Atomic Mass of Sulfur

Sulfur is 94.99 % ³²S with measurable amounts of ³³S, ³⁴S and ³⁶S, and the ratios vary enough between volcanic, biogenic and sedimentary sources that IUPAC gives an interval of 32.059 to 32.076. Those variations are a forensic tool: sulfur isotope signatures trace acid rain back to the smokestack that produced it and distinguish biologically reduced sulfide from the geological kind.

The atomic weight is what turns a fuel specification into a mass balance. Ultra-low-sulfur diesel at 15 ppm S, burned completely, produces SO₂ at 64.06/32.06 = twice the mass of the sulfur it contained; before the limits came down, that stream was the main source of acid rain across industrial Europe and North America. In water analysis the same number converts sulfate at 96.06 g/mol to sulfur, and sulfate is the ion that pairs with calcium to form the gypsum scale that acid dosing cannot dissolve.