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.

Sulfur Dioxide (SO2)


Sulfur dioxide (SO2) is part of the sulfur oxides (SOx) group, formed during the combustion of fuels with high sulfur content. The main anthropogenic source of sulfur dioxide is the combustion of fossil fuels, such as in thermal power plants and household sources (domestic heating). Metallurgy and the chemical industry are also sources of sulfur dioxide pollution. SO2 and NOx are key components of "acid rain."

Impact on Human Health

Sulfur dioxide enters the body through the respiratory system. At high concentrations, its absorption can reach up to 90% in the upper respiratory tract and less in the lower parts of the respiratory system.
During short-term exposure to Sulfur dioxide, the respiratory system is primarily affected. There is a wide range of individual sensitivity to Sulfur dioxide, but individuals with bronchial asthma are particularly sensitive. The effects of Sulfur dioxide on the respiratory system are usually combined with the effects of particulate matter. Sensitive groups of the population to sulfur dioxide exposure include children, the elderly, people with asthma, cardiovascular diseases, or chronic respiratory diseases. The health effects of SO2 manifest as respiratory disturbances, respiratory diseases, impairment of the immune defense of the lungs, aggravation of existing respiratory and cardiovascular diseases. It is difficult to separate the effects of Sulfur dioxide from those of particulate matter, with both being associated with increased hospitalization rates and mortality. People with asthma are 10 times more sensitive to SO2 than healthy individuals. Children with asthma are particularly sensitive, and exposure to Sulfur dioxide can lead to inflammatory respiratory diseases.


Information on the impact of atmospheric pollutants on human health is coordinated with the Ministry of Health (MH) and the National Center for Public Health and Analyses under Art. 44, para. 2 of Regulation No. 12 of July 15, 2010, and Order No. RD-09-159/14.04.2003 of the MH.
Regulation No. 12 of July 15, 2010 (prom. SG, No. 58 of July 30, 2010) establishes norms for Maximum Permissible Concentrations (MPC) for nitrogen dioxide, ozone, sulfur dioxide, and fine particulate matter. The introduced MPCs aim to protect against their harmful effects on human health and the environment. The following norms are regulated for different types of pollutants:

Average Daily Standard - 125 µg/m3 (not to be exceeded more than 3 times per year)
Average Hourly Standard - 350 µg/m3 (not to be exceeded more than 24 times per year)
Alarm threshold * - 500 µg/m3 (measured over three consecutive hours by the respective AIS and DOAS)
*Exceeding the alarm concentrations requires the application of measures to limit the harmful effects of the pollutant, including:

  • avoiding strenuous outdoor physical activities. If necessary, it is recommended to perform them early in the morning or late in the evening, if the control authorities have warned of lower air pollution levels. Certain pollutants (Ozone) reach very high levels during midday and afternoon hours;
  • teachers should cancel outdoor physical education activities such as running, soccer, basketball, or other outdoor sports with non-competitive activities or those held indoors or in classrooms;
  • continue to stay indoors until the intense atmospheric pollution episode subsides by tightly closing room windows;
  • avoid smoking and avoid areas where smoking is allowed;
  • avoid staying in areas with intense traffic, where vehicle emissions are massive, as well as presence in workplaces with additional exposure to aerosols, dust, and other irritating substances;
  • limit activities that produce irritating substances to the nose, eyes, and lungs such as cooking, cleaning, or engaging in inappropriate hobbies;
  • patients with coronary heart disease should avoid outdoor physical exertion on days with alarm levels of atmospheric pollutants due to the risk of acute myocardial ischemia or myocardial infarction;
  • specific therapeutic preparations for the treatment of respiratory and cardiovascular diseases related to air pollution do not exist.