Constraints On Global And Regional Sources Of Atmospheric Organic Compounds From Space-Based Measurements.

Abstract

Emission changes over the tropics and developing regions of the world are causing major adverse effects on human health and air quality. For many of these regions, in-situ measurements are sparse or non-existent; consequently, satellite measurements provide a valuable tool for understanding and predicting atmospheric composition. In this research, I have used the GEOS-Chem chemical transport model to interpret space-based observations of key trace gases such as formic acid (HCOOH) and formaldehyde (HCHO) from multiple satellite instruments in terms of the constraints they provide on volatile organic compound (VOC) emission sources, with a particular focus on Africa and the Indian subcontinent. I demonstrate that current models severely underestimate the abundance of atmospheric formic acid. This discrepancy is most prominent over tropical burning regions, suggesting a major missing source of organic acids from fires. Next, I developed a new modeling framework to analyze formaldehyde observations from two satellite sensors and better quantify regional VOC emissions over the Indian subcontinent. Inverse analyses based on the satellite data reveal that biogenic VOC emissions in the prior bottom-up inventory are overestimated (by ~30-60%) for the Indian subcontinent. The satellite-derived anthropogenic VOC emissions are slightly higher (13-16%) than the prior bottom-up estimate, with some larger regional and seasonal discrepancies. Our analysis reveals that terrestrial vegetation represents the largest VOC source type over the Indian subcontinent (47-53% of the total flux). Anthropogenic emissions account for 37-50% of the annual regional VOC flux and fires provide only a minor fraction (<7%) of the total. Finally, I quantify the decadal (2005-2016) trends in HCHO columns over the Indian subcontinent. After correcting for variability driven by the temperature dependence of biogenic emissions, I interpret the resulting changes in terms of changing anthropogenic and fire VOC emissions in this region.