Move workouts to the morning
Ozone peaks on hot, sunny afternoons. Mornings are usually cleaner.
Ozone guide →Air quality in Coos County, NH
EPA monitor readings, 2021 to 2025 · 31,000 people
For today's air and tomorrow's forecast, check AirNow by ZIP code.
Bad-air days a year
2
days with an AQI over 100
10 bad-air days in 5 years of readings, 2021 to 2025. That's down from about 12 a year in the early 2000s. Coos County has the 2nd most bad-air days of the 7 New Hampshire counties with monitors.
0days unhealthy for everyoneAQI over 150, a year
43AQI on a typical dayGood: fine for everyone
Mar to Mayworst monthsOzone on hot afternoons
174worst day since 2016Mar 18, 2017, ozone
How to read the AQIThe EPA's air score runs from 0 to 500. Higher is worse. Over 100 counts as a bad-air day.
Typical day 43 (Good)Worst day 174 (Unhealthy)
Good0 to 50Moderate51 to 100Sensitive groups101 to 150Unhealthy151 to 200Very unhealthy201 to 300Hazardous301 to 500
When bad air happens in Coos County
Average bad-air days in each month, from 10 years of daily readings since 2016. Most fall in March, April and May.
Jan0
Feb0
Mar0.3
Apr0.4
May0.4
Jun0.3
Jul0.2
Aug0.2
Sep0
Oct0.2
Nov0
Dec0
Fine particles (smoke, soot)Ozone (smog)Bars stack in that order, from the bottom.
See the numbers by month
| Month | Ozone | Fine particles | All |
|---|---|---|---|
| January | 0 | 0 | 0 |
| February | 0 | 0 | 0 |
| March | 0.3 | 0 | 0.3 |
| April | 0.4 | 0 | 0.4 |
| May | 0.4 | 0 | 0.4 |
| June | 0.3 | 0 | 0.3 |
| July | 0.2 | 0 | 0.2 |
| August | 0.2 | 0 | 0.2 |
| September | 0 | 0 | 0 |
| October | 0.2 | 0 | 0.2 |
| November | 0 | 0 | 0 |
| December | 0 | 0 | 0 |
The worst day since 2016 was March 18, 2017: AQI 174, from ozone.
What causes it
The pollutant that pushed the AQI over 100 on each of the 20 bad-air days since 2016.
100%Ozone: smog that forms in sunlight on hot days
Most bad days here are ozone days: smog that builds on hot, sunny afternoons.
CDC estimates by month, 2001 to 2022
The CDC's model counts bad-air days at the county's worst spot, from monitors and satellites. Particles (brown) fill the inside of the ring and ozone (blue) the outside.
See the numbers by month
| Month | Fine particles | Ozone |
|---|---|---|
| January | 0 | 0 |
| February | 0 | 0 |
| March | 0 | 0 |
| April | 0 | 0.3 |
| May | 0 | 0.4 |
| June | 0 | 0.5 |
| July | 0.1 | 0 |
| August | 0 | 0.4 |
| September | 0 | 0.1 |
| October | 0 | 0 |
| November | 0 | 0 |
| December | 0 | 0 |
What helps in Coos County
Most bad days here are ozone, which builds on hot afternoons. Timing helps most; filters don't remove ozone.
Check tomorrow's forecast
AirNow posts an air quality forecast by ZIP code, usually the day before.
AirNow →Keep one room clean on smoky days
Shut the windows and run an air purifier sized for the room.
Choosing a purifier →For today's reading and tomorrow's forecast, check AirNow by ZIP code. Its fire and smoke map adds smoke plumes.
Purifiers catch smoke but don't remove ozone, and smoky days are rare here. If you want one for wildfire season anyway, see the 3 models we'd buy, each with a verified smoke rating.
Every year since 2000
Bad-air days each year. The striped part is days unhealthy for everyone, over AQI 150. The worst recent year was 2023, with 4 bad-air days.
Unhealthy for sensitive groups (101 to 150)Unhealthy or worse (over 150)
See the numbers by year
| Year | Bad-air days | Over 150 |
|---|---|---|
| 2000 | 1 | 0 |
| 2001 | 15 | 0 |
| 2002 | 19 | 3 |
| 2003 | 14 | 0 |
| 2004 | 11 | 3 |
| 2005 | 14 | 0 |
| 2006 | 3 | 0 |
| 2007 | 15 | 3 |
| 2008 | 9 | 0 |
| 2009 | 1 | 0 |
| 2010 | 5 | 0 |
| 2011 | 2 | 0 |
| 2012 | 4 | 0 |
| 2013 | 2 | 0 |
| 2014 | 0 | 0 |
| 2015 | 7 | 0 |
| 2016 | 4 | 0 |
| 2017 | 3 | 1 |
| 2018 | 3 | 0 |
| 2019 | 0 | 0 |
| 2020 | 0 | 0 |
| 2021 | 2 | 0 |
| 2022 | 0 | 0 |
| 2023 | 4 | 0 |
| 2024 | 0 | 0 |
| 2025 | 4 | 0 |
Coos County and its neighbors
Bad-air days a year, 2021 to 2025. New Hampshire counties with monitors averaged about 2 bad-air days a year, weighted by population.
Nearest county with a full report: Cumberland County, ME (3 bad-air days a year).
Questions people ask about air in Coos County
How often is the air bad in Coos County?
From 2021 to 2025, monitors in Coos County recorded about 2 bad-air days a year with an AQI above 100, which is unhealthy for sensitive groups or worse. The worst year in that stretch was 2023, with 4 bad-air days.
What causes bad air in Coos County?
Most bad days here are ozone days: smog that builds on hot, sunny afternoons. Bad days cluster in March, April and May.
Where can I see today's air quality in Coos County?
AirNow, run by the EPA and its partners, shows the current AQI and tomorrow's forecast for your ZIP code. Its fire and smoke map adds smoke plumes. On a typical day the AQI in Coos County is about 43, which is good, fine for everyone. Check it most in March, April and May, when bad days here cluster.
About these numbers
Day counts come from the EPA's county air quality summaries, which take the worst reading across a county's monitors each day. Monitors here reported on about 359 days a year from 2021 to 2025. A county is large, and your street can be cleaner or worse. CDC's model, which estimates every county from monitors and satellites, gives the worst spot in Coos County almost no high-particle days and almost no high-ozone days a year from 2018 to 2022.
Sources: EPA AirData county AQI summaries (2000 to 2025) and daily county AQI (2016 to 2025); CDC Environmental Public Health Tracking Network modeled PM2.5 and ozone (2001 to 2022). Updated November 8, 2026.