Satellite Retrieval and Ground Based Measurements of NO2

The Ozone Monitoring Instrument aboard the NASA EOS-Aura satellite has been making daily global measurements of a wide range of trace atmospheric chemical species since November 2004. As an important component of anthropogenic air pollution, nitrogen dioxide (NO2) is among the more significant trace gases retrieved from OMI. Its principal sources are fossil fuel and biomass combustion, and so elevated levels are often seen around urban areas, coal-fired power plants, and agricultural burning. The NO2 retrieval algorithm rests on a set of assumptions about the vertical profiles of NO2 concentration in the atmosphere: these were obtained from chemistry and transport models that use emissions inventories as input. The algorithm is known to be rather sensitive in certain parameter regimes. The algorithm is being revised, with a new data release expected to be made later this year. In addition to an updated set of climatological NO2 profiles, the algorithm will use a database of surface reflectivity derived from OMI data. Toronto is an industrial and urban center in a relatively flat area, in which the Ontario Ministry of the Environment operates a network of in situ monitoring instruments, each a few meters above the surface. We present a statistical analysis of the OMI-retrieved NO2 using the agreement between OMI and the in situ measurements as an avenue to characterizing the sensitivity of the OMI product to various parameters in the retrieval, and to help characterize the change in the product due to the algorithm revision.