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Downtown Springfield.

(Flickr)

The air quality in Hampshire and Hampden counties could put the health of residents -- especially babies and those with asthma -- at risk, according to an American Lung Association report released this week.

The "State of the Air 2016," a compilation of air monitoring data collected between 2012 and 2014, shows that both Hampshire and Hampden counties received F grades for their total number of days with unhealthy smog levels.

Hampshire County averaged 4.3 days of high ozone levels per year, while Hampden County averaged 4.7. Anything more than 3.2 days was an F.

Both counties received C grades in the 2015 report.

"Keep in mind, we refer to New England as the 'tailpipe of the nation,'" said Casey Harvell, American Lung Association director of public policy for Massachusetts. "That jet stream come through and brings pollution from other parts of the country."

The levels of smog -- otherwise known as ozone -- in these areas were high enough to potentially harm sensitive populations, including newborns, the elderly and those with chronic respiratory conditions such as asthma.

Ozone is a powerful irritant that damages lung tissue, the association said. It forms in the atmosphere from chemical reactions of air pollutants such as unburned fuel and gases, and is usually produced on hot, windless days.

Suffolk County received an overall D on the 2016 report card, while Worcester County got a C.

Climate scientists say the amount of ozone in cities and other populated areas will increase as the earth continues to warm. Harvell said that this trend is partly to blame for poor air quality in the western part of the state.

While Western Massachusetts' grades for this report are disconcerting, Harvell added, it doesn't mean improvements aren't being made -- in fact, the U.S. is seeing an "overall trend up." Cleaner air is possible as the Clean Air Act is strengthened, she said.

On a brighter note, the Springfield metropolitan area was the No. 1 cleanest metro region in the U.S. for short-term levels of particle pollution, the report says. Harvell said this is due, in part, to the closing of Massachusetts coal fire plants.

Mount Tom Power Station, a former Holyoke coal-burning plant, was shuttered in 2014.

Particle pollution can be harmful even if it is inhaled over just a few hours or days, even if the annual averages are low, the association. "Short-term levels" account for such spikes. This data was not collected for Hampshire County.

Bakersfield, Calif., was the No. 1 worst city for particle pollution spikes; six California metropolitan areas landed in the top-10 worst cities for this metric.

In the 25 cities with the worst pollution, most saw improvements from 2015, the association said; and many saw their lowest levels ever of year-round particle or ozone pollution.

"Yet, even as most cities experienced strong improvement, too many cities suffered worse episodes of unhealthy air," the report said. "While most of the nation has much cleaner air quality than even a decade ago, a few cities reported their worst number of unhealthy days since the report began, including some that experienced extreme weather events."

For air quality information on other counties in Massachusetts and the U.S., check out the report here.

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