Task 124

Evaluating Potential for Satellite Observations to Improve Soil NOx Emissions Estimates by Satellite/Emissions/Photochemical Model Intercomparison

Principal Investigator(s):

S. Ehrman

Collaborators:

D. Allen, H. Plata, and E. Achinivu

Sponsor(s):

K. Pickering

Last Updated:

October 26, 2012 15:25:28

Description of Problem

Soil NOx emissions contribute to the tropospheric NO2 column. Soil bacteria produce NO through the processes of nitrification and denitrification. Field experiments, model simulations [e.g., Davidson et al., 1998] and satellite observations indicate that NO emissions pulse following rain on dry soils, particularly after recent application of fertilizer. Satellite-based observations have been instrumental in determining the magnitude of soil NOx emissions. Globally, soil emissions of NO contribute perhaps 5-10 Tg N per year to the global NOx budget. Jaeglé et al. [2004, 2005] and Bertram et al. [2005] estimated the soil NOx source using top-down approaches based on satellite data from the GOME and SCIAMACHY instruments, respectively. Their results suggest that biospheric models underestimate soil NOx emissions by a factor of 2. The increasingly high resolution of satellite data makes it possible to constrain emission sources over smaller and smaller regions. Reducing uncertainties in this source is an active area of research.

Scientific Objectives and Approach

Soil NOx emissions are included in EPA’s Biogenic Emission Inventory System (BEIS); however, they are parameterized and it is likely they are underestimated. The method of parameterization was investigated. Emissions were compared with OMI observations. We first screened the OMI tropospheric NO2 data to eliminate contributions from other sources. We used satellite mapping technology to focus on low population density regions. We then created a smoothed CMAQ grid that corresponded with the OMI grid. Comparisons were made for several precipitation episodes in the spring of 2005 and 2006. 26 cases were identified and detailed analyses performed.

Accomplishments

In most cases, but not all, the satellite observations did pick up the NO2 signal, presumably from the pulse following a precipitation event. However, no generalized trends were observed, with respect to over- or under-predicting the magnitude of the pulse. Present work is focused on identifying other dominant sources of NO2 that may be playing a role in these regions at this time of year and also identifying air parcel histories for each case.

Other Publications and Conferences

Achinivu E., Chou S.T., Plata H., Allen D., Pickering K., Pierce T., Gleason J. and Ehrman SH, “Towards improve emissions inventories of soil NOx via model/satellite measurement intercomparisons” CMAS annual meeting, October 2009.

Plata H., Allen D., Pickering K., Pierce T., Ehrman S.H. “Soil NOx model/satellite measurement intercomparisons” CMAS annual meeting, October 2010.