The partitioning of reactive nitrogen (NO y) was measured over the remote North Pacific during spring 2006. Aircraft observations of NO, NO 2 , total peroxy nitrates (total alkyl and multi-functional nitrates (and nitric acid (HNO 3), made between 25 • and 55 • N, confirm a controlling role for peroxyacyl nitrates in NO x production in aged Asian outflow. account for more than 60 % of NO y above 5 km, while thermal dissociation limits their con-tribution to less than 10 % in the lower troposphere. Using si-multaneous observations of NO x , HNO 3 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 NO y from East Asia. Observations of NO x , and HO x are used to constrain a 0-D photochemical box model for the calculation of net photochemical ozone production or tendency (3) as a function of aircraft altitude and NO x concentrations. The model analysis indicates that the photochemical environment of the lower troposphere (altitude < 6 km) over the north Pa-cific is one of net O 3 destruction, with an experimentally de-termined crossover point between net O 3 destruction and net O 3 production of 60 pptv NO x . Qualitative indicators of in-tegrated net O 3 production derived from simultaneous mea-surements of O 3 and light alkanes (Parrish et al., 1992), also indicate that the north Pacific is, on average, a region of net O 3 destruction.
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