On the export of reactive nitrogen from Asia: NO x partitioning and effects on ozone
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 (ΣPNs), total alkyl and multi-functional nitrates (ΣANs) 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. ΣPNs account for more than 60% of NO y above 5 km, while thermal dissociation limits their contribution to less than 10% in the lower troposphere. Using simultaneous observations of NO x, ΣPNs, ΣANs, 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 (Δ O 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 Pacific is one of net O 3 destruction, with an experimentally determined crossover point between net O 3 destruction and net O 3 production of 60 pptv NO x. Qualitative indicators of integrated net O 3 production derived from simultaneous measurements 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.