2018 Reports

Comparison of CMAQ Simulation to Satellite Observations: NO₂ Column versus OMI NO₂

Qin, Momei; Odman, Talat

Compared to the sparse ground-based monitoring network, satellite observations have the advantage of coverage in unmonitored areas. This document describes a procedure for comparing tropospheric NO₂ columns simulated by the regional CMAQ model to those retrieved from the OMI satellite, with an example application in the Great Lakes Region. The tropospheric NO₂ profile shapes from CMAQ are used to derive new tropospheric vertical column densities (VCD) of NO₂ for comparison. The use of modeled NO₂ profile shapes ensures self-consistency and can improve retrieval accuracy through the improved spatial representation of the air mass factor that converts slant columns to vertical columns. The algorithm detailed in this document follows Goldberg et al. (2017). An implementation of the algorithm in R is appended to the document. Also included are instructions on how to download the data, how to use the algorithm to recalculate NO₂ VCD, how to regrid the data with WHIPS (the Wisconsin Horizontal Interpolation Program for Satellites), and how to perform the model-satellite data comparison.