Smog is a kind of air pollution and is caused by a mixture of smoke and sulphur dioxide

Reducing was occurred before the introduction of cleaner air controls in the mid 1950s and this type of smog was once much more common that it is today. It is made up of a mixture of smoke and sulphur dioxide pollution, and particulates. When the weather is foggy and winds were low, the pollution becomes trapped over the cities. The smoke and fog mixed to produce smog. More coal was burnt in wintertime for heating and so reducing smog pollution was greatest at this time of year. The  of 1952 caused 4000 deaths and persuaded the Government to clean up Britain's air.

Photochemical or summer smog

• First found in the 1950s
• It is the chemical reaction of sunlight,  (NOx) and  (VOC's) in the atmosphere to form harmful substances such as ground-level ozone (O3), aldehydes and peroxyacetylnitrate (PAN)
• Lately it is more common, due to the increase in cars and machineries which cause exhaust from internal combustion engines to concentrate in the atmosphere. Due to this fact photochemical smog is considered to be a problem of modern industrialization.
• All of these chemicals are usually highly reactive and oxidizing
• Photochemical smog is travels with the wind, so it can affect sparsely populated areas

Formation of secondary pollutants in photochemical smog

• During the early morning rush hour there is a build up of hydrocarbons and nitrogen oxides from car exhaust. When the sun comes out the nitrogen dioxide absorbs sunlight and breaks down to form nitric oxide and oxygen radicals.
• Nitric oxide can remove ozone by reacting with it to form nitrogen dioxide and oxygen
• Oxygen radicals react with oxygen to form Ozone and with water to form Hydroxyl radicals
•   These secondary photochemical oxidants can react with a variety of molecules including nitrogen oxides to form nitric acid and hydrocarbons to form peroxides ROOR, aldehydes RCHO, and ketones RCOR.
• Peroxides are extremely reactive, and a chain reaction can occur when they react with nitrogen dioxide to form peroxyacylnitrates, PANs which cause eye irritants and plaint toxicity
• The result, then, is an accumulation of ozone and volatile organic compounds such as PAN. These are referred to as secondary pollutants, because they are formed by the reaction of primary pollutants

Ground level ozone

• The formation of  in  is the most important example of a subsequent air pollutant.
• It is a colourless, odourless gas at ambient concentrations and is a major component of smog
• It results from photochemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOCs) in the presence of sunlight. High levels typically occur from May to September, between noon and early evening.
• Remains in the lower atmosphere until weather systems flush out a given area and dissipate them

Effects of smog on health

• harmful for seniors, children, and people with heart and lung conditions.
• inflame breathing passages
• decreasing the lung's working capacity
• cause shortness of breath, pain when inhaling deeply, wheezing, and coughing
• cause eye and nose irritation
• dry out the protective membranes of the nose and throat
• interfere with the body's ability to fight infection
• Ozone can inflame the lung's lining. These photos show a healthy lung air way (left) and an inflamed lung air way (right)

Here we can see the table which shows the health effects of different Air Quality Index (AQI) levels caused by ground-level ozone

How to reduce smog?

Reduce energy use, for example:

• Use alternative transportation:  walking, cycling and using public transit systems
• Drive within the speed limit
• Use fluorescent or energy-saving incandescent lighting
• Use oil-based paints and solvents: gasoline and mineral spirit
• Buy energy-efficient appliances

Generally,

Since smog is primarily a result of fuel burning, reducing energy use and making wise buying decisions we can all contribute to cleaner air and healthier life.