Annals of Work Exposure and Health A new measurement method was deployed to investigate potential occupational exposure to diacetyl, and the related compound 2,3 pentanedione, at eight companies involved in the coffee industry. Airborne concentrations of diacetyl were 5 ppb, with those at coffee shops generally 1 ppb. However, diacetyl concentrations in ~40% of the long term personal samples, mainly originating from one site, were found to be in excess of the newly adopted European TWA OEL of 20 ppb.