Rising levels of ozone, an air pollutant that can cause breathing problems, make it potentially unsafe to break a sweat outdoors Tuesday in Charlotte.
By 3 p.m., ozone levels in the Charlotte region had reached well into Code Red territory on the air-quality index. That means most people – especially those with lung diseases such as asthma – should avoid prolonged or heavy exertion outdoors.
Ozone is an invisible gas that forms in the air from motor vehicle exhaust and industrial emissions when the weather is hot, sunny and still, as it is Tuesday.
It’s been the bane of Charlotte summers for decades, but had shown marked improvement in recent years as state and federal measures reduced emissions.
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But midway through June, metro Charlotte has already experienced the worst air since 2012. That’s when the area logged its last Code Red ozone day, along with 11 slightly less ominous Code Orange days.
The federal threshold for safe ozone levels dropped last October. That makes comparisons with previous years tricky.
Still, said Tom Mather of the N.C. Division of Air Quality, “it’s definitely safe to say these are the worst levels since 2012.”
While year-to-year variations are expected, weather plays a powerful role in how much ozone forms. Charlotte was on the edge of a weather front Tuesday that brought in sinking air, high pressure and lower humidity, Mather said – good conditions in which ozone can form.
Shelley Lanham, a Mecklenburg County air quality specialist, said high ozone levels most often occur in June. The days before the summer solstice are among the longest of the year, yielding more sunlight to help transform emissions into ozone.
Still, she said, “it’s important to note that downward trend” of days with poor air quality. The Charlotte region had only two Code Orange days last year, and none in 2014 or 2013.
Wednesday’s forecast is for a Code Orange day, better but potentially unhealthy for the young, elderly and people with breathing problems.