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Quantification of the emission rates of various gases from soils at night remains a challenge, confronting climate science (in the case of CO2 and CH4) and agriculture science (for NH3 and N2O, among others). In the stable conditions prevailing at night, concentrations of such emitted gases build up at the surface during the night, with intermittent interruptions commonly attributed to the passage of packets of turbulence. The utility of conventional micrometeorological experimental methods in such circumstances is questionable, and chamber methods have been developed to meet the challenge. Here, a statistical approach is proposed, in which micrometeorological field data are used to replicate the likely characteristics of a chamber experiment, yielding estimates of surface fluxes at the surface itself and not at some height above it. The methodology proposed is developmental at this time, with details intended to correspond to the use of both closed and vented chambers. Its application to three recent field studies is explored: (1) a study of nocturnal CO2 emission from two test areas (one previously tilled and the other not) in Ohio in 2015; (2) a similar experiment conducted in Zimbabwe in 2013 (one area previously tilled and a second left fallow), and (3) an investigation of NH3 effluxes from a crop previously treated with urea ammonium nitrate (UAN), in Illinois in 2014. There are few measurements with which to compare the results presented here, however the values obtained are within the range of available field data. [ABSTRACT FROM AUTHOR]

Highlights • Modeling the bi-directional NH 3 exchange at the field scale using SURFATM-NH 3. • Integrating an operational parameterization of emission potentials in the model. • Parameterizing the effect of urease inhibitor on NH 3 volatilization. • Satisfactory simulations of NH 3 fluxes by integrating the effect of urease inhibitor. • Good predictions of dynamic and order of magnitude of emission potentials by the model. Abstract Agriculture is the main source of ammonia (NH 3) emissions in the atmosphere. NH 3 is precursor to secondary fine particulate matter, which is of concern for its impacts on health and visibility. There are a limited number of field measurements of NH 3 emissions from fertilizer application in the US, and this limits our understanding of the importance of individual NH 3 source and sink processes in controlling timing and magnitude of NH 3 emissions. In this study, a new parameterization of the effect of urease inhibitor on NH 3 emissions from urea-based fertilizer was developed on the basis of experimental results found in the literature. This parameterization was combined with an existing operational parameterization of soil and stomatal emission potentials (Γ g , Γ s) and was implemented in a surface-atmosphere transfer model for NH 3 (SURFATM-NH 3) in order to evaluate the bi-directional fluxes of NH 3 at the field scale. The model was evaluated with field measurements obtained by the flux-gradient (FG) and relaxed eddy accumulation (REA) methods in a fertilized corn field in central Illinois. By integrating the effect of urease inhibitor, the timing of the highest NH 3 emission peak was successfully predicted and its magnitude was close to that measured (predicted 2106 ng m−2 s−1, measured by FG 2312 ± 582 ng m−2 s−1). Based on the model results, urease inhibitor has a considerable effect on the dynamics and order of magnitude of NH 3 fluxes. Furthermore, the model simulated the inhibiting action of N- (n -butyl) thiophosphoric (nBTPT) and suggests that it can reduce NH 3 volatilization by 32%. The model also successfully predicted environmental parameters, such as soil temperature. Finally, this new version of SURFATM-NH 3 is a valuable tool to estimate the NH 3 bi-directional fluxes at the field scale, which describes dynamic modeling of Γ s and Γ g by taking into account the effect of urease inhibitor which is commonly used in the US to improve the efficiency of urea fertilizers. [ABSTRACT FROM AUTHOR]

The objective of this research is to quantify NH 3 flux above an intensively managed cornfield in the Midwestern United States to improve understanding of NH 3 emissions and evaluations of new and existing emission models. A relaxed eddy accumulation (REA) system was deployed above a corn canopy in central Illinois, USA (40°3′46.209″N, 88° 11′46.0212″W) from May through September 2014 (day of year 115–273) to measure NH 3 fluxes due to chemical fertilizer application. NH 3 flux was measured in four-hour periods during mornings and afternoons. Mean atmospheric NH 3 concentration during the complete measurement period was 2.6 ± 2.0 μg m −3 . Larger upward fluxes of gaseous NH 3 were measured during the first 30 days after fertilization, with variations observed throughout the field campaign. Measured NH 3 fluxes ranged from −246.0 ng m −2 s −1 during wintertime background measurements to 799.6 ng m −2 s −1 within two weeks of fertilization (where negative flux indicates deposition). Mean positive flux was 233.3 ± 203.0 ng m −2 s −1 in the morning and 260.0 ± 253.3 ng m −2 s −1 in the afternoon while mean negative flux was −45.3 ± 38.6 ng m −2 s −1 in the morning and −78.35 ± 74.9 ng m −2 s −1 in the afternoon. NH 3 volatilization during the first 21 days after fertilization accounted for 79% of total nitrogen loss during the growing season. Such measurements are critical to improve understanding of agricultural NH 3 emissions in managed agricultural ecosystems dominated by rotations of highly fertilized corn and moderately to lightly fertilized soybeans, such as the plot studied herein. These measurements are also important to improve understanding of how managed agricultural ecosystems impact air quality, and contribute to the global nitrogen cycle, and to evaluate current NH 3 emission models. [ABSTRACT FROM AUTHOR]