Bad Air Days in Washington County, Ohio: under 1 a Year

under 1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 705 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (0% particle days).

Which months to watch

Most bad days here fall in June and September and July. Averaged over 2016 to 2025.

What actually helps here

Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
On the odd bad day, check AirNow and keep windows shut.

The record for Washington

In 2000 to 2009 this county averaged 27 bad days a year; in 2016 to 2025, under 1. The air has improved. The worst recent year was 2018, with 3 bad days on 245 monitored days.

Date	AQI	Main pollutant
2020-07-06	108	Ozone
2018-06-16	105	Ozone
2025-09-12	105	Ozone
2025-09-19	105	Ozone
2018-06-09	101	Ozone

Most days, not the worst ones

Across 2,408 monitored days from 2016 to 2025, the air in Washington County rated Good on 89% of them, more often than the 72% typical of monitored counties, and Moderate on 10%. The median day sat at AQI 40; one day in ten went above 52.

The pollutant setting the AQI on an ordinary day here:

ozone100%2,408 days

Washington County by year

Year	Days monitored	Good	Moderate	Over 100	Median AQI	Highest AQI
2025*	242	214	26	2	40	105
2024	244	212	32	0	41	90
2023	238	206	32	0	42	100
2022	245	222	23	0	39	84
2021	245	222	23	0	39	87
2020	245	233	11	1	38	108
2019	245	219	26	0	41	87
2018	245	216	26	3	39	105
2017	245	219	26	0	41	97
2016	214	189	25	0	40	90
2015	214	181	32	1	40	115
2014	200	169	29	2	42	112
2013	213	192	20	1	41	112
2012	214	134	73	7	47	150
2011	211	158	49	4	42	143
2010	214	130	74	10	46	129

*2025 may be a partial year in EPA's file.

Elsewhere in Ohio

How this is counted

A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day, and on why a purifier does not touch ozone in smoke vs ozone.