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Stratosphere troposphere exchange and its influence on surface ozone concentrations in the lower Fraser Valley Bovis, Paul E.

Abstract

7Be activity concentration data collected at the University of British Columbia and ozone data collected throughout the Lower Fraser Valley (LFV), British Columbia, Canada from April 1996 - March 2001 were used to investigate the frequency, magnitude and source regions of possible stratosphere-troposphere exchange (STE) episodes that may have influenced surface ozone concentrations in the LFV. With the aid of synoptic and back trajectory analysis, it was determined that the bulk of the intruded stratospheric ozone, which resulted in elevated surface ozone concentrations in the LFV, originated within intense Eastern Asian/Western Pacific cutoff low pressure systems and troughs. This stratospheric air was then transported by the synoptic scale flow to the LFV region where it descended to the surface via synoptic scale high pressure systems. During these STE episodes, it was estimated that stratospheric ozone concentrations of up to 40 ppb (depending on the season and time of day) were contributing to the total surface ozone concentrations in the LFV. Since anthropogenic ozone production is already a major concern of air quality management programs in the LFV, this stratospheric contribution cannot be ignored when decisions are being made with regards to surface ozone reduction initiatives in this region.

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