We perform the first tests of various proposed explanations for observed features of the Moon ’ s argon exosphere , including models of : spatially varying surface interactions ; a source that reflects the lunar near-surface potassium distribution ; and temporally varying cold trap areas . Measurements from the Lunar Atmosphere and Dust Environment Explorer ( LADEE ) and the Lunar Atmosphere Composition Experiment ( LACE ) are used to test whether these models can reproduce the data . The spatially varying surface interactions hypothesized in previous work can not reproduce the persistent argon enhancement observed over the western maria . They also fail to match the observed local time of the near-sunrise peak in argon density , which is the same for the highland and mare regions , and is well reproduced by simple surface interactions with a ubiquitous desorption energy of 28 kJ mol ^ { -1 } . A localised source can explain the observations , with a trade-off between an unexpectedly localised source or an unexpectedly brief lifetime of argon atoms in the exosphere . To match the observations , a point-like source requires source and loss rates of \sim { 1.9 \times 10 ^ { 21 } } atoms s ^ { -1 } . A more diffuse source , weighted by the near-surface potassium , requires much higher rates of \sim { 1.1 \times 10 ^ { 22 } } atoms s ^ { -1 } , corresponding to a mean lifetime of just 1.4 lunar days . We do not address the mechanism for producing a localised source , but demonstrate that this appears to be the only model that can reproduce the observations . Large , seasonally varying cold traps could explain the long-term fluctuation in the global argon density observed by LADEE , but not that by LACE .