Potential regional air quality impacts of cannabis cultivation facilities in Denver, Colorado

Abstract

The legal commercialization of cannabis for recreational and medical use has effectively created a new and almost unregulated cultivation industry. In 2018, within the Denver County limits, there were more than 600 registered cannabis cultivation facilities (CCFs) for recreational and medical use, mostly housed in commercial warehouses. Measurements have found concentrations of highly reactive terpenes from the headspace above cannabis plants that, when released in the atmosphere, could impact air quality. Here we developed the first emission inventory for cannabis emissions of terpenes. The range of possible emissions from these facilities was 66-657 t yr −1 of terpenes across the state of Colorado; half of the emissions are from Denver County. Our estimates are based on the best available information and highlight the critical data gaps needed to reduce uncertainties. These realizations of inventories were then used with a regulatory air quality model, developed by the state of Colorado to predict regional ozone impacts. It was found that most of the predicted changes occur in the vicinity of CCFs concentrated in Denver. An increase of 362 t yr −1 in terpene emissions in Denver County resulted in increases of up to 0.34 ppb in hourly ozone concentrations during the morning and 0.67 ppb at night. Model predictions indicate that in Denver County every 1000 t yr −1 increase in terpenes results in 1 ppb increase in daytime hourly ozone concentrations and a maximum daily 8 h average (MDA8) increase of 0.3 ppb. The emission inventories developed here are highly uncertain, but highlight the need for more detailed cannabis and CCF data to fully understand the possible impacts of this new industry on regional air quality.

Ambient measurements of monoterpenes near Cannabis cultivation facilities in Denver, Colorado

“…In subsequent work, Wang et al (2019) developed a monoterpene emissions inventory of CCFs across Colorado and estimated that total emissions could be as high as 362 tons year À 1 for Denver County alone. There is considerable uncertainty in this estimate as assumptions were needed regarding the number of plants per facility (0-50,000), dry weight per plant (1-2500 g) and emission capacity (10-100 μg dwg À 1 h À 1 ).…”

“…Prior to the introduction of this industry, it was estimated that Denver County had total emissions of biogenic VOCs (BVOCs) of ~265 tons year À 1 (IWDW, 2017). Thus, the addition of the Cannabis industry could increase BVOC emissions by up to 362 (þ136%) tons year À 1 in Denver County (Wang et al, 2019). Monoterpenes are highly reactive; their atmospheric lifetimes range from seconds to hours and the products of their oxidation reactions include secondary air pollutants such as ground-level ozone and particulate matter (PM) (Seinfeld and Pandis, 2006).…”

“…Monoterpenes are highly reactive; their atmospheric lifetimes range from seconds to hours and the products of their oxidation reactions include secondary air pollutants such as ground-level ozone and particulate matter (PM) (Seinfeld and Pandis, 2006). When Wang et al (2019) included monoterpene emissions from CCFs in an air quality model in the configuration used by the State of Colorado and EPA, they demonstrated these emissions were sufficient to increase hourly average ozone levels by as much as 1 ppbv per 1000 tons per year of monoterpenes released from CCFs.…”

“…Given the considerable uncertainties in CCF emissions estimates and the importance of understanding their impacts on local air quality, we carried out a series of ambient sampling studies in the vicinity of CCFs in Denver County, home to 42% of CCFs and 50% of Cannabis plants in the state of Colorado (CDOR, 2018). These experiments were designed to determine the composition of monoterpenes released into the atmosphere from active CCFs to constrain model predictions (Wang et al, 2019) and reduce uncertainties associated with emission factors (Wang et al, 2019b). This study focused on Park Hill, River North Art District, Sunnyside, Lincoln Park and Northeast areas across Denver County each of which contain high numbers of CCFs.…”

The ozone climate penalty, NAAQS attainment, and health equity along the Colorado Front Range

“…Furthermore, communities with the highest minority and lowincome populations would also be expected to benefit most directly from actions to lower ozone precursor emissions and their associated co-pollutants because these communities are often located near major sources; Many of the precursor and copollutant gases are themselves harmful. For example, the majority-Hispanic residents of Denver's Globeville-Elyria-Swansea neighborhood cluster live in close proximity to three interstate highways, numerous marijuana grow operations [33], a power plant, and the state's largest oil and gas refinery. Community organizers have asked the state to revoke the refinery's operating license over concerns about hydrogen cyanide and VOC emissions [34].…”