Cowlitz County, Washington air quality history

Daily Air Quality Index summaries from EPA monitors in Cowlitz, Washington, 1986–2025.

90%

Good days in 2025

Median daily AQI, 2025

Days above 100 in 2025

250

Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Cowlitz, Washington on 250 days. 226 of those days (90%) were in the Good range, and the median daily AQI was 22. That median is lower than the typical monitored county in Washington (median 28 across 30 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 250 days. Across the years with fuller monitoring, the share of Good days fell: an average of 97% in 1997–1999 versus 91% in 2023–2025.

EPA did not report an AQI for every day of 2025 here (250 of 365 days). Figures describe monitored days only; seasonal monitoring (for example, ozone measured only in warmer months) can make a county look cleaner or dirtier than a full-year record would.

Years with fewer than 120 monitored days (1994, 1995, 1996, 2000, 2001, 2002…) 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)	250	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	250	226	24	0	0	0	22	49	72	PM2.5
2024	366	349	17	0	0	0	22	41	67	PM2.5
2023	365	323	42	0	0	0	22	52	89	PM2.5
2022	363	316	45	2	0	0	21	54	144	PM2.5
2021	365	355	10	0	0	0	21	38	64	PM2.5
2020	366	331	26	1	3	5	21	50	282	PM2.5
2019	360	301	59	0	0	0	24	54	79	PM2.5
2018	365	310	51	2	2	0	27	54	153	PM2.5
2017	365	301	62	1	1	0	26	57	156	PM2.5
2016	363	331	32	0	0	0	23	49	77	PM2.5
2015	362	308	53	1	0	0	27	54	109	PM2.5
2014	323	274	49	0	0	0	28	53	86	PM2.5
2013	365	283	82	0	0	0	29	60	84	PM2.5
2012	351	304	47	0	0	0	26	53	74	PM2.5
2011	363	311	52	0	0	0	18	53	80	PM2.5
2010	364	338	26	0	0	0	21	46	68	PM2.5
2009	348	296	52	0	0	0	27	54	74	PM2.5
2008	361	303	58	0	0	0	24	55	76	PM2.5
2007	336	278	58	0	0	0	23	59	80	PM2.5
2006	343	286	57	0	0	0	22	56	96	PM2.5
2005	310	243	67	0	0	0	24	59	100	PM2.5
2004	345	251	94	0	0	0	27	64	96	PM2.5
2003	218	166	52	0	0	0	29	65	98	PM2.5
2002	23	15	8	0	0	0	44	69	78	PM2.5
2001	61	49	9	3	0	0	25	57	132	PM2.5
2000	61	60	1	0	0	0	17	28	56	PM10
1999	188	185	3	0	0	0	27	42	67	Ozone
1998	242	230	9	2	1	0	30	45	159	Ozone
1997	242	237	4	1	0	0	31	43	108	Ozone
1996	99	97	2	0	0	0	22	32	53	PM10
1995	61	60	1	0	0	0	20	31	55	PM10
1994	62	61	1	0	0	0	21	32	56	PM10
1993	61	59	2	0	0	0	22	38	65	PM10
1992	60	60	0	0	0	0	19	35	43	PM10
1991	60	58	2	0	0	0	23	39	79	PM10
1990	64	60	4	0	0	0	20	42	62	PM10
1989	119	107	12	0	0	0	22	51	89	PM10
1988	92	81	11	0	0	0	27	51	72	PM10
1987	88	81	7	0	0	0	29	49	82	PM10
1986	92	77	15	0	0	0	30	56	77	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 Washington with a similar median AQI in 2025

All monitored counties in Washington

Source: U.S. EPA AirData, “Annual AQI by County” files for 1986–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem