Using Elemental Ratios
to Predict the Density of Organic
Material Composed of Carbon, Hydrogen, and Oxygen
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Abstract
A governing equation was developed to predict the density
ρ<sub>org</sub> of organic material composed of carbon, oxygen,
and hydrogen
using the elemental ratios O:C and H:C as input parameters: ρ<sub>org</sub> = 1000 [(12 + 1(H:C) + 16(O:C)]/[7.0 + 5.0(H:C) + 4.15(O:C)]
valid for 750 < ρ<sub>org</sub> < 1900 kg m<sup>–3</sup>. Comparison of the actual to predicted ρ<sub>org</sub> values
shows that the developed equation has an accuracy of 12% for more
than 90% of the 31 atmospherically relevant compounds used in the
training set. The equation was further validated for secondary organic
material (SOM) produced by isoprene photo-oxidation and by α-pinene
ozonolysis. Depending on the conditions of SOM production, ρ<sub>org/SOM</sub> ranged from 1230 to 1460 kg m<sup>–3</sup>,
O:C ranged from 0.38 to 0.72, and H:C ranged from 1.40 to 1.86. Atmospheric
chemistry models that simulate particle production and growth can
employ the developed equation to simulate particle physical properties.
The equation can also extend atmospheric measurements presented as
van Krevelen diagrams to include estimates of the material density
of particles and their components. Use of the equation, however, is
restricted to particle components having negligible quantities of
additional elements, most notably nitrogen
