Atmos. Chem. Phys., 13, 12537-12547, 2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.
Free-troposphere ozone and carbon monoxide over the North Atlantic for 2001–2011
A. Kumar1, S. Wu1,2, M. F. Weise1,*, R. Honrath1,2,†, R. C. Owen3, D. Helmig4, L. Kramer2, M. Val Martin5, and Q. Li6
1Department of Civil & Environmental Engineering, Michigan Technological University, Houghton, Michigan, USA
2Department of Geological and Mining Engineering and Sciences, Michigan Technological University, Houghton, Michigan, USA
3US EPA, Research Triangle Park, North Carolina, USA
4Institute of Alpine and Arctic Research, University of Colorado at Boulder, Boulder, Colorado, USA
5Department of Atmospheric Sciences, Colorado State University, Fort Collins, Colorado, USA
6Department of Atmospheric {&} Oceanic Sciences, University of California Los Angeles, Los Angeles, California, USA
*now at: ARCADIS, Novi, Michigan, USA

Abstract. In situ measurements of carbon monoxide (CO) and ozone (O3) at the Pico Mountain Observatory (PMO) located in the Azores, Portugal, are analyzed together with results from an atmospheric chemical transport model (GEOS-Chem) and satellite remote sensing data (AIRS (Atmospheric Infrared Sounder) for CO, and TES (Tropospheric Emission Spectrometer) for O3) to examine the evolution of free-troposphere CO and O3 over the North Atlantic for 2001–2011. GEOS-Chem captured the seasonal cycles for CO and O3 well but significantly underestimated the mixing ratios of CO, particularly in spring. Statistically significant (using a significance level of 0.05) decreasing trends were found for both CO and O3 based on harmonic regression analysis of the measurement data. The best estimates of the possible trends for CO and O3 measurements are −0.31 ± 0.30 (2-σ) ppbv yr−1 and −0.21 ± 0.11 (2-σ) ppbv yr−1, respectively. Similar decreasing trends for both species were obtained with GEOS-Chem simulation results. The most important factor contributing to the decreases in CO and O3 at PMO over the past decade is the decline in anthropogenic emissions from North America, which more than compensate for the impacts from increasing Asian emissions. It is likely that climate change in the past decade has also affected the intercontinental transport of O3.

Citation: Kumar, A., Wu, S., Weise, M. F., Honrath, R., Owen, R. C., Helmig, D., Kramer, L., Val Martin, M., and Li, Q.: Free-troposphere ozone and carbon monoxide over the North Atlantic for 2001–2011, Atmos. Chem. Phys., 13, 12537-12547, doi:10.5194/acp-13-12537-2013, 2013.
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