Quantifying the importance of stratospheric-tropospheric transport on surface ozone concentrations at high- and low-elevation monitoring sites in the United States

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• 作者：Allen S. Lefohn ; Heini Wernli ; Douglas Shadwick ; Samuel J. Oltmans ; Melvyn Shapiro
• 关键词：Background ozone ; Stratosphere&ndash ; troposphere exchange ; Stratosphere-to-troposphere transport ; Surface ozone
• 刊名：Atmospheric Environment
• 出版年：2012
• 出版时间：December, 2012
• 年：2012
• 卷：62
• 期：Complete
• 页码：646-656
• 全文大小：983 K

文摘

In this study, we quantify the frequency of stratosphere-troposphere exchange (STE) events that result in ozone (O<sub>3sub>) concentration enhancements (i.e., hourly average concentrations?¡Ý50?ppb) observed at 39 high- and low-elevation monitoring sites in the US during the years 2007-2009. We employ a refined forward trajectory-based approach to address the relationship between stratospheric intrusions and enhancements in hourly average O<sub>3sub> concentrations. The model is applied to high-resolution European Center for Medium-Range Weather Forecasting (ECMWF) analyses to identify specific days when the potential for stratosphere-to-troposphere transport (STT) exists to affect surface O<sub>3sub> levels. Our results indicate that STT down to the surface (STT-S) frequently contributes to enhanced surface O<sub>3sub> hourly averaged concentrations at sites across the US, with substantial year-to-year variability. The O<sub>3sub> concentrations associated with the STT-S events appear to be large enough to enhance the measured O<sub>3sub> concentrations during specific months of the year. Months with a statistically significant coincidence between enhanced O<sub>3sub> concentrations and STT-S occur most frequently at the high-elevation sites in the Intermountain West, as well as at the high-elevation sites in the West and East. These sites exhibit a preference for coincidences during the springtime and in some cases, the summer, fall, and late winter. Besides the high-elevation monitoring sites, low-elevation monitoring sites across the entire US experience enhanced O<sub>3sub> concentrations coincident with STT-S events.