National Institute of Geophysics, Geodesy and Geography-
Bulgarian Academy of Science
National Institute of Meteorology and Hydrology





Nitrogen Dioxide (NO2) Ozone
Sulfur Dioxide
Fine Particulate Matter(PM10) Fine Particulate Matter(PM2.5) Air Quality Index
Dominant pollutant (DPI) Universal Thermal Climate Index (UTCI)

Within the framework of the National Scientific Program " Environmental Protection and Reduction of Risks of Adverse Events and Natural Disasters" funded by the Ministry of Education and Science, the System for Chemical Weather Forecast (air pollution) was created. The System present the 72 hours forecast for air pollution in real-time, starting from 00:00 of the current day and extending two more days ahead for the territory of Bulgaria, with a spatial resolution of 3 km and for three selected cities - Sofia, Plovdiv, and Varna, with a resolution of 1 km each.

For each of the mentioned domeins, one of the five main pollutants can be selected - Nitrogen Dioxide (NO2), Ozone (O3), Sulfur Dioxide (SO2), Fine Particulate Matter with a diameter below 10 µm (PM10), Fine Particulate Matter with a diameter below 2.5 µm (PM2.5), from which the Air Quality Index (AQI) is calculated and visualized. The system also forecasts the Universal Thermal Comfort Index (UTCI), indicating the thermal comfort/discomfort of the human body.

Universal Thermal Climate Index (UTCI)

The Universal Thermal Climate Index (UTCI) is determined by ambient air temperature, humidity, wind speed, and sunshine. In addition, the heat radiation from surrounding bodies is also involved in determining the index. It reflects the feeling of thermal comfort in different weather conditions, because of the physiological reactions of human individuals related to the thermoregulation system. Its numerical value is in temperature units (degrees Celsius), categorized into ten classes, according to the magnitude of the heat load at high positive and low negative temperatures.

UTCI (°C) Thermal Stress category Physiological responses
Above 46 Extreme heat stress Increase in the time gradient of the rectal temperature. Steep decrease in total net heat loss. Steep increase of the sweat rate.
38 ÷ 46 Very strong heat stress The rectal temperature increase in 30 min.
32 ÷ 38 Strong heat stress Sweat rate increase. The body core temperature increase in 120 min. Instantaneous change in skin temperature.
26 ÷ 32 Moderate heat stress Change of slopes in sweat rate, mean skin temperature, face skin temperature and hand skin temperature. Occurrence of sweating at 30 min. Steep increase in skin wettedness.
9 ÷ 26 No Thermal stress Plateau in the time gradient of the body core temperature.
9 ÷ 0 Slight cold stress Local minimum of the skin temperature of the hands. Wear gloves!
0 ÷ -13 Moderate cold stress Decreasing of skin temperature of the hands. Emerging of time gradient of the body core temperature. Decrease in facial skin temperature (pain).
-13 ÷ -27 Strong cold stress Decreasing of skin temperature of the hands (numbness). The body core temperature decreases in 30 to 120 minutes.
-27 ÷ -40 Very strong cold stress Occurrence of shivering. Steeper decrease in body core temperature. Numbness in 30 minutes. Risk of frostbite in 120 minutes. High risk of frostbite in facial skin temperature decreasing.
Below -40 Extreme cold stress Steeper gradient of the body core temperature. Frostbite in 30 minutes.