Why is Houston's Air So Bad?

October 7, 1999 was a typical day for students in Deer Park, a small community east of Pasadena and south of the Houston Ship Channel. After school, kids on soccer, football and cross-country teams went outside to practice, as usual. And for the 44th time that year, one of the 23 ozone monitors in the Houston-Galveston 8-county area exceeded the federal health standard for ozone - 125 parts per billion (ppb).

This would not be an unusual event for the Houston area except that the Deer Park monitor measured ozone at 251 ppb - twice the national health standard - and the highest ozone concentration in the nation for 1999. Since ozone levels were so high that day, normally healthy high school athletes experienced difficulty breathing, pain in their chests, and coughing episodes. This wasn't the first time, however, that Houston had recorded the highest ozone concentration in the nation. It also happened in 1997 at a measurement of 234 ppb (Figure 2 below).

Something unusual was happening in Los Angeles, too. After years of having many fewer days of high ozone than Los Angeles, Houston tied LA for the number of high ozone days in the country. This had never happened before. Los Angeles has always had more high ozone days than Houston. But October 7 would not be the last day in 1999 when air monitors in the Houston-Galveston area would record ozone concentrations over the health standard. Three more days in October and five days in November would bring the total number of high ozone days for the year to 52, twelve more days than in 1998 and 8 more days than Los Angeles.

Was this signaling a trend of worsening air pollution in Houston? Not necessarily. The number of high ozone days in the Houston area for the past 10 - 12 years has been fairly stable, averaging about 50 days per year. However, the trend in Los Angeles has been a rather dramatic reduction in the number of high ozone days (Figure 1).

Why is Houston's air so bad when Los Angeles' air has gotten so much better? Los Angeles has recognized their air quality problem and has been making steady progress on it for a number of years. They have reduced emissions that cause ozone formation from 55-75%, whereas Houston has only achieved reductions of 20% for one class of pollutants.

Although the major sources of pollutants in the two cities are different (vehicles in LA and industry in Houston), Los Angeles has been much more aggressive at reducing those pollutants than Houston. Los Angeles has found that technological changes such as cleaning burning fuels and cleaner burning vehicles are more acceptable to the public than behavioral changes such as "no-drive days" and lower speed limits. We should be able to learn from the experience in Los Angeles when it comes to adopting a plan for emissions reductions in the Houston-Galveston area.