Monitoring Air Quality in North Korea from Space

Despite the severity of air pollution in North Korea, air quality in this country has not been well understood due to the lack of reliable information. To investigate spatial distributions and temporal changes of aerosols and their precursors in North Korea, we analyze multi-year satellite observations from the Geostationary Ocean Color Imager (GOCI) and the Ozone Monitoring Instrument (OMI). We find that aerosol optical depths (AODs) observed from GOCI over South and North Korea are comparable, while GOCI-derived PM_2.5 concentrations are typically higher in North Korea. Both AOD and PM_2.5 concentration in North Korea show decreasing trends in 2011–2018, possibly attributed to decreasing amounts of transboundary aerosols into the country and the decline of domestic coal-fired energy supply. By oversampling OMI retrievals onto 0.05° × 0.05° grids with a tessellation approach, we detect three cities in North Korea (Pyongyang, Pukchang, and Munchon) as hotspots of NO₂ and SO₂. Vertical columns of SO₂ over North Korea and those cities show decreasing linear trends ranging from –7.0 % yr^–1 to –3.7 % yr^–1 in 2005–2018, likely connected to the decrease of coal-fired energy supply. In contrast, NO₂ columns over the same regions have increased by 3.1–4.1 % per year, which can be attributed to increasing trends of gross thermal energy supply or the number of motor vehicles. We perform the same oversampling and time series analyses for OMI formaldehyde (HCHO) and find that its column amounts have increased from 2005 to 2018. This increase is particularly notable in some fields and mountainous regions in North Korea, which can be attributed to isoprene oxidation or biomass burning resulting in increased amounts of organic aerosols. Based on NO₂ observations from the TROPOspheric Monitoring Instrument (TROPOMI) oversampled onto 0.01° × 0.01° grids, we anticipate air quality in North Korea will be assessed more explicitly by newer and upcoming spaceborne instruments having higher spatial resolutions.