WASHINGTON — Ryan Miller has a unique perspective on air quality. The ABC7 meteorologist is also a teacher of environmental science at Washington and Lee High School in Arlington.

“I can see air quality from a weather standpoint; I can see air quality from an environmental standpoint,” he says.

That gives him rare insight into the air quality index used by the Metropolitan Washington Council of Governments.

He says the most typical reading in the summer is the one most local residents just ignore. It’s Code Yellow, which stands for moderate air quality.

But if the air becomes stagnant, with lots of sunshine and little breeze, conditions can deteriorate to Code Orange, which is unhealthy for sensitive people, including small children and the elderly. Further deterioration can result in the ultimate in local foul air — a Code Red day, which is not good for anyone.

A lot of factors can contribute to a poor air quality reading, which is the result of ground ozone produced by cars and power plants mixing with microscopic particles that can be inhaled deep into the lungs and cause respiratory issues.

Miller says polluted air can do real damage, and the more exposure someone gets, the worse the harm will be.

“If you are exercising, you are going to breathe deeper into your lungs and take those particles deeper into your lungs, and your body is going to have a harder time expelling some of that material,” he explains, adding that in the summer it’s important to limit outdoor workouts to the early morning.

He says that as the day progresses, “we see a lot of environmental factors come together — the sunshine, the heat — that work to pollute the atmosphere even more and add to the deterioration in air quality.”

That is why the air is always at its worst in the mid-afternoon all the way through to the evening.

But there is good news. While we experience Code Orange air quality from time to time, the region has not seen a Code Red day since July 2012.

Again, a number of factors are at play, Miller says. People are buying less gasoline and utilizing more mass transit and car pools. Clean air regulations are having an inpact, along with new technologies that have made the region a bit less dependent on fossil fuels.

But we’ve also had a good dose of weather luck.

“We haven’t had these prolonged, really really hot periods where you see little movement in the atmosphere, little wind,” Miller says.

Hot days in the D.C. area often have a breeze or a sudden shower, and cold fronts move through the region from time to time, causing temperatures in the 90s to dip into the 80s.

“That works to stir up the atmosphere, to push some of the pollution away from the region,” says Miller, adding that the summer rain also helps to clear the air.

And he reminds Washingtonians that no matter how bad our air seems to be, it is a lot worse in other world capitals.

His favorite example: That Code Red day in 2012 had an air quality index of 67. In January 2013, Beijing had a reading of 755.

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