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On the export of reactive nitrogen from Asia: NOx partitioning and effects on...

Bertram, T. H., A. Perring, P. J. Wooldridge, J. Dibb, M. Avery, and R. C. Cohen (2013), On the export of reactive nitrogen from Asia: NOx partitioning and effects on ozone, Atmos. Chem. Phys., 13, 4617-4630, doi:10.5194/acp-13-4617-2013.

The partitioning of reactive nitrogen (NOy ) was measured over the remote North Pacific during spring 2006. Aircraft observations of NO, NO2 , total peroxy nitrates ( PNs), total alkyl and multi-functional nitrates ( ANs) and nitric acid (HNO3 ), made between 25◦ and 55◦ N, confirm a controlling role for peroxyacyl nitrates in NOx production in aged Asian outflow. PNs account for more than 60 % of NOy above 5 km, while thermal dissociation limits their contribution to less than 10 % in the lower troposphere. Using simultaneous observations of NOx , PNs, ANs, HNO3 and average wind speed, we calculate the flux of reactive nitrogen through the meridional plane of 150◦ W (between 20◦ and 55◦ N) to be 0.007 ± 0.002 Tg N day−1 , which provides an upper limit of 23 ± 6.5 % on the transport efficiency of NOy from East Asia. Observations of NOx , and HOx are used to constrain a 0-D photochemical box model for the calculation of net photochemical ozone production or tendency ( O3 ) as a function of aircraft altitude and NOx concentrations. The model analysis indicates that the photochemical environment of the lower troposphere (altitude < 6 km) over the north Pacific is one of net O3 destruction, with an experimentally determined crossover point between net O3 destruction and net O3 production of 60 pptv NOx . Qualitative indicators of integrated net O3 production derived from simultaneous measurements of O3 and light alkanes (Parrish et al., 1992), also indicate that the north Pacific is, on average, a region of net O3 destruction.

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Tropospheric Composition Program (TCP)