January 2007: Surface and lightning sources of nitrogen oxides over the United States: magnitudes, chemical evolution, and outflow

We use observations from two aircraft during the ICARTT campaign over the eastern United States and North Atlantic during summer 2004, interpreted with a global 3-D model of tropospheric chemistry (GEOS-Chem) to test current understanding of regional sources, chemical evolution, and export of NO_x. Mean NO_x concentrations were 0.55 +/- 0.36 ppbv, much larger than in previous U.S. aircraft campaigns (ELCHEM, SUCCESS, SONEX) though consistent with data from the NOXAR program aboard commercial aircraft. We show that regional lightning is the dominant source of this upper tropospheric NO_x and increases upper tropospheric ozone by 10 ppbv. Simulating NO_x observations with GEOS-Chem requires a factor of 4 increase in simulated NO_x yield per flash (to 500 mol/flash).

The above figure shows mean upper tropospheric NO_x concentrations (8-12 km) during ICARTT (July -August 2004).Observations mapped on the 2^ox2.5^o GEOS-Chem model grid (left) are compared to model values for the improved simulation (right). The improved simulation has a factor of four increase in the United States lightning emissions relative to the standard GEOS-Chem version.

A full description of this work is given in Hudman et al. [2007].