Smog days

As summer begins, a string of Code Oranges last week has put the Charlotte region ahead of its usual pace of high-ozone days. Code Orange signals conditions that can be unhealthy for children, seniors and those with asthma.

Through Friday, sensors in Mecklenburg, Union, Lincoln or Rowan counties had registered Orange ozone concentrations on eight days this spring, and on June 9 hit the more threatening Code Red.

Over the past decade, the region averaged 5.4 Code Orange days and slightly less than one Code Red day through June 20. The region's ozone forms mostly from vehicle, power plant and industry emissions, but hot, sunny, stagnant weather drives up readings on some days. Bruce Henderson