--- title: "EPA AQI Breakpoints for PM2.5 (2024) | Aethair" description: "EPA Air Quality Index PM2.5 breakpoints (2024): the concentration at the top of each AQI category, who uses the index, and a recommended configuration." url: https://aethair.io/standards/epa_aqi/ --- Compliance · US EPA # US EPA Air Quality Index (AQI): PM2.5 breakpoints (2024) Ambient air: public air quality reporting (USA) The **US EPA Air Quality Index (AQI)** turns pollutant concentrations into a 0-to-500 scale with six color-coded categories, so the public can read air quality at a glance. EPA revised the PM2.5 breakpoints in 2024 with the tighter annual NAAQS. For **24-hour PM2.5**, the top of each category is **9.0 µg/m³ for Good (AQI 50), 35.4 for Moderate (100), 55.4 for Unhealthy for Sensitive Groups (150), 125.4 for Unhealthy (200), and 225.4 for Very Unhealthy (300)**; above that is Hazardous, and **AQI 500 is 325.4 µg/m³**. [Schedule a call](https://calendly.com/d/ctdd-mkr-v9v/aethair-demo-website) [Configure EPA AQI Monitoring](https://aethair.io/build/?params=pm2_5\&setting=outdoor) At a glance **US EPA** Ambient air: public air quality reporting (USA) 1 parameter · 5 limit values [PM2.5](https://aethair.io/parameters/pm2_5/) 1 device measures them all - **Aethair PRO** [Official text from US EPA](https://document.airnow.gov/technical-assistance-document-for-the-reporting-of-daily-air-quailty.pdf) The standard ## What the Air Quality Index Is The AQI also covers ozone, PM10, carbon monoxide, sulfur dioxide, and nitrogen dioxide, each with its own breakpoints. For real-time reporting, EPA's NowCast weights recent hours so the index follows fast changes such as wildfire smoke. Limit values ## EPA AQI Limit Values Every value US EPA publishes for the parameter below, with its averaging period, as the standard states it. [**PM2.5** Particulate Matter](https://aethair.io/parameters/pm2_5/) **9 µg/m³** *24-hour, top of Good (AQI 50)* **35.4 µg/m³** *24-hour, top of Moderate (AQI 100)* **55.4 µg/m³** *24-hour, top of Unhealthy for Sensitive Groups (AQI 150)* **125.4 µg/m³** *24-hour, top of Unhealthy (AQI 200)* **225.4 µg/m³** *24-hour, top of Very Unhealthy (AQI 300)* Hazardous above; AQI 500 is 325.4 µg/m³ Who it applies to ## Who Uses It Air agencies report daily air quality through AirNow, schools and employers use it to decide on outdoor activity, and some regulations use it as a trigger: California's wildfire smoke rule for workers (section 5141.1) applies from a current AQI of 151. Monitoring ## How Monitoring Relates to It The official AQI comes from regulatory monitors. A local monitor converted to the AQI with the same breakpoints shows conditions where people actually are, which can differ sharply from the nearest regional station during a smoke event; it is screening information rather than an official index. [Customize this configuration](https://aethair.io/build/?params=pm2_5\&setting=outdoor) ### Who measures each parameter | Parameter | Aethair PRO | Aethair IAQ | External | | - | - | - | - | | [PM2.5](https://aethair.io/parameters/pm2_5/) | Built in | Built in | [3 instruments](https://aethair.io/parameters/pm2_5/) via Thiamis | Devices ## Devices That Cover EPA AQI How much of this standard one Aethair monitor covers, followed by the third-party instruments in the sensor catalog that measure its parameters. Each connects to Environet through a Thiamis gateway, which adds whatever the monitor leaves out. Aethair monitors [**Aethair PRO** Built-in sensors Covers it](https://aethair.io/products/pro/) Covers it on its own [**TSI DustTrak** Particulate & Dust Monitors](https://aethair.io/sensors/tsi-particulate-dust-monitors/) [**Met One E-BAM** Particulate & Dust Monitors](https://aethair.io/sensors/met-one-particulate-dust-monitors/) [**Trolex** Particulate & Dust Monitors](https://aethair.io/sensors/trolex-particulate-dust-monitors/) Solutions ## Solutions Judged Against EPA AQI ### [Outdoor Monitoring](https://aethair.io/solutions/outdoor-monitoring/) Continuous outdoor air quality networks that sit alongside reference monitors ### [Wildfire Air Monitoring](https://aethair.io/solutions/wildfires/) Smoke plumes, black carbon, and community exposure [All solutions](https://aethair.io/solutions/) Article Library ## Articles on EPA AQI ### [Wildfire Smoke Air Quality Monitoring: Detection & Response](https://aethair.io/resources/wildfire-smoke-air-quality-monitoring/) Wildfire smoke monitoring for EHS and public health teams: real-time PM2.5, the AQI 151 respirator trigger, and how to alert workers before smoke arrives. ### [Indoor Air Quality in Schools: Standards & Monitoring 2026](https://aethair.io/resources/indoor-air-quality-schools/) Indoor air quality in schools: which standards apply, what to monitor, and how CO2 and ventilation affect student attendance, health, and test scores. ### [Types of Air Quality Monitors: Indoor, Outdoor, and Combined](https://aethair.io/resources/types-of-air-quality-monitors/) Learn the three types of air quality monitors (indoor, outdoor, and combined), what each one measures, and when to use each one. ### [OSHA Air Quality Standards 2026: PELs & 29 CFR 1910.1000](https://aethair.io/resources/osha-air-quality-standards-compliance/) OSHA air quality standards for indoor and outdoor work: permissible exposure limits, Table Z-1, 29 CFR 1910.1000, and the heat and wildfire smoke triggers. ### [PM2.5 Exposure Limits & Monitoring: OSHA and NAAQS Standards](https://aethair.io/resources/pm25-monitoring-health-regulatory-guide/) What are the OSHA and NAAQS exposure limits for PM2.5? Fine particulate thresholds explained, plus how continuous monitoring keeps workplaces compliant. [All articles](https://aethair.io/resources/) Questions ## EPA AQI FAQ What PM2.5 level is Unhealthy on the AQI? From 55.5 to 125.4 µg/m³ as a 24-hour average (AQI 151 to 200) under EPA's 2024 breakpoints; 35.5 to 55.4 µg/m³ is Unhealthy for Sensitive Groups. What PM2.5 level is Good on the AQI? 0 to 9.0 µg/m³ as a 24-hour average, AQI 0 to 50, under the 2024 breakpoints. What is the NowCast? EPA's method for the current, hourly AQI, which weights recent hours more heavily so the index follows quickly changing conditions.