The automobiles are operated by burning fossil fuels like coal and petroleum oil including diesel. Automobiles give out the highest amount of carbon monoxide into the atmosphere. Diesel cars emit oxides of nitrogen and partly oxidised hydrocarbon. Often tetraethyle lead is mixed with petrol. When such petrol is burnt, lead escapes into the atmosphere. Lead combined with some particulate materials in the aerosol may become a real danger to biosphere.
Burning of agricultural wastes and wild fire in forest is a nasty source of air pollution. According to a study at least six hundred million tonnes of agricultural waste and wood are burnt annually. In many countries including Bangladesh, India and Pakistan remains of the crops after harvest are burnt in the fields itself. The burning of agricultural wastes throws up the dust of carbon and ashes into the atmosphere. Astronauts have noticed masses of brownish dust hanging over the landmass of India, China and West Asia. This is created by the smoke and dust emitted from burning of agricultural waste and forests in the entire region.