Trans-Pacific Transport of Ozone and Reactive Trans-Pacific Transport of Ozone and Reactive Nitrogen During SpringNitrogen During Spring

Thomas W. Walker1 (thomas.walker@dal.ca), Randall V. Martin1,2, Aaron van Donkelaar1, Richard Leaitch3, Anne Marie Macdonald3, Ronald C. Cohen4, Greg Huey5, Melody Avery6,

Andrew Weinheimer7, Frank Flocke7, David Tarasick3, Anne Thompson8, Jerry R. Ziemke9,10, Eric Buscela10

1 Dalhousie University, 2 Harvard-Smithsonian Centre for Astrophysics, 3 Environment Canada, 4 UC Berkeley, 5 Georgia Institute of Technology, 6 NASA LaRC, 7 NCAR, 8 Penn State University, 9 University of Maryland Baltimore County, 10 NASA GSFC

SUMMARYSUMMARY

We interpret aircraft observations from three platforms during INTEX-B in spring 2006 using a chemical transport model (GEOS-Chem) to examine sensitivities of the Pacific and North American free troposphere to East Asian anthropogenic emissions. Timely satellite trends in tropospheric NO2 (8.1% yr-1) constrain trends in Asian NOx emissions. Our baseline simulation reproduces mean vertical profiles in aircraft O3, NOx, and peroxyacyl nitrates (PN's). Asian anthropogenic emissions have a mean contribution of >6.9ppbv to simulated ozone profiles; lightning emissions contribute >3.6ppbv to these profiles on average. A sensitivity study decoupling PN's from the model's chemical mechanism establishes that a significant fraction of ozone production in the east Pacific (>27%) relies on transport of PN's from Asia. While the ozone production due to PN transport is greatest in the East Pacific, persistent winds advect this ozone northeastward into western Canada. Transport events observed by the aircraft confirm that airmasses with enhanced O3 (>95ppbv), CO (>150ppbv), and PN's (>500pptv) were advected this way.

TRANSPORT PATHWAYSTRANSPORT PATHWAYS

OPEN ISSUESOPEN ISSUESCONCLUSIONSCONCLUSIONS

IMPACTS OF CHANGING EMISSIONSIMPACTS OF CHANGING EMISSIONS

Asian 2006 NOx emissions:

We begin with 2000 East Asian anthropogenic NOx emissions from Streets et al [2003] and scale forward to 2003 using factors derived from fossil fuel tallies (CDIAC). We then use the ratio of 2003 and 2006 SCIAMACHY tropospheric NO2 columns to scale up to 2006. The scaling results in a 28% increase in total anthropogenic emissions over the region. Differences between tropospheric NO2 columns from satellite and simulated columns with the new inventory are small (<2x1015 molec/cm2).

Why is the ozone simulations in the Pacific low compared to observations?How does simulated CO compare with observation?

Is stratospheric air significantly mixed with trans-Pacific transport plumes?Does a PV-tracing ozone residual product provide additional information about downward ozone fluxes?

Remote sensing can provide a timely constraint on trace gas emissions Aircraft observations over the Pacific are impacted by:

East Asian NOx emissions (lower troposphere)Lightning NOx emissions (upper troposphere)Contribution to tropospheric ozone columns from each of these sources is ~4-10 DU

Gross ozone production in East Pacific depends on PN transport35% of East Pacific PN's originate in East Asia>27% of Ox production in East Pacific due to East Asian PN's

Aircraft observe PN subsidence and subsequent transport into western Canada

AGU 2007 Fall MeetingSan Francisco, CADecember 10-14, 2007

Streets et al. An inventory of gaseous and primary aerosol emissions in Asia in theyear 2000. JGR, 2003Ziemke et al. Tropospheric ozone determined from Aura OMI and MLS: Evaluation of measurements and comparison with the Global Modelling Initiative's Chemical Transport Model. JGR, 2006

This work was supported by the National Science and Engineering Research Council Special Research Opportunity program.

ACKNOWLEDGEMENTACKNOWLEDGEMENT

REFERENCESREFERENCES

aircraft mean2006 emissions2000 emissionsno lightningno Asian anthro

Difference b/w observed and simulated tropospheric NO2 columns

Observed and simulated vertical profiles of O3, NOx, and PN's

Comparison to Pacific troposphereUsing the 2006 Asian emissions, we sample the model along the aircraft tracks and average onto the model resolution to create vertical profiles. We also perform this analysis for model runs:

using emissions from 2000, without lightning NOx emissions, without Asian anthropogenic emissions.

The latter two provide means of evaluating the contribution to Pacific concentrations of reactive nitrogen and ozone due to these respective sources.

Tropospheric O3 columns from OMI and from simulation

Comparison to satelliteSatellite tropospheric columns of O3 exhibit a broad feature, decreasing from west to east, indicative of outflow and transport of Asian pollution. Our simulation reproduces this feature. Sensitivity studies show a contribution to the column of >4 DU at the west coast of North America. The contribution from lightning NOx decreases away from the tropics.

Differentiation PN transportTransport of PN's in the upper troposphere redistributes O3 production from NOx source regions to remote areas. A model study decoupling PN's showed that 35% of PN's in the East Pacific originate in Asia, and 27% of the gross ozone production is due to transport of these PN's.

A pathway into North AmericaThe primary subsidence region for PN's in the East Pacific is in a persistent high pressure center off the California coast. Winds in spring tend to advect air from this subsidence region northeastward around the Aleutian low. Ozone transport along this path occurs in episodes. In an event on May 4-5, 2006, 20% of the ozone being advected was due to PN transport from Asia.

Corroboration by aircraftThe event of May 4-5 was observed by the aircraft, which saw elevated levels of O3 (>95ppbv), CO (>150ppbv), and PN's (>500pptv) in a plume at 800hPa.