View source for Concentration in parts per

[[Category:Done 2018-08-03]] 
[[File:Visualisation_parts_per.png|350px|thumb|right|Figure 1. Diagram showing percentage, parts per thousand, ten thousand and ppm.<ref>Wikimedia Commons. (August 15th, 2017). By Cmglee - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=52371683 [Online]. Available: https://en.wikipedia.org/wiki/Parts-per_notation#/media/File:Visualisation_parts_per.svg</ref> Click on image to see a larger version.]]
<onlyinclude>[[Pollutant]]s can be problematic even in low concentrations, so it's necessary to be able to talk about very small amounts of a substance in a larger substance. This means it's useful to think of a total and how many parts of that total are a pollutant, or whatever scarce substance is being considered. If we divide a gas into a million parts, then the ppm is how many of those parts is the substance that we're interested in.</onlyinclude> In some situations it's important to distinguish between percent (or ppm, etc.) by mass, percent by volume, or percent by number. When not stated, amount by number is implied.

For example, the amount of [[carbon dioxide]] (<chem>CO2</chem>) in the atmosphere is now more than 400 parts per million (ppm), means that there are 400 <chem>CO2</chem> [[molecule]]s for every million molecules of air. Written another way, this is 0.4% a surprisingly small number, given that this is enough of a shift to cause [[climate change]]. 

{| class="wikitable sortable"
|-
! Amount !! Written as !! Number 
|-
| '''percent''' || '''%''' || 0.01
|-
| '''part per thousand''' || '''‰''' || 0.001
|-
| '''part per ten thousand''' || '''‱''' || 0.000 1
|-
| '''part per million''' || '''ppm''' || 0.000 000 1
|-
| '''part per billion''' || '''ppb''' || 0.000 000 000 1
|}

These are all dimensionless quantities used to describe the ratio of an amount of substance within another substance. For instance, 32 seconds would be roughly equivalent to one ppm of a year,<ref><math>31557600 \frac{seconds}{year} \div 1 000 000 = 31.557 seconds \approx 32 seconds </math></ref> and a [[millimeter]] is one ppm of a [[kilometer]]. 

Ppm is commonly used to describe quantities of trace substances in order to communicate abundance; such as [[mercury]] in fish or the abundance of [[uranium]] within the Earth's [[Cross section of the Earth|crust]]. 

<gallery caption="A mm is one ppm of a kilometer." mode=packed heights=250px>
dimethickness.jpg|A dime is one millionth of a kilometer.<ref>Image taken from https://www.coincommunity.com/forum/topic.asp?TOPIC_ID=30015 August 15th, 2017.</ref>
Kingdom_Tower,_Jeddah,_render.jpg|The Jeddah Tower, intended to be 1 km tall, which is the tallest structure humans have ever built.<ref>Image taken from wikimedia commons by: Adrian Smith+Gordon Gill Architecture, available https://en.wikipedia.org/wiki/File:Kingdom_Tower,_Jeddah,_render.jpg, accessed August 15th, 2017.</ref>
</gallery>

==For Further Reading==
*[[Pollution vs waste]]
*[[Pollutant]]
*[[Biomagnification]]
*[[Mercury]]
*Or explore a [[Special:Random|random page]]
==References==
{{reflist}}
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