2019 CEQ Annual Report

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Air Quality

Air Days

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Quick Summary - check check check


Connecticut residents breathed healthful air on 342 days in 2019: an increase of five days from the 10-year average.

The number of statewide “good air days” increased in 2019 (342) from 341 days in 2018; however, there was an increase in the number of days (2) that exceeded the standard for particulate matter (PM 2.5).

A “good air day” is when every monitoring station in the state records satisfactory air quality. “Satisfactory air quality” is defined here as air that meets the health-based National Ambient Air Quality Standard (NAAQS) for all of the following six pollutants: sulfur dioxide, lead, carbon monoxide, PM, nitrogen dioxide, and ground-level ozone. The goal is for Connecticut residents to have a “good air day”, every day. 

A consequence of the air pollution controls that were put in place after the 1971 Clean Air Act can be seen in the long-term improvement in the State’s air.

Earth Day Retrospective: The chart shows the decrease since 1980 in days when one or more pollutant exceeded its federal standard in Connecticut from 1980 to the present.

Earth Day Retrospective: The chart below shows that in the 1980’s, exceedances for sulfur dioxide (SO2) and nitrogen dioxide (NO2) were common. Statewide exceedances of those pollutants no longer are seen, due to federal restrictions on emitters, mostly to Connecticut’s west and southwest. The state continues to suffer from ozone (O3) exceedances, and occasionally from small particulate (PM2.5) exceedances (see chart below). Lead (Pb) is not shown.** 

Air Pollutants

The map (below) illustrates a bad-air day in 2019 that was more intense than average but followed the typical pattern of Connecticut having the worst ozone pollution in New England. The yellow areas met the air quality standard for ground-level ozone, while the orange and red areas did not. Some residents in yellow areas, who are unusually sensitive to pollution, might have been affected. Much of Connecticut's ground-level ozone originates in states to the west. Unless emissions in those states are reduced substantially, Connecticut residents could continue to breathe unhealthful air.

2019 AQI for region - bad air day example

Cities and towns in coastal regions of the state usually see more bad ozone days than inland locations. Coastal towns with monitoring stations that saw the most unhealthful days in 2019, included Westport and Madison (11 each); Stratford (10); Greenwich (8); and Groton, Middletown, and New Haven (7 each); while Cornwall (0) saw the fewest. 

No other New England state had more days with unhealthful levels of ozone than Connecticut, which had a total of 21 in 2019. Massachusetts was the next highest with 5 unhealthful days.


Technical Notes: * Bad air days include days in which any of the criteria pollutants exceeded their respective standard. The federal air quality standard for ozone was revised prior to the 2016 ozone season. The new standard (0.070 parts per million over eight hours) is slightly more protective of human health than the older standard (0.075). Source of the data represented in the charts is EPA reports that are derived from data received from DEEP’s monitors. **Connecticut’s lead levels have been below the national standard (NAAQS) since 1994. Since 2010, the average monthly level has not exceeded three percent of the standard.