![\"i-54cced2edcf95f4db81bcbfc1c403d92-dice.jpg\"](\"http:\/\/scienceblogs.com\/principles\/wp-content\/blogs.dir\/467\/files\/2012\/04\/i-54cced2edcf95f4db81bcbfc1c403d92-dice.jpg\")
There’s a new “Ask a ScienceBlogger” question out:<\/p>\nThere’s a new “Ask a ScienceBlogger” question out:<\/p>\n
\n“A question from a friend’s 9-year old son:
\n What is in the air we breathe? What is it’s chemical composition?”<\/p>\n<\/blockquote>\nThe short answer to this is “a little bit of everything.” Pretty much
\nany substance we have on Earth can be found in the atmosphere
\nsomewhere<\/strong>. The atmosphere is a pretty big place– roughly
\n1044<\/sup> molecules worth of stuff (that’s
\n100,000,000,000,000,000,000,000,000,000,000,000,000,000,000, give or
\ntake). In a collection that big, you’ll find just about anything you
\nwant.<\/p>\nAll we can really do when asked about the composition of the
\natmosphere is make statistical statements. We know how much of various
\ngases there are in the atmosphere on average, but it can vary quite a
\nbit from place to place, and moment to moment. On a humid summer day
\nin New York, there’s a lot of water vapor in the air, but on that same
\nday in the middle of the Sahara desert, there’s hardly any water at
\nall.<\/p>\n<\/p>\n
The composition of the atmosphere is usually given in either
\npercentages, or “parts per million.” In either case, the answer comes
\ndown to “if you grabbed a million molecules at random out of the air,
\nand counted how many of different things you had, what would you
\nfind.” The vast majority of the atmosphere is nitrogen– about 78%, or
\n780,000 out of every million molecules. Oxygen is next, at about 21%,
\nand a good thing, because we need it to breathe. Then there’s about 1%
\nargon, and a whole bunch of other things.<\/p>\nCarbon dioxide, that you hear about all the time when people talk
\nabout global warming, is somewhere around 400 parts per million– that
\nmeans that in a random sample of one million molecules, you expect to
\nget about 400 CO2<\/sub> molecules. There would be about five
\nhelium molecules in that sample (unless you’ve been filling a lot of
\nballoons recently), and krypton is a one-in-a-million gas– roughly 1
\nkrypton atom for every 1,000,000 molecules in the atmosphere (unless
\nyou’re in my lab, where I use krypton in my research, and the
\nconcentration is probably a little higher).<\/p>\nThese are all really guesses, though. Nobody is ever going to count
\nall of the molecules in a room, let alone the entire atmosphere, and
\ntell you exactly what’s in the air you breathe– there’s just too much
\nof it. All we can do is put limits on what’s likely to be there, based
\non lots of measurements at different places at different times. We
\nthink that there will be about 10,000 molecules of water vapor in
\nevery million molecules that you breathe, but it could be 40,000 on a
\nreally humid day, or it could be 5,000 on a dry desert afternoon.<\/p>\nThere’s no way to know exactly<\/strong>, but we know in a general way, and
\nthat’s good enough for most practical purposes.<\/p>\n","protected":false},"excerpt":{"rendered":"There’s a new “Ask a ScienceBlogger” question out: “A question from a friend’s 9-year old son: What is in the air we breathe? What is it’s chemical composition?” The short answer to this is “a little bit of everything.” Pretty much any substance we have on Earth can be found in the atmosphere somewhere. The… Continue reading Ask a ScienceBlogger: What’s in the Air?<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"1","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[41,7,11],"tags":[],"class_list":["post-2514","post","type-post","status-publish","format-standard","hentry","category-ask_a_scienceblogger","category-physics","category-science","entry"],"_links":{"self":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts\/2514","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/comments?post=2514"}],"version-history":[{"count":0,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/posts\/2514\/revisions"}],"wp:attachment":[{"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/media?parent=2514"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/categories?post=2514"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/chadorzel.com\/principles\/wp-json\/wp\/v2\/tags?post=2514"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}