Direct observations of megacity emissions and lifetimes of nitrogen oxides using OMI

Emission inventories in megacities are uncertain, particularly in developing countries. Can we use OMI to better quantify these emissions without a model?

By analyzing the downwind patterns of Nitrogen Dioxide (NO₂) for different wind conditions, we simultaneously determine megacity Nitrogen Oxides (NO_x) emissions and lifetimes from Aura's Ozone Monitoring Instrument (OMI). Estimated daytime lifetimes are ~4 hours at low and mid-latitudes, but ~8 hours in wintertime for Moscow. Derived NO_x emissions are is reasonable agreement with global emission inventories, but are higher by a factor of 3 for the Saudi-Arabian capital Riyadh.

The wind dependency of NO₂ column densities around Riyadh.

Left: Mean NO2 tropospheric columns in the Middle East from OMI measurements during 2005-2009 for calm (w<2 m/s) conditions with <30% cloud cover. The grey box indicates Riyadh and the surrounding area.

Right: Mean NO₂ column densities around Riyadh (white cross) for different wind conditions, i.e. calm (center panel) and 8 main wind direction sectors (surrounding panels; arrows indicate the mean of the respective ECMWF winds).

The resulting NO_x emissions and lifetimes. Scatterplot of the resulting NOx emissions for the considered megacities and power plants versus the respective EDGAR emissions (V4.1, integrated over 250_250 km2). Resulting NO_x lifetimes are color coded.

Credit : Beirle et al. (2011) Science, courtesy F. Boersma (KNMI)

11.04.2011