Interannual variability of ozone and carbon monoxide at the Whistler high elevation site: 2002–2006

Abstract. 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 O₃ and CO at Whistler. Annual mean mixing ratios of O₃ 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 O₃ peak differs from previously-reported high altitude sites in the western US. The highest monthly-averaged O₃ and CO mixing ratios relative to the 5-yr monthly means were seen in fall 2002 and spring 2003 with increased O₃ 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 O₃ 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 in trans-Pacific air masses were 6 ppbv and 16 ppbv for O₃ and CO respectively. In summers 2002–2006, higher CO and O₃ mixing ratios were almost 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 O₃ and CO were seen in 2004, a record year for forest fires in Alaska and the Yukon Territory with average O₃ and CO mixing ratios 13 and 43 ppbv above background values.