Norfolk County, Massachusetts air quality history

Daily Air Quality Index summaries from EPA monitors in Norfolk, Massachusetts, 1980–2025.

84%

Good days in 2025

Median daily AQI, 2025

Days above 100 in 2025

365

Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Norfolk, Massachusetts on 365 days. 308 of those days (84%) were in the Good range, and the median daily AQI was 39. That median is about the same as the typical monitored county in Massachusetts (median 38 across 13 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 298 days. Across the years with fuller monitoring, the share of Good days rose: an average of 72% in 1980–1982 versus 82% in 2023–2025.

Years with fewer than 120 monitored days (1996, 1997, 1998, 1999, 2000, 2001) are shown in the table but left out of comparisons and trend statements.

How the days broke down each year

Each bar is one year. The colored segments show the share of monitored days that fell in each AQI category.

Good
Moderate
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Hazardous

Typical and high-end AQI over time

The median is the middle day of the year. The 90th percentile is the level that only the highest 10% of days exceeded.

Median daily AQI
90th-percentile daily AQI

Main pollutant by day, 2025

On each monitored day, the AQI reflects whichever measured pollutant had the highest index. This counts how many days each pollutant set the AQI. A pollutant that was not measured here cannot appear.

Pollutant	Days as main pollutant	Share of monitored days
Ozone	298	82%
Fine particles (PM2.5)	64	18%
Nitrogen dioxide (NO₂)	3	1%

Year-by-year data

Annual AQI summary by year
Year	Days with AQI	Good	Moderate	Unhealthy for Sensitive Groups	Unhealthy	Very Unhealthy	Median AQI	90th pct.	Max AQI	Main pollutant
2025	365	308	55	2	0	0	39	55	126	Ozone
2024	366	319	47	0	0	0	39	54	90	Ozone
2023	365	276	85	4	0	0	41	58	136	Ozone
2022	365	304	60	1	0	0	40	55	105	Ozone
2021	365	280	82	3	0	0	37	57	133	Ozone
2020	366	330	36	0	0	0	34	50	74	Ozone
2019	362	352	10	0	0	0	34	44	100	Ozone
2018	353	337	15	1	0	0	32	45	105	Ozone
2017	364	337	23	4	0	0	36	48	147	Ozone
2016	365	326	36	3	0	0	37	51	143	Ozone
2015	365	287	76	1	1	0	40	57	156	Ozone
2014	365	286	77	2	0	0	42	56	105	Ozone
2013	365	291	70	4	0	0	39	57	115	Ozone
2012	363	268	89	6	0	0	41	60	133	PM2.5
2011	360	253	102	5	0	0	43	61	119	PM2.5
2010	365	281	75	9	0	0	40	64	143	PM2.5
2009	365	268	93	4	0	0	38	61	136	PM2.5
2008	366	231	126	9	0	0	44	72	140	PM2.5
2007	334	212	101	15	6	0	44	80	174	PM2.5
2006	346	244	91	9	2	0	41	73	154	PM2.5
2005	318	215	80	19	4	0	41	84	195	PM2.5
2004	279	191	78	8	2	0	41	78	187	Ozone
2003	197	142	44	6	4	1	40	90	204	Ozone
2002	240	112	84	25	15	4	52	140	230	Ozone
2001	48	22	26	0	0	0	53	78	91	PM2.5
2000	63	34	29	0	0	0	48	65	89	PM2.5
1999	116	54	61	1	0	0	52	78	128	PM2.5
1998	48	47	1	0	0	0	12	28	53	PM10
1997	47	46	1	0	0	0	14	26	54	PM10
1996	51	49	2	0	0	0	17	36	69	PM10
1995	364	348	16	0	0	0	31	42	72	NO2
1994	365	337	27	1	0	0	35	48	101	NO2
1993	365	318	47	0	0	0	37	52	86	NO2
1992	366	338	27	1	0	0	36	49	102	NO2
1991	365	321	43	1	0	0	37	52	102	NO2
1990	365	314	50	1	0	0	37	54	101	NO2
1989	365	293	71	1	0	0	39	60	102	NO2
1988	366	276	88	2	0	0	42	63	103	NO2
1985	203	124	48	17	9	5	45	133	224	Ozone
1984	213	136	52	13	11	1	44	119	201	Ozone
1983	197	108	40	26	15	8	48	156	251	Ozone
1982	180	126	37	10	7	0	41	100	192	Ozone
1981	185	130	36	14	5	0	42	105	177	Ozone
1980	340	262	50	10	13	5	34	93	218	Ozone

What this data can and can’t tell you

It is a county-level summary. EPA reports one AQI per day for the county, based on the monitors operating there. Air at a particular street, school or home can differ, especially near roads, industry or wildfire smoke.

It is not a health assessment. The AQI is EPA’s scale for communicating daily air quality. A county’s history can’t tell you what the health risk is for any particular person. For daily conditions and health guidance, see AirNow.

Rules change over time. EPA has revised AQI breakpoints, most recently for fine particles in 2024, so some year-to-year change can reflect the scale rather than the air.

Counties in Massachusetts with a similar median AQI in 2025

All monitored counties in Massachusetts

Source: U.S. EPA AirData, “Annual AQI by County” files for 1980–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem