The American Lung Association released its 2021 State of the Air report last week. For this corner of New Hampshire, the report contained good news that Cheshire County’s outdoor air quality ratings had improved since the previous year’s report. That’s a welcome development indeed, but it would be premature for the region to think assuring good air quality is a done deal.

The Lung Association’s annual report summarizes exposure to particle and ozone pollution over the most recent three-year period of the available data. Both types are worth tracking as one measure of general environmental progress. But both are also a public health concern, as exposure to them can cause serious health effects such as asthma attacks, cardiovascular damage and lung cancer.

The just-released report covers the 2017 to 2019 three-year period, and Cheshire County earned an “A” — the highest assigned rating — for low levels of both kinds of pollution, with its ranking for ozone levels being an improvement from the prior year’s “B” grade. Nationwide, the Lung Association reported more than 40 percent of Americans lived with polluted air, so the local results are indeed encouraging.

Of the measures the annual report tracks, particle pollution, has been a concern over the years for Cheshire County and especially Keene. The city sits in a geological bowl, and airborne particulates, particularly from woodstove use in winter months and automobile emissions, can get trapped through weather inversion and stall overhead rather than dissipate. Keene has taken steps to address that generally as part of its climate action plan calling for reductions in carbon and other greenhouse gas emissions, and more immediately through recent programs to incentivize upgrading to less polluting wood stoves.

Thus, the Lung Association’s report that Cheshire County — which in this case also means Keene itself, since the county’s sole monitor is located on Water Street — maintained its “A” for particle pollution can be seen as a credit to those efforts, especially since the rating is achieved based on both average annual levels and having no short-term spikes of particle pollution. As the association’s national assistant vice president for state public policy, Michael Seilback, summed it up, “Certainly any time you could receive ‘A’s without any levels of elevated pollution is something to be really happy about.”

Still, there are reasons for caution about the results. As recently as early last year, state environmental officials issued a three-day air quality health warning for Keene due to inversion conditions. While there were no similar warnings this past winter, it’s too early to tell whether that’s consistent with the Lung Association’s findings over the preceding three years or a short-term reflection of curtailed driving and other activity during the COVID-19 pandemic. Indeed, with reports nationally of reduced air pollution in some cities during the pandemic, the Lung Association may find its annual reports skewed to a degree over the next three or so years until the country is fully beyond the pandemic.

And even within the latest report there are signs requiring continued vigilance locally. For example, despite its “A” grade, Cheshire County nevertheless had higher rates of asthma than, for instance, Fairbanks, Alaska, and Fresno, Calif., which, according to the report, are among the nation’s cities with the highest level of particle pollution. Since the Lung Association’s report does not address indoor air quality, which likely is a contributor to the asthma rates, certainly that finding deserves continued attention from public health and other officials.

The Lung Association’s most recent annual report gives area residents additional incentive to step outside and enjoy a deep breath of refreshing spring air. But it’s certainly no reason to take their air quality for granted.