Measured in parts per
million. Stated accuracy of the ATX-620 is +/- 5% at 20º C. Ground observers estimate that most readings
were taken between 0º C. and 25º C. An increase in H2S may be related to an
increase in methane, since sulfur-reducing bacteria thrive in an anoxic
environment, which could be created by a preponderance of methane stripping the
soil of oxygen.