A https://phys.org/print405072203.html … the Japanese moon orbiting spacecraft, Kaguya, has found evidence of oxygen from Earth's atmosphere ending up on the surface of the moon for a few days each month. The moon is continually bombarded by particles from the solar wind but once a month the earth is situated between the moon and the sun. It is therefore temporarily protected from the solar wind – but just for a few days each month. At the same time it seems that oxygen ions from earth are able to invade the moon. These are ionised in earth's upper atmosphere when struck by ultra violet light, and they congregate in the magnetosphere (or can become lodged in the magnetosphere of the earth). It would seem that the magnetosphere of the earth is able to envelope the moon in that time slot of a few days. This may be the reason why some soil samples from the moon contained oxygen isotopes.
See also https://tallbloke.wordpress.com/2017/02/01/moon-found-to-be-periodically… … and has a slightly different take.