- For computer memory comparisons, see computer storage density. For other meanings, see Density (disambiguation)
The area density (also known as areal density or surface density) of a two-dimensional object is calculated as the mass per unit area. The SI derived unit is: kilogram per square metre (kg m−2).
It can be calculated as:
or
where
-
ρA = average area density M = total mass of the object A = total area of the object ρ = average density l = average thickness of the object
A special type of area density is called columnar density; it is obtained integrating volumetric density ρ over a vertical column:[1]
where z denotes the vertical coordinate (e.g., height or depth). An example is the Dobson unit for atmospheric ozone. Columnar density ρA is closely related to the vertically averaged volumetric density 
as
where 
; notice that , ρA, and Δz have units of, e.g., g/m3, g/m2, and m, respectively.
Usage
The area density is often used to describe the thickness of paper, e.g. 80 g/m2 is very common. It is also an important quantity for the absorption of radiation.
References
- ^ Visconti, Guido (2001). Fundamentals of physics and chemistry of the atmosphere. Berlin: Springer. pp. 470. ISBN 978-3-540-67420-7.
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