Atmospheric Gases

• Atmospheric gases include sulphur dioxide , carbon dioxide , oxygen & ozone .
• In the presence of moisture they contribute to the formation of acids that attack certain materials such as metals , concrete , other cementitious products & stones .
• Sulphur dioxide gases with other hydrocarbon emissions from power stations & other industrial pollutants , form what is generally known as acid rain .
• Its injurious attack on building materials inclues erosion of brickwork & corrosion of metals .
• The presence of carbon dioxide in the atmosphere is generally beneficial is reacting with lime products to form a protective carbonated layer .
• However if carbonation is allowed to proceeed as far as the reinforcement in concrete , it can cause the corrosion of the steel bars .
• Oxygen can cause oxidation of organic materials such as paints , plasters & sealants & is particularly severe on unprotected steelwork .
• Ozone , which is an unstable modification of oxygen , is very much more reactive towards organic materials . It plays a major role in the degradation of rubber , mastics , bituminous compounds , paints & plastics , which can result in their embrittlement & eventual failure .