The percentage of days for which air quality was monitored and found to be good, indicating healthy air both for sensitive groups, such as people with asthma, and for the population as a whole. The Air Quality Index (AQI) summarizes levels of ground-level ozone, particulate matter (soot and other particles), carbon monoxide, sulfur dioxide, and nitrogen dioxide into one measure.
Exposure to these pollutants can cause short-term health effects such as irritation to the eyes, nose and throat, coughing, sneezing, runny nose, and shortness of breath. Continued exposure can also worsen medical conditions such as asthma and heart disease.
In 2021, 89% of days with air quality measurements in Essex County were good air days, down from the rate in 2020, and a 21 percentage point increase from 2000.
Lake County, IL had the lowest percentage of good air days in 2021, at 74%. Middlesex County, MA had the highest at 93% and Westchester County, NY was similar to Essex County. Since 2000, most counties have had an increase in the number of good air days.
Comparable national and state data is not available due to the quantity and location of EPA monitoring stations. Data for this indicator are expected to be released annually in July.