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Ozone Isopleth

An Explanation of the Ozone Isopleths 

The isopleths were created by running ChemTest, a computer model created by Dr. Harvey Jefferies, that simulates the complex chemical reactions occurring in the atmosphere between NOx and VOCs to produce ozone.

To interpret the graph, it should be broken into three parts:

The x-axis – this displays increasing concentrations of VOC’s from left to right
The y-axis – this displays increasing concentrations of NOx from bottom to top
The isopleths - these are c-shaped curves in the body of the graph that represent increasing concentrations of ozone from the bottom left corner to the top right corner; the concentration of ozone remains constant along each isopleth but changes between each isopleth.

The isopleths are used for determining ozone levels at specific combinations of NOx and VOCs in the atmosphere and to determine whether a region is NOx or VOCs limited.  If a region is situated in the bottom right corner of the graph, it is NOx limited since the amount of NOx determines the amount of ozone created.  This is because an increase in NOx moves the point to another isopleth where an increase in VOCs only moves the point in question along the same isopleth, not increasing the ozone concentration.

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