai saw a significant decrease in contributions from transportation sources in autumn. From a seasonal perspective, the overall PM_2.5 concentration was higher in winter than in autumn. This was particularly marked by increased contributions from agricultural, industrial, and power generation sources, indicating either greater emission intensity or poorer atmospheric dispersion conditions during winter. By tracking the transport pathways across the Yangtze River Delta (YRD) urban agglomeration in both seasons, we found the following: In winter, the contribution percentages from local sources, intra-regional transport, and extra-regional transport were 15.05 %–36.3 %, 35.60 %–62.10 %, and 16.9 %–36.23 %, respectively. In autumn, the respective contributions were 26.00 %–45.13 %, 31.51 %–56.44 %, and 17.56 %–27.59 %. Overall, compared to autumn, the contribution of local sources to PM_2.5 decreased during winter, while the proportion from long-range transport increased.