Has China been exporting less particulate air pollution over the past decade?

Particulate matter (PM) pollution from China is transported eastward to Korea and Japan and has been suggested to influence surface air quality on the West Coast of the United States. However, remote sensing studies have been inconclusive as to recent trends in Chinese emissions and transport. We reconciled different passive remote sensing points of view and found that while aerosol optical thickness (AOT) as an indicator of particulate pollution has increased from the start of the observation period (2000) to 2006–2007 from the main Chinese coastal outflow regions, since then there has been a 10–20% decrease in AOT (with respect to 2007). Reductions were observed in spring, summer, and fall seasons. No improvement in exported PM pollution is found for the winter season. Plain Language Summary Particulate matter pollution from China is transported eastward to Korea and Japan and has been suggested to influence surface air quality on the West Coast of the United States. However, remote sensing studies have been inconclusive as to recent trends in Chinese emissions and transport. We reconciled different passive remote sensing points of view and found that while aerosol optcial thickness (AOT) as an indicator of particulate pollution has increased to 2006–2007 in the main exit regions of China’s coast, since then there has been a 10–20% decrease in AOT (with respect to 2007). Reductions were observed in spring, summer, and fall seasons. No improvement in exported particulate matter pollution is found for the winter season.