Journal article

Trans-pacific transport of reactive nitrogen and ozone to Canada during spring

Walker T, Martin R, Van Donkelaar A, Leaitch W, MacDonald A, Anlauf K, Cohen R, Bertram T, Huey L, Avery M, Weinheimer A, Flocke F, Tarasick D, Thompson A, Streets D, Liu X ...see all

Atmospheric Chemistry and Physics, vol. 10, issue 17 (2010) pp. 8353-8372

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We interpret observations from the Intercontinental Chemical Transport
Experiment, Phase B (INTEX-B) in spring 2006 using a global chemical
transport model (GEOS-Chem) to evaluate sensitivities of the free
troposphere above the North Pacific Ocean and North America to Asian
anthropogenic emissions. We develop a method to use satellite
observations of tropospheric NO2 columns to provide timely estimates of
trends in NOx emissions. NOx emissions increased by 33% for China and
29% for East Asia from 2003 to 2006. We examine measurements from three
aircraft platforms from the INTEX-B campaign, including a Canadian
Cessna taking vertical profiles of ozone near Whistler Peak. The
contribution to the mean simulated ozone profiles over Whistler below
5.5 km is at least 7.2 ppbv for Asian anthropogenic emissions and at
least 3.5 ppbv for global lightning NOx emissions. Tropospheric ozone
columns from OMI exhibit a broad Asian outflow plume across the Pacific,
which is reproduced by simulation. Mean modelled sensitivities of
Pacific (30 degrees N-60 degrees N) tropospheric ozone columns are at
least 4.6 DU for Asian anthropogenic emissions and at least 3.3 DU for
lightning, as determined by simulations excluding either source.
Enhancements of ozone over Canada from Asian anthropogenic emissions
reflect a combination of trans-Pacific transport of ozone produced over
Asia, and ozone produced in the eastern Pacific through decomposition of
peroxyacetyl nitrates (PANs). A sensitivity study decoupling PANs
globally from the model's chemical mechanism establishes that PANs
increase ozone production by removing NOx from regions of low ozone
production efficiency (OPE) and injecting it into regions with higher
OPE, resulting in a global increase in ozone production by 2% in spring
2006. PANs contribute up to 4 ppbv to surface springtime ozone
concentrations in western Canada. Ozone production due to PAN transport
is greatest in the eastern Pacific; commonly occurring transport
patterns advect this ozone northeastward into Canada. Transport events
observed by the aircraft confirm that polluted airmasses were advected
in this way.

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  • T. W. Walker

  • R. V. Martin

  • A. Van Donkelaar

  • W. R. Leaitch

  • A. M. MacDonald

  • K. G. Anlauf

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