In this contribution , we test our previously published one-dimensional PDR model for deriving total hydrogen volume densities from HI column density measurements in extragalactic regions by applying it to the Taurus molecular cloud , where its predictions can be compared to available data .
Also , we make the first direct detailed comparison of our model to CO ( 1-0 ) and far-infrared emission .

Using an incident UV flux G _ { 0 } of 4.25 ( \chi = 5 ) throughout the main body of the cloud , we derive total hydrogen volume densities of \approx 430 cm ^ { -3 } , consistent with the extensive literature available on Taurus .
The distribution of the volume densities shows a log-normal shape with a hint of a power-law shape on the high density end .
We convert our volume densities to { H _ { 2 } } column densities assuming a cloud depth of 5 parsec and compare these column densities to observed CO emission .
We find a slope equivalent to a CO conversion factor relation that is on the low end of reported values for this factor in the literature ( 0.9 \times 10 ^ { 20 } { cm ^ { -2 } ( K~ { } km~ { } s ^ { -1 } ) ^ { -1 } } ) , although this value is directly proportional to our assumed value of G _ { 0 } as well as the cloud depth .
We seem to under-predict the total hydrogen gas as compared to 100 \mu m dust emission , which we speculate may be caused by a higher actual G _ { 0 } incident on the Taurus cloud than is generally assumed .