Conversion rates of tritium gas (T2) to tritiated water are reported for tritium in ambient air and in nitrogen mixtures for initial tritium concentrations between 10−3 and 1 Ci/m3. Evidence suggests that, for air mixtures, production of condensable species, primarily HTO, occurs at a rate commensurate with the tritium decay rate. Nitrogen with less than 0.05% oxygen decreases this rate by a small (∼25%) amount. Irradiation with up to 10 Krad 60Co does not measurably affect the conversion rate in ambient air. This new data, along with the data from other authors, reveals that over the range of 10−3 to 106 Ci/m3, there are three reaction order regimes: (1) first order between 10−3 and 10 Ci/m3; (2) approximately second order between 10 and 104 Ci/m3; and (3) first order above 104 Ci/m3.