New Bidirectional Ammonia Flux Model in an Air Quality Model Coupled With an Agricultural Model

Abstract

Ammonia surface flux is bidirectional; that is, net flux can be either upward or downward. In fertilized agricultural croplands and grasslands there is usually more emission than deposition especially in midday during warmer seasons. In North America, most of the ammonia emissions are from agriculture with a significant fraction of that coming from fertilizer. A new bidirectional ammonia flux modeling system has been developed in the Community Multiscale Air Quality (CMAQ) model, which has close linkages with the Environmental Policy Integrated Climate (EPIC) agricultural ecosystem model. Daily inputs from EPIC are used to calculate soil ammonia concentrations that are combined with air concentrations in CMAQ to calculate bidirectional surface flux. The model is evaluated against surface measurements of NH 3 concentrations, NH 4 + and SO 4 2− aerosol concentrations, NH 4 + wet deposition measurements, and satellite retrievals of NH 3 concentrations. The evaluation shows significant improvement over the base model without bidirectional ammonia flux. Comparisons to monthly average satellite retrievals show similar spatial distribution with the highest ammonia concentrations in the Central Valley of California (CA), the Snake River valley in Idaho, and the western High Plains. In most areas the model underestimates, but in the Central Valley of CA, it generally overestimates ammonia concentration. Case study analyses indicate that modeled high fluxes of ammonia in CA are often caused by anomalous high soil ammonia loading from EPIC for particular crop types. While further improvements to parameterizations in EPIC and CMAQ are recommended, this system is a significant advance over previous ammonia bidirectional surface flux models.Plain Language Summary Ammonia is one of many pollutants that are added to the air by human activities. Ammonia contributes to degraded air quality mainly because it adds to the concentration of very fine particles suspended in the air that are called aerosols. Hazy conditions with poor visibility are often the result of high concentrations of aerosols. Also, breathing air with high amounts of aerosols is bad for human health. Ammonia can get into water bodies where it contributes to algae growth and fish kills due to low oxygen. Much of the ammonia that gets into the air comes from fertilizer in agricultural fields. This paper is about improved methods for modeling the ammonia from agricultural fertilizer by linking together an air quality computer model with an agricultural management model. The agricultural model predicts the amount and types of fertilizer that farmers use and the amount of ammonia in the soil. The air quality model then uses information from the agriculture model to predict how much ammonia gets into the air. The study describes these models and shows how well they predict the amount of ammonia in the air compared to ground-based and satellite measurements.

An Integrated Agriculture, Atmosphere, and Hydrology Modeling System for Ecosystem Assessments

“…Despite the tendency to be lower than the reported usage, simulated demand‐based inorganic fertilization for 2011 at the county level follows the agricultural land distribution better than USGS sales‐based usage. Integrated air quality modeling is demonstrated for 2011 over the same domain using CMAQ configured with a bidirectional NH 3 modeling approach that directly uses EPIC‐simulated soil properties including soil NH 3 content (Pleim et al, ). With spatially and temporally better represented soil NH 3 information from EPIC and consequently improved representation of land‐atmosphere NH 3 flux, CMAQ shows better performance in simulating gas‐phase NH 3 and NH 4 + wet deposition in comparison to the traditional approach based on NH 3 emission estimates solely from fertilizer sales data.…”

“…Since then, the system has gone through many updates and advances to the current release of CMAQv5.3 (https://github.com/USEPA/CMAQ). Different from the previous bidirectional NH 3 approach using the fertilization information to simulate soil NH 3 in CMAQ, a new approach of bidirectional flux modeling, which directly uses EPIC‐simulated soil properties including soil NH 3 concentration (Pleim et al, ), is implemented in the current release of CMAQ. The new approach directly follows the bidirectional flux box model based on field studies demonstrated by Pleim et al () and has additional updates to some key parameterizations.…”

Ammonia measurements from space with the Cross-track Infrared Sounder (CrIS): characteristics and applications

“…The CrIS NH3 product can be used for many applications such as monitoring, air quality model evaluation (e.g. Whaley et al, 2018;Pleim et al, 2019), dry deposition estimates , and emissions estimates for larger agriculture sources, industrial point sources (Dammers et al, 2018), and wildfires (Adams et al, 2019). Here we provide examples that demonstrate and expand upon these applications.…”

“…vegetation) can be re-released into the atmosphere later depending on the ammonia balance between the air and leaf apoplastic concentrations (compensation point) (do that there is bi-directional flow) (e.g. Massad et al, 2010;Bash et al, 2013;Pleim et al, 2019). fires) overlaid in red.…”

“…In that study a newly implemented ammonia bidirection flux scheme and inclusion of biomass burning into Environment and Climate Change Canada's air quality forecast model, the Global Environmental Multi-scale -Modelling Air quality and CHemistry (GEM-MACH) model (Gong et al, 015;Makar et al, 2015a,b;Pendlebury et al, 2018), were evaluated over northern Canada using CrIS NH3 observations. CrIS NH3 observations have also recently been used to evaluate improvements to the Community Multiscale Air Quality Model (CMAQ) 10 (Pleim et al, 2019). They demonstrated that CMAQ underestimated NH3 concentrations in the spring, but also that CMAQ and CrIS present the same pattern of high NH3 in the California Central Valley, the Snake River Valley and western High Plains, all regions with high soil pH resulting in high NH3 fluxes, suggesting that CMAQ modeling of soil pH and the fluxes dependent on this parameter are reasonably well modeled.…”