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Global ozone-CO correlations from OMI and AIRS: Constraints on tropospheric ozone sources

by P. S. Kim, D. J. Jacob, X. Liu, J. X. Warner, K. Yang, K. Chance, V. Thouret, P. Nedelec
Atmospheric Chemistry and Physics ()
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We present a global data set of free tropospheric ozone-{CO} correlations with 2 degrees x 2.5 degrees spatial resolution from the Ozone Monitoring Instrument ({OMI)} and Atmospheric Infrared Sounder ({AIRS)} satellite instruments for each season of 2008. {OMI} and {AIRS} have near-daily global coverage of ozone and {CO} respectively and observe coincident scenes with similar vertical sensitivities. The resulting ozone-{CO} correlations are highly statistically significant (positive or negative) in most regions of the world, and are less noisy than previous satellite-based studies that used sparser data. Comparison with ozone-{CO} correlations and regression slopes ({dO(3)/dCO)} from {MOZAIC} (Measurements of {OZone}, water vapour, carbon monoxide and nitrogen oxides by in-service {AIrbus} {airCraft)} aircraft profiles shows good general agreement. We interpret the observed ozone-{CO} correlations with the {GEOS} (Goddard Earth Observing System)-Chem chemical transport model to infer constraints on ozone sources. Driving {GEOS-Chem} with different meteorological fields generally shows consistent ozone-{CO} correlation patterns, except in some tropical regions where the correlations are strongly sensitive to model transport error associated with deep convection. {GEOS-Chem} reproduces the general structure of the observed ozone-{CO} correlations and regression slopes, although there are some large regional discrepancies. We examine the model sensitivity of {dO(3)/dCO} to different ozone sources (combustion, biosphere, stratosphere, and lightning {NOx)} by correlating the ozone change from that source to {CO} from the standard simulation. The model reproduces the observed positive {dO(3)/dCO} in the extratropical Northern Hemisphere in spring-summer, driven by combustion sources. Stratospheric influence there is also associated with a positive {dO(3)/dCO} because of the interweaving of stratospheric downwelling with continental outflow. The well-known ozone maximum over the tropical South Atlantic is associated with negative {dO(3)/dCO} in the observations; this feature is reproduced in {GEOS-Chem} and supports a dominant contribution from lightning to the ozone maximum. A major model discrepancy is found over the northeastern Pacific in summer-fall where {dO(3)/dCO} is positive in the observations but negative in the model, for all ozone sources. We suggest that this reflects a model overestimate of lightning at northern midlatitudes combined with an underestimate of the East Asian {CO} source.

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