Terpene exhaust emissions and impact ozone modeling from cannabis plants at commercial indoor cultivation facilities in Colorado

In 2019, an air emission field sampling study was conducted by the Colorado Department of Public Health and Environment (CDPHE) Air Pollution Control Division (APCD) at three commercial cannabis cultivation facilities. The goal of the study was to quantify biogenic-terpene volatile organic compound (VOC) emissions from growing cannabis at cultivation facility exhaust points to estimate a VOC emission rate by a top-down approach. The resulting VOC emission rates were then used in combination with 2019 commercial cannabis cultivation facility biomass production volumes (harvest weight) and cultivation locations from the Colorado Department of Revenue’s Marijuana Enforcement Division (MED) to model the potential ozone and PM_2.5 formation impacts of the cannabis industry in the Denver Metro North Front Range (DM/NFR) Ozone Nonattainment Area (NAA). Despite cannabis cultivation facilities’ high nuisance odors, this study found the biogenic VOC emission rate from the sampled indoor facilities to be low (2.13 lbs to 11.12 lbs of VOC/ton of cannabis harvested), even at large production facilities. The dominant terpenes from this sampling study present in most samples were β-caryophyllene, D-limonene, terpinolene, α-pinene, β-pinene, and β-myrcene, respectively, by concentration. Interestingly, the cannabis emissions exhaust profile lacked isoprene, a terpene commonly emitted from other plants that is highly reactive and has great potential to contribute to ozone formation (Sharkey et al. 2008). The low biogenic VOC emission rate and the lack of isoprene from the cannabis cultivation facilities sampled resulted in a very low to negligible impact on both ozone formation (0.005–0.009% increase in ozone from cannabis cultivation) and PM_2.5 formation (largest maximum 24-hr PM_2.5 difference of 0.009 µg/m³) in the DM/NFR NAA. <i>Implications</i>: This study concluded that even though cannabis cultivation facilities can have overwhelming nuisance odor impacts, based on samples collected and production rates they actually have a low VOC emission rate (2.13 to 11.12 lbs of VOC/ton of cannabis harvested), even at large high-volume production facilities. Additionally, the dominant VOC emissions from samples collected at the three cannabis cultivation facilities were β-caryophyllene, D-limonene, terpinolene, α-pinene, β-pinene, and β-myrcene. The low biogenic VOC emission rate and the lack of isoprene from the cannabis cultivation facilities sampled resulted in a very low to negligible impact on both ozone formation (0.005%–0.009% increase in ozone from cannabis cultivation) and PM_2.5 formation (largest maximum 24-hr PM_2.5 difference of 0.009 µg/m³) in the DM/NFR NAA.