Trace gas Trace gas The most abundant gases in the atmosphere are nitrogen (78.1%), oxygen (20.9%), and argon (0.934%). Combined, oxygen, argon, and nitrogen make up 99.934% of the gases in the atmosphere (not including water vapor). The other gases that are not part of the 99.934% of the atmosphere are called trace gases. The abundance of a trace gas can range from a few parts per trillion (ppt) by volume to several hundred parts per million by volume (ppmv). When a trace gas is added into the atmosphere, that process is called a "source". There are two possible types of sources
Gas mask as blister agent or nerve agent, a gas mask alone is not sufficient protection, and full protective clothing must be worn in addition, to protect from contact with the atmosphere. For reasons of civil defense and personal protection, individuals often buy gas masks believing that they protect against the harmful effects of an attack with nuclear, biological, or chemical (NBC) agents; which is only partially true, as gas masks protect only against respiratory absorption. Whilst most military gas masks are designed to be capable of protection against all NBC agents, they can have filter canisters proof against those agents (heavier)