New Hampshire and Maine are probably not the first places that come to mind when you think of air pollution. In fact, cities from both states were recently ranked among the country's 25 cleanest.
But under the heat "dome" that currently engulfs the U.S. Northeast and Mid-Atlantic regions, the condition of the air in these and other typically-pristine places is plummeting, according to the EPA. The result is a double-whammy of health concerns -- particularly for young children, the elderly and anyone with breathing or heart problems.
"Most people just think about the direct effects of heat. But there are secondary effects that occur with very high temperatures," said Jonathan Levy, an air pollution expert at the Boston University School of Public Health.
The combination of sunlight with nitrogen oxide and sulfur dioxide emissions from cars and coal-fired power plants, for example, can create a cocktail of unhealthy pollutants.
"On days when you have more sunlight, you have more ozone formation," Levy explained. "And on hot, humid days, sulfate particulate matter forms more readily in the atmosphere."
Dr. Tom Kosatsky, medical director of environmental health services at the BC Center for Disease Control, noted that most heat-related deaths result from heart or lung complications, usually lagging a day or two after the hot spell, rather than happening from immediate overheating. Air pollution targets the same organs: ozone (the main ingredient in "smog") and particulate matter can penetrate the lungs, aggravating asthma and other breathing problems, and even extending their harm to the heart.
Generally, the health consequences are the sum of the heat hazard plus the pollution's effects. "But at very high temperatures and very high levels of ozone, the effect is more than additive," Kosatsky added.
"A little ozone ordinarily doesn't make much of a difference," he said. "But when it gets really hot, every little bit of ozone has a big effect on mortality."
Still, the recipe for ozone or particulate matter pollution generally calls for some man-made emissions, and a place like Maine is not necessarily a hotbed of heavy traffic or power plants.
Levy explained that both ozone and fine particulate matter can travel hundreds of miles. Air pollution emitted by cars and trucks in the Boston area, for example, could push north via prevailing winds, react with the sun along the way and then spread the toxic concoction over a broad region.
"As this extremely hot summer weather continues, we again predict that New England will experience unhealthy air quality," Curt Spalding, administrator of EPA's New England office said in a statement on Friday. "On these days, EPA and the medical community suggest that people limit their strenuous outdoor activity. Everybody can help reduce smog-forming emissions by driving less, by using public transportation and by setting air conditioner thermostats a few degrees higher."
Particularly for people who are sensitive to air pollution -- the same group that is also likely to be more vulnerable to high temperatures -- Levy also recommends staying indoors or in an air-conditioned setting.
"Ozone doesn't penetrate indoors well," he said. "Particulate matter does penetrate, but air conditioning can remove some of the particles."