Background ozone and carbon monoxide over the North Atlantic for 2001-2011

The mountaintop PICO-NARE station located in the North Atlantic provides unique measurement of a variety of atmospheric species that can be used to examine the continental outflow from North America and evolution of atmospheric composition in the remote free troposphere. Long-term in-situ measurement of ozone and CO for 2001-2011 together with atmospheric chemical transport modeling results as well as satellite remote sensing data are examined in this study. The background ozone and CO have shown a slightly decreasing trend, possibly reflecting the emission reductions in North America during the past decade (which may have more than offset the impacts on North Atlantic background ozone and CO associated with increases in emissions from other regions). Additional factors that could potentially contribute to these decreases include climate change during this period. These hypotheses are tested through both statistical analysis and sensitivity model studies.