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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 ()

Abstract

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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