AirNow.gov. Residents can check current air quality by zip code. AirNow reports air quality using the official U.S. Air Quality Index (AQI), which is color coded to indicate if the air is healthy or unhealthy.
Air Monitoring in MA. Provides daily air quality updates for MA. Note, if there is an active alert, it will appear as a yellow banner across the top of the page. Select "MassAir online" for current air quality and forecasts.
CDC resources on air quality and your health. Includes a link to the CDC's sub-page on Particle Pollution (e.g. dust, dirt, soot, smoke, drops of liquid).