AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Assessment of Model-Simulated Global Atmospheric Ammonia with Satellite Remote Sensing Measurements
ARSHAD NAIR, Fangqun Yu, Gan Luo, The State University of New York at Albany
Abstract Number: 593 Working Group: Aerosol Chemistry
Abstract Atmospheric ammonia, by virtue of its alkalinity and abundance, plays multiple roles in atmospheric chemistry and composition and consequently has wide-ranging effects on the environment. A myriad of effects such as increased reactive N deposition, eutrophication, acidification by nitrification, neutralization of atmospheric particles, modification of particle hygroscopicity, increasing particle uptake of acidic gases, and modification of particle mass and number concentration distributions are consequent of the presence and variability of ammonia in the atmosphere. Of recent interest is the role of ammonia in atmospheric new particle formation (nucleation), where ammonia even at the pptv levels has been shown to radically increase rates of inorganic nucleation as well as play a role in organic nucleation. This has implications for aerosol radiative forcing, which remains the largest source of uncertainty in climate change modeling. These aspects combined with the increasing trend of gas-phase ammonia across most of the globe motivate the current assessment of multi-year GEOS-Chem (a 3D global atmospheric chemistry model) simulated ammonia with satellite remote sensing measurements, which provide the advantage of a continuous global scope over in situ measurements. Model simulated ammonia is in good spatial agreement with satellite observations, with co-located ammonia source regions and hotspots. While simulated magnitude of column ammonia is generally underestimated (Mean Fractional Bias (MFB): −1.4±0.6(1σ)), there is a marked contrast between land (MFB: −1.0±0.7) and ocean (MFB: −1.5±0.5). Over ammonia source regions, this underestimation is less pronounced (MFB: −0.7±0.6). We will discuss the model-observation deviations, reasons for these deviations, limitations of in-model processes and satellite data, avenues for improvement, and the consequent implications especially for atmospheric new particle formation.