about 0.4 part per billion


Is "0.4 part per billion" ="0.4/10^9"?

Sorry I've not checked up "part" in Google but simply looking into our dictionary (it appears to be "portion").

Using SAM, Webster and his colleagues have found a persistent background level of methane in the atmosphere above Gale Crater over the last five years of about 0.4 part per billion—a scarcely detectable trace, to be sure, but enough to pique astrobiologists’ interest. Tellingly, the methane levels appear to periodically spike in time with Martian seasons, being about three times higher in the sunny summertime than in the darker, colder winter.

-Scientific American

  • Franco-filly

    Senior Member
    English - Southern England
    Correct, see this WRdefinition of part 5.any of a number of more or less equal quantities that compose a whole or into which a whole is divided:Use two parts sugar to one part cocoa.


    Senior Member
    English (UK then US)
    Quite common and also known as ppb
    It is typically written parts per billion: the expression “part per billion” is only used for 1 ppb.
    1. Measures parts per billion.
    Also, p.p.b.
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