The number of days of poor air quality in Vermont in 2023 spiked up from 2022 (a relatively good air quality year) due to two primary factors.  First, many will remember the unusually high number of days impacted by wildfire smoke from Canada and the western US.  Second, the EPA strengthed the fine particulate standard in early 2024, thereby lowering the PM concentration considered Moderate on the air quality index; therefore, an additional 55 days were included for 2023 that would not have been under the prior standard.  Sources of air pollution that contribute to the worst air quality days in Vermont include local woodsmoke in winter (particulate matter), power plant and transportation emissions from upwind states (ozone), as well as wildfire smoke from fire-prone regions.  While the target number of days with poor air quality is zero, in reality this is unrealistic because air quality is affected by natural phenomenon (such as wildfire smoke) and emissions from jurisdictions outside of Vermont's direct control.  These factors, in addition to changes in meteorology from year to year, result in great year-to-year variability, but there is a significant improvement in the long term air quality trend.

This metric counts the number of calendar days that the “air quality index” (AQI) was categorized as “Moderate,” “Unhealthy for Sensitive Groups” (USG), or "Unhealthy" (in order of increasing severity) on the air quality index for at least one pollutant at one monitoring site in Vermont based on the National Ambient Air Quality Standards (NAAQS) for ozone and fine particulate matter (PM2.5).  Air quality categorized as USG--or worse--exceeds the NAAQS; moderate air quality poses some risk to those with respiratory illnesses and can have environmental and visibility impacts.