Del Norte County, California air quality history

Daily Air Quality Index summaries from EPA monitors in Del Norte, California, 1987–2025.

82%

Good days in 2025

Median daily AQI, 2025

Days above 100 in 2025

352

Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Del Norte, California on 352 days. 288 of those days (82%) were in the Good range, and the median daily AQI was 32. That median is lower than the typical monitored county in California (median 45.5 across 46 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 352 days. Across the years with fuller monitoring, the share of Good days fell: an average of 97% in 1988–1990 versus 81% in 2023–2025.

Years with fewer than 120 monitored days (2007, 2008, 2010, 2012, 2014, 2015…) 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
Fine particles (PM2.5)	352	100%

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	352	288	64	0	0	0	32	54	70	PM2.5
2024	289	232	55	2	0	0	32	54	125	PM2.5
2023	328	268	52	6	2	0	32	55	187	PM2.5
2022	344	299	45	0	0	0	29	52	74	PM2.5
2021	323	259	64	0	0	0	31	54	72	PM2.5
2020	292	193	90	4	3	2	42	61	245	PM2.5
2019	248	210	38	0	0	0	26	53	74	PM2.5
2018	180	134	46	0	0	0	33	58	80	PM2.5
2017	298	241	55	0	1	1	27	56	251	PM2.5
2016	177	156	21	0	0	0	26	52	69	PM2.5
2015	114	101	13	0	0	0	20	51	72	PM2.5
2014	115	108	7	0	0	0	16	43	60	PM2.5
2013	126	121	5	0	0	0	16	27	75	PM2.5
2012	119	117	2	0	0	0	12	31	54	PM2.5
2011	120	117	3	0	0	0	17	38	54	PM2.5
2010	110	109	1	0	0	0	14	30	57	PM2.5
2009	125	121	4	0	0	0	14	34	86	PM2.5
2008	118	111	7	0	0	0	17	40	72	PM2.5
2007	115	113	2	0	0	0	16	36	56	PM2.5
2006	124	116	8	0	0	0	16	42	79	PM2.5
2005	131	129	2	0	0	0	16	30	53	PM2.5
2004	159	155	4	0	0	0	15	36	53	PM2.5
2003	148	147	1	0	0	0	14	28	53	PM2.5
2002	120	115	5	0	0	0	20	41	57	PM2.5
2001	125	121	4	0	0	0	17	41	56	PM2.5
2000	134	131	3	0	0	0	18	38	59	PM2.5
1999	141	130	10	0	1	0	17	41	167	PM2.5
1998	144	141	3	0	0	0	16	32	58	PM2.5
1997	135	123	12	0	0	0	20	47	74	PM2.5
1996	127	121	6	0	0	0	18	42	61	PM2.5
1995	281	273	8	0	0	0	31	40	63	Ozone
1994	365	361	4	0	0	0	31	42	71	Ozone
1993	360	351	9	0	0	0	29	38	66	Ozone
1992	360	344	15	1	0	0	31	44	102	Ozone
1991	354	341	13	0	0	0	28	42	71	Ozone
1990	340	330	10	0	0	0	30	43	67	Ozone
1989	329	320	9	0	0	0	26	37	66	Ozone
1988	344	334	10	0	0	0	28	40	67	Ozone
1987	72	68	4	0	0	0	27	35	56	PM10

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 California with a similar median AQI in 2025

All monitored counties in California

Source: U.S. EPA AirData, “Annual AQI by County” files for 1987–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem