Bad Air Days in Navajo County, Arizona: under 1 a Year

under 1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 758 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (14% particle days).

Which months to watch

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

What to buy, and what not to

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 Navajo

In 2000 to 2009 this county averaged 4 bad days a year; in 2016 to 2025, under 1. The air has improved. The worst recent year was 2018, with 2 bad days on 363 monitored days.

Date	AQI	Main pollutant
2020-06-17	136	Ozone
2018-07-20	115	Ozone
2019-06-20	112	Ozone
2020-06-20	109	PM2.5
2017-06-14	101	Ozone

An ordinary day in Navajo

Across 3,644 monitored days from 2016 to 2025, the air in Navajo County rated Good on 84% of them, more often than the 72% typical of monitored counties, and Moderate on 16%. The median day sat at AQI 38; one day in ten went above 53.

The pollutant setting the AQI on an ordinary day here:

ozone77%2,818 days
coarse dust (PM10)18%650 days
fine particles (PM2.5)5%176 days

Navajo County by year

Year	Days monitored	Good	Moderate	Over 100	Median AQI	Highest AQI
2025*	365	363	2	0	13	54
2024	361	359	2	0	13	53
2023	364	290	74	0	43	84
2022	364	307	57	0	44	93
2021	365	292	72	1	44	101
2020	366	314	50	2	43	136
2019	365	294	70	1	44	112
2018	363	260	101	2	44	115
2017	365	278	86	1	44	101
2016	366	299	67	0	43	90
2015	365	316	49	0	39	100
2014	365	272	91	2	44	101
2013	365	246	119	0	46	100
2012	366	245	114	7	45	126
2011	365	246	118	1	46	105
2010	364	279	83	2	44	112

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

Arizona compared

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.