smog is a combination of both smoke and fog, caused by exhaust and particles from cars and factories ,causing difficulty in breathing, asthma, reduced resistance to lung infections, colds and eye infections.furthermore, the exposure to smog can reduce life expectancy by as much as 15 years and it can slow down plant growth and the tiny pollutant particles may also be deposited on soil and water surfaces, thereby entering the food chain and poisoning animals , thus harming the environment