The legal commercialization of Cannabis for recreational and medical use in certain US states has effectively created a new and nearly unregulated cultivation industry. Within the city limits of Denver, Colorado, there are now more than 600 registered Cannabis spp. cultivation facilities (CCFs) for recreational and medical uses, each containing thousands of plants. Ambient measurements collected inside growing operations pre-legalization have found concentrations as high as 50-100 ppbv of terpenes; a group of highly reactive biogenic volatile organic compounds (BVOCs) and known precursors for the formation of ozone and particulate matter (PM). Due to its illicit nature there has been insufficient experimental data produced to determine Cannabis spp. emission rates. This study used, for the first time, an enclosure chamber and live Cannabis spp. plants during a 90-day growing period consisting of four different strains of Cannabis spp.: Critical Mass, Lemon Wheel, Elephant Purple, and Rockstar Kush. These measurements enabled characterization of terpenes and estimates of emission capacity (EC, μgC g −1 hr −1 ) at standard conditions. During peak growth, the percentages of individual BVOC emissions were dominated by β-myrcene (18-60%), eucalyptol (17-38%), and d-limonene (3-10%) for all strains. Our results showed large variability in the rate and composition of terpene emissions across different strains. For the Critical Mass and Lemon Wheel, the dominant terpenoid was eucalyptol (32% and 38%), and it was β-myrcene (60% and 45%) for the Elephant Purple and Rockstar Kush. Critical Mass produced the highest terpene emission capacity (8.7 μgC g −1 hr −1 ) and Rockstar Kush the lowest (4.9 μgC g −1 hr −1 ). With 600 CCFs in Denver, and assuming 10,000 plants per CCF, an emission capacity of 8.7 μgC g −1 hr −1 would more than double the existing rate of BVOC emissions to 520 metric ton year −1 . Using Maximum Incremental Reactivity (MIR) values the total ozone formation potential from all these emitted species could produce 2100 metric tons year −1 of ozone, and based on published secondary organic aerosols yields 131 metric tons year −1 of PM. It is likely that the ECs calculated here are lower than those achieved in CCFs where growing conditions are optimized for rapid growth and higher biomass yields. Further studies including a greater number of the 620 available Cannabis spp. strains and a wider range of treatments are needed to generate a representative dataset. Such a dataset could then better enable assessments of the potential impacts of this new industry on indoor and regional air quality.

Fine particulate matter (PM 2.5 ) is known to have an adverse impact on public health and is an important climate forcer. Secondary organic aerosol (SOA) contributes up to 80% of PM 2.5 worldwide and multiphase reactions are an important pathway to form SOA. Aerosol-phase state is thought to influence the reactive uptake of gas-phase precursors to aerosol particles by altering diffusion rates within particles. Current air quality models do not include the impact of diffusionlimiting organic coatings on SOA formation. This work examines how α-pinene-derived organic *

We use the extensive set of aircraft and ground‐based observations from the NSF/National Center for Atmospheric Research (NCAR) and State of Colorado Front Range Air Pollution and Photochemistry Éxperiment and the NASA DISCOVER‐AQ experiments in summer 2014 together with the regional chemical transport model Weather Research and Forecast Model with Chemistry (WRF‐Chem) to study the ozone production and chemical regimes in the Northern Colorado Front Range (NFR). We apply the model's Integrated Reaction Rate capability and chemical tendencies diagnostics and present results from an in‐depth analysis of the ozone formation in various NFR regions for a case study of 12 August 2014. We further apply these diagnostics along a WRF online trajectory to assess the chemical evolution of an airmass during transport. The results show efficient ozone production within the NFR driven by the availability of NOx and an abundance of highly reactive volatile organic compound and also continued ozone production during the transport into the mountains. We identify CO, formaldehyde, higher alkanes, acetaldehyde, and isoprene among the volatile organic compound species with the highest efficiency in ozone production. Formaldehyde and acetaldehyde concentrations in the NFR have a significant contribution from photochemical production, which in turn is linked back to methane oxidation and to emissions of higher alkanes, isoprene, ethane, and propane. This study provides valuable policy information into the chemical fingerprint of surface ozone in the NFR, an area that is in nonattainment of the U.S. EPA ozone health standards and demonstrates the capability of the newly added diagnostic tool in WRF‐Chem to address the drivers behind secondary production of pollutants in greater detail.

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.

� Measurements near cannabis facilities increased background concentrations of monoterpenes by four times. � The types of monoterpenes that were measured varied widely across Denver, suggesting a diverse set of emission profiles. � Composition of measurements near emission sources were dominated by d-limonene, bmyrcene, and a-pinene.