EnviroNearby

Boise County, Idaho air quality history

Daily Air Quality Index summaries from EPA monitors in Boise, Idaho, 2002–2025.

70%
Good days in 2025
42
Median daily AQI, 2025
1
Days above 100 in 2025
365
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Boise, Idaho on 365 days. 257 of those days (70%) were in the Good range, and the median daily AQI was 42. That median is higher than the typical monitored county in Idaho (median 35 across 18 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 365 days. Across the years with fuller monitoring, the share of Good days fell: an average of 73% in 2004–2009 versus 64% in 2023–2025.

Years with fewer than 120 monitored days (2002, 2003, 2006, 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.

Share of monitored days in each AQI category, by year0%25%50%75%100%2002: Good 10 of 21 days2002: Moderate 11 of 21 days20022003: Good 42 of 58 days2003: Moderate 16 of 58 days2004: Good 221 of 285 days2004: Moderate 62 of 285 days2004: Unhealthy for Sensitive Groups 2 of 285 days20042005: Good 209 of 361 days2005: Moderate 151 of 361 days2005: Unhealthy for Sensitive Groups 1 of 361 days2006: Good 39 of 111 days2006: Moderate 65 of 111 days2006: Unhealthy for Sensitive Groups 6 of 111 days2006: Unhealthy 1 of 111 days20062008: Good 13 of 21 days2008: Moderate 8 of 21 days2009: Good 274 of 326 days2009: Moderate 52 of 326 days20092015: Good 194 of 275 days2015: Moderate 76 of 275 days2015: Unhealthy for Sensitive Groups 5 of 275 days2016: Good 251 of 363 days2016: Moderate 106 of 363 days2016: Unhealthy for Sensitive Groups 5 of 363 days2016: Unhealthy 1 of 363 days20162017: Good 209 of 365 days2017: Moderate 146 of 365 days2017: Unhealthy for Sensitive Groups 6 of 365 days2017: Unhealthy 1 of 365 days2017: Very Unhealthy 3 of 365 days2018: Good 169 of 365 days2018: Moderate 190 of 365 days2018: Unhealthy for Sensitive Groups 6 of 365 days20182019: Good 223 of 365 days2019: Moderate 139 of 365 days2019: Unhealthy for Sensitive Groups 2 of 365 days2019: Unhealthy 1 of 365 days2020: Good 199 of 366 days2020: Moderate 155 of 366 days2020: Unhealthy for Sensitive Groups 6 of 366 days2020: Unhealthy 5 of 366 days2020: Very Unhealthy 1 of 366 days20202021: Good 186 of 365 days2021: Moderate 167 of 365 days2021: Unhealthy for Sensitive Groups 10 of 365 days2021: Unhealthy 2 of 365 days2022: Good 238 of 365 days2022: Moderate 123 of 365 days2022: Unhealthy for Sensitive Groups 2 of 365 days2022: Unhealthy 2 of 365 days20222023: Good 250 of 365 days2023: Moderate 115 of 365 days2024: Good 189 of 366 days2024: Moderate 128 of 366 days2024: Unhealthy for Sensitive Groups 17 of 366 days2024: Unhealthy 29 of 366 days2024: Very Unhealthy 3 of 366 days20242025: Good 257 of 365 days2025: Moderate 107 of 365 days2025: Unhealthy for Sensitive Groups 1 of 365 days2025
  • 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 and 90th-percentile daily AQI, by year0501001502002: 90th percentile AQI 742003: 90th percentile AQI 572004: 90th percentile AQI 582005: 90th percentile AQI 682006: 90th percentile AQI 752008: 90th percentile AQI 552009: 90th percentile AQI 552015: 90th percentile AQI 632016: 90th percentile AQI 642017: 90th percentile AQI 712018: 90th percentile AQI 702019: 90th percentile AQI 652020: 90th percentile AQI 722021: 90th percentile AQI 722022: 90th percentile AQI 592023: 90th percentile AQI 582024: 90th percentile AQI 1382025: 90th percentile AQI 582002: Median AQI 582003: Median AQI 342004: Median AQI 332005: Median AQI 432006: Median AQI 572008: Median AQI 482009: Median AQI 302015: Median AQI 382016: Median AQI 382017: Median AQI 462018: Median AQI 522019: Median AQI 442020: Median AQI 462021: Median AQI 492022: Median AQI 392023: Median AQI 392024: Median AQI 482025: Median AQI 422002200420062009201620182020202220242025
  • 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.

PollutantDays as main pollutantShare of monitored days
Fine particles (PM2.5)365100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536525710710004258135PM2.5
202436618912817293048138265PM2.5
20233652501150000395898PM2.5
202236523812322003959188PM2.5
2021365186167102004972161PM2.5
202036619915565104672223PM2.5
201936522313921004465170PM2.5
201836516919060005270130PM2.5
201736520914661304671268PM2.5
201636325110651003864157PM2.5
20152751947650003863128PM2.5
2009326274520000305580PM2.5
2008211380000485579PM2.5
2006111396561005775169PM2.5
200536120915110004368109PM2.5
20042852216220003358131PM2.5
20035842160000345784PM2.5
20022110110000587491PM2.5

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 Idaho with a similar median AQI in 2025

All monitored counties in Idaho

Source: U.S. EPA AirData, “Annual AQI by County” files for 2002–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem