Meteorological controls on observed peroxyacetyl nitrate at Mount Bachelor during the spring of 2008

A suite of gas phase and aerosol measurements were made during spring 2008 at the summit of Mount Bachelor (2763 m asl), located in central Oregon. Here we focus on observations of peroxyacetyl nitrate ( PAN) for the period of 3 April to 18 June 2008. During this period, PAN mixing ratios ranged from below detection limit to 527 pptv, with a campaign mean of 119 pptv. Our analysis indicates that the variability in PAN was predominantly a function of synoptic scale processes. Three plumes containing elevated PAN were analyzed in detail. Two of these plumes were of Asian origin, and one was associated with North American sources. The Asian plumes were observed on 17-18 April and 12-13 May. Both were associated with elevated PAN, CO, O-3, and aerosol scattering (sigma(sp)). The relationship between PAN and O-3 varied with air mass temperature within the 17-18 April plume, and we exploited this to derive an O-3 production efficiency per unit of PAN decomposed of 51-73 mol mol(-1). The second Asian plume (12-13 May) was more dilute, characterized by lower CO and sigma(sp). This event had a larger PAN/CO slope, consistent with relatively colder subsidence as calculated by trajectories. We traced the pathways of the plumes using a global chemical transport model (GEOS-Chem) alongside trajectories to show that the plumes crossed the Pacific at different rates and following different routes. The plume observed on April 17-18 traveled over the great circle, while the later plume took a slower more southern path across the Pacific.