NOx: Air Pollution & Tropospheric Ozone
- Sylvia Rose
- 2 days ago
- 2 min read
NOx are nitrogen compounds, mainly nitric oxide (NO) and nitrogen dioxide (NO2). These gases create serious environmental problems, including smog, acid rain and high amounts of ground-level ozone.
Nitric oxide and nitrogen dioxide are the most prevalent and reactive forms. These gases are often byproducts of combustion in vehicles, power plants, industry or agriculture. When fuel burns at high heat, nitrogen in the air reacts with oxygen to forming NOx.
Smog
The most visible impact of NOx emissions is smog formation. Smog is the hazy, brownish or yellowish fog hanging over urban areas. It's a mix of pollutants like ground-level ozone, particulate matter (PM) and chemicals.
While ozone in the stratosphere protects the planet from UV radiation, ozone at ground level is a potent air pollutant. In presence of sunlight, NO2 breaks down, releasing a free oxygen atom.
The atom combines with molecular oxygen (O2) to form ozone (O3). Smog irritates the respiratory system, worsening ailments like asthma or bronchitis. It causes eye and throat problems, coughing and wheezing.
In Los Angeles (above), the smoggiest city in the US, most ozone in the air comes from NOx reacting with volatile organic compounds (VOCs) and sunlight.
Acid Rain
NOx also contributes to acid rain. When released into the atmosphere, NOx can react with water, oxygen, and other chemicals to form nitric acid (HNO₃).
Nitric acid then falls to earth as acid rain or precipitation. Acid rain has devastating ecosystem effects. It acidifies lakes and streams, destroying aquatic life.
In forests, acid rain damages leaves, weakens trees, and makes them susceptible to disease and pests. It decreases agricultural output. Buildings and monuments of limestone and marble are corroded by acid rain.
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