Local versus external dust source contributions to northern China and selected downwind cities: Evidence from...

In spring 2025, several high-impact dust events caused widespread PM₁₀ pollution across Northern China and downwind regions. However, the relative contributions of dust emitted within Northern China and dust transported from external source regions, particularly Mongolia and Central Asia, remain insufficiently quantified at both regional and city scales. Here, we use the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to simulate three representative spring 2025 dust events, and quantify source contributions through source-specific sensitivity experiments. Across the three events, dust emissions from Northern China dominated total dust loading over Northern China, accounting for 87.52%, whereas external contributions varied substantially among events, ranging from 7.73% to 14.03%. City-scale source contributions showed much stronger spatial heterogeneity. In particular, Hohhot exhibited a Mongolian contribution of 51.93%, reflecting its proximity to Mongolian source regions and exposure to cross-border inflow under favorable circulation conditions. Beijing and Tianjin, located along major transport pathways, also showed event-dependent increases in Mongolian dust contributions, reaching 33.59% and 35.55%, respectively. For Shanghai, external contributions could exceed those in some inland cities such as Xi'an, suggesting that long-range transport pathways, circulation patterns, and removal processes can reshape source contributions beyond simple source-region distance. Overall, this study shows that dust pollution over Northern China during the analyzed spring 2025 events resulted from the combined influence of dominant emissions from source regions within China and episodically enhanced dust transport from outside China. These findings suggest that event-dependent circulation regimes and city-specific geographic settings should both be considered when interpreting dust source contributions over downwind urban areas. Although based on three cases, the results provide useful quantitative insight for coordinating dust-source management within China with broader regional dust mitigation strategies.