Which air quality category a 24-hour PM2.5 reading falls into
Enter a 24-hour average fine particle (PM2.5) concentration and the reading you are comparing it with. The page returns the category each reading falls into, the index range tied to that category, the concentration band itself, the change in µg/m³ between the two readings, how many categories the air moved, and how far today's figure sits from the next band up.
The bands used, and where they come from
The fine particle bands are 0.0-9.0 for Good, 9.1-35.4 for Moderate, 35.5-55.4 for Unhealthy for Sensitive Groups, 55.5-125.4 for Unhealthy, 125.5-225.4 for Very Unhealthy and 225.5 upward for Hazardous, with the matching index ranges shown beside them. These took effect on May 6, 2024, when the Good to Moderate line moved down from 12.0 to 9.0; the 35 µg/m³ figure stayed put, so the 101-150 band did not change, and the two former top bands were merged into one Hazardous band. Source: US Environmental Protection Agency breakpoints, current as of October 2026. Readings are rounded to one decimal before the lookup because the bands are set to one decimal.
Limits and disclaimer
These are outdoor index breakpoints, not a standard for indoor measurement, so a reading from an indoor monitor is only a rough comparison here. Coarse particle (PM10) breakpoints are not included, and the page does not convert a concentration into a single index number. No ventilation frequency or duration is suggested, because no authoritative figure for that is offered here. Follow local air quality advisories for action.
Frequently Asked Questions
The breakpoints that took effect on May 6, 2024 moved the Good to Moderate line down from 12.0 to 9.0 µg/m³ to match the tightened annual standard. The 35 µg/m³ 24-hour figure stayed in place, so the 101-150 band was unaffected.
You can see which band a number falls into, but these are outdoor index breakpoints rather than a standard for indoor air. Do not treat the result as an authoritative verdict on indoor air quality.
No. Only fine particle (PM2.5) breakpoints are included. Coarse particle breakpoints are a separate table and are not part of this lookup.