The lower-left panel shows observed vertical profiles of concentrations for two major transpacific Asian pollution plumes, May 5 and May 17, sampled by the ITCT-2K2 aircraft: CO (black) , O3 (red) and (right) NOy components: PAN (solid blue), HNO3 (solid green), and NO (purple). The May 5 plume was sampled at 5-8 km altitude with CO up to 275 ppbv but no elevated ozone, and the May 17 was sampled at 2.5-4 km altitude with CO up to 225 ppbv and ozone up to 90 ppbv. We show that the elevated ozone in the latter plume is consistent with production from PAN decomposition during subsidence of the plume over the northeast Pacific. This production is particularly efficient because of the strong radiation and low humidity of the subsiding environment. The top panel shows mean simulated ozone production efficiency per unit NOx consumed (OPE) for May 2002 averaged between 2 - 4 km. The average OPE for the NE Pacific is 60-80; in comparison, urban boundary layer conditions are ~5. We argue that PAN decomposition represents a major and possibly dominant component of the ozone enhancement in transpacific Asian pollution plumes. The lower-right panel shows observed 8-h ozone at Sequoia National Park (1800 m) in May 2002 vs. corresponding simulated (GEOS-CHEM) Asian pollution ozone enhancement (May 17th plume in red). Asian enhancements are 6-10 ppbv during NAAQS exceedances(black line); unlike at surface sites, Asian pollution influence is not minimum under high-ozone conditions! For more information see Hudman et al. 2004 [PDF]