CEQ Annual Air Pollution Index

Average Levels of All Air Pollution Combined Into a Single Index of Over-all Air Quality 


Connecticut saw a slight increase in low levels of air pollution in 2018, but remained below the 10 year average.


The chart shows the average level of pollution in Connecticut's air.

Five air pollutants -- sulfur dioxide, carbon monoxide, fine particles, nitrogen dioxide and ground-level ozone -- are measured continuously across the state by DEEP. At the end of every year, the Council calculates the average level of each pollutant on a numerical scale where zero equals no pollution and 100 would represent the “unhealthful” level of the specified pollutant. The Council takes this annual number for each of the five pollutants and averages them to yield the single index value on the chart. 
Connecticut's air quality was, on average, slightly worse in 2018 than in 2017. Encouragingly, levels of air pollution in 2018 remained below the current 10-year average.
The trend in sulfur dioxide (which is a component of the index value above but not shown separately) is worth noting. The average concentration in Connecticut's air in 2017 was a 47 percent reduction from 10 years prior. Since late 2014, heating oil sold in Connecticut and several other northeastern states has, by law, contained very low concentrations of sulfur. Given this, we can expect the trend in sulfur dioxide specifically to continue downward.


Lead is Out 

Until 2012, this indicator charted the combined average level of six pollutants, not five as it now does. The sixth pollutant was lead. In the early 1980s, lead was a serious problem, but unleaded gasoline and other advances have reduced lead levels dramatically. Levels of lead have dropped so low that in recent years they barely registered in this indicator. By removing lead from this indicator, the Council declared victory on behalf of Connecticut residents. (Lead still is subject to regulation and health-based standards and still is monitored by DEEP, so it can be brought back into this indicator if levels rise unexpectedly in future years.)