Nitrogen is the gaseous compound mostly found (72%) in our atmosphere. Nitrogen gas is useful for the existence of all living beings in our ecosystem. Nitrogen oxides are compounds that consist of both Nitrogen and Oxygen. Even your domestic appliances like heaters, and gas stoves can emit nitrogen oxides in poorly ventilated situations.
Do You Know? Nitrogen oxide and nitrogen dioxide are collectively called NOx.
When the NOx exceeds the usual concentrations that can be withstood by nature, those become air pollutants causing smog and acid rain.
Through this discussion let's understand
- How different nitrogen oxides are formed
- What are the effects of nitrogen oxides
- How to control air pollution by nitrogen oxides
How different nitrogen oxides are formed
Both nitrogen oxide (NO) and nitrogen dioxide (NO2) are found as air pollutants. By knowing the primary sources of pollutants, we can either isolate them or minimize the effects that such pollutants can create.
Different sources of nitrogen oxides
There are natural and anthropogenic sources. Naturally, nitrogen oxides are generated by lightning, volcanoes, and microbial activities that occur in decaying processes.
When lighting, the vicinity of a lightning bolt has a very high temperature. This very high temperature causes the reaction between gaseous nitrogen and gaseous oxygen in the air and then it forms nitric oxide which is a colorless, flammable gas with a slight odor.
When nitric acid sooner reacts with more oxygen, nitrogen dioxide is generated which is acidic and has an odor. It is a deep red-orange gas. Nitrogen dioxide is poisonous but not flammable. Nitrogen dioxide reacts with other compounds faster because it's a strong oxidizing agent.
Anthropogenic nitrogen oxide generation is associated with combustion. Because gaseous nitrogen and oxygen in the atmosphere don't react together at normal temperatures. It needs a high temperature in the atmosphere.
- Mostly when atmospheric nitrogen and oxygen combine directly in flames, it produces nitrogen oxides.
- When nitrogen compounds in fuel burn, it produces nitrogen oxides.
Anthropogenic nitrogen oxide emission sources (mobile and stationary) can be
- Power stations (when using coal and oil)
- Motor vehicles
- Industrial activities
- Domestic combustions
Environmental and health effects of nitrogen oxides
- The human respiratory tract can be damaged by elevated levels of NOx. Then people can suffer from respiratory infections and asthma. But this can seriously affect people with respiratory infections and asthma increasing the severity.
- Whenever you are exposed to high levels of nitrogen oxides in the long term, it can cause chronic lung disease.
- You will experience a reduced ability to smell an odor since NOx can affect the senses.
- Plants show damaged foliage, decreased growth, and reduced crop yields due to increased levels of NOx.
- When nitrogen oxides are released into the atmosphere, it can result in acid rain. Because when rain water contact with nitrogen oxides it can create nitric acid (HNO3).
- As well as nitrogen oxides can reduce the visual smog in the atmosphere. Because nitrogen dioxide with aerosols forms reddish-brown color smog. It is highly toxic when a high concentration of nitrogen dioxides is available and can cause serious lung damage to both humans and animals. In unpolluted air, nitrogen dioxide concentration is around 10 parts per billion (ppb). But in smog, it is about 200 ppb.
How to measure nitrogen oxide concentration
A technique called Chemiluminescence is used to measure nitrogen oxides which is an exothermic chemical reaction.
Here the oxidation of Nitric oxide by ozone resulting nitrogen dioxide and oxygen. It emits energy in the form of light. The intensity of emitted light is measured by a photomultiplier. It is considered that the intensity of the chemiluminescence reaction is directly proportional to the Nitric oxide concentration. Because in the reaction one nitric oxide molecule is needed to form one nitrogen dioxide molecule.
How can we control air pollution by nitrogen oxides
Since there is a link between NOx and acid rain, ground-level ozone, global warming, water quality deterioration, and numerous health effects, if we control the emissions ultimately it will reduce many environmental and health hazards.
- There are developed techniques to effectively control both fuel and thermal NOx generation including low-excess-air-firing, stage-combustion, and flue gas recirculation, etc. Among such techniques, the use of low-NOx burners and the use of low-nitrogen fuels such as natural gas can be suggested as the most cost-effective methods of reducing NOx emissions.
- Whenever we need to limit emissions from stationary sources, we can consider the choice of fuel, combustion control, process modifications, modifications in operating conditions, and flue gas treatment.
What we have done so far to control air pollution by nitrogen oxides
Currently, it is well-investigated that there are a lot of consequences have been created by nitrogen oxides. So people are working to reduce and control the emissions. Several organizations have presented the relevant concentrations of nitrogen oxides that we need to consider. According to the Environmental Protection (Air) Policy 2019, the level of nitrogen dioxide should be 0.12 parts per million (ppm) for an exposure period of one hour. For an annual exposure period, it should be 0.03 ppm.
A lot of industries have already moved for improved technologies to control NOx emissions. Interestingly there are certain national parks like Yosemite and Sequoia where vehicle traffic has been banned. By this step, they hope to reduce air pollution which can damage their plants and trees.
For your additional knowledge
Uses of nitrogen oxides
Whether nitrogen oxides have been identified as pollutants in certain events, still there are many usages of nitrogen oxides in industrial activities. Nitric acid is industrially synthesized for different purposes. Here nitric oxides have to be manufactured by a process. What happens here is Ammonia (NH3) is combined with Oxygen (O2). H2O is a byproduct. Chemical fertilizers, explosives, and other important compounds are manufactured then by using these nitrogen-rich compounds.