| Abstrakt: |
We investigated the impacts of cold fronts on area-wide peak O 3 and regional background O 3 mixing ratios on a daily scale over the Houston-Galveston-Brazoria (HGB) area of southeastern Texas during the O 3 seasons (April–October) of 2003–2016. Back trajectories showed that an 18h time lag existed between arrival of cold fronts in the HGB area and onset of a predominately northerly flow. Cold fronts showed increasing effects on both peak and background O 3 over the HGB area. Compared to no front days, average peak O 3 mixing ratios during the cold front 1st days, cold front 2+ days, and post frontal days increased 0.7, 5.9, and 9.0 ppbv, respectively while average background O 3 increased 2.9, 6.8, and 8.6 ppbv, respectively. The change in wind direction from southerly to northerly was the most important factor causing increasing O 3 levels. Wind direction shifts caused variation of other meteorological factors (i.e., wind speed, precipitation, temperature, cloud cover, and relative humidity) and tended to overshadow their effects on O 3 over the HGB area. On a long-term and large-scale view, cold fronts over the HGB area could be regarded as interruptions in the cleansing effects of predominantly marine southerly flow from the Gulf of Mexico. [ABSTRACT FROM AUTHOR] |
