Description:
<jats:p>We examine the implications of new estimates of the anthropogenic and lightning nitrogen oxide (NO<jats:sub><jats:italic>x</jats:italic></jats:sub>) source for the budget of oxidized nitrogen (NO<jats:sub><jats:italic>y</jats:italic></jats:sub>) over the United States in summer using a 3‐D global chemical transport model (Model of Ozone and Related Tracers‐4). As a result of the Environmental Protection Agency (EPA) State Implementation call, power plant NO<jats:sub><jats:italic>x</jats:italic></jats:sub> emissions over the eastern United States decreased significantly, as reflected by a 23% decrease in summer surface emissions from the 1999 U.S. EPA National Emissions Inventory to our 2004 inventory. We increase the model lightning NO<jats:sub><jats:italic>x</jats:italic></jats:sub> source over northern midlatitude continents (by a factor of 10) and the fraction emitted into the free troposphere (FT, from 80% to 98%) to better match the recent observation‐based estimates. While these NO<jats:sub><jats:italic>x</jats:italic></jats:sub> source updates improve the simulation of NO<jats:sub><jats:italic>x</jats:italic></jats:sub> and O<jats:sub>3</jats:sub> compared to the Intercontinental Chemical Transport Experiment‐North America aircraft observations, a bias in the partitioning between nitric acid (HNO<jats:sub>3</jats:sub>) and peroxyacetylnitrate (PAN) remains especially above 8 km, suggesting gaps in the current understanding of upper tropospheric processes. We estimate a model NO<jats:sub><jats:italic>y</jats:italic></jats:sub> export efficiency of 4%−14% to the North Atlantic in the FT, within the range of previous plume‐based estimates (3%−20%) and lower than the 30% exported directly from the continental boundary layer. Lightning NO<jats:sub><jats:italic>x</jats:italic></jats:sub> contributes 24%−43% of the FT NO<jats:sub><jats:italic>y</jats:italic></jats:sub> export from the U.S. to the North Atlantic and 28%−34% to the NO<jats:sub><jats:italic>y</jats:italic></jats:sub> wet deposition over the United States, with the ranges reflecting different assumptions. Increasing lightning NO<jats:sub><jats:italic>x</jats:italic></jats:sub> decreases the fractional contribution of PAN to total NO<jats:sub><jats:italic>y</jats:italic></jats:sub> export, increases the O<jats:sub>3</jats:sub> production in the northern extratropical FT by 33%, and decreases the regional mean ozone production efficiency per unit NO<jats:sub><jats:italic>x</jats:italic></jats:sub> (OPE) by 30%. If models underestimate the lightning NO<jats:sub><jats:italic>x</jats:italic></jats:sub> source, they would overestimate the background OPE in the FT and the fractional contribution of PAN to NO<jats:sub><jats:italic>y</jats:italic></jats:sub> export. Therefore, a model underestimate of lightning NO<jats:sub><jats:italic>x</jats:italic></jats:sub> would likely lead to an overestimate of the downwind O<jats:sub>3</jats:sub> production due to anthropogenic NO<jats:sub><jats:italic>x</jats:italic></jats:sub> export. Better constraints on the lightning NO<jats:sub><jats:italic>x</jats:italic></jats:sub> source are required to more confidently assess the impacts of anthropogenic emissions and their changes on air quality over downwind regions.</jats:p>