Bachelor observatory

Abstract. Interannual variations in background tropospheric trace gases (such as carbon monoxide, CO) are largely driven by variations in emissions (especially wildfires) and trans-port pathways. Understanding this variability is essential to quantify the intercontinental contribution to US air quality. We investigate the interannual variability of long-range trans-port of Asian pollutants to the Northeast Pacific via measure-ments from the Mt. Bachelor Observatory (MBO: 43.98 ◦ N, 121.69 ◦ W; 2.7 km a.s.l.) and GEOS-Chem chemical trans-port model simulations in spring 2005 vs. the INTEX-B cam-paign during spring 2006. Measurements of CO at MBO were significantly enhanced during spring 2005 relative to the same time in 2006 (the INTEX-B study period); a de-cline in monthly mean CO of 41 ppbv was observed between April 2005 and April 2006. A backtrajectory-based meteoro