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Why Cannabis Smells Skunky Vehicles are an Under-recognized Source of
From the ACS Press Room Why Cannabis Smells Skunky
“Identification of a New Family of Prenylated Volatile Sulfur Compounds in Cannabis Revealed by Comprehensive Two-Dimensional Gas Chromatography”
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ACS Omega
As cannabis is legalized in more areas, it has become increasingly popular as a medicinal and recreational drug. This plant produces a pungent, skunk-like odor that is pleasing to some but repulsive to others. Now, researchers reporting in ACS Omega have discovered a new family of prenylated volatile sulfur compounds (VSCs) that give cannabis its characteristic skunky aroma. The findings open up opportunities to investigate the molecules for medicinal benefits, the researchers say.
Cannabis sativa L. produces more than 200 known aroma compounds. Prior studies have focused mainly on terpenoids — molecules that range in odor from fuel-like to woody, citrusy or floral. Different cannabis cultivars have diverse mixtures of these compounds that contribute to their unique aromas. However, although terpenoids are the most abundant aroma compounds in cannabis, there is little evidence that they provide the underlying skunk-like smell of many cultivars. Skunks use several VSCs in their smelly defense sprays, so Iain Oswald and colleagues suspected that there could be similar molecules in cannabis. The team decided to use sensitive analytical techniques to find out. The researchers analyzed flowers from 13 cannabis cultivars using a custom-built 2D gas chromatography system with three different types of detectors. Then, a four-person panel ranked the pungency of the cultivars on a scale from 0 to 10. The most pungent one, called Bacio Gelato, had the highest concentration of VSCs. The team identified seven VSCs in this cultivar, some of which were also present in other cultivars. Five of the VSCs contained the prenyl functional group and had skunk-like or sulfuric aromas. One compound in particular, 3-methyl-2-butene-1 -thiol, referred to as VSC3, was the most abundant VSC in the cultivars that the panel reported to be most pungent. This compound has previously been implicated in the flavor and aroma of “skunked beer” — beer that goes bad after being exposed to UV light. To confirm that VSC3 was the main source of the skunk-like aroma, the team added it to a mixture of 10 other major aroma compounds from cannabis, producing a combined odor very similar to the characteristic scent of cannabis. They also detected VSC3 in cannabis concentrates, such as those used for
vaping. Finally, in greenhouse experiments, the researchers determined that the prenylated VSCs increased significantly toward the end of the flowering stage of cannabis growth, reached a maximum during curing and then dropped substantially after 10 days of storage. Because the molecular structures of the VSCs resemble compounds from garlic that have anticancer and cardioprotective effects, the new family of prenylated odor molecules should be investigated for medicinal properties, the researchers say. The authors do not acknowledge any external funding sources for this study. Three of the authors have filed a patent related to the findings.
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From the ACS Press Room Vehicles are an Under-recognized Source of Urban Ammonia Pollution
“COVID-19 Lockdowns Afford the First Satellite-Based Confirmation That Vehicles Are an Under-Recognized Source of Urban NH3 Pollution in Los Angeles” Environmental Science & Technology Letters
By disrupting normal societal activities, such as driving, COVID-19 lockdowns afforded a unique opportunity to study their impacts on the environment. Researchers now report in ACS’ Environmental Science & Technology Letters that satellite data from before and during the spring 2020 lockdown in Los Angeles shows that vehicles, rather than agriculture, are the main source of urban airborne ammonia (NH3), which forms small particles that contribute to air pollution and harm human health. When emitted into the atmosphere, NH3 is converted into tiny particles of inorganic compounds, including ammonium sulfate and ammonium nitrate. On a national or global scale, most NH3 pollution comes from agricultural sources, such as livestock manure. But vehicles also contribute to the problem because their catalytic converters or selective catalytic reduction systems — which are designed to reduce emissions of nitrogen oxide (NOx) pollutants including NO2 — have the undesirable side-effect of producing ammonia emissions. In cities, it’s been hard to tell whether agriculture or traffic emits more NH3, and the default assumption has been that agriculture is the greater culprit, despite some labor-intensive measurement studies that suggested otherwise in a few cities. Daven K. Henze and colleagues wanted to see if satellite data could be used to answer this question for the first time from space, since such an approach, in principle, could be applied more broadly to urban areas throughout the world. The researchers focused on western Los Angeles, where previous on-the-ground measurements found that vehicle emissions of NH3 were being underestimated. The team analyzed satellite readings of NH3, as well as NO2. Because the main source of NO2 in the region is on-road transportation, the compound can serve as a proxy for changes in traffic volume and an indicator of vehicular as opposed to agricultural ammonia emissions. The team correlated concentrations of the two pollutants, and also took meteorological effects into account, to calculate the amount of ammonia emissions that can be traced to vehicles. They found that vehicles
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