Photochemical smog is a type of air pollution that is formed when sunlight reacts with certain pollutants in the air, such as nitrogen oxides (NOx) and volatile organic compounds (VOCs). These pollutants are emitted by sources such as transportation, industrial processes, and solvent usage.

 

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The formation of photochemical smog occurs when NOx and VOCs react with each other and with sunlight in the presence of oxygen to form ozone (O3) and other harmful compounds such as peroxyacyl nitrates (PANs). This process is known as the photochemical reaction. Ozone is a highly reactive gas that can cause a variety of health problems, including respiratory issues and eye irritation.

 

One of the major effects of photochemical smog is its impact on human health. Ozone can irritate the respiratory system and worsen conditions such as asthma. It can also damage plants, reducing crop yields and contributing to deforestation.

 

There are several ways to mitigate photochemical smog, including reducing the emission of NOx and VOCs through stricter emission standards for vehicles and industrial processes, and promoting the use of alternative transportation modes such as public transit and bicycles. Planting trees and other vegetation can also help to absorb NOx and VOCs from the air.

 

The 1999 Gothenburg Protocol is a legally binding agreement under the United Nations Economic Commission for Europe's (UNECE) Convention on Long-range Transboundary Air Pollution that aims to reduce the emission of pollutants that contribute to photochemical smog, including NOx and VOCs. It sets emission reduction targets for signatory countries and requires them to develop and implement action plans to achieve these targets. The protocol has been successful in reducing the emission of these pollutants and improving air quality in the countries that have ratified it.