Friday 23 June 2023 marks the 10th International Women in Engineering Day and we are celebrating by devoting two episodes of the Physics World Weekly podcast to women engineers who are doing cutting edge research.

This week our guest is Kavita Jeerage, who is a research engineer at the US National Institute of Standards and Technology (NIST) in Boulder, Colorado. She is an expert in nanoparticle metrology and neurotoxicology and some of her research focuses on developing breath-test technology.

While roadside breath tests for alcohol are a standard part of policing, there is currently no device that can reliably determine whether a driver has recently consumed cannabis. This is not for lack of trying, it turns out that creating a breath test is very difficult.

Recently, Jeerage and colleagues set out to measure the amount of tetrahydrocannabinolic acid (THC, the active ingredient in cannabis) in users’ breath, and to monitor how it changes over time. While the team was able to address some of the challenges that have been holding back the development of practical cannabis breath tests, they concluded that their research does not support the idea that detecting THC in breath as a single measurement could reliably indicate recent cannabis use.

In a conversation with Physics World’s Margaret Harris, Jeerage explains why a breath test for cannabis is so hard to create.