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 (PM_2.5), 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.

Nitrogen Dioxide (NO₂)

Sources

Nitrogen dioxide is formed during combustion processes. The main sources are motor vehicles, thermal power plants (TPPs), some industrial manufacturing, and tobacco smoking. Under the influence of intense sunlight and in the presence of volatile organic compounds in the atmospheric air, Nitrogen dioxide chemically reacts, resulting in the formation of the secondary pollutant - Ozone.

Impact on Human Health

Nitrogen dioxide enters the human body through breathing. Most of the nitrogen dioxide is absorbed into the body, and a significant portion of it can remain in the lungs for a long time. Prolonged exposure to concentrations above the Maximum Permissible Concentration (MPC) can cause structural changes in the lungs. The harmful effects of this pollutant primarily affect respiratory functions. People with chronic respiratory infections are adversely affected, and individuals suffering from bronchial asthma are particularly sensitive to increases in nitrogen dioxide levels.
It has been established that for short-term exposure, the lowest concentration at which an effect on asthmatics is observed (within 1 hour) is 560 µg/m³, which serves as the basis for determining the allowable limits for air pollution.

Legislation

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 Annual Norm - 40 µg/m³
Average Hourly Norm - 200 µg/m³ (not to be exceeded more than 18 times annually)
Alarm Threshold* - 400 µg/m³ (measured over three consecutive hours by the respective Automatic Information Systems (AIS) and Automatic Air Quality Monitoring Systems (AAQMS))
*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.

https://eea.government.bg/bg/output/daily/2004-air/november/30-11.html