The predicted impact of VOC emissions from Cannabis spp.cultivation facilities on ozone concentrations in Denver, CO.

Colorado was the first US state to legalize the industrial-scale cultivation of Cannabis spp. for recreational purposes. There are now around 600 cannabis cultivation facilities (CCFs) in operation in the greater Denver area with an estimated 550,000 mature plants (higher than 8 inches) under cultivation at the end of 2017. We hypothesize that emissions of volatile organic compounds (VOC) from these plants may have an impact on the local and regional ozone formation. To investigate this, we calculated basal emission rates (BER) of VOC emitted from common Cannabis spp. clones by sampling the air from whole plant enclosures. Measured dry-weight normalized VOC emission rates averaged 8 g g^-1 hr^-1 and were as high as 11.5 g g^-1 hr^-1. The emissions consisted mainly of myrcene (21-61%) and eucalyptol (17-40%). BER and VOC composition varied among the four different clones that were studied. We then applied the Comprehensive Air Quality Model with Extensions (CAMx) to a regulatory model protocol developed for the Western Air Quality Study to predict the impact of additional CCF emissions on simulated ozone formation. This is the first study to predict VOC emissions from CCFs using the new emission factor data and the latest public cannabis tracking system data from state agencies in Colorado for estimating the plant count and dry plant weight. Additional model simulations were performed to assess the sensitivity of model outcomes to uncertainties in emission factors, plant biomass, and plant numbers. The sensitivity results show that terpene emissions from CCFs in Colorado increased total biogenic emissions by 500-7,000 ton/year. It was predicted that Denver county alone increased BVOC emission up to 14 times with rates of 3,500 ton/year. Using an ensemble of CAMx sensitivity runs we will report the predicted impacts on ozone formation and atmospheric chemistry of this new industry in Colorado.