Odor and Emissions Analysis of Air from Marijuana Growing Facilities

The Spokane Clean Air Agency has received numerous odor complaints from residents living near marijuana growing facilities in Spokane, Washington. Currently, little is known about the environmental impact and emissions of marijuana growing operations. To further the understanding of emissions from these operations, air samples were collected from four indoor growing facilities in Spokane. In conjunction with the facility air samples, direct headspace samples were taken from marijuana products. The air samples were analyzed using gas chromatography-mass spectroscopy to identify terpenes and other volatile organic compounds (VOCs) that might contribute to odor. Results from all samples indicate high concentrations of monoterpenes, principally β-myrcene, followed by D-limonene, α/β-pinene, and β-ocimene. The sesquiterpene caryophyllene was identified in the headspace samples as well. Isopropyl alcohol and acetone were very abundant in the facility samples as a result of their use as disinfectants. Various esters and aldehydes were also identified in both the facility and headspace samples. Results suggest the majority of the characteristic marijuana odor comes from a combination of terpenes emitted by the plants. There were differences in the relative amounts of monoterpenes present between plant varieties, however, for the purposes of air quality and odor modeling a generic emissions inventory was derived from the data. Terpene reaction rates with ozone (O₃), the hydroxyl radical (HO), and the nitrate radical (NO₃) were calculated to determine the lifetime of terpenes after leaving the growing facility. α/β-Pinene have longer lifespans compared to terpenes such as caryophyllene and terpinolene, indicating they can travel longer distances. This information can be used in the future to model the trajectory of odor and determine if a facility will impact a residential area.