Keene Air Quality Index (AQI)

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Keene, New Hampshire, nestled in the southwestern corner of the state, presents a unique geographic context influencing its air quality. The city occupies a rolling upland plateau, part of the New England Upland physiographic province, at an elevation averaging around 800 feet. This terrain, sculpted by glacial activity, contributes to localized air drainage patterns. Keene is not directly adjacent to a major body of water, though the Ashuelot River flows through it, offering limited influence on regional air circulation. The surrounding landscape is predominantly forested, transitioning to agricultural lands – primarily dairy farming – to the west and more extensive woodlands to the east, towards the Monadnock region. While Keene isn’t situated within a heavy industrial belt, its proximity to larger metropolitan areas like Boston and New York City means it can receive transported pollutants. The urban-rural gradient is relatively sharp; Keene itself is a compact city, but quickly gives way to sparsely populated, heavily forested areas. This gradient impacts pollutant dispersion, with limited urban heat island effects but potential for stagnation during stable atmospheric conditions. The prevailing winds, often from the west, can carry pollutants from upwind sources, while local topography can trap them in the valley. This interplay of factors creates a complex air quality profile.

Keene’s air quality follows a distinct seasonal pattern. Spring brings increased pollen counts, impacting those with allergies, but generally good air quality as winter pollutants are dispersed by increasing winds. However, agricultural activities beginning in April can contribute to particulate matter from tilling and fertilizer application. Summer typically offers the cleanest air, with prevailing winds flushing out pollutants and ample sunshine promoting photochemical breakdown of ozone precursors. August can see occasional ozone exceedances due to hot, stagnant conditions. Fall is marked by vibrant foliage but also increased wood smoke from residential heating, becoming noticeable by October and peaking in November. This is often coupled with temperature inversions, trapping pollutants near the ground. Winter presents the most challenging air quality period. Cold temperatures drive increased reliance on fossil fuel heating, leading to elevated levels of particulate matter (PM2.5) and carbon monoxide. Snow cover reduces deposition, and frequent temperature inversions exacerbate pollution. Sensitive groups – children, the elderly, and those with respiratory conditions – should limit strenuous outdoor activity during prolonged cold snaps and periods of wood smoke. February and early March are typically the months with the poorest air quality.