Himalayan Salt is hygroscopic, so the lamps attract water molecules from the air; this means the lamps trap dirt, pollen, and smoke particles which are carried in water vapor.
Once these airborne contaminants have been locked in the salt, clean water is re-released and thus it has a purifying effect on the air. Theoretically that is.
Scientists know that salt does absorb water from the air but that it quickly reaches an equilibrium state (it doesn’t take up anymore water because it is saturated)
What’s more is that the heat from the bulb inside that warms up the lamp releases negative ions. And there are the health-boosting effects of salt itself too.