Nitrogen oxides (NOx) are a group of gases composed of nitrogen and oxygen. They are primarily formed during fuel combustion processes (fuel NOx) when nitrogen and oxygen in the air react (thermal NOx), especially at high temperatures, and they are significant air pollutants. The two most common nitrogen oxides are nitric oxide (NO) and nitrogen dioxide (NO₂). NO₂ is a reddish-brown toxic gas, while NO is colorless. For these reasons, these oxides are products of fossil fuel or biomass combustion. Both oxides are soluble in water, forming HNO₂ (from NO) and HNO3 (from NO₂). This property of NO (and NO₂) causes acid rain, which adversely affects the entire ecosystem (vegetation, food production, aquatic and animal life), as well as material goods (especially those soluble under acidic conditions). Both oxides cause secondary pollution, as NO can transform into nitrite particles (aerosols) and NO₂ into nitrate particles (aerosols), contributing to fine particulate pollution (PM2.5). The main anthropogenic sources of emissions of these pollutants are combustion of fossil fuels and biomass in all energy processes (production of energy and heat in thermal power plants, combustion in industry and construction, transport, household and administrative combustion, landfill fires, agricultural waste burning, and forest fires). Nitrogen oxides are key substances that, together with volatile organic compounds (VOC), react in the presence of sunlight to form photochemical smog. Today, in our country, the largest sources of NOx emissions are transportation, combustion in industry and construction, and energy installations for electricity and heat production.
Emissions of non-methane volatile organic compounds (NMVOCs) come from many different sources and can be divided into two main process groups: incomplete combustion and evaporation. Small combustion units (e.g., wood burning in households) are a major source of NMVOCs from combustion. Other sources include vehicles and other transport sources such as national navigation vessels. NMVOCs from road transport vehicles have decreased since 1990 due to the introduction of catalytic converters. Evaporative emissions mainly come from the use of solvents and extraction, agriculture, handling and storage of oil, petroleum derivatives, and natural gas. Today, in our country, the largest source of NMVOC emissions is the use of solvents and extraction within industrial processes, while combustion in households and administrative buildings and fugitive emissions from fuels are also important categories of NMVOC emissions.
Sulfur dioxide (SO₂), an important air pollutant, is a colorless gas with a sharp, irritating odor often described as the smell of burnt matches. It is soluble in water, forming H2SO3, and if oxidized to SO3 and dissolved in water, forms H2SO4. This property of SO₂ (and SO3) causes acid rain, which adversely affects the entire ecosystem (vegetation, food production, aquatic and animal life) as well as material goods (especially those soluble under acidic conditions). SO₂ causes secondary pollution as it can transform into sulfate particles (aerosols), contributing to fine particulate pollution (PM2.5). The main anthropogenic sources of SO₂ emissions are combustion of sulfur-containing fossil fuels (coal, mazut, oil, diesel) and industrial processes such as oil refineries, fertilizer production, lead and zinc ore smelting, steel production, paper production, etc. Today, in our country, the largest sources of SO₂ emissions are the thermal power plants REK Bitola and REK Oslomej, which use lignite and mazut as fuel.
Ammonia (NH3) is an air pollutant in both indoor and outdoor air, with a sharp odor. It is naturally released during the decomposition of organic matter, including animal and human waste. Almost all atmospheric ammonia emissions result from agricultural activities. Most agricultural emissions come from livestock manure, with the largest releases occurring during manure handling and storage systems. The second largest source is agricultural soils, mainly due to mineral fertilizer and animal manure application. Ammonia is toxic and can irritate the eyes, nose, and throat. At high concentrations, it can be fatal if inhaled. Ammonia also participates in the formation of secondary particles (PM2.5), mainly through reactions with acidic oxides such as nitrogen oxides and sulfur dioxide, linked to various health issues including reduced lung function, heart problems, and respiratory diseases. Ammonia contributes to acidification, nitrification, and eutrophication of aquatic ecosystems.
CO is a colorless, poisonous gas without smell or taste. Globally, it is estimated that 94% of atmospheric carbon monoxide originates from natural sources or as a secondary product (an intermediate product in the oxidation of methane by hydroxyl radicals). Therefore, any oxidation of methane producing CO as an intermediate significantly contributes to the total CO burden, probably about two-thirds of total CO. Nature limits CO increase through oxidation to CO2 and by soil bacteria converting it to CO2. The atmospheric lifetime of CO ranges from 36 to 110 days, allowing its concentration to be limited in the atmosphere. The remaining 6% comes from human activities such as incomplete combustion of carbon-based fuels like coal, mazut, oil, diesel, and wood. Primary CO sources include vehicle exhaust, combustion of solid and liquid fuels in households, industrial processes (metal processing and chemical production), incomplete combustion of solid waste, and natural sources like forest fires. Indoor exposure sources include domestic stoves and cigarette smoke. Urban atmospheric CO levels correlate positively with traffic density and negatively with wind speed. Urban areas can show average CO levels much higher than remote areas. Today, in our country, the largest source of CO emissions is combustion in households and administrative buildings.
PM stands for particulate matter (also called suspended particles): a term for a mixture of solid particles and liquid droplets (aerosols) found in the air. Some particles like dust, dirt, soot, or smoke are large or dark enough to be seen with the naked eye. Others are so small they can only be detected with an electron microscope. Particles can also be primary or secondary. Primary particles come directly from natural or anthropogenic sources, while secondary particles form in the atmosphere through complex chemical reactions involving sulfur dioxide, nitrogen oxides, ammonia, VOCs, various radicals, and other substances. TSP (total suspended particles) is a type of air pollution including all suspended particles regardless of size. PM10 is a type of air pollution consisting of inhalable particles with diameters of 10 micrometers or less. These particles are small enough to be inhaled into the lungs and may cause various health problems. PM2.5 consists of fine inhalable particles with diameters of 2.5 micrometers or less. These are extremely small particles that can penetrate deep into the lungs and bloodstream, causing various health issues. Today, in our country, the largest source of TSP emissions is combustion in households and administrative buildings and energy production (lignite thermal power plants). For PM10 and PM2.5 emissions, the largest source is combustion in households and administrative buildings.
Black carbon, commonly known as soot, is a type of air pollution formed by incomplete combustion of fossil fuels, biomass, and biofuels. It is a major component of particulate matter (PM2.5) and a significant contributor to climate change and negative health impacts. Main sources of black carbon include: 1. Combustion of fossil fuels (diesel engines, coal power plants, and other fossil fuel combustion sources). 2. Biomass burning (wood burning for heating and agricultural burning releases black carbon). 3. Industrial processes (certain industrial processes involving incomplete combustion also produce black carbon). Today, in our country, the main sources of black carbon are combustion in households and administrative buildings, fuel combustion in industry and construction, and transport.
Lead (Pb) in the air exists as particles and compounds transported through the air, mainly from industrial sources (lead smelting, ore and metal processing, battery production), combustion sources (coal, oil, waste), and the use of leaded aviation fuel (piston engine aircraft, mostly at general aviation airports, still using leaded avgas, making them a significant source of lead emissions). Today, in our country, the largest sources of Pb emissions are combustion in households and administrative buildings and energy installations for electricity and heat production.
Cadmium (Cd) in the air primarily comes from industrial processes such as metal production (smelting) and waste combustion, including plastics and batteries, as well as fossil fuel combustion (coal and oil). It exists as particles, usually small in size, and can travel long distances in the atmosphere before depositing on soil or water through wet and dry processes. Exposure to cadmium, especially by inhalation, can lead to negative health effects including kidney damage and potential cancer risk (classified as a probable human carcinogen by the U.S. EPA). Volcanic eruptions and vegetation can also contribute naturally to cadmium presence in the air but are generally less significant than anthropogenic sources. Today, in our country, the largest cadmium sources are combustion in households and administrative buildings and industrial processes.
Mercury (Hg) in the atmosphere exists in gaseous elemental form (GEM), which is the most common form, gaseous oxidized mercury (GOM), and particle-bound mercury (PBM). Total gaseous mercury (TGM), which includes GEM and GOM, usually constitutes over 95% of atmospheric mercury. Mercury is concerning due to its toxicity and bioaccumulation potential, impacting human health and ecosystems. Mercury
Arsenic (As) in the air originates from both natural and anthropogenic sources, with the latter often dominating in localized areas. While natural sources such as volcanic eruptions and forest fires contribute, industrial activities (coal combustion, ore and metal smelting), agricultural practices (use of pesticides), and burning of arsenic-treated wood are significant anthropogenic sources. Arsenic, particularly when adsorbed onto particles (PM10), can be transported over long distances. Inorganic arsenic, its more toxic form, is often found in airborne particles. Inhalation of arsenic-containing particles can lead to respiratory problems, including asthma, bronchitis, and lung cancer. Chronic exposure has been linked to cardiovascular disorders and other types of cancer. Currently, in our country, the largest emissions of arsenic come from the category of electricity production (lignite-fired power plants).
Chromium (Cr) in the air mainly comes from combustion and metallurgical industry, with hexavalent chromium (Cr VI) being of particular concern. While trivalent chromium is generally less toxic and poorly absorbed, hexavalent chromium is a known human carcinogen and irritant, with potential to cause lung cancer as well as skin and respiratory irritation. At present, the largest sources of chromium emissions in our country are energy-related combustion processes, particularly lignite-fired power plants, transportation, and combustion in households and public buildings.
The main sources of copper (Cu) emissions into the air are tire and brake wear from vehicles and the use of fireworks.
Nickel (Ni) in the air is primarily present in particulate form, with generally low concentrations, though higher levels may occur near emission sources. These particles are often found as nickel sulfate, nickel oxide, or complex nickel–iron oxides. While nickel also originates from natural sources (wind-blown dust, volcanic activity, sea-salt spray, and forest fires), human activities such as industrial processes (mining, smelting, manufacturing) and combustion (coal, oil, waste) are the main contributors. Exposure to nickel in the air is associated with respiratory problems such as asthma and pneumoconiosis (lung disease caused by inhalation of dust). Nickel is also a known skin and respiratory allergen. Some nickel compounds are classified as carcinogenic, and occupational exposure has been linked to nasal and lung cancers. Currently, almost all nickel emissions in our country come from the category of electricity production (lignite-fired power plants).
The main sources of selenium (Se) emissions into the air are electricity production (lignite-fired power plants) and combustion in households and public buildings.
The main sources of zinc (Zn) emissions into the air are combustion in households and public buildings, transport, electricity production (lignite-fired power plants), and fuel combustion in industry and construction.
Polycyclic Aromatic Hydrocarbons (PAHs) are a group of chemical compounds formed during the incomplete combustion of fossil fuels, biomass (coal, oil, wood), and waste. They are present in the air both in gaseous form and adsorbed onto particles, particularly fine particulate matter (PM), which poses significant respiratory health risks. Certain industrial activities, such as coke production, release PAHs into the atmosphere. Vehicle exhausts, especially from diesel engines, are also a major contributor. PAHs can also be produced naturally from events like forest fires and volcanic eruptionsCurrently, the largest source of PAH emissions in our country is combustion in households and public buildings.
Dioxins (PCDD/F) are a group of toxic compounds found in the air as a result of various combustion processes, including waste incineration, industrial activities, and natural events like forest fires. Although typically present at low levels in the air, they can accumulate in the body, primarily through food, and cause harmful health effects. Main sources of dioxins in the air include: 1. Combustion processes: waste burning (municipal, medical, industrial), fossil fuel combustion (oil, wood, coal), and forest fires. 2. Industrial processes: steel production and certain manufacturing activities, including pesticide and herbicide production. 3. Other sources: vehicle exhaust, household wood burning, and even cigarette smoke. Dioxins are released as by-products of incomplete combustion. Once emitted, they can travel long distances in the air and deposit onto soil and water. Health effects: Exposure occurs mainly through ingestion (contaminated food) and, to a lesser extent, inhalation. Once in the body, dioxins accumulate in fatty tissues. Long-term exposure can cause various health problems. Currently, the largest source of dioxin emissions in our country is combustion in households and public buildings.
Combustion processes are the main source of hexachlorobenzene (HCB) emissions. In our country, the largest sources are waste burning and combustion in households and public buildings.
Polychlorinated Biphenyls (PCBs) may be present in the air, both indoors and outdoors, and can pose risks to human health. Although PCBs are no longer produced in many countries, they persist in the environment due to their chemical stability and may be released from older products and materials. Currently, the largest sources of PCB emissions in our country are lead production and the use of electrical equipment by households.
