From Science Mag

Leaf enclosure measurements for determining volatile organic compound

emission capacity from Cannabis spp.

Summary

Air pollution researchers are going to pot. The expansion of legal pot farms in the 10 U.S. states and Washington, D.C., that have legalized recreational marijuana has researchers and regulators concerned about their impacts on air quality and worker health. Cannabis plants are rich sources of volatile organic compounds that can contribute to smog. One recent study suggested the more than 600 indoor pot farms located within Denver could be worsening the city’s air pollution, which already violates federal standards. Next month, in a bid to better understand that issue, Colorado officials will launch one of the largest and most sophisticated studies to date of emissions from pot farms. Such data have been scarce, largely because the federal government still considers cannabis an illegal industry. That has made it difficult for academic researchers to obtain funding or study permits from major U.S. research agencies. So scientists interested in studying pot, one researcher says, “are stuck in a position where we have to cobble this together on our own.”

• ↵* Jason Plautz is a journalist in Denver.

A B S T R A C T
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.

Link to full paywalled study

HT/Willie Soon