What air pollutants does smog consist of? How are they caused?What adverse effects do they have on human beings and the environment?
Smog is a combination of the words smoke and fog and classically is a mixture of sulfu dioxide (from coal burning) and smoke. Nowadays it comes mainly from vehicle emissions rather than heavy coal burning. It can include the following:
- nitrogen oxides, such as nitrogen dioxide
- tropospheric ozone
- volatile organic compounds (VOCs)
- peroxyacyl nitrates (PAN)
- aldehydes (RCHO)
There are a number of possible side effects to humans when smog is heavy, one of the reasons that certain cities have smog alerts and warn people to stay inside on certain days or urge citizens to drive as little as possible on days when smog is of particular concern.
Some of the most heavily affected cities in the world are London, Mexico City and Tehran and LA is likely the most seriously affected in the United States. Smog has been the cause of a number of deaths, as it was a particularly serious problem when heating using coal was a common practice and it was a serious problem in some US cities during that time.
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Smog was originally a term used to describe a combination of smoke and fog. Today, smog is defined as many different pollutants but is made up of mostly ground level ozone.
The 1990 Clean Air Act established an approach to reduce the harmful effects that these pollutants can have on the environment.
Smog has many adverse effects. It can cause respiratory illnesses, aggravate allergies, etc. Smog also contains carcinogens. In the environment is can be very harmful to animals and their habitats.
The term smog has been formed by combination of two separate words, smoke and fog. The term was first used in 1905 to describe the condition of thick smoke and fog that simultaneously hung over cities in England. Smog is caused by moisture in air condensing on smoke particles. The smog frequently contains sulphur dioxide also which is a gas that affects lungs and makes breathing difficult.
The term smog is now also used for conditions created by action of sunlight on exhaust from vehicles and factories. It is called Photochemical smog. This type of smog is created by the action of sunlight on hydrocarbons and nitrogen oxides emitted in the air by the by the burning of petrol and other petroleum products. Under action of sufficient sunlight, these compounds undergo a chemical reaction producing gases called oxidants. These includes substances such as Ozone, nitrogen dioxide and peroxyacetyl nitrate that irritate the eyes, nose, and throat and damage the lungs.
Smog is caused by weather conditions such as lack of wind and a layer of warm air settling over a layer of cool air near the ground, which prevents smoke from rising up and scattering. Mountain ranges near a city or a factory may also prevent smog from scattering.
Heavy concentrations destroys plant life and speeds deterioration of building materials.