Cannabis Smoke Reacts With Indoor Ozone to Create Harmful Ultrafine Particles

Ultrafine particle formation occurred when cannabis smoke was exposed to ozone levels greater than 10 ppb, across all observed primary particle concentrations. Monoterpenes and sesquiterpenes decayed rapidly upon ozone exposure while oxygen-containing species formed. OH radicals generated from ozone-terpene reactions likely play an important role in the oxidation mechanism.

Environmental chamber study monitoring particle size distribution and gas-phase and particle-phase composition in real time when cannabis smoke was exposed to ozone. Primary particle diameter ranged from 0.1 to 1 micrometer. Gas and particle measurements tracked chemical changes during oxidation.

Ultrafine particles penetrate deep into the lungs and can enter the bloodstream. Indoor environments often contain ozone from outdoor infiltration and indoor sources (printers, air purifiers). This study reveals that simply smoking cannabis indoors creates conditions for secondary particle formation that adds to the already known health risks of cannabis smoke.

Cannabis smoke research has focused on what's in the smoke itself, but this study shows the environment where cannabis is smoked also matters. The terpenes that give cannabis its distinctive aroma are highly reactive with ozone, transforming cannabis smoke into something chemically different -- and potentially more harmful -- than what's initially inhaled.

Chamber study may not perfectly replicate real-world indoor conditions where air exchange, humidity, and other factors affect particle formation. The study did not directly measure health effects of the ultrafine particles produced. Cannabis smoke composition varies by strain and consumption method.