Some of the largest changes in OMI NO₂ levels between 2005 and 2014 occurred over China, Japan, and Korea.  Large increases occurred over the North China Plain of China, which is consistent with the country's booming economy over the last decade.  China's phenomenal economic growth has been fueled by the country's abundant coal reserves, but at the cost of air quality. However, the OMI data indicate that levels decreased over several of China's cities, including Beijing, Shanghai, Taipei, and the cities of the Pearl River Delta, including Hong Kong.  These cities have implemented ambitious environmental regulations to improve air quality.  National environmental regulations in Japan and South Korea have also lead to large decreases over their cities, as much as 40% over Tokyo, for instance.  Increases southwest of Seoul (Korea) are likely associated with intensive industrial infrastructure development, including petrochemical complexes.  Given that increases occurred over the ocean, it is possible that Chinese pollution impacted air quality in North Korea, South Korea and western Japan.