What air pollution is

Air pollution is the presence of substances in the air that harm health or nature in large enough amounts. The pollutants watched most often are the fine particles PM2.5 and PM10, nitrogen dioxide, ground level ozone and sulphur dioxide. The European Air Quality Index has bands for each of them.

Nitrogen dioxide comes mostly from burning fuel in transport and industry. Sulphur dioxide comes from burning coal and oil and from smelting ores. Ozone is not emitted directly. It forms in the air from other gases in the presence of sunlight. How clean the air is also depends on the weather. Wind and rain dilute pollution, and still cold weather holds it in place.

Kanarche shows mainly particulate matter, because that is what the citizen sensors measure. The metric menu also lists nitrogen dioxide, ozone and sulphur dioxide, but only where official stations report them.

PM2.5 and PM10 in brief

PM means particulate matter. PM10 are particles up to 10 microns across, and PM2.5 are the smaller part of them, up to 2.5 microns. They are measured in micrograms per cubic metre of air (µg/m³). In Bulgarian they are called ФПЧ10 and ФПЧ2.5.

PM2.5 is small enough to reach deep into the lungs and to pass into the bloodstream. PM10 also includes coarser dust from roads and building sites. On dry, windy days PM10 can rise with no burning at all. More on each: What is PM2.5 and What is PM10.

Where the pollution in Bulgaria comes from

In winter the main source of particulate matter is home heating with wood and coal. Smoke from chimneys stays near the ground, especially on cold, still evenings.

Road traffic adds exhaust and particles from tyres, brakes and the road surface. All year round, cars also lift dust from the road. Industry, construction, farming and natural dust from the soil contribute as well.

The European Environment Agency (EEA) describes these as the main sources across Europe. Which one dominates differs between towns, neighbourhoods and seasons.

The heating season and temperature inversions

In Bulgaria particulate matter is usually highest from late autumn to early spring. That is when many homes heat with solid fuel, and the weather is often cold and still.

Normally the air is warmer near the ground. It rises and carries pollution upwards. In a temperature inversion it is the other way round. A warmer layer sits above the cold air near the ground and acts like a lid. Smoke and dust stay low and build up, especially in basins and valleys.

Inversions form mostly during long winter spells of high pressure, when the sky is clear at night and the ground cools quickly. Pollution can then stay near the ground until the weather changes. Wind or a change in the weather usually clears it.

Air pollution and health

The World Health Organization (WHO) calls air pollution a major environmental health problem that affects everyone, and one of the greatest environmental risks to child health. Exposure to particulate matter causes cardiovascular and respiratory disease and cancers. The European Environment Agency (EEA) calls it the largest environmental health risk in Europe.

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. For PM10 the values are 15 µg/m³ yearly and 45 µg/m³ over 24 hours. These are guideline values, not law. The WHO found no level below which there is no harm to health.

Legal limits are different. Today they are set in Directive 2008/50/EC and in Bulgarian Ordinance No. 12 of 2010. From 12 December 2026 Directive 2008/50/EC is replaced by Directive (EU) 2024/2881, and its stricter PM limits apply from 1 January 2030. This page is not medical advice. If you have questions about your own health, talk to a doctor.

What is the AQI

AQI stands for Air Quality Index. It turns measured concentrations into a few bands that are easy to read. Kanarche uses the European Air Quality Index of the European Environment Agency (EEA).

The index has 6 bands: good, fair, moderate, poor, very poor and extremely poor. 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. For PM10 the same bands end at 15, 45, 120, 195 and 270 µg/m³.

The European index rates a site by its worst pollutant. In the sensor table on the area pages, a sensor's band is the worse of its PM2.5 and PM10 bands. If PM2.5 is moderate and PM10 is poor, the sensor is poor. The map itself is coloured by the measurement you have chosen.

Many apps show the US AQI, a scale from 0 to 500 with different thresholds. We use the European one, because Bulgaria is in the EU. You see the value in µg/m³ and its band, with no conversion into points.

The index bands apply to hourly values. Citizen sensors are low-cost optical devices that we do not calibrate. So the band for their readings is indicative and is not a reference-method measurement.

What the Kanarche map shows

Each point on the map is a sensor or an official station, coloured by the band of the chosen measurement. Grey means there is not enough data. The map fetches new readings from citizen sensors every 5 minutes.

The pages for provinces, cities and Sofia districts show the median of sensors with recent data and a 24-hour chart. We publish a value only when at least three separate locations report usable readings. All provinces, ranked by PM2.5, are in Areas.

The official stations publish hourly averages several hours late. How accurate the sensors are and why they differ from the stations is explained in About the data.

What you can do

Check the map before you plan a long walk, a run or outdoor play with children. If values in your neighbourhood are high, pick another time or a place further from busy roads. Air your home when outdoor values are lower, for example after wind or rain.

If you heat with wood, burn only dry, untreated wood and do not burn waste in the stove. That means less smoke for you and your neighbours.

You can also help with data. Every new sensor makes the map more accurate for the air in your neighbourhood. To build or adopt a station, see airbg.info.

Common questions about air pollution

How bad is the air pollution in Sofia today?

Open the Sofia page or the map. It shows the current median of citizen sensors and a chart of the last 24 hours. The value is indicative and is updated every 5 minutes.

What is the AQI?

The AQI is an air quality index. Kanarche uses the EEA European Air Quality Index, with 6 bands from good to extremely poor.

What is the limit for PM2.5 and PM10?

The WHO recommends a 24-hour average of no more than 15 µg/m³ for PM2.5 and 45 µg/m³ for PM10. These are guideline values, not law. Legal limits are today in Directive 2008/50/EC and Bulgarian Ordinance No. 12 of 2010. From 12 December 2026 Directive 2008/50/EC is replaced by Directive (EU) 2024/2881.

Why is the air dirtier in winter?

In winter many homes heat with wood and coal. Cold, still weather and temperature inversions can keep pollution near the ground.

How accurate is the air quality data on the map?

Most readings come from low-cost optical sensors that we do not calibrate. They show change over time and differences between places well. Their values are indicative and should not be checked against a legal limit.

What do the colours on the air quality map mean?

The colours follow the 6 bands of the European index for the chosen measurement, from blue green for good to purple for extremely poor. Grey means there is not enough data.

What is the difference between the European and the US AQI?

The US AQI is a scale from 0 to 500 with different thresholds. The European one shows a band next to the concentration in µg/m³, and the EEA rates stations across Europe with it.

How do I check the air quality in my town today?

The Areas page lists every province, the 27 provincial cities and the 24 Sofia districts. Each has a current value and a 24-hour chart.