<p>The giant impact hypothesis, generally considered as the origin of the Moon, predicts a dry Moon lacking volatile elements, but in situ observations provide evidence that volatile elements such as carbon, nitrogen and oxygen are stored on the lunar surface and are being supplied to its exosphere. Such volatile sources and dynamics remain poorly understood. Here we investigate the chemical composition and time variations in the lunar exosphere using an ion mass analyser onboard the Kaguya satellite. We reported sporadic changes in the C⁺/O⁺ ratio occurring immediately after meteoroid showers. We also observed daily variations in the C⁺/O⁺ and N⁺/O⁺ ion ratios, suggesting two possible sources: a nitrogen-rich reservoir with a higher N/C ratio than the solar value or N-free CO/CO₂ gases. Our findings indicate that the mechanism for the production of C⁺, N⁺ and O⁺ ions during the daytime is solar wind sputtering—ejection through collision with solar wind particles—of the nitrogen-rich reservoir, whereas micrometeoroid impacts and photoionization are not dominant processes. We propose that the nitrogen-rich regolith reported in Apollo samples and indigenous volcanic gases constitute the source of volatile ions in a thin lunar atmosphere.</p>