We analyze 2011–2022 trends in wintertime fine particulate matter (PM 2.5 ) and its composition in South Korea using surface network data and machine learning. PM 2.5 decreased nationwide by 1.2 μg m −3 per year after correcting for meteorology. However, Seoul PM 2.5 declined only after 2019 and its composition has shifted toward particulate nitrate (pNO 3 − ) and organic aerosol (OA). Trends in pNO 3 − , OA, nitrogen dioxide (NO 2 ), and ozone (O 3 ) suggest that nighttime formation of the nitrate radical (NO 3 ) from the NO 2 + O 3 reaction is a key driver of pNO 3 − and secondary OA (SOA) formation. Increasing O 3 as nitrogen oxide (NO x ) emissions decline has increased nighttime NO 3 production over the 2012–2022 period, promoting pNO 3 − and SOA formation. As NO x emissions in South Korea continue to decline, transition from NO x ‐saturated to NO x ‐limited conditions for NO 3 formation should lead to rapid decreases in nighttime PM 2.5 formation.
No takes yet. Share an insight, caveat, or question.
Pendergrass et al. (2025) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: