Constraining hydrocarbon emissions over the Indian subcontinent based on HCHO observations from OMI and GOME-2

The Indian subcontinent is one of the global hotspots for air pollution-related mortality, and among the most under-studied regions of the world in terms of atmospheric composition and air pollution. A primary obstacle to scientific progress on this front has been a lack of atmospheric measurements to diagnose the sources and processes driving air quality over India. Formaldehyde (HCHO), as a high-yield product of atmospheric VOC oxidation, can be used as a proxy to understand the emissions of its reactive precursors from biogenic, pyrogenic and anthropogenic sources. In this work, we combine a new high-resolution GEOS-Chem simulation nested over the Indian sub-continent with space-based observations of HCHO from two satellite instruments (Ozone Monitoring Instrument, OMI; and Global Ozone Monitoring Experiment, GOME-2) to derive new constraints on VOC emission sources in India. Over the sub-continent as a whole, the model-measurement comparisons reveal a model HCHO underestimate during winter but no significant bias during summer. We interpret these comparisons in an inverse modeling framework to better quantify the emissions of HCHO precursor VOCs from biogenic, pyrogenic and anthropogenic sources in India, and assess the implications of the results for air quality predictions in this region.