Short answers about air pollution, sensors and humidity. Each answer includes a link to a more detailed article.
AQI is an index that translates pollutant concentrations into an easy-to-understand scale: the higher the number, the greater the risk associated with pollution. AirQuality.am uses US AQI. The colour indicates an air quality category and helps you choose appropriate precautions; the index itself is not measured in µg/m³. More about AQI
These are airborne particles and droplets up to 2.5 and 10 micrometres in size, respectively. PM2.5 is included in PM10, so the two readings should not be added together. Fine particles penetrate deep into the lungs, and exposure to air pollution is associated with respiratory and cardiovascular diseases. More about particles and health
WHO recommends an annual average PM2.5 level of 5 µg/m³ and a daily guideline level of 15 µg/m³. These are recommendations for reducing risk, rather than a threshold of complete safety. When comparing readings, the averaging period matters: a single one-minute reading, a daily average and an annual average mean different things. More about WHO guidelines
In winter, heating adds to urban emissions, while light winds and temperature inversions prevent pollution from dispersing. AirQuality.am observations for the winter of 2025/2026 show a rise in pollution in the evening. However, a single chart cannot establish the exact contribution of heating, traffic and other sources. Read the winter report
You cannot reliably distinguish them by appearance: fog and pollution can occur together, and harmful pollutants are not necessarily visible or detectable by smell. A white haze alone does not establish whether the air is clean or heavily polluted. Consider measurements alongside weather conditions. More about air pollutants
It can: particles absorb water and scatter light differently, affecting optical sensor measurements. However, in AirGradient’s study covering 15,000 days of colocation — measurements taken alongside reference instruments — the effect of humidity was small. Sensor design also matters: heat from operating components inside the enclosure can lower relative humidity in the measurement area and reduce PM2.5 overestimation. Humidity also influences aerosol formation, so an entire increase in PM2.5 cannot automatically be dismissed as a measurement error. AirQuality.am additionally applies corrections that account for humidity to several networks. More about humidity and measurements
These sensors are useful for tracking changes in pollution, but their accuracy depends on the model, calibration, particle composition and installation conditions. Studies show that some models agree well with reference instruments after suitable correction. This does not mean that all sensors are equally accurate in all conditions. More about AirGradient sensor testing
Services may use different stations, update times, averaging periods and measurement corrections. There are also different AQI scales. For a meaningful comparison, compare the same pollutant in the same units, measured at similar locations and times; for AQI, also check the calculation method. More about data sources and processing
Construction and soil dust may consist mainly of larger particles. A sensor that measures PM2.5 well does not necessarily measure coarse dust equally well; some models provide a calculated estimate of PM10. A low PM2.5 reading therefore does not prove that there is no dust pollution near a construction site. More about sensors and construction dust
When pollution is high, reduce the duration and intensity of outdoor activity, especially near roads. Children and people with heart or respiratory conditions are more sensitive to pollution. Choose your time and route using current measurements: there is no universal rule that the air is always cleaner in the morning or evening. More about protection
An air purifier with an effective particle filter, such as HEPA, reduces indoor PM2.5 concentrations. When choosing one, consider its clean air delivery rate (CADR), the volume of the room and the availability of replacement filters. Keeping windows open during severe outdoor pollution reduces the effectiveness of air cleaning. More about choosing an air purifier
An ultrasonic humidifier can disperse minerals contained in the water into the air, creating particles that the sensor detects. This is not necessarily just a measurement error. To reduce this dust, use water with a low mineral content in accordance with the device's instructions; a humidifier does not filter the air or replace an air purifier. More about humidification and air cleaning
Certified FFP2, N95 or KN95 respirators that meet the relevant standard are used for protection against PM2.5. Protection depends on a close fit: air should not leak around the edges near the nose and cheeks. Ordinary medical and cloth masks do not provide the same protection, and a particle-filtering respirator is not designed to remove gases. More about respirators
You can buy a ready-made device or build a sensor from an open-source design. For outdoor measurements, suitable equipment and correct placement are essential: follow the manufacturer's instructions and protect the device from precipitation and direct sunlight. If your aim is to monitor neighbourhood air, avoid placing it directly beside chimneys or exhaust outlets. Guide to choosing and installing a sensor
This is an approximate analogy that helps illustrate the scale of PM2.5 risk using evidence on long-term exposure. It does not mean that polluted air and cigarette smoke have the same composition or effects on health, and it cannot precisely estimate the harm from an individual walk. More about the cigarette equivalent