Ozone levels in Connecticut have come down considerably over the last 35 years, but generally remain above the standards set by the federal Environmental Protection Agency and have grown worse in the last few years. In 1997, the standard was set at 84 parts per billion (ppb). In 2008 that standard was lowered to 75 ppb. The EPA is proposing a new level that is a range – 65 to 70 ppb.
The ozone level is an index known as the “design value.” Each state has ozone monitors — in Connecticut there are 10 — that run continuously during the summer ozone season. The monitor readings are averaged over eight hours. The fourth highest of those each day is averaged with three years of such readings to come up with the number — known as the design value — that must meet EPA’s standard.
Green columns signify those areas that do meet the 75 ppb standard.