What Is the Air Quality in Merrimack, New Hampshire?

Merrimack, New Hampshire earns a C — air quality is fair, but not great. With a 5-year median AQI of 37, the city sees a meaningful number of "Moderate" days each year, when the EPA flags air as a concern for unusually sensitive people.

Merrimack, New Hampshire's 5-year median AQI of 37 is 4 points below the national average of 41 — meaningfully cleaner than the typical U.S. metro tracked here. Within New Hampshire, Merrimack, New Hampshire's air quality is roughly typical for the state, where the average city posts a 5-year median AQI of 38.

For context within New Hampshire: Rockingham, New Hampshire currently holds the state's cleanest grade (B, AQI 40), while Coos, New Hampshire sits at the bottom (B, AQI 42).

Air quality in Merrimack, New Hampshire has been getting worse over the past decade, with median AQI climbing by roughly 0.7 points per year. That bucks the national trend of broad improvement, and most often reflects either growing wildfire smoke exposure (particularly across the West) or rising local emissions from population and freight growth.

In 2014, Merrimack, New Hampshire posted a median AQI of 33. By 2023 that figure was 39 — a rise of 6 AQI points dirtier across 10 years of EPA records.

Across the past five years, this area has logged just 1 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 0 days per year, or roughly one every other month. That is a low count by national standards.

Healthy adults can continue normal outdoor activity in most weather, but should pay attention to AQI alerts during the worst pollution windows. People with asthma, heart disease, or pregnancy should reduce prolonged or intense outdoor exertion on flagged days, and consider running an indoor HEPA air cleaner during peak season. Because ozone peaks in the afternoon on hot sunny days, plan outdoor exercise for early morning or after sunset on bad-air days.