Abstract
Abstract. We examine the interannual variability in the NO2 column over North America measured by the Ozone Monitoring Instrument (OMI) in 2005–2008. By comparison to a model of soil NOx emissions driven by the North American Regional Reanalysis precipitation and 0–10 cm soil temperature fields, we show the source of this observed interannual variability over much of the central United States in June is fertilizer application. We find that dry, warm conditions followed by convective precipitation induces pulsed emissions of NOx over the agricultural Great Plains. In June 2006 we infer a 50% increase in soil NOx emission and a 30% increase in the tropospheric NO2 column relative to the June 2005–2008 mean. In a case-study of fertilized corn and soybean fields over SE South Dakota, we find an associated rain-induced pulsing event reaching 4.6×1015 molec cm−2, equivalent to a surface concentration of ~2 ppbv. We calculate that soil NOx emissions resulted in a mean daily maximum 8-h ozone enhancement over the agricultural Great Plains of 5 ppbv in June 2006 (with predicted events reaching 16 ppbv) compared with a mean enhancement of 3 ppbv for soil NOx in the years 2005–2008.
Highlights
Nitrogen oxide (NOx = Nitric oxide (NO) + NO2) emissions from soils (SNOx ) affect local ozone air quality, secondary organic aerosol formation, ecosystem acidification and eutrophication, and the atmospheric lifetime of important greenhouse gases (e.g., CO2 and CH4) through its effect on OH (Intergovernmental Panel on Climate Change, 2007)
To bridge the gap between global analyses that identify a need for enhanced emissions at regional scales (100 s of km) and observations that can define processes affecting NOx at meter scales, Bertram et al (2005) used daily NO2 columns retrieved from SCIAMACHY at 30 km × 60 km to explore SNOx following N-fertilization to dry agricultural fields
To determine whether this interannual variability should be visible in the Ozone Monitoring Instrument (OMI) tropospheric NO2 column, we examine the GEOS-Chem ratio of soil column NO2 to total tropospheric column NO2, where the soil column is defined as the difference between a simulation with and without SNOx
Summary
To bridge the gap between global analyses that identify a need for enhanced emissions at regional scales (100 s of km) and observations that can define processes affecting NOx at meter scales, Bertram et al (2005) used daily NO2 columns retrieved from SCIAMACHY at 30 km × 60 km to explore SNOx following N-fertilization to dry agricultural fields They found that the information contained in satellite observations is such that inverse modeling studies could tune mechanistic parameters that respond to climate and soil rather than a single parameter scale factor. We use GEOS-Chem, a chemical transport model, which represents the variability in N emissions to examine implications of this variability for ozone air quality
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