Photochemical smog consists of primary and secondary pollutants. Primary pollutants are released into the environment by vehicles, industry and natural environments. Primary pollutants Industry-related Vehicle-related natural processes Sulfur dioxide Hydrocarbons Sulfur oxides Nitrogen dioxide Carbon nitric oxide Dioxide Carbon monoxide Carbon monoxide Volcanic dust Hydrogen sulfide smoke Secondary pollutants form when primary pollutants react in the atmosphere, such as the presence of direct sunlight. These secondary pollutants are ozone, nitric acid, peroxyalnitrate and toxic organic compounds such as formaldehyde. It is the mixture of these primary and secondary pollutants that forms photochemical smog. Photochemical smog is more prolific in warmer climates with modern industrial areas and numerous automobiles. Smog is not a big problem in Australia, but in larger cities and developing countries where pollution levels are much higher smog is an everyday occurrence. Due to the large population, these smog-affected cities release a large amount of primary pollutants, which react with the atmosphere and in particular with ultraviolet light. The chemical reaction between primary pollutants and ultraviolet light gives rise to secondary pollutants resulting in the formation of photochemical smog. Toxic chemicals within photochemical smog Sources of chemicals (human activities) Environmental effects Nitrogen oxides (NO and NO2) - Burning of oil, coal, gas in automobile and industry - Forest fires - Decreased visibility at causes the yellowish color of NO2 - Contributes to lung problems - Suppresses plant growth - Decreases resistance to infections - Encourages the spread of cancer Volatile organic compounds (VOCs) - Evaporation of solvents - Evaporation of fuels - Incomplete combustion of fossil fuels - Eye irritation - Respiratory tract irritation - Some are carcinogenic - Decreased visibility due to blue and brown haze of ozone (O3) - Formed by photolysis of NO2 - Decreases crop yields - Retards plant growth - Damages plastic - Breaks rubber - Sour odor - Respiratory irritation Peroxyacetyl nitrates (PAN) - Forms due to reaction of NO2 and VOC - High toxicity to plants - Damage to proteins - Respiratory irritation - Eye irritation Problem Photochemical smog is one of the main responsible for air pollution. Photochemical smog has been linked to many negative health conditions; in particular respiratory conditions. These health conditions are not only linked to humans, but also to plants and animals. Effects on humans/plants/synthetics• Smog has been responsible for the loss of lung capacity and lung elasticity in humans and animals exposed to photochemical smog.• In plants ozone, a secondary pollutant is responsible for the damage of the leaf tissue, significantly influencing the plant's ability to grow and thrive. • Smog not only affects living things but also affects synthetic products. With low level exposure for just a month the smog can break down rubber and with continuous exposure it can cause complete disintegration.