Scientists, who termed the air pollutants persistent free radicals (PFRs), say they form on fine airborne particles, usually the main culprit behind air pollution alerts in a lot of cities. Even worse are the particles with metals like copper and iron, which are more likely to persist. When inhaled, the lungs and other tissues absorb the PFRs, causing health effects similar to smoking. While more research is needed to tie PFRs to certain diseases, scientists believe this could explain why 10 to 15 percent of those diagnosed with lung cancers are non-smokers.