PHOTOCHEMICAL SMOG

The industrial revolution has been a great cause of the increase in pollutants in the atmosphere over the last three centuries. Most of the pollution was created from the burning of coal in space heating (boilers), cooking and transportation. Under suitable conditions, the smoke and sulphur dioxide produced can combine to form Industrial Smog. Today, Industrial smog is far less common, but the burning of fossil fuels such as Petroleum can create another atmospheric problem known as photochemical smog.

This condition developes when Primary Pollutants(Oxides of Nitrogen and volatile organic compounds created from fossil fuel combustion) combine under the influence of sunlight to give off a mixture of many different and hazardous chemicals know as Secondary Pollutants.

These conditions mainly occur in large cities eg: Johannesburg, Cape Town, Vancouver.

Major Chemical Pollutants in Photochemical Smog:
Sources and Environmental Effects

Chemical	Sources	The Environmental Effects	Other Information
Nitrogen Oxides (NO and NO2)	- Burning of oil, coal, gas in both vehivles and industry - bacteria in soil - forest fires - volcanic eruptions - lightning	- decreased visibility due to the yellowish color of NO2 - NO2 can be a cause of heart and lung problems - NO2 can stop plant growth - less resistance to disease - Can be a cause of the spread of cancer	- all combustion account for only about 5% of NO2 in the atmosphere, most is created from operations involving NO - amounts are likely to continue rising as time goes on
Unstable Living Compounds (VOC's)	- the evaporation of solvents eg: Polystyrene - the evaporation of fuels eg: Petrol or parafin - the burning of fossil fuels eg: most vehicles	- eye problems - respiratory problems - some are carcinogenic - visibility problems due to a blue-brown haze	- the effects of VOC's are dependant on the type of chemical - samples have shown that there are over 600 different VOC's in the atmosphere - amounts are likely to continue rising as time goes by
Ozone (O3)	- created as a result of photolysis of NO2 - sometimes results from ozone destuction	- breathing problems - coughing, wheezing - eye problems - Less crop yeilds - stunts plant growth - causes damage plastic - breaks down rubber - harsh smell	- amounts of 1.0 molecule per million can decrease photosynthesis by up to 50% - people with asthma and breathing problems are influenced the most - can only be formed during daylight hours
Peroxyacetyl Nitrates (PAN)	-formed by the reaction of NO2 with VOC's (can be formed naturally in some environments)	- eye problems - very poisonous to plants - breathing problems - causes damage to proteins	- was not detected until it was recognized in smog - more poisonous to plants than ozone

Development of Photochemical Smog
Certain conditions are required in order to create photochemical smog

1. A constant source of nitrogen oxides, mostly obtainable from Industrial activities; Transportation; created through burning of fossil fuels.
2. The time of day is also a very important factor when concidering the amount of photochemical smog.
   • Early morning traffic increases the emissions of both nitrogen oxide and VOC's as people drive to work.
   • Later in the morning, traffic dies down and the nitrogen oxides and volatile organic compunds start to react forming nitrogen dioxide increasing it's concentration
   • As the sunlight becomes stronger later in the day, the nitrogen dioxide is broken down and it's by-products are formed.
   • At the same time, some of the nitrogen dioxide can react with unstable organic compounds to produce compounds such as PAN.
   • As the sun goes down, the creation of ozone is halted. The ozone that remains is consumed by several other reactions
3. Some environmental factors can affect production of photochemical smog.
   
   • Pecipitation can decrease photochemical smog as the pollutants are washed out of the atmosphere by rainfall
   • Winds can blow photochemical snog away replacing it with fresh air. However problems may arise in other areas
   • Temperature changes can change dramatically the severity of the pollution
4. Topography is another important factor influencing the severity of photochemical smog. Settlements in valleys are much more susceptable, because hills and mountains allow pollutants to rise. Valleys are also places in which relatively strong temperature changes occur.

Effects on the Environment

Photochemical smog has devastating effects on the environment. The production of the smog is especially apparent in the summer months, as the high temperatures support the formation of photochemical smog. Photochemical smog kills many kinds of animals and plants, because they are not adapted to breathing photochemical smog. The table above gives all the effects of photochemical smog.

Major Events

There have been no major events as yet because this is an ongoing process and is also a newly discovered problem.

Solutions

There a few solutions to this problem, the first one is to decrease harmful emissions such as those from car exhausts (carbon monoxide) and other gases contributing to the formation of photochemical smog. You can do this by using one car to take one's entire family to their place of work, or you could use a form of transport that does not have harmful emissions such as a bicycle.