The salt purifies the air by attracting water molecules & anything attached to them such as smells, dust, pollen, smoke, etc. These things then get absorbed back into the salt. Because the lamp gets warmed up by the light, the water evaporates into the air...but the particles that got brought in, lock into the salt.
Consider putting a salt lamp in your main living or office space, this can help alleviate allergy symptoms and people with asthma should notice an improvement after several days.
Lets Live Better.