Answer:The correct answer is 'emissions'.
Explanation:
An emission is defined as discharge of something into an open atmosphere especially gas or any radiation.Many toxic gases are released into atmosphere when combustion of fuel takes place in a vehicle. Not only from vehicles but also industries , factories etc also releases toxic gases and into our atmosphere which is one of the main cause of air pollution.
Photo-chemical smog is a type of smog formed when ultraviolet light of sun reacts with nitrogen oxides present in our atmosphere.
Carbon monoxide is a colorless, odorless and poisonous gas one of the air pollutant.
Radon is a radioactive gas woith no color and odor used for treatment of cancer and other diseases.
