Index Geophysics

On the export of reactive nitrogen from Asia: NOx 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, NO₂, total peroxy nitrates (&Sigma;PNs), total alkyl and multi-functional nitrates (&Sigma;ANs) and nitric acid (HNO₃, made between 25° and 55° N, confirm a controlling role for peroxyacyl nitrates in NO_x production in aged Asian outflow. &Sigma;PNs 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, &Sigma;PNs, &Sigma;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 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 (&Delta; O₃) 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 O₃ destruction, with an experimentally determined crossover point between net O₃ destruction and net O₃ production of 60 pptv NO_x. 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.

Bertram, T. H.

Perring, A. E.

Wooldridge, P. J.

Dibb, J.

Avery, M. A.

Cohen, R. C.

2018-01-15

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10.5194/acp-13-4617-2013

https://acp.copernicus.org/articles/13/4617/2013/

eISSN: 1680-7324

eng