Converting Units, Gases

The concentration of contaminants in air are frequently expressed as parts per million or ppm. That is volume of contaminant per million volumes of contaminated air.

So if you have 1000 liters (the correct symbol for liter is lower case l, which looks like the number one, so I will use upper case, L.) of carbon monoxide (CO) and place it in 999,000 L of clean air, you get how many ppm . Converting between ppm and mg/m³ is not too difficult, if you remember two things. First you need to know what a "mole" is. (Click here if you've forgotten what a mole. is.) The second thing you need to know is that one mole of a gas occupies 24.45 L at room temperature (25 C) and atmospheric pressure.

So how many moles are there in 1000 L of CO? You try it, then click here. Now how many grams do that many moles weigh? Got it?

And the number of moles is the weight in grams of 1000 L of CO. The units commonly used to express quantities are chosen so answers are most frequently small whole numbers, because they are easier for our brains to grasp and remember. For no better reason, air contaminants are express in mg per m³, if they are not express in ppm. So the final conversion is straight forward, if you remember that there are 1000 L in a cubic meter and 1000 mg in a gm. Try to get the answer, how many mg / m³ is 1000 ppm of CO? When you've got it, click here.

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