Assessment of air quality in North Korea from satellite observations.

North Korea's air quality is poorly understood due to a lack of reliable data. Here, we analyzed urban- to national-scale air quality changes in North Korea using multi-year satellite observations. Pyongyang, Nampo, Pukchang, and Munchon were identified as pollution hotspots. On a national scale, we found that North Korea experienced 6.7, 17.8, and 20.6 times greater amounts of nitrogen dioxide (NO), sulfur dioxide (SO), and carbon monoxide (CO) per unit primary energy supply (PES) than South Korea from 2005 to 2018. Besides, North Korea had a 24.3 times larger aerosol optical depth (AOD) per PES than South Korea from 2011 to 2018. Severe CO and aerosol pollution is aligned with extensive biofuel combustion. High SO pollution corresponds with the strong coal dependence of the industry. The change rates of the national average columns for NO, SO, and CO were + 3.6, -4.4, and -0.4 % yr, respectively. The AOD change rate was -4.8 % yr. Overall decreasing trends, except for NO, are likely due to a decline in coal-fired PES. Positive NO trends are consistent with increasing industrial activities. Each pollutant showed consistent patterns of linear trends, even after correcting the influence of transboundary pollution. Flue gas control and biofuel consumption reduction seem necessary to improve North Korea's air quality.