Air quality and limit values (PM10, PM2.5, NO₂, benzo[a]pyrene)
Air pollution at a place against the legal annual limits. ČHMÚ calculates it for every 1 × 1 km square as a five-year average.
A limit value is the highest permitted concentration of a pollutant in the air we breathe. It is set by Act No. 201/2012 Coll. on air protection, Annex 1. Ambient concentration is what is in the air where people live, as opposed to emissions, which is what a chimney or exhaust releases.
Which pollutants are monitored and their annual limits
- PM10 (particulate matter up to 10 micrometres): 40 µg/m³ per year, plus a daily limit of 50 µg/m³ that may be exceeded at most 35 times a year
- PM2.5 (fine particles up to 2.5 micrometres, reaching deep into the lungs): 20 µg/m³ per year
- NO₂ (nitrogen dioxide, mainly from traffic): 40 µg/m³ per year
- benzo[a]pyrene (a carcinogen in dust, mainly from household coal and wood stoves): 1 ng/m³ per year
- benzene: 5 µg/m³ per year
How the value for a specific place is determined
There are only a few hundred monitoring stations, so the Czech Hydrometeorological Institute (ČHMÚ) builds area maps from measurements, dispersion models and other inputs (traffic emissions, altitude, population density). The result is a value for every 1 × 1 km square. Under the Air Protection Act, exceedance of a limit is assessed on the average of the previous five calendar years, which is why the five-year average is shown.
How to read the percentage
"PM10 45" means that the five-year average around the home is 45 % of the annual limit. Below 100 % the limit is met. The value is an average for the whole square and the whole year: next to a busy road or during the heating season the air can be worse, in the back garden better.
Frequently asked questions
Why is benzo[a]pyrene often close to the limit even in villages?
It comes mainly from burning coal and wood in household boilers and stoves. In villages where many homes heat with solid fuel it tends to be higher in winter than in towns with district heating.
Does a value below the limit mean the air is healthy?
Not necessarily. Legal limits are a compromise. World Health Organization guidelines are stricter, for example an annual average of 5 µg/m³ for PM2.5. The value is mainly useful for comparing places.
Want this information for a specific property?
Before you buy, we find, analyse and clearly present data about the place: land register, utilities from the operators, floods, zoning plan. An address is enough, within 48 hours, CZK 5,900.
The explanation is general and informative, not legal advice. The land register, the zoning plan and other official sources are binding.