There’s an ozone alert for Saturday for the metro area, meaning unhealthy concentrations of ground-level ozone.

The primary concern is for active children and adults and those with respiratory disease such as asthma, all of whom are advised to limit prolonged outdoor exertion. Officials suggest that drivers avoid fueling vehicles until after sundown; the vapors released during fueling create ozone when exposed to sunlight. Officials also advise putting off mowing, as lawnmowers and other gas-powered lawn equipment put off a surprising amount of pollution. Those who are active outdoors, such as people exercising or doing yard work, are advised to so early in the morning or late in the evening.

Officials also suggest driving less and considering public transit. Both the KCATA and IndeBus have 75-cent bus fares on ozone alert days.

The Mid-America Regional Council posts a “skycast” – green, yellow, orange or red – each day from April through October. Orange and red are ozone alerts. This is the 13th orange day so far this year, one more than in all of 2011. There hasn’t been a red day since 2006.

The conditions that lead to ozone alerts – sunny days with high temperatures, plus light breezes that do little to dissipate pollutants – are expected to stick around for days. The National Weather Service sees a highs around 100 at least through Thursday. The predicted high is 107.

The skycast is posted at www.marc.org/airQ