Influence of Cold Fronts on Variability of Daily Surface O3 over the Houston-Galveston-Brazoria Area in Texas USA during 2003–2016

We investigated the impacts of cold fronts on area-wide peak O3 and regional backgroundO3 mixing ratios on a daily scale over the Houston-Galveston-Brazoria (HGB) area of southeasternTexas during the O3 seasons (April–October) of 2003–2016. Back trajectories showed that an 18h timelag existed between arrival of cold fronts in the HGB area and onset of a predominately northerlyflow. Cold fronts showed increasing effects on both peak and background O3 over the HGB area.Compared to no front days, average peak O3 mixing ratios during the cold front 1st days, coldfront 2+ days, and post frontal days increased 0.7, 5.9, and 9.0 ppbv, respectively while averagebackground O3 increased 2.9, 6.8, and 8.6 ppbv, respectively. The change in wind direction fromsoutherly to northerly was the most important factor causing increasing O3 levels. Wind directionshifts caused variation of other meteorological factors (i.e., wind speed, precipitation, temperature,cloud cover, and relative humidity) and tended to overshadow their effects on O3 over the HGB area.On a long-term and large-scale view, cold fronts over the HGB area could be regarded as interruptionsin the cleansing effects of predominantly marine southerly flow from the Gulf of Mexico.