Ozone is a by product of long sunny days, light winds and plenty of car exhaust. Industrial pollution can also cause the formation of ozone.
Houston has seen a string of unhealthy moderate ozone days since the weekend. If your sensitive to ozone or have another respiratory disorder, you should avoid the peak ozone levels of the afternoon and early evening.
That's when ozone levels reach there highest one hour average readings as measured by the Texas Commission on Environmental Quality (TCEQ).
Daily readings and forecast are available at the TCEQ link posted on this blog. Wind currents are expected to pick up in the next 24-48hrs. This should help improve the code orange unhealthy levels to just moderate or code yellow by Tuesday and Wednesday.