Dimethylmercury evaporates to a known degree. Way way more than elemental mercury.

To detect elemental mercury vapor, the air is drawn in to a controlled chamber where if present it amalgamates with pure gold as the reference (zero) material, and determined electronically.

I don't think this works with organic mercury like dimethylmercury. It is an organo-metallic compound and behaves very unlike elemental mercury.

I'd be running the AA's from the analytical labs in mercury-vapor mode, putting them on carts if necessary since they do not need gas supplies for mercury detection & measurement.

Before plasma-emission spectrometers became widespread, more people were familiar with the traditional atomic-absorption (AA) instruments.

Instead of measuring the combined emission of any elements present in the sample, the AA used the steady emission of the target element alone as reference, from a (expensive) lamp having that specific element present within its hollow cathode.

AA normally uses a clean acetylene flame to vaporize the sample, with the reference light beam passing above the flame. If the target element is present in the sample, it absorbs some of the characteristic wavelength from the beam and is detected as a negative deviation from baseline.

For trace mercury though, the flame was not good enough, so an even more expensive and complex graphite furnace was installed in place of the burner.

Either way the light beam passes through a few inches of lab air to get from the lamp to the optical detector.

And you don't need the burner or the furnace to detect things that are already vaporized.

The graphite furnace would be good to calibrate with later if you couldn't do it in advance.

I wonder if their contractor has as good detection ability as MIT itself.