Volcanic eruptions mainly produce steam (H2 0 ), sulfur dioxide (SO 2 ) and carbon dioxide (CO 2 ). They do release other gases in lesser amounts, such as carbon monoxide (CO), helium (He), hydrogen (H 2 ), hydrogen chloride (HCL), hydrogen fluoride (HF) and hydrogen sulfide (H 2 S).
Some of these gases do affect the environment. For instance, sulfur dioxide converts to sulfuric acid; in the atmosphere, these act as a reflection, pushing solar rays away from the Earth and resulting in cooling temperatures. SO 2 also deteriorates the ozone layer, and it can cause respiratory problems in humans.
CO 2 is harmful to humans and animals, though it generally dilutes into the air without causing harm. it can collect in pockets as it is heavier than air.