Comparison of ground-based and satellite-based NO2 column measurements: First steps to correlating in-situ and remote measurements

Determining ground-level trace-gas mixing ratios via satellite measurements is limited by the satellite’s spatial resolution (typically on the order of 100 km^2), the relationship between the integrated column of air “seen” by a satellite instrument to a surface concentration, and the overpass schedule. Although satellite-based spectrometers such as Ozone Monitoring Instrument (OMI) aboard Aura are capable of observing regional-to-large urban area pollution events, these measurements are limited temporally by one overpass per day. In support of NASA’s GEO-CAPE mission, the CAPABLE site at NASA Langley Research Center has been established in coordination with the U.S. Environmental Protection Agency and Virginia’s Department of Environmental Quality to provide insight into the relationship between geostationary high temporal resolution measurements from space and continuous in situ surface observations. The focus of this study is to determine the correlation of in situ NO2 measurements with ground-based column NO2 measurements using a direct-sun photometer. Our investigation also incorporates the measurement of boundary-layer parameters (e.g. height, winds) into the interpretation of the analyses. In addition, we present an analysis of how satellite NO2 columns are impacted by pixel size and the distance of the measurement from the LaRC site. From our results, we hope to be able to propose further steps that will lead to better understanding between surface and integrated column measurements so that satellite observations can be better utilized by the air quality user community. Disclaimer: Although this work was reviewed by the U.S. Environmental Protection Agency and National Aeronautics and Space Administration, and approved for publication, it may not necessarily reflect official Agency policy.