What is NOx and SOx ?

Air Pollutants

In general, air pollutants are divided into two main groups: gases and particulate matters. The gases include Carbon Monoxide, nitrogen oxides (NOx), sulfur oxides (SOx), and Hydrocarbon. On the other hand, the particulate matters include dust, smoke, smog, and soot. The National Air Pollutants Emission data provides the emission data of air pollutants such as SOx, NOx, Carbon Monoxide, TSP and Volatile Organic Compounds that cause harm to human and the environment.

Air Pollutants Emission data

As the most basic data needed to establish the national environmental policy in securing clean air, air pollutants emission data provides the data on types, sources and the amounts of air pollutants. With this regard, In regard to this, the National Institute of Environmental Research is in charge of estimating the national air pollutants emission each year and managing the data as the nation's official statistics.

Sulfur oxides (SOx)

Sulfur compounds, which are prevalent in fuels, combine with oxygen when fuels are burned, and produce SOx gases in the atmosphere. When sulfur is oxidized, it forms sulfur dioxide or SO2. If it is more oxidized, it becomes SO3. These SO2 and SO3 are in the family of SOx. SO2 is easily oxidized in the atmosphere to SO3 and becomes sulfate, or reacts with water vapor to form micrometer-size droplets of sulfuric acid, H2SO4. SOx is a pungent, colorless gase that causes respiratory illness if concentrations reach a certain level. Even at the low level, however, it can be toxic enough to kill plants.

SOx, along with NOx, is mostly formed in the combustion of fuels containing sulfur such as coal and oil. SOx is responsible for the formation of acid rain, corrosion of metal structures and is harmful to people and other living organisms. Acid rain causes limited damage to any cities or industrial complexes, but the damage can spread across wide geographic areas if a large amount of acid rain is released. Acidification of lakes, surface waters, groundwater can do damage to aquatic creatures, forests and farming lands.

SOx reduction measures are divided into the precautionary measures and the post measure. The precautionary measures include the use of low sulfur fuels (low sulfur oil and coal) or clean fuels (natural gas and LPG) and the desulfurization of oil products. On the other hand, the post measure refers to exhaust gas desulfurization, a process to remove SOx gases from flue gas generated from combustion of oil and coal before releasing the gas from smokestacks. Exhaust gas desulfurization, however, has limitations in that this method can only apply to large-scale facilities due to the economic viability.

Nitrogen oxides (NOx)

NOx gases are emitted from high temperature combustion. Although most of the NOx gases are generated from the combustion of nitrogen present in the air, some are produced from the oxidation of nitrogen contained in fuels. Nitrogen generates various nitrogen oxides including nitrogen monoxide or NO, nitrogen dioxide or NO2, and Dinitrogen trioxide or N2O3. NO and NO2 are the most prominent nitrogen oxides and are often referred to as NOx. NO is easily oxidized to NO2, which is then dissolved in water to make HNO3. Like sulfur oxides, nitrogen oxides are the sources of acid rain.

NOx is harmful to human health. In direct way, it causes or worsens respiratory disease, and can do damage to plants, whereas it plays a significant role in photochemical reaction. N2O, or Nitrous Oxide, also known as laughing gas, is used as anesthetic, and is one of the air pollutants that cause global warming.

Volatile Organic Compound (VOC)

VOC means petrochemical products, organic solvent and other substances among hydrocarbons, and are notified by minister of environment in consultation with directors of relative executive agencies. VOC's steam pressure is over 0.02psi and its boiling point is under 100℃.

VOC is produced by organic combination of carbon and hydrogen and exists in diverse types. It is also generated by using oil product and incompletely incinerating oil, alcohol, and other organic acid. VOC includes Polycyclic Aromatic Hydrocarbons(PAHs) such as aldehyde, ketones, benzene, and benzopyrene, some of which is a carcinogen. In addition, many of VOC has a strong smell.

Photochemical reaction can be generated by mix of VOC and nitrogen oxides in the sunlight, causing pollutants including peroxyacetylnitrate. These pollutants can lead to visibility obstruction, eye disease, and respiratory disease, and damage to plants.

DUST

Dust means particles which are floating or scattering in the air. According to chemical composition and size of particles, dust has different influences on human health. The smaller a particle is, the worse effect it has on a lung. In addition, minute particles provide wide adhesion area, playing a role of vehicles for heavy metals, persistent organic pollutants, and endocrine disruptor. In general, diameter of particles in the air is from 0.001 to 500㎛ and particles of 0.1 to 10㎛ accounts for the largest portion. 1㎛ is 1/1000㎜ or 10000Å.

The density of dust in the air can be shown by the following units: TSP, PM10, and PM2.5. Total Suspended Particulate(TSP) means the total amount of dust scattering in the air, and PM10 indicates the amount of dust whose diameter is under 10㎛. Also, PM2.5 means the amount of dust whose diameter is under 2.5㎛.

CO

CO is produced by incomplete incineration of carbon. CO, which is colorless and odorless, can cause toxication and can be fatal only by a small quantity. When a man inhale CO, it joins with Hb in blood instead of O2, producing CO-Hb. Because CO is 200times powerful to combine with Hb than O2 it reduces the capability of conveying O2 by Hb. Main causes are heating and auto exhaust.

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