ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-11-17621-2011 Interannual variability of ozone and carbon monoxide at the Whistler high elevation site: 2002–2006 Macdonald A. M. 1 Anlauf K. G. 1 Leaitch W. R. 1 Chan E. 1 Science and Technology Branch, Environment Canada, 4905 Dufferin Street, Toronto, Ontario, Canada 22 06 2011 11 6 17621 17664 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/11/17621/2011/acpd-11-17621-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/11/17621/2011/acpd-11-17621-2011.pdf

In spring 2002, an atmospheric measurement site was established at the peak of Whistler Mountain in British Columbia, Canada to measure trace gases, particle chemistry and physics, and meteorology. This paper uses continuous measurements from March 2002 to December 2006 to investigate the influence of trans-Pacific transport and North American forest fires on both O<sub>3</sub> and CO at Whistler. Annual mean mixing ratios of O<sub>3</sub> and CO were 41 ppbv (monthly means of 35–48 ppbv) and 145 ppbv (monthly means of 113–177 ppbv) respectively with both species exhibiting an annual cycle of late-winter to early-spring maxima and summer minima. The absence of a broad summer O<sub>3</sub> peak differs from previously-reported high altitude sites in the western US. The highest monthly-averaged O<sub>3</sub> and CO mixing ratios relative to the 5-year monthly means were seen in fall 2002 and spring 2003 with increased O<sub>3</sub> and CO of 10 % and 25 % respectively. These increases correspond to anomalously-high values reported at other Northern Hemisphere sites and are attributed to fires in the Russian Federation. Air mass back trajectory analysis is used to associate the mean enhancements of O<sub>3</sub> and CO with trans-Pacific transported or North American air masses relative to the Pacific background. Mean values of the enhancements for March to June were 6 ppbv and 16 ppbv for O<sub>3</sub> and CO respectively. In summers 2002–2006, higher CO and O<sub>3</sub> mixing ratios were always observed in North American air masses and this relative enhancement co-varied for each year with the western US and Canada total wildfire area. The greatest enhancements in O<sub>3</sub> and CO were seen in 2004, a record year for forest fires in Alaska and the Yukon Territory. In August 2004, average O<sub>3</sub> and CO mixing ratios were 13 and 44 ppbv above background values.

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