On the export of reactive nitrogen from Asia: NO x partitioning and effects on ozone

This is the authors' abstract. We don't add key points for this paper.

The partitioning of reactive nitrogen (NOy) was measured over the remote North Pacific during spring 2006. We use these observations to assess the impact of increasing emissions of nitrogen oxides in East Asia on ozone (O3) production rates over the remote Pacific and the intercontinental transport of O3 and its precursors to North America. Aircraft observations of speciated NOy, made between 25° and 55° N, confirm a controlling role for peroxyacyl nitrates in NOx production in aged Asian outflow, accounting for more than 60% of NOy above 5 km, while thermal dissociation limits their contribution to less than 10% in the lower troposphere. The observations reveal the extreme sensitivity of the remote Pacific to future changes in NOx loadings, with an experimentally determined crossover point between net Oxdestruction and net Ox production of 60 pptv NOx. Using simultaneous observations of speciated NOy and wind speed, we calculate the flux of reactive nitrogen through the meridional plane of 150° W (between 25° and 55° N) to be 0.007 ± 0.002 Tg N day−1, which provides an upper limit of 15% on the export efficiency of NOy from East Asia. Analysis of the subsiding plumes in the sampling domains suggests that episodic dry subsidence events play an important role in the intercontinental transport of ozone and its precursors from East Asia to North America.