Validation of NH₃ observations from AIRS and CrIS against aircraft measurements from DISCOVER-AQ and a surface network in the Magic Valley

Abstract

Abstract. Ammonia is a significant precursor of PM2.5 particles and thus contributes to poor air quality in many regions. Furthermore, ammonia concentrations are rising due to the increase of large scale, intensive agricultural activities, which are often accompanied by greater use of fertilizers and concentrated animal feedlots. Ammonia is highly reactive, and thus highly variable and difficult to measure. Satellite based instruments, such as the Atmospheric Infrared Sounder (AIRS), and the Cross-Track Infrared Sounder (CrIS) sensors, have been shown to provide much greater temporal and spatial coverage of ammonia distribution and variability than is possible with in situ networks or aircraft campaigns, but the validation of these data is limited. Here we evaluate ammonia retrievals from AIRS and CrIS against ammonia measurements from aircraft in the California Central Valley and in the Colorado Front Range. The satellite datasets were small and in California were obtained under difficult conditions. We show that the surface values of the retrieved profiles are biased very low in California and slightly high in Colorado, and that the bias appears to be primarily due to smoothing error. We also compare three years of CrIS ammonia against an in situ network in the Magic Valley in Idaho We show that CrIS ammonia captures both the seasonal signal and the spatial variability in the Magic Valley, though it is biased low here also. In summary, analysis adds to the validation record but also points to the need for more validation under different conditions.

Summertime Airborne Measurements of Ammonia Emissions From Cattle Feedlots and Dairies in Northeastern Colorado

“…Historical challenges in measuring NH 3 (i.e., Miller et al, 2014;Roscioli et al, 2016) have limited progress on emissions estimates for this pollutant. Recent advances in measuring NH 3 , including in-situ measurements (e.g., Ellis et al, 2010;Pollack et al, 2019;Roscioli et al, 2016) and satellite retrievals (e.g., Cady-Pereira et al, 2023;Van Damme et al, 2018), have increased our awareness of the importance of measuring NH 3 from large point sources. The availability of new observations has helped models to represent NH 3 emissions in the United States (Zhu et al, 2015) and worldwide (Clarisse et al, 2009) better and shine light on the potential underestimation of emission inventories on NH 3 emissions (e.g., Heald et al, 2012;Nowak et al, 2012).…”