Annual Summary Information for Ozone

DEEP headquarters at 79 Elm Street in Hartford is currently closed due to recent water damage impacting multiple areas of the building. We are working to remediate the situation and get the building back open to staff and the public as soon as possible. While the building is closed, Staff continue to work either remotely or in alternate locations. We continue to be able to receive documents via U.S. Mail or courier service, and our electronic file submittal protocols remain unchanged. For updates, please click here

Annual Summary Information for Ozone

Prior to 2008, the 8-hour ozone exceedance day tables reflect the 1997 NAAQS (84 ppb) and from 2008 forward, the tables reflect the 2008 NAAQS (75 ppb). Tables from 2016 forward reflect the 2015 NAAQS (70 ppb). EPA's 2004 Implementation Rule revoked the 1-hour NAAQS, effective June 15, 2005, but states are not allowed to backslide from existing 1-hour ozone requirements. Note that the ozone season was expanded in 2017 to include March through September.

Year	2025	2024	2023	2022	2021	2020	2019	2018	2017	2016	2015	2014	2013
8-hr Ozone Exceedance Days	22	23	19	23	21	17	21	23	20	31	22	8	18
Year	2012	2011	2010	2009	2008	2007	2006	2005	2004	2003	2002	2001	2000
8-hr Ozone Exceedance Days	27	14	24	6	22	17	13	20	6	14	36	26	35

Current Year 8-Hour Ozone Tables

2025
8-hour Tables	March	April	May	June	July	August	September

*CT had an out-of-season ozone exceedance on October 5, 2025, bringing the total to 22.

Year	Previous Year Ozone Tables
2024	-	8-hour Ozone
2023	-	8-hour Ozone
2022	-	8-hour Ozone
2021	-	8-hour Ozone
2020	-	8-hour Ozone
2019	1-hour Ozone	8-hour Ozone
2018	1-hour Ozone	8-hour Ozone
2017	1-hour Ozone	8-hour Ozone
2016	1-hour Ozone	8-hour Ozone
2015	1-hour Ozone	8-hour Ozone
2014	1-hour Ozone	8-hour Ozone
2013	1-hour Ozone	8-hour Ozone
2012	1-hour Ozone	8-hour Ozone
2011	1-hour Ozone	8-hour Ozone
2010	1-hour Ozone	8-hour Ozone
2009	1-hour Ozone	8-hour Ozone
2008	1-hour Ozone	8-hour Ozone
2007	1-hour Ozone	8-hour Ozone
2006	1-hour Ozone	8-hour Ozone
2005	1-hour Ozone	8-hour Ozone
2004	1-hour Ozone	8-hour Ozone
2003	1-hour Ozone	8-hour Ozone
2002	1-hour Ozone	8-hour Ozone
2001	1-hour Ozone	8-hour Ozone
2000	1-hour Ozone	8-hour Ozone
1999	1-hour Ozone	8-hour Ozone
1998	1-hour Ozone	8-hour Ozone

Air Quality Index

Content last updated on October 8, 2025

Connecticut Department of Energy & Environmental Protection

Annual Summary Information for Ozone