Investigation of Central Texas Surface Ozone Concentrations 1980–2015

The Austin Northwest ozone monitoring station operated by the Texas Commission on Environmental Quality (Site 484530014) has been collecting surface ozone concentration data for the Austin metropolitan area for the past three decades. The length and quality of this record provides a unique opportunity to observe the surface ozone concentrations in the city at a variety of timescales.  This study seeks to investigate the effect of increasing population on the Austin region’s surface ozone concentrations. Furthermore, this time frame allows for study of the surface ozone concentration during the three most recent very strong El Niño Events (1982, 1997, 2015). A study into the surface ozone concentration for a major southern city has not been conducted over such a large time span. This study not only allows for a better understanding of the effect of increasing anthropogenic precursors associated with population increase in the Austin region on surface ozone concentrations over the allotted time frame, but also provides insight into the effect ENSO has on Austin’s surface ozone concentration.
The warm phase of the El Niño Southern Oscillation (ENSO) plays a predominant role in the climate of southern states, such as Texas. Though the effects of this phenomenon are thoroughly studied, the effect that El Niño has on surface ozone concentration in Texas has not. To study the effects of “very strong” El Nino events (A Southern Oscillation Index, or SOI, of 4), climatological data for temperature, precipitation, and hourly surface ozone concentration were obtained for Site 14 through the Texas Commission on Environmental Quality (TCEQ) over the period of 1980 to 2015. Stratifying the data by only precipitation, the monthly ozone concentration for the peak ozone season, April through September, was determined for both the very strong El Niño events and the neutral or very weak ENSO events.  Monthly ozone concentrations for these two sets of ENSO events were compared.  Suppression of ozone concentrations was observed for the very strong ENSO years relative to ENSO neutral years (SOI of 0) for April and May, no significant change in concentrations relative to neutral years for June and July, and an increase in ozone relative to neutral years for August and September. Looking into composite climatological data from NOAA’s Earth System Research Laboratory (ESRL), we found that for these very strong El Nino events there were anomalously lower temperatures and indicators of more precipitation for April and May than compared to the same period for the neutral events, no significant anomalous behavior in June and July, and anomalously higher temperatures and indicators of less precipitation for August and September. These results suggest a meteorological explanation for the changes observed in surface ozone concentrations during very strong ENSO years; however, more investigation is required to understand whether very strong El Nino events are the cause of this climatological phenomena and how ENSO is causing this meteorological behavior to occur.
Further investigation will include examining precipitation, wind speed, wind direction, temperature, and surface reflectivity, all of which influence the surface ozone concentrations. Once all natural drivers have been appropriately identified, the remaining surface ozone concentration could be attributed to local anthropogenic production of ozone precursors in Austin. In addition, having reliable surface ozone concentrations, including a robust understanding of regional background ozone, will allow for study of anthropogenic trends in Austin’s surface ozone concentrations. Such an analysis should yield a better understanding of the effect of policy changes directed at reducing ozone precursors in the area over the past thirty years.