Cannabis Smoke Reacts With Indoor Ozone to Create Harmful Ultrafine Particles | Research

The takeaway

When cannabis smoke encounters ozone at levels commonly found indoors, it generates ultrafine particles through the oxidation of cannabis terpenes, adding a previously unrecognized health hazard to cannabis smoking.

Indoor air quality researchers; cannabis consumers concerned about secondhand exposure.

Ultrafine particle formation at ozone levels as low as 10 ppb

What the researchers found

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.

Why it matters

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.

The numbers in context

UFP formation occurred at ozone levels > 10 ppb. Primary particle concentration range: 1,030-4,580 micrograms/m3. Primary particle diameter: 0.1-1 micrometer. Monoterpene and sesquiterpene levels decayed rapidly with ozone exposure. Nitrogen-containing species increased in particles during oxidation.

How the study worked

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.

What this study cannot tell us

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.

How to read the evidence

Moderate: controlled chamber study with real-time chemical analysis, though translation to real-world indoor environments requires further study.

When this study was published

2024 study.

The bigger picture

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.

Questions still open

How do ventilation and air purification strategies affect secondary particle formation from cannabis smoke? Do vaporizers produce the same ozone-reactive terpene emissions as combustion?

Common questions

What are ultrafine particles and why are they dangerous?

Ultrafine particles are smaller than 0.1 micrometers. They can penetrate deep into lung tissue and even enter the bloodstream. They are associated with respiratory and cardiovascular health effects and are not captured by standard air filters.

Where does indoor ozone come from?

Indoor ozone comes from outdoor air infiltration, some air purifiers (ionizers), laser printers, and photocopiers. Levels above 10 ppb -- the threshold for this reaction -- are common in many indoor environments.

Read the original research

Ultrafine Particle Generation from Ozone Oxidation of Cannabis Smoke.

Environmental science & technology, 58(52), 23099-23107

View on PubMed ↗Publisher’s paper ↗

Citation

Yeh, Kristen; Ditto, Jenna C; Rivellini, Laura-Helena; Askari, Amirashkan; Abbatt, Jonathan P D. (2024). Ultrafine Particle Generation from Ozone Oxidation of Cannabis Smoke.. Environmental science & technology, 58(52), 23099-23107. https://doi.org/10.1021/acs.est.4c08311