Following the smell: terpene emission profiles through the cannabis life-cycle

Cannabis cultivation and processing are emerging sources of air pollutants, particularly malodorous volatile organic compounds (VOCs), yet uncertainties remain regarding their emission rates and chemical composition. Emission rates are typically the starting point for an air quality assessment; not addressing their uncertainty and chemical profile may lead to under/over estimation of impacts. This study aims to quantify terpene emissions from indoor cannabis operations in the Lower Fraser Valley, BC, Canada a region already affected by odorous sources and peak ozone concentrations in the summer due to imbalance of VOC and nitrogen oxides (NO_x) emissions. We assessed terpene concentration variability across activities, and evaluated their potential odor impacts during peak summertime. For this, we developed an automated gas chromatography sampling and processing protocol to measure concentrations of 22 key cannabis terpenes in (1) eight rooms of an indoor cultivation facility and (2) six rooms of a processing and extraction facility. Emission rates varied widely, ranging from 1.05 × 10^-3 to 3.09 × 10^-1 kg h^-1, with the highest emissions occurring during trimming (i.e., buds' extraction). We observed substantial temporal variability; individual terpene concentrations fluctuated by up to 1500% depending on activity type and lighting conditions. Pearson correlation analysis revealed non-linear relationships between individual terpenes and total emissions, suggesting shifts in chemical composition during peak emissions. To assess odor implications, we conducted screening dispersion modeling for β-myrcene, a terpene considered a tracer of cannabis emissions. Of the 7560 dispersion scenarios evaluated, 88 exceeded the odor threshold under average emissions, increasing to 241 scenarios during peak trimming emissions. Because emission rates and chemical compositions vary significantly depending on activity type and conditions, and dispersion modeling results showed that average conditions are sufficient to cause odor episodes, it is important to characterize both the temporal and chemical profiles of terpene emissions in cannabis facilities to avoid mis-estimating their air pollution and odor impact. Given the growing industry and the potential for odor complaints and secondary air pollution impacts (e.g., ozone formation), it is crucial to understand these emissions in detail. Policymakers, scientists, and industry stakeholders can use our findings to develop better mitigation strategies and inform environmental regulations.