An ozone climatology of the Dallas-Fort Worth area and its relationship to meteorology

Abstract

The Environmental protection agency has established a hics. National Ambient Air Quality Standard for surface ozone through the Clean Air Act and its amendments. The Dallas / Fort Worth area is in violation of these standards, and to date, no extensive studies on ozone in this area have been published. This study presents a broad overview of the ozone problem in the DFW area. An ozone spatial and temporal climatology was constructed using ozone data at 23 different monitoring sites from 1980-1996. Temporally, the high ozone threat was found to extend from 16 Apr-l5 Oct, a period one month longer than the traditional period used in cities further north. Strong persistence was found over synoptic time periods, consistent with studies in other cities. The spatial study was challenged by the lack of a consistent monitoring network, but in general relatively depressed ozone values are observed in urban areas, with increasing ozone values in rural areas especially downwind. Northern rural areas had the highest ozone averages. Ozone-meteorology relationships were examined using scatterplots and correlation coefficients, Most of the meteorology variables only displayed a rate-limiting role with ozone. Correlation values displayed significant seasonal variation, with temperature having a much lower correlation than expected based on results from other studies. Conditional Climatology Tables were constructed to explore which combination of variables pointed to the highest ozone days. Yesterday's ozone, wind speed, and wind direction were found the most predictive. In general, low wind speeds and wind directions from the E-SE were most favorable for high ozone. Wind direction biases were examined using windroses and by examining upwind vs. downwind behavior at the periphery sites. Evidence suggests that high ozone in the east, south, and west has occurred, but has gone undetected due to a lack of consistent monitoring there. There is also some evidence that winds from the E-SE may be transporting precursors from outside the DFW area, although further research is required.