Ammonia Emissions, Deposition, and Variability through In Situ, Ground-Based, and Remote Sensing Observations

Abstract

Atmospheric ammonia (NH3) emissions are primarily anthropogenic and pose great threats to human health and environment, but these emissions remain largely unregulated globally. A full understanding of NH3 emissions and their variabilities on all spatiotemporal scales is important for policy purposes, yet difficult to achieve due to challenges in measuring gas-phase NH3. My research aims to advance the knowledge of NH3 emissions and deposition using in situ, ground-based, and remote sensing observations. I start by discussing the heterogeneity of NH3 fluxes observed in two adjacent natural ecosystems in the southeastern United States measured using open-path, quantum cascade laser (QCL)-based sensors I developed. I then introduce the development of an algorithm to validate satellite NH3 observations at single pixel scales and show that NH3 total columns from the Infrared Atmospheric Sounding Interferometer (IASI) and the Cross-track Infrared Sounder (CrIS) are comparable to those integrated from collocated airborne and ground-based measurements during the DISCOVER-AQ/FRAPPÉ Colorado experiment. Finally, I compare oversampled IASI NH3 observations with ground monitoring networks to characterize the similarities and differences in the spatiotemporal variabilities of NH3 in the United States and China, followed by a discussion of factors that need to be considered when comparing column measurements and surface concentrations. My research demonstrates that in situ measurements help identify sub-grid variabilities of NH3 exchange between land and air. Satellite observations are capable of capturing the variabilities of NH3 on small spatiotemporal scales and can be aided by ground monitoring, but more work is needed to measure the vertical distribution of NH3 in the atmosphere to bridge the gap between satellite and ground-based observations.