Spatial and temporal analysis of HCHO response to drought in South Korea

Though drought is known to affect biogenic emissions of volatile organic compounds (BVOC), its effect on isoprene and formaldehyde (HCHO), a high yield product of isoprene, has not been investigated in East Asia where incidences of drought have increased in recent years. In this work, we analyzed the impact of drought on HCHO in the South Korea region during the summer period (June, July, and August) from 2005 to 2018 and found increased HCHO due to drought. The tropospheric HCHO column density retrieved by OMI increased by 8.02 % during extreme drought compared to the non-drought period, whereas no significant effect of drought on the NO₂ column was found. Regional variation of HCHO response to drought correlates significantly with the tree percentage of the region. This correlation indicates that the drought-led HCHO increases are most likely driven by the increase in isoprene emissions during drought. Indeed, model predicts isoprene emissions to be higher by 27.87 % during the extreme drought compared to the non-drought period in South Korea. From 2005 to 2018, the HCHO column has been increasing in South Korea by 0.16 × 10¹⁵ molecules/cm²/year (1.56 % per year) during summer months, correlated with the increasing incidences of drought. HCHO increase is linked to higher ozone as most of South Korea is in the NOx-saturated or transitional regime.