Public domain info obtained from NASA:
Moon Fact Sheet
Lunar Atmosphere Diurnal temperature range: >100 K to <400 K (roughly -250 F to +250 F) Total mass of atmosphere: ~25,000 kg Surface pressure (night): 3 x 10-15 bar (2 x 10-12 torr) Abundance at surface: 2 x 105 particles/cm3
Estimated Composition (particles per cubic cm):
- Helium 4 (4He) - 40,000
- Neon 20 (20Ne) - 40,000
- Hydrogen (H2) - 35,000
- Argon 40 (40Ar) - 30,000
- Neon 22 (22Ne) - 5,000
- Argon 36 (36Ar) - 2,000
- Methane - 1000
- Ammonia - 1000
- Carbon Dioxide (CO2) - 1000
Composition of the tenuous lunar atmosphere is poorly known and variable, these are estimates of the upper limits of the nighttime ambient atmosphere composition. Daytime levels were difficult to measure due to heating and outgassing of Apollo surface experiments.
Although the Moon is relatively inert geologically, the lunar atmosphere continues to replenished by lunar outgassing events.