The presence of unwanted substances in the lowest layer of the atmosphere results in tropospheric pollution. Major gaseous pollutants include oxides of sulphur, nitrogen, carbon and hydrocarbons.Burning of fossil fuels (coal, automobile fuel) produce oxides of sulphur and nitrogen. They react with water in presence of oxygen of air and form nitric acid and sulphuric acid. This causes acid rain which is harmful to agriculture plants and trees. It causes various respiratory ailments.Burning of hydrocarbons (carcinogens) produce oxides of carbon. CO is poisonous and can lead to death. CO2​ is responsible for global warming. Particulates of smoke dust mist and fume are harmful for human health and cause respiratory ailments.