Spaceborne evidence for significant anthropogenic VOC trends in Asian cities over 2005-2019

Trends of formaldehyde (HCHO) linked to anthropogenic activity over large cities located in the Asian continent are calculated for the period 2005-2019 using the Quality Assurance for Essential Climate Variables dataset from the Ozone Monitoring Instrument aboard the Aura satellite. Contributions due to anthropogenic emissions are isolated by applying a correction based on near-surface temperature in order to account for interference from local biogenic emissions. Strong positive trends are derived over the Middle East and the Indian subcontinent (up to 3.6% yr(-1) and 2.4% yr(-1) respectively) where regulations of anthropogenic non-methane volatile organic compound (NMVOC) emissions are currently limited. Weaker trends are observed over cities located in China, where the air pollution action plan (2013) may have mitigated NMVOC trends early on, but targeted legislature concerning VOC emissions was only recently introduced. HCHO trends for cities located in South and Equatorial Asia are mostly not significant or very uncertain. Cities located in Taiwan and Japan (regions in Asia where legislation has been in place since the early 2000s) display mostly negative trends.