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.

2019年，科罗拉多州公共卫生与环境部（Colorado Department of Public Health and Environment, CDPHE）下属空气污染控制部门（Air Pollution Control Division, APCD）在三家商业大麻种植设施开展了空气排放现场采样研究。本研究旨在量化大麻种植过程中，设施排气口排放的生物源萜类挥发性有机化合物（biogenic-terpene volatile organic compound, VOC）排放量，并通过自上而下法估算VOC排放速率。随后，研究团队结合科罗拉多州税务局大麻执法部门（Marijuana Enforcement Division, MED）提供的2019年商业大麻种植设施生物质产量（收获重量）与种植区位数据，对丹佛都会区北前山（Denver Metro North Front Range, DM/NFR）臭氧未达标区（Ozone Nonattainment Area, NAA）内大麻产业可能造成的臭氧与细颗粒物（PM₂.₅）生成影响开展建模分析。
尽管大麻种植设施常伴随强烈的扰民异味，但本研究发现，受访室内种植设施的生物源VOC排放速率较低：每收获1吨大麻的VOC排放量为2.13~11.12磅，即便在大规模生产设施中亦是如此。按浓度由高至低排序，多数采样样本中的优势萜类化合物依次为β-石竹烯（β-caryophyllene）、D-柠檬烯（D-limonene）、萜品油烯（terpinolene）、α-蒎烯（α-pinene）、β-蒎烯（β-pinene）与β-月桂烯（β-myrcene）。值得注意的是，大麻排放的排气特征中未检出异戊二烯（isoprene）——这是一类常见于其他植物排放的高反应性萜类化合物，对臭氧生成具有较高贡献潜力（Sharkey et al. 2008）。
由于受访大麻种植设施的生物源VOC排放速率较低且未排放异戊二烯，其对DM/NFR臭氧未达标区内的臭氧生成与PM₂.₅生成影响均极低，甚至可忽略不计：臭氧浓度增幅为0.005%~0.009%，最大24小时PM₂.₅浓度差值为0.009 μg/m³。
研究启示：本研究得出结论，尽管大麻种植设施可能带来严重的异味困扰，但基于本次采样数据与生产速率测算，即便在大规模高产能种植设施中，其VOC排放速率仍处于较低水平（每收获1吨大麻的VOC排放量为2.13~11.12磅）。此外，三家大麻种植设施的采样样本中占主导的VOC排放物依次为β-石竹烯、D-柠檬烯、萜品油烯、α-蒎烯、β-蒎烯与β-月桂烯。受访设施的低生物源VOC排放速率与无异戊二烯排放的特征，使其对DM/NFR臭氧未达标区内的臭氧生成（增幅0.005%~0.009%）与PM₂.₅生成（最大24小时PM₂.₅浓度差值为0.009 μg/m³）的影响极低且可忽略。