Daily Cropland Soil NO<sub>x</sub> Emissions Identified by TROPOMI and SMAP
Daniel E. Huber, Allison L. Steiner, E. A. Kort
Abstract
Abstract We use TROPOMI (TROPOspheric Monitoring Instrument) tropospheric nitrogen dioxide (NO 2 ) measurements to identify cropland soil nitrogen oxide (NO x = NO + NO 2 ) emissions at daily to seasonal scales in the U.S. Southern Mississippi River Valley. Evaluating 1.5 years of TROPOMI observations with a box model, we observe seasonality in local NO x enhancements and estimate maximum cropland soil NO x emissions (15–34 ng N m −2 s −1 ) early in growing season (May–June). We observe soil NO x pulsing in response to daily decreases in volumetric soil moisture (VSM) as measured by the Soil Moisture Active Passive (SMAP) satellite. Daily NO 2 enhancements reach up to 0.8 × 10 15 molecules cm −2 4–8 days after precipitation when VSM decreases to ~30%, reflecting emissions behavior distinct from previously defined soil NO x pulse events. This demonstrates that TROPOMI NO 2 observations, combined with observations of underlying process controls (e.g., soil moisture), can constrain soil NO x processes from space.