Springtime surface measurements of 7Be and speciated Hg and their relationships with dynamical indicators of stratospheric air in Houston, TX

Ambient monitoring data show that ozone levels in Houston, TX have been decreasing over the past decade due to reductions in both NOx and VOC emissions. However, the Houston area still exceeded the EPA National Ambient Air Quality 8 hour standards (O3 mixing ratio > 75ppbv) nearly 50 times in 2011. The stratosphere contains approximately 90% of atmospheric ozone; making stratospheric air a potent ozone source which influences the composition of the free troposphere through Stratosphere-Troposphere Exchange (STE). The most common STE phenomena in extratropical regions are tropopause folds. It is thought that STE may contribute to surface ozone in the Houston area, but currently the magnitude of STE contribution to surface ozone is poorly quantified. Previous studies have used high 7Be concentration, atmospheric layers with high O3 with low relative humidity, low Hg0 along with high HgII mixing ratios, and enhanced potential vorticity to identify stratospherically impacted air masses. We performed a 2012 Spring and Fall measurement campaign targeted to capture cold frontal passages at the University of Houston's Main Campus using ozonesondes, High-Volume Total Suspended Particulate sampler (for 7Be concentration), speciated Hg, and insitu ozone measurements. Several frontal passages were analyzed using both the SUNY-Albany Global Forecast System (GFS) model of potential vorticity and tropopause height and the NOAA Air Resources Laboratory (ARL) HYSPLIT trajectory model. These goal of this analysis is to better estimate the amount of ozone brought down to the surface through springtime STE events.