Lewis County, Washington air quality history

Daily Air Quality Index summaries from EPA monitors in Lewis, Washington, 1995–2025.

91%

Good days in 2025

Median daily AQI, 2025

Days above 100 in 2025

323

Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Lewis, Washington on 323 days. 295 of those days (91%) were in the Good range, and the median daily AQI was 20. 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 323 days. Across the years with fuller monitoring, the share of Good days fell: an average of 98% in 1996–1998 versus 90% in 2023–2025.

Years with fewer than 120 monitored days (1995, 1999, 2001, 2006, 2007, 2008) 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)	323	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	323	295	28	0	0	0	20	48	74	PM2.5
2024	360	336	23	1	0	0	22	43	129	PM2.5
2023	362	314	46	1	1	0	25	54	159	PM2.5
2022	365	285	70	7	3	0	26	66	198	PM2.5
2021	350	328	22	0	0	0	23	46	71	PM2.5
2020	335	314	20	0	0	1	25	46	258	PM2.5
2019	365	308	57	0	0	0	27	54	66	PM2.5
2018	365	298	61	3	3	0	28	58	172	PM2.5
2017	365	302	60	1	2	0	26	57	162	PM2.5
2016	366	340	26	0	0	0	26	44	70	PM2.5
2015	361	311	49	0	1	0	30	53	154	PM2.5
2014	365	312	53	0	0	0	31	54	78	PM2.5
2013	330	241	89	0	0	0	30	58	82	PM2.5
2012	366	314	51	1	0	0	28	54	106	PM2.5
2011	364	305	59	0	0	0	28	54	78	PM2.5
2010	365	336	29	0	0	0	25	46	64	PM2.5
2009	120	117	3	0	0	0	7	28	91	PM2.5
2008	118	114	4	0	0	0	7	19	74	PM2.5
2007	116	116	0	0	0	0	5	19	35	PM2.5
2006	109	105	4	0	0	0	7	29	61	PM2.5
2005	190	186	4	0	0	0	30	43	61	Ozone
2004	208	186	22	0	0	0	34	51	87	Ozone
2003	209	154	45	10	0	0	42	84	133	Ozone
2002	159	136	23	0	0	0	30	61	100	PM2.5
2001	119	110	9	0	0	0	9	36	83	PM2.5
2000	195	174	21	0	0	0	30	53	99	Ozone
1999	109	107	2	0	0	0	28	42	77	Ozone
1998	177	172	5	0	0	0	29	44	77	Ozone
1997	137	137	0	0	0	0	29	38	47	Ozone
1996	158	154	4	0	0	0	31	44	61	Ozone
1995	59	59	0	0	0	0	28	38	46	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 Washington with a similar median AQI in 2025

All monitored counties in Washington

Source: U.S. EPA AirData, “Annual AQI by County” files for 1995–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem