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'Ozone alert,' a sure sign that summer’s coming … if not here already

After temperature cracks 90 for first time, "code orange" ozone alert extended into Thursday.

Not to be confused with the good stuff in the upper atmosphere that has become a perennial source of anxiety, conditions will be ripe again Thursday for a harvest of ground-level ozone.

For the first time this season, and on the first day that the official temperature nudged past 90, the EPA on Wednesday issued a "code orange" alert for so-called bad ozone.

The official high of 91 was one shy of the May 17 record set in 1974. Thursday's forecast high, 92, would be two shy of the record for the date, set in 1962.

Commonly called smog, ground ozone is an unpleasant respiratory cocktail brewed from sunlight interacting with motor-vehicle and other emissions.

Inhaling ozone can set up breathing problems for children; the elderly; and anyone with chronic lung conditions, such as asthma.

The ozone alert covers the entire region, including all of Delaware and all but a tiny portion of New Jersey.

Philadelphia is particularly ripe for bad ozone, as our Frank Kummer reported last month.

But it is not to be confused with the benign ozone layer in the upper atmosphere that helps screen out the sun's most-harmful rays.

As Sean Greene at the Air Quality Partnership points out, people are prone to confuse ground ozone not only with the high-up stuff but also with pollen.

It so happens that tree pollen levels were reported "very high" in the Wednesday morning report from the Asthma Center.

But as allergy sufferers well know, pollen constitutes a torment of a different stripe.