The air quality reached the highest level of pollution on a new system implemented earlier this year. Yesterday, the color-coded smog alert reached purple which means very unhealthy air. That means more high ozone levels are expected.
Ozone can become a respiratory irritant that forms when other pollutants mix.
That was also the nation's highest. Because of a number of high readings, Houston ended 1999 with the largest number of ozone violations in the nation, surpassing Los Angeles for the first time.