The impact of North American anthropogenic emissions and lightning on long-range transport of trace gases and their export from the continent during summers 2002 and 2004

In summer 2004, net downward radiative flux at the tropopause due to ozone produced from anthropogenic emissions ranged from 0.15 to 0.30 W m⁻² across the North Atlantic, while that due to ozone produced from lightning NO emissions ranged from 0.20 to 0.50 W m⁻². Enhanced lofting of polluted air followed by stronger westerly winds led to more net export of NOx, NOy, and ozone in early summer 2004 than 2002 despite reduced anthropogenic emissions.

Ozone export fluxes across the eastern NA boundary due to anthropogenic emissions were factors of 1.6 and 2 larger than those due to lightning in 2004 and 2002, respectively. Doubling the NA lightning NO source increased downwind ozone enhancements due to lightning NO emissions by one third.