The Environmental Protection Agency says in 2013 New Hampshire experienced only three days with poor air quality due to ground-level ozone – or smog. This fits into the overall trend of declining smog over the last three decades.
Smog primarily is formed when pollution out of car tailpipes and power plant emissions interacts with light, and it forms more quickly (and so is worse) on hot summer days.
But in New Hampshire, smoggy days peaked in the summer of 1988, with 36 poor air quality days, and has been declining slowly ever since.
Dave Conroy, chief of air programs at New England EPA, credits cap and trade schemes for nitrous oxide emissions. “As a result of those facilities have installed pollution controls but also have begun to phase in the cleaner burning units as well,” says Conroy.
He also notes that large declines have also come from cleaner burning car engines, and more power plants burning natural gas than ever before.
In 2009 and 2011, New Hampshire hit an all-time low of two poor air quality days. Neighboring Vermont had zero days, while Massachusetts had six.