Indicators:  Air

On a Good Air Day, every monitoring station in the state records satisfactory air quality. “Satisfactory air quality” is defined here as air that meets the health-based ambient air quality standards for all of the following six pollutants: sulfur dioxide, lead, carbon monoxide, particulates, nitrogen dioxide, and ground-level ozone. Connecticut’s goal is to have air that meets health-based standards for all pollutants except particulates by the year 2010.

Violations of the health-based air quality standards have been eliminated for all pollutants except ground-level ozone and fine particulates.

Ozone is created when nitrogen oxides and organic compounds in the air react in the presence of sunlight. Weather is a big factor in year-to-year fluctuations. Motor vehicles remain a major source of ozone-forming emissions despite improvements in tailpipe standards. Much ground-level ozone originates in states to Connecticut’s west. Looking at ground-level ozone data from the past seven years, we see that 2005 was worse than average but that 2006, with 13 days when health standards were violated, was a little better than average. The 2007 ozone season, with 17 bad days, was average in duration but odd in some respects. No single town or city recorded more than eight bad ozone days. Most coastal communities, which during many summers have the worst air, saw fewer bad days than inland locations.

Fine particles, such as those found in smoke and haze, are 2.5 micrometers in diameter and smaller. These particles can form when gases emitted from power plants, industries and automobiles react in the air. Violations of the standard occur mostly in summer and winter, rarely in spring and fall. Connecticut must meet the new air quality goals for fine particles by 2015.

NOTE: The graph above was revised this year to reflect violations of the health-based standard for fine particles since 2002. In December 2006, the federal government tightened the daily standard for fine particles in the air. Monitoring data for 2002 through 2007 was reviewed to determine how many days would have seen “violations” of the new standard if that standard had been in effect. Between six and 16 days saw “violations” of this new standard in each of those six years. After accounting for the days that were already counted as bad because of ozone violations, these days of fine-particle violations were subtracted from the count of Good Air Days. On average, the graph now shows seven fewer Good Air Days for each year since 2002. The years prior to 2002 were not analyzed, and the graph was not changed for those years.