Biogenic NOxemissions from soils are a large natural source with substantial uncertainties in global bottom-up estimates (ranging from 4 to 15 Tg N yr-1). We reduce this range in emission estimates, and present a top-down soil NOxemission inventory for 2005 based on retrieved tropospheric NO2columns from the Ozone Monitoring Instrument (OMI). We use a state-of-science soil NOxemission inventory (Hudman et al., 2012) as a priori in the GEOS-Chem chemistry transport model to identify 11 regions where tropospheric NO2columns are dominated by soil NOxemissions. Strong correlations between soil NOxemissions and simulated NO2columns indicate that spatial patterns in simulated NO2columns in these regions indeed reflect the underlying soil NOxemissions. Subsequently, we use a mass-balance approach to constrain emissions for these 11 regions on all major continents using OMI observed and GEOS-Chem simulated tropospheric NO2columns. We find that responses of simulated NO2columns to changing NOxemissions are suppressed over low NOxregions, and account for these non-linearities in our inversion approach. In general, our approach suggests that emissions need to be increased in most regions. Our OMI top-down soil NOxinventory amounts to 10.0 Tg N for 2005 when only constraining the 11 regions, and 12.9 Tg N when extrapolating the constraints globally. Substantial regional differences exist (ranging from-40% to +90%), and globally our top-down inventory is 4-35% higher than the GEOS-Chem a priori (9.6 Tg N yr-1). We evaluate NO2concentrations simulated with our new OMI top-down inventory against surface NO2measurements from monitoring stations in Africa, the USA and Europe. Although this comparison is complicated by several factors, we find an encouraging improved agreement when using the OMI top-down inventory compared to using the a priori inventory. To our knowledge, this study provides, for the first time, specific constraints on soil NOxemissions on all major continents using OMI NO2columns. Our results rule out the low end of reported soil NOxemission estimates, and suggest that global emissions are most likely around 12.9 ± 3.9 Tg N yr-1.
CITATION STYLE
Vinken, G. C. M., Boersma, K. F., Maasakkers, J. D., Adon, M., & Martin, R. V. (2014). Worldwide biogenic soil NOxemissions inferred from OMI NO2observations. Atmospheric Chemistry and Physics, 14(18), 10363–10381. https://doi.org/10.5194/acp-14-10363-2014
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