Meteorologically adjusted long-term ozone air quality trends over the South Texas Region

摘要

Ground-level ozone (O3) is a secondary air pollutant that forms from chemical reactions involving NOx and volatile organic compounds subjected to favorable weather conditions such as temperature and low wind speed. Control of emissions of NOx and VOCs from human activities has been the major focus in ground level ozone reduction program. This study was performed to evaluate meteorologically independent long-term ozone trends over South Texas cities so as to assess historical ozone decrease caused by changes in the precursor emissions. The Texas Commission on Environmental Quality (TCEQ) has been gathering information through monitoring stations at strategic urban locations within the state and has established a historical record on certain atmospheric parameters in order to measure air quality. For this study the temporal and spatial characteristics of ground-level (tropospheric) O3 were measured at 9 monitoring stations in inland and coastal Texas sites of varying populations from 1983 to 2003. In order to evaluate the O3 trend caused by changes in precursor emissions, moving average filters were applied to decompose original ozone data into long-term, seasonal and short term trends and a linear least-squared regression model were adopted to eliminate effects of temperature from the original data. The results showed a significant decrease in the number of days exceeding the National Ambient Air Quality Standards (NAAQS) and a small change in total O3 variation. The influence of changes in emissions explained about 29% of the total O3 variation. Spatially, ground-level O3 varied largely in different urbanscale types in Texas. There was a stronger seven days cycle in major urban sites than in minor urban sites indicating that traffic emissions are major sources contributing to ozone formation in urban areas.