A visibility-based estimation of PM_2.5 concentrations in Pyongyang, North Korea: Current status and long-term trends

In the absence of direct measurements of fine particles (particulate matter with aerodynamic diameters ≤ ∼2.5 μm; PM_2.5), visibility can be a useful alternative indicator of particulate air quality. This study estimated the current status and long-term trends of PM_2.5 in the North Korean capital, Pyongyang, using an empirical visibility–relative humidity (RH)–PM_2.5 relationship obtained from the South Korean capital, Seoul. The visibility–RH–PM_2.5 relationship was derived from PM_2.5 and meteorological variables for the period of 2003–2018 in Seoul, excluding days affected by hydrometeor conditions; it was applied to long-term meteorological data for the period of 1983–2018 in both Seoul and Pyongyang. In recent years (2016–2018), the average estimated PM_2.5 concentration in Seoul was ∼23 μg m⁻³, which was close to the measured concentration of ∼25 μg m⁻³. The average estimated PM_2.5 concentration in Pyongyang for the same period was ∼35 μg m⁻³. The estimated PM_2.5 concentration in Seoul was generally high before 2000 (∼34 μg m⁻³); it decreased beginning in the 2000s (−5.2 μg m⁻³ per 10 years) because of the emission control policy and meteorological phenomena. The estimated PM_2.5 concentration in Pyongyang significantly decreased until 1998 (−5.9 μg m⁻³ per 10 years), then increased from 1999 to 2018 (+8.5 μg m⁻³ per 10 years). The growth in gross national income, total primary energy supply, and coal-fired thermal electricity generation implied that the long-term changes in the estimated PM_2.5 concentration in Pyongyang were closely related to the economic contraction and recovery of North Korea. This study provides estimates of North Korean air quality, along with information that can be used to validate chemical transport models.