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PM2.5, AQI, and a consumer smoke sensor are not three versions of the same number. PM2.5 is a measurement of fine particle pollution, usually expressed as a concentration. The U.S. Air Quality Index (AQI) converts pollutant data into color-coded health categories. A household sensor estimates particle conditions at one location, often at short intervals. During wildfire smoke, use a sensor to understand what is happening near you, but use AirNow’s official U.S. AQI and Fire and Smoke Map for the public-health context.
What PM2.5 means
PM2.5 means particulate matter with an aerodynamic diameter of 2.5 micrometers or smaller. These fine particles are a major component of wildfire smoke and can also come from traffic, wood burning, cooking, industrial activity and other combustion. A PM2.5 reading is a pollutant measurement, not a health category.
Most displays show PM2.5 as a concentration, commonly in micrograms per cubic meter (µg/m³). The value describes how much fine particle mass is estimated to be in a volume of air during a stated sampling or averaging period. A short-term sensor value can rise quickly when smoke enters a room; a longer average will change more slowly.
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Fine particles matter because they can penetrate deep into the respiratory system. People with asthma or heart and lung disease, children, older adults and people who are pregnant can be more vulnerable, although high particle pollution can affect anyone. The number alone does not diagnose an individual health risk; exposure time, activity, indoor conditions and personal health all matter.
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- 【Professional 10-in-1 Air Quality Monitor】This professional 10-in-1 air quality monitor accurately measures carbon dioxide (CO2), formaldehyde (HCHO), total volatile organic compounds (TVOC), temperature, humidity, AQI, PM2.5, PM1.0, PM10 in real time, and features a clock (Connect your phone to the monitor via Bluetooth: MT13S, and it will automatically calibrate the time). It helps you keep track of your indoor air quality at a glance, making it ideal for home use.
- 【3-Color Visualization System】This CO2 detector features a high-definition color screen that displays data in real time, ensuring clear readings. It provides a comprehensive assessment of air quality and tracks the average concentration of each gas, enabling data visualization. When air quality exceeds safety thresholds, the screen intelligently changes color, allowing potential air quality risks to be detected immediately—even from a distance.
- 【High Accuracy and Reliability】Built with a high-performance smart chip and advanced sensor array, this tester adopts dedicated intelligent sensing technology for CO2 detection, paired with precision electrochemical sensors for HCHO and TVOC monitoring. Unlike ordinary detectors, it features smart calibration and stable sensitivity, ensuring long-term accurate data output without frequent manual adjustments.
- 【Simple Operation】Air Quality Tester: Press and hold the "Power button" for 3 seconds to turn the air quality monitor on or off, and it automatically initiates full-range detection the moment it’s turned on; and press once to switch temperature settings ℃/℉; press twice to turn the sound on or off; press 3 times to enter the calibration mode; press 4 times to put the screen to sleep(then press once to wake the screen). You can calibrate the time by connecting your phone to the MT13S via Bluetooth.
- 【Wide Range of Applications】This compact and portable indoor air quality monitor can measure air quality in bedrooms, living rooms, kitchens, offices, cars, schools, hotels, basements, restaurants, campsites, and other environments. It is suitable for use in homes, vehicles, grow rooms, maternity and infant care rooms, and public spaces.
Why wildfire smoke makes PM2.5 especially important
AirNow identifies PM2.5 as the key pollutant to watch in wildland-fire smoke. Smoke concentrations can vary sharply across a city as winds, terrain and the fire plume change. An official monitor several miles away may therefore report a different concentration from a sensor in your home, even when both devices are functioning.
What the U.S. AQI means
The U.S. Environmental Protection Agency describes the AQI as its tool for communicating daily air quality and associated health implications. It combines measurements for five regulated pollutants and expresses the result on a 0-to-500-plus scale. The pollutant that produces the highest health concern for the reporting period determines the displayed AQI.
For particle pollution, the daily AQI uses a 24-hour period. That is why a daily AQI value should not be read as an instantaneous measurement from a nearby sensor. AirNow’s current conditions use a NowCast: several recent hourly observations are combined, with longer averaging when conditions are stable and shorter averaging when pollution changes quickly, such as during a wildfire.
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- High Accuracy & Fast Refresh Data: With this smart sensor, the PM2.5 accuracy is ±15 µg/m³ while temperature and humidity accuracies are ±0.54°F and ±3%RH.The two-second correction data feature shows the latest changes in PM2.5, temperature, and humidity.Keep sensor clear for accurate detection.
- Multifunctional Air Quality Detector: The GoveeLife Air Quality Monitor conveniently measures 3 important indexes for indoor air quality, including PM2.5, temperature, and humidity.
- Switchable Display: Press the top button for the clock & PM2.5 display. Long press for 2 seconds to switch to bright screen mode & night mode. The LED indicator displays 4 levels of ambient air quality. 2.4G Wi-Fi is required to display the time.
- Connect with GoveeHome Appliances: Set your target air quality and link with your other GoveeHome smart appliances. GoveeLife air purifiers, humidifiers, and space heaters will turn on and off automatically when the indoor air quality changes.
- H5106 needs to be connected to a power source and supports GoveeLife devices: Smart Air Purifiers - H7126, H7120, H7124, H712C, H7122, H7123; Humidifiers - H7140; Fans - H7100, H7102
U.S. AQI categories
| Category | U.S. AQI | Meaning |
|---|---|---|
| Good | 0–50 | Air quality is considered satisfactory, with little or no expected risk for the general population. |
| Moderate | 51–100 | Air quality is generally acceptable, but some unusually sensitive people may experience effects. |
| Unhealthy for Sensitive Groups | 101–150 | Sensitive groups may experience health effects and may need to reduce exposure. |
| Unhealthy | 151–200 | Some members of the general population may experience effects; sensitive groups can experience more serious effects. |
| Very Unhealthy | 201–300 | Health alert conditions; the risk of health effects is increased for everyone. |
| Hazardous | 301 and higher | Emergency conditions in which the entire population is more likely to be affected. |
An AQI above 100 is considered unhealthy, first for sensitive groups and then for a progressively larger share of the population as the value rises. The categories communicate what to do about exposure; they are not direct concentrations and cannot be substituted for a PM2.5 value without knowing the pollutant, averaging period and applicable AQI method.
PM2.5 versus AQI: the practical difference
| Question | PM2.5 | AQI |
|---|---|---|
| What is it? | A pollutant concentration or estimate. | A health-communication index derived from pollutant data. |
| Typical display | Often µg/m³, sometimes particles per volume. | A number paired with a color and category. |
| Time basis | May be instantaneous, rolling or averaged; the display must specify which. | Daily particle AQI uses 24 hours; current AirNow conditions use a multi-hour NowCast. |
| Source | Official monitor, temporary monitor or low-cost sensor estimate. | EPA/AirNow calculation from pollutant observations and quality controls. |
| Best use | Track local particle changes and compare trends under consistent conditions. | Understand the public-health significance and recommended caution level. |
A monitor may show “AQI” even though it first measured PM2.5 and then applied its own conversion. Private applications can use different breakpoints, averaging windows, correction factors or even a different pollutant. AirNow specifically advises checking the official U.S. AQI when a private app or sensor displays a conflicting AQI.
Can you trust a consumer smoke sensor?
A low-cost particle sensor can be useful, especially where official monitors are widely spaced. It can reveal that particles are rising in your neighborhood, show whether closing windows reduced indoor smoke, and help you see the effect of running an air cleaner. Its strongest use is local context and trend detection, not regulatory measurement.
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- Improve Your Comfort & Health: Air Quality Monitor + Indoor Thermometer This smart air quality monitor continuously tracks PM2.5 and AQI, while also serving as a precise indoor thermometer and thermo-hygrometer for temperature and humidity. Understand whether your environment is both healthy and comfortable.
- Visualize Your Indoor Environment: A 2-in-1 device that combines environmental comfort detection (temperature + humidity) with air quality detection (PM2.5/AQI). The right temperature and humidity keep you comfortable; clean air keeps you healthy. One screen, total peace of mind.
- Sensitive & Accurate Sensors: Equipped with a digital temperature and humidity sensor that delivers higher accuracy than traditional hygrometers. The built-in miniature laser particle sensor provides reliable PM2.5 measurements, making this air quality monitor as accurate as it is versatile.
- 60-Day Battery Life – Energy-Efficient Design: Advanced algorithms reduce laser sensor energy consumption by 80%. This portable indoor thermo-hygrometer and air quality meter runs up to 60 days on a single charge – perfect for moving from nursery to office to bedroom.
- Compact, Portable & Easy to Use: Small enough to carry anywhere, with a clear display showing temperature, humidity, AQI, and PM2.5 at a glance. Ideal for home, office, school, or travel.
Consumer devices estimate particle concentration with optical methods. Their response can vary with particle size, color, humidity and the composition of the aerosol. A device may also fail, lose its network connection, report stale data or be installed in a location that does not represent the surrounding air.
- Bias: readings can be systematically high or low compared with a reference monitor. EPA has reported that uncorrected PurpleAir readings tend to overestimate PM2.5 mass concentration while generally following trends seen by collocated monitors.
- Siting: a sensor beside a cooking appliance, open window or exhaust vent measures that local source rather than neighborhood background.
- Transmission and aggregation: a map value can be delayed, unavailable or erroneous because of measurement, transmission or data-aggregation problems.
- Intended use: EPA does not use low-cost sensor data for regulatory purposes or official daily AQI reporting.
AirNow’s Fire and Smoke Map combines permanent and temporary monitors with crowdsourced sensor information and smoke/fire context. The map quality-controls low-cost sensor readings and applies a correction equation, but the corrected values remain informational. EPA’s inclusion of a sensor brand or network on a map is not an endorsement.
Why your monitor and AirNow show different numbers
Differences are expected when two displays describe different measurements. Before assuming that one device is broken, compare the following items:
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- 7-in-1 Air Quality Monitor with Upgraded Dart Sensor – Track PM2.5, PM10, HCHO, VOCs, humidity, temperature, and AQI in one device. Powered by a laser particle sensor (3-year designed lifespan) and Dart electrochemical HCHO sensor – not cheap semiconductor – delivering lab-tested accuracy with R² up to 0.999. Real-time AQI calculation included.
- Designed for Trend Detection, Not Just Spot Readings – Track PM2.5 and HCHO fluctuations to identify pollution sources like cooking, incense, or renovation fumes. Built-in 12-hour trend histogram helps you spot peaks and verify ventilation effectiveness instantly.
- 3-Month Data Export for Professional Reporting – Log all 7 parameters continuously via USB and export to Excel spreadsheets. Ideal for renovation monitoring, long-term health tracking, or sharing data with professionals – no subscription or app required.
- Plug-in Continuous Monitor + Portable Spot-Check – Built-in battery supports 6-8 hours of room-to-room spot checks. For 24/7 monitoring, simply connect via the included Type-C cable. Large IPS color display shows green/yellow/red at a glance – no complicated menus.
- Pre-Calibrated & Ready to Use – Factory-calibrated for hassle-free startup. For most accurate readings, avoid using alcohol, perfumes, disinfectant sprays, or strong cleaning agents near the device during testing. Also allow 10 minutes for warm-up after moving between hot and cold environments – this ensures stable, reliable data every time.
- Pollutant: confirm that both displays refer to PM2.5. An AQI dial may be showing ozone, PM10 or another pollutant instead.
- Units: identify whether one value is µg/m³ and the other is an AQI number. They are not interchangeable.
- Averaging window: an instantaneous or one-minute estimate can swing much faster than AirNow’s NowCast or a daily AQI.
- Location: compare the distance and surroundings of each measurement. A kitchen, bedroom, rooftop and roadside monitor do not sample the same air.
- Correction and quality control: determine whether the consumer reading is raw, manufacturer-corrected or corrected by a public map.
- Update time: check when each value was last received. A delayed wireless reading can make an old condition look current.
During wildfire smoke, AirNow directs people to its Fire and Smoke Map rather than relying on an isolated private AQI calculation. Use your sensor to understand your immediate indoor or neighborhood trend, then interpret that trend alongside the official map and health guidance.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Where to put an air-quality sensor indoors
Placement determines whether a sensor represents the room or merely a nearby source. The EPA placement guidance in its 2023 sensor fact sheet recommends positioning the device about 3–6 feet above the ground, close to breathing height, with air able to move freely around it.
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- Keep it away from exterior doors and windows, where drafts can create abrupt local spikes.
- Do not place it next to a stove, fireplace, candle, aerosol spray or smoking area unless you are intentionally measuring that source.
- Avoid heating and cooling vents, fans and other forced-air outlets that can distort the sample.
- Keep the device in the room you actually want to assess; readings in a hallway may not represent a closed bedroom.
The cited 3–6-foot recommendation comes from EPA-452/F-23-004 (2023). EPA’s factsheet index lists a June 2026 sensor factsheet as well, so consult the current edition if its placement instructions differ.
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- Know your air – An Alexa air quality monitor that makes it easy to understand what’s in your indoor air.
- Track and measure – Our indoor air quality monitor keeps tabs on 5 key factors: particulate matter (PM 2.5), volatile organic compounds (VOCs), carbon monoxide (CO), humidity, and temperature.
- Stay informed – Get an indication of current indoor air quality from the color-coded LED, and detailed information and an easy-to-understand air quality score in the Alexa app.
- Real-time alerts - Get notifications on your phone or announcements on Echo devices when Alexa detects poor indoor air quality.
- Automate climate control - Enable Routines to turn on or off your compatible Alexa devices, such as air purifiers, dehumidifiers, and fans, when the indoor air quality sensors detect changes.
Using a sensor with an air cleaner
If indoor smoke is the concern, put the sensor in the room where you plan to operate a portable air cleaner. Close doors and windows when outdoor smoke is high, run the cleaner continuously when practical, and watch the particle trend rather than chasing every short-lived fluctuation. A falling reading suggests that indoor particle levels are declining in that room; it does not certify that the air is safe or replace public-health advice.
A wildfire-smoke routine that uses all three numbers correctly
- Check the official context: open AirNow’s Fire and Smoke Map and note the current U.S. AQI category for your area.
- Identify the pollutant: during smoke, confirm whether the alert is driven by PM2.5 rather than ozone or another pollutant.
- Check the time basis: distinguish the map’s current NowCast from the daily AQI and from your sensor’s short-term estimate.
- Reduce indoor infiltration: close windows and exterior doors, avoid adding indoor particles through cooking or combustion, and use a portable air cleaner if available.
- Watch the local trend: use the indoor sensor to see whether particles rise, stabilize or fall after those actions.
- Follow health guidance: when AQI conditions are unhealthy, reduce strenuous outdoor activity as appropriate; sensitive people may need stronger precautions at lower categories.
If the sensor suddenly reports an extreme value while the official map is unchanged, inspect the device for a nearby source, blocked inlet, condensation, unusual humidity or a stale network timestamp before treating the number as a regional condition.
How to choose and interpret a PM2.5 air-quality monitor
For household use, prioritize transparency over a large number of features. Look for a device that clearly identifies PM2.5, states its averaging period, shows the update time, explains whether values are estimated or corrected, and allows the reading history to be exported or reviewed. A device that displays AQI should identify the AQI method and pollutant used.
- For trend tracking: consistent placement and a readable history are more valuable than a precise-looking single number.
- For wildfire response: rapid updates can help reveal indoor infiltration, but they should be paired with AirNow’s NowCast and official category.
- For comparing rooms: move the same sensor between rooms under similar conditions rather than comparing two uncalibrated devices and assuming their values are equivalent.
- For official compliance: a consumer sensor is not a substitute for a regulatory monitor or official AQI report.
No general accuracy percentage applies to every low-cost sensor. Performance depends on the sensor technology, particle type, humidity, calibration, maintenance and placement. Treat the number as an estimate with known limitations, while treating persistent trends under controlled conditions as more informative than isolated readings.
Quick Recap
Key takeaways
- PM2.5 tells you about fine-particle pollution; AQI translates pollutant data into health categories.
- AirNow’s current NowCast, daily AQI and a sensor’s instantaneous estimate use different time bases and should not be compared as identical numbers.
- Low-cost sensors are useful for local trends, especially where official monitors are sparse, but they can be biased and are not used for regulatory reporting.
- During wildfire smoke, use AirNow’s Fire and Smoke Map and official U.S. AQI for context, then use a properly placed indoor sensor to evaluate local changes.
- Place a sensor roughly 3–6 feet high in open airflow, away from windows, doors, vents and particle-generating sources.
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