VOCs or HAPs per weight of solids

The older regulations were concerned with VOCs,while the newer ones have been written with the focus on HAPs.The calculation methods are very similar. The description below is written in terms of VOCs,but the formulas apply if everything applying to VOC solvents below is taken simply to apply to HAP solvents.

Another way to handle the presence of non-VOCs is to calculate the ratio of the weight of the VOC solvents to the weight of the solids, rather than to the volume of the solids. Again, neither the numerator nor the denominator depends on non-VOCs, so the ratio does not change when thinners are added. One advantage is that the weight of the solids is easily determined. Rather than being indirectly calculated, like the solids volume as in the last section, the weight can be measured directly. Another advantage is that, in some cases, it really is the weight, rather than the thickness, of the deposited coating that matters. An example would be coating over porous or absorbent surfaces, where the coating does not form a well-defined layer.

It might be argued that there is still a loophole in this method. Powder Paint or liquid paint manufacturers could presumably formulate a paint which is in compliance, but which does not improve the environmental impact of the paint. Manufacturers could increase the weight of the solids (for example, by adding heavier metallic compounds that don’t significantly affect the performance of the coating), and thereby bring the formulation into compliance without changing the VOC content. Whether any manufacturer would actually try to take advantage of this type of loophole is speculation at this point. It might be easier in practice simply to find non-VOC alternatives for the solvents (which is, after all, the point of the regulation), rather than to tinker with the solids.

For VOCs, the formula used by the Emissions Calculator is:

VOCs emitted per weight of solids =

wt of VOC1 per gal + wt of VOC2 per gal + …
wt of solid1 per gal + wt of solid2 per gal + …

On the right hand side, “wt of X per gal” always means the weight of component X in a gallon of the final coating mixture.

For HAPs, the formula is:

HAPs emitted per weight of solids =

wt of HAP1 per gal + wt of HAP2 per gal + …
wt of solid1 per gal + wt of solid2 per gal + …