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Atmospheric formaldehyde (HCHO) has significant adverse health effects at higher concentrations. It is an unstable and inflammable organic compound, and is an index for atmospheric pollution. Although the ambient HCHO is due to methane oxidation, the localised enhancement in HCHO is mostly from the emissions of non-methane volatile organic compounds (NMVOCs). Therefore, assessment of spatial and temporal changes in NMVOCs are key for monitoring air quality and climate change. Here, we analyze two decades of atmospheric HCHO measurements and investigate the HCHO sources in India using satellite observations in 1997–2020. The measurements show very high HCHO concentrations in the Indo-Gangetic Plain (IGP), and south and east India, about 8–12 × 1015 molec. cm−2. The northwest region shows moderate concentrations, but Kashmir and northern regions of northeast show very small values of about 1–2 × 1015 molec. cm−2. Our analyses reveal significant increase in HCHO over India in all seasons, with the highest trends during March–May, about 0.3–0.5 × 1015 molec. cm−2 yr−1; suggesting the spread of pollution even to rural regions. Many ports and mining areas exhibit high positive HCHO trends, which also show new source regions and transport pathways of pollution. Furthermore, the analyses for the COVID-19 lockdown period expose significant contributions from sources other than anthropogenic origin (e.g. biogenic and pyrogenic). Therefore, this study indicates the need of new policy interventions for controlling Volatile Organic Compound (VOC) pollution in rural and urban India, and at the international seaports of Indian Ocean.
Kuttippurath et al. (Tue,) studied this question.