Texas Air Quality Study 2000

Late last summer when many of us were wondering if temperatures would ever cool down, 300 scientists and technicians were studying Houston regional air pollution in planes and on the ground. In a $20 million study, scientists from over 40 universities and government agencies boarded five aircraft equipped with sophisticated instruments and also conducted measurements at 17 ground sites. Scientists established one of the sites on the 62nd floor of the Williams Tower (formerly called the Transco Tower) in the Galleria. From Aug 15 - Sept 19, 2000 they collected massive amounts of data about wind, temperature, and pollutants from the ground up to 1000 feet. Peter Daum, one of the participating scientists from the Department of Energy in Brookhaven, N.Y. called it "the most detailed characterization of sources, transformation processes, and meteorology controlling ozone and aerosol concentration."

Houston's unique air pollution

In the year since the Texas Air Quality Study (TexAQS 2000), scientists have revealed some amazing facts about air pollution in the Houston region. They have determined that ozone formation in Houston is unique because of its location near water, the intense sources of chemicals that form ozone, the day to day variation in ozone concentrations, and the meteorology. In comparison with other cities the scientists have studied (Nashville and Phoenix), ozone formation in the Houston region is much more rapid and more efficient.
Peter Daum explained that Houston wouldn't have an ozone problem if it weren't for industry and the weather. Daum says that in most cities, the very high ozone is caused by transportation sources and meteorology. But in Houston, emissions coming from industry are causing the very high formation rates. Daum explained further that "In Houston, ozone formation can be as high as four times faster than in a typical city. Planes flying over Houston were able to measure how fast ozone forms. Formation of ozone over the center of the city is moderate, but the rate of ozone formation increases over the Ship Channel. The highest rates of ozone formation occur over the Ship Channel in late morning."

Weather affects ozone formation

Weather patterns in the Houston region are affected by the coast which cause the wind to change direction on some days. This change, called a flow reversal, is partly responsible for the region's high ozone. In the morning, the winds may come from the northwest and carry pollution from the Ship Channel to the south. Later in the morning, the winds may shift in a clockwise direction and carry those pollutants back north of the city. This flow reversal pattern explains why ozone concentrations are often high north of the city late in the afternoon. Scientists explain that every ozone exceedance for the past five years has some circulatory path associated with it.

High Ozone Events

During the study period, measurements indicated that the federal ozone standard of 125 parts per billion (ppb) was exceeded almost every day. Scientists attribute extremely high ozone exceedances called "transient high ozone events" (THOEs) to rapid and efficient ozone formation that occurs north of the Ship Channel. THOES are characterized by an increase of at least 40 ppb ozone the hour before the episode and a decrease of at least 40 ppb ozone afterwards. These compact plumes of very high ozone can be blown in such a way that ozone exceedances can occur without being recorded on any monitor in the area.
Scientists will continue to analyze the data they collected in 2000 for another two to three years. From information about how ozone forms and moves across the region, business, industry and policy makers will be able to determine how to reduce it. For the latest detailed information, look on the TNRCC Air Quality Science Evaluation website http://www.tnrcc.state.tx.us/air/aqp/airquality_science.html#topic1.