State officials say current unhealthy ozone concentrations will spread in New Hampshire through mid-week.
Rockingham County remains under an air quality alert through Wednesday. Joining it Tuesday and Wednesday are Hillsborough County and any area above 3,000 feet in elevation – some mountainous parts in the North Country.
Jeff Underhill is the state's chief air quality scientist. He says the high ozone levels come from heat, sun and winds carrying pollution.
"Air pollution can travel long distances faster at higher elevations, so it's not uncommon for us to see – when the air quality turns bad, for it to start to turn bad at higher elevations first,” he says.
Underhill says children, the elderly and people with certain health issues should avoid outdoor activity in the next few days, if they're in an affected area.
But on the whole, he says New Hampshire's ozone concentrations are improving. These days, he says the smog comes less from Midwestern pollution, and more from vehicle emissions in East Coast cities.
"You know, that's why it's important that we keep our cars tuned up,” Underhill says. “The newer cars tend to be cleaner than the older cars, and the more we head in that direction, the better it'll be.”
As for this week's poor air quality, he says, a cold front and cleaner winds should move in to the region by late Wednesday and clear the air.