What is PM2.5?

PM2.5 is the name for the smallest dust particles that are routinely measured in outdoor air. This page explains what they are, where they come from, what the WHO guideline says, and how the map shows them.

What PM2.5 is

PM2.5 means particulate matter up to 2.5 microns across. It is measured in micrograms per cubic metre of air (µg/m³). In Bulgarian it is called ФПЧ2.5. The particles are solid or liquid and come in many compositions, from soot to salts.

Where PM2.5 comes from in Bulgaria

Burning wood and coal for home heating is a main source in winter, and cold still evenings let the smoke stay near the ground. Road traffic adds exhaust, tyre and brake wear. Industry, farming and natural dust contribute as well. The European Environment Agency (EEA) describes these as the main sources across Europe. Which one dominates differs between towns and between seasons.

What it means for health

The World Health Organization (WHO) explains that PM2.5 is small enough to reach deep into the lungs and to pass into the bloodstream. Long exposure is linked with heart and lung disease. Short rises in the level matter most for children, older people and people with heart or lung conditions. The size of the effect depends on how high the level is and how long it lasts, and one reading on its own does not describe your personal risk.

Guideline values and map colours

The map colours follow the bands of the European Air Quality Index. For PM2.5, good is up to 5 µg/m³, fair up to 15, moderate up to 50, poor up to 90, very poor up to 140, and above that extremely poor. Grey means there is not enough data.

The WHO 2021 Global Air Quality Guidelines recommend a PM2.5 yearly average of no more than 5 µg/m³ and a 24-hour average of no more than 15 µg/m³. The index bands apply to hourly values, so they are not the same test as the WHO guideline. Always check the official source for legal limits.

How Kanarche measures it

Most readings come from low-cost optical sensors that volunteers run in the Sensor.Community network. The value for an area is the median of the sensors that reported recently, and we show a value only when at least three separate locations report. Official stations of the Executive Environment Agency (ИАОС) are shown too where they exist, with data from the European Environment Agency. Low-cost sensors are not reference instruments and high humidity makes them read higher, so the numbers are indicative. They show change over time and differences between places well.

What to do when the level is high

On a day with high values, people usually cut down strenuous activity outdoors, keep windows closed during the worst hours, and ventilate when the level drops. People with heart or lung conditions should follow their doctor's advice. This map gives no health advice. For official alerts, follow the Ministry of Health, the regional health inspectorates (РЗИ) and the Executive Environment Agency (ИАОС).