Sulfur dioxide can have a short-term effect on the weather. This aerosol blocks the sun and causes cooler temperatures globally. The sulfur dioxide eventually depletes, but is replenished by each eruption rich in sulfur dioxide. Fluorine can be a deadly to animals after an eruption. The fluorine is poisonous to animals that eat the fluorine-coated grass and plants.
Chlorine is emitted as hydrochloric acid into the atmosphere.
Water vapor is the only one of these gases that helps society by replenishing the water supply. There are many hazards from volcanic eruptions. Lava flows have killed a relatively small number of people. The damages can be increased with the change of human population is certain areas. The more people that live in hazardous areas, the higher the risk is.