Does the location of aircraft nitrogen oxide emissions affect their climate impact?

Abstract

We present results from 112 one-year global chemistrytransport model integrations: a base case, then variants with extra aircraft nitrogen oxide (NO x) emissions added to specific regions in the first month (July). The NO x stimulates ozone (O 3) production and methane (CH 4) destruction. Responses vary spatially: low background NO x regions are most sensitive. Integrated (100-year time horizon) radiative forcings (IRF) are calculated. Net (O 3 + CH 4) IRFs for July aviation NO x are generally negative: the global average, weighted by emissions, is -1.9 mWm -2 yr (TgNO2) -1. The positive IRF associated with the shortterm O 3 increase (4.1 mWm -2 yr (TgNO2) -1) is overwhelmed by the effects of the long-term CH 4 decrease. Aircraft NO x net IRFs are spatially variable, with July values over the remote Pacific approximately balancing the IRF associated with aviation CO 2 emissions (28 mWm -2 yr (TgNO 2) -1 J. The overall climate impact of global aviation is often represented by a simple multiplier for CO 2 emissions. These results show that this is inappropriate. Copyright 2009 by the American Geophysical Union.