The Science of Cannabis Odor Removal: A Q&A With Byers Scientific

In the days of prohibition in Colorado, the smell of cannabis was often enough to get the owner in trouble with the law. Oddly enough, eight years after smoking cannabis became legal in the state, the same can still be said for large cannabis operators.

Over the years, at the behest of local residents and businesses, multiple counties and jurisdictions across the state have enacted marijuana smell-free zones – and breaching these odor embargos can incur a high fine.

So what can cannabis greenhouses in Colorado and other states do to trap in their unwanted scents? Well, they can start with some proper air filtration systems.

To learn more about such systems, last year Analytical Cannabis spoke to Marc Byers, president and founder of the odor mitigation company Byers Scientific.

Now, to appreciate the science and research that helps inform such solutions, Analytical Cannabis caught up with Dr. William Vizuete and Dr. Alex Guenter, chief scientific officer and senior scientist, respectively, at Byers.

Leo Bear-McGuinness (LBM): So, at the time when you both joined Byers Scientific, how much was known about cannabis emissions science? And how much work did you have to do yourselves?

William Vizuete (WV): Well, Alex and I work together in our primary job as professors researching air quality and formation of pollution in the atmosphere. And one of the major inputs of air pollution in the atmosphere are emissions that come from plants: trees, shrubs, crops, things like that. I was hanging with another colleague of ours and she was telling me about the legalization of cannabis in Denver and how it’s concentrated in warehouses. And so out of curiosity, I thought, ‘Well, let’s look up what the emissions from those cannabis plants are and maybe I can build an inventory or run a model and we can see the impacts.’ And I quickly found out there was nothing there. There’s no information on any emissions that come from these plants, more or less – how they change, what species they are, how they respond to light, or any of those things. A lot of the techniques and experiments that we’ve developed for many other plants just haven’t been applied to [cannabis].

And so, because we don’t know an emission rate, we don’t know how much [cannabis] impacts air quality. Since we don’t know what molecules come out of the plant, we had no idea at the time what molecules are even driving odor. Where does that odor come from? Nobody had a clue, and that was when I first started in this business.

So, yeah, there was absolutely nothing known there. We literally had to build it from scratch. My first PhD student did three publications, for which we did the very first leaf enclosure measurements, working with colleagues of Alex’s, and then building an inventory for the state of Colorado and running an air quality model. Those are three peer-reviewed publications, and they were the first. Since that time, Alex and I have been working together on this company and been building more data on this.

Alex Guenther (AG): As Will said, we’ve been working on this for a long time. On a global scale, the amount of these plant volatiles emitted in the atmosphere is five to ten times higher than all those from cars and factories and everything else. In a clean environment, these plant volatiles really aren’t doing very much to produce pollution, but when they mix with the anthropogenic [pollutants], then they produce a lot of pollution. For example, in the county of Los Angeles, we estimate that the amount of these plant volatiles being emitted is about equal to that coming from the cars. And LA is famous for its cars and its pollution. But no one’s looking at odor, until Will started doing this work.

And now we’ve surveyed literally thousands of plants and none of them are quite like cannabis. The amount and the complexity of its emissions are really incredible. And so what we’ve done is applied these approaches that we’ve designed looking at thousands of plants to try to develop these air quality models. And we’ve tested these techniques by putting up towers in forests and flying aircraft over [them], so we can really see the amount of molecules coming off these plants. And if you track the number of molecules coming off the plants, you can get the exchange rate, so we can calculate the number of molecules that you’d expect in a greenhouse for a given number of plants and situation.

Analytically, we can then look at the huge variety of compounds [in the odor], which are mostly terpenoid compounds, but [also] sulfur compounds, these thiols. And it’s a real challenge because the thiols are present a thousandfold less than the terpenoid compounds. It’s like looking for a needle in a haystack. But we were able [to find them] by working with other scientists that use the olfactometers, where they’re using their nose to smell this stuff. And that’s key. You can have the best analytical instrument in the world, you’re still not going to know what the odor is. The human nose has to be part of these studies. When we combine that with our analytical techniques, we’re able to identify the main thiols causing that stinky odor.

LBM: Wow. So it really went from knowing nothing to knowing that the odor consisted of terpenes and thiols?

WV: Yeah, that’s right. I can’t tell you how many people came up to me and told me it’s terpenes that’s driving odor. The thing with the terpenes that’s also different with the thiols is their reactivity in the atmosphere; their lifetime is different. In fact, they’re quite shorter. And we’ve seen data from colleagues who are looking at terpenes as a tracer for odor and there are times when there’s a high odor and there’s high terpene [count], but there’s also times when there’s high odor and very little terpenes. So terpenes can’t be used as a surrogate for odor.

What we’ve been looking at lately is terpene drift, or the eucalyptol that’s being emitted by the cannabis. Could it impact grape tissues and grape leaves? To answer all those questions, we need Alex’s data. And we need to know what those emissions of those molecules are by strain and plant’s life cycle. And there’s hundreds of different strains, which means there could be hundreds of different kinds of profiles. And that’s why Alex was getting at how incredibly complex these plants really are. And so that means every business that has a farm must have site specific emission profiles. But once we have those profiles, we can use existing modelling tools to tell us what the downwind concentrations were, tell us what the downwind deposition was, tell us what the air quality would be, tell us what the thiol concentrations would be downwind. But without the inventory, without the emissions, none of that can be done. And that’s what’s key about this.

LBM: And speaking of odor, how does Byers go about removing it? By sequestering or vaporizing?

WV: There are two stages of mitigation that we have: there’s our vapor phase control, as well as our ionization carbon capture and molecular sequestration. What’s nice about being able to identify the molecules that we think are driving odor is that we can control technologies for those specific molecules, and engineer and design them so that they capture them and then show, with quantitative data, the efficiency of capturing those particular molecules. That’s one thing.

Then the other is the combination of those two. So there’s different applications that are required for those specific controls. And they’re as wide and varied as the cannabis farms are. We’ve got indoor grows, outdoor grows, farm grows, canopy grows. There’s all kinds of different grows that have different needs as far as capturing these things. Carbon does absolutely perfect if you’re in an enclosed structure right where you’re controlling all the air and it allows air to go through that. So indoor greenhouses are ideal for carbon capture. But if you’re in an open greenhouse, that’s not so ideal sometimes, and so perhaps you use carbon for some of the processing rooms, then use a ridgeline vapor phase system to capture the remaining odor. And a lot of times we do them in combination. And then you get the fugitives that make it out of the ridge vents using the vapor capture fist system. So, in both cases, we’re removing the molecules from the air stream, whether it’s in the vapor phase or in the carbon itself.

AG: And one thing I’d add to that is that this odor perception is related to the mixture of compounds, the ratios of the terpenes. And the thiols are really important for how we perceive odors. And so we need to know the starting point, which is how the ratios are coming off these different plants. But we also need to know, as it goes through these mitigation techniques, what’s changing those ratios. Because you could make the odor worse if you weren't changing the ratio in the right way. So actually measuring and quantifying the compounds and abundances and ratios, both before and after the mitigation, is necessary to make sure that we’re getting rid of that perceived odor.

WV: Right, we actually use odor panels. So we’re using professional sniffers, people whose living is to do this. But what’s important here is that it’s the mixture that is as much important for the odor as anything else. So it’s not like you can just go out and say, ‘Thiols should be below this concentration and you’re never going to have an odor again.’ Because of this ratioing, you could have that level or even higher and not have an odor because of the ratio of terpenes to thiols. And because the ratio is lower, that may present itself as an odorous thing. That kind of perception and ratio and unveiling of the odor, in addition to the subjective nature of our own perception of odor, makes this a really difficult thing to put a bright line to say, ‘Thou shall not exceed this kind of threshold.’ And so what we’ve relied on is the actual human nose and using these odor panels.

LBM: You talked about something interesting there. I know that certain counties have odor thresholds for cannabis greenhouses, but you mentioned the subjective nature of smell. How do those two square?

WV: Well, what molecule are they basing that odor threshold on? It’s probably not sulfur. So now you’ve set an odor detection threshold with a molecule that isn’t really driving the odor at all. And in some cases, that terpene is in fact masking the odor. So what does that mean? That means you’re controlling for something that is not actually addressed, which means that you could do false positives. You could control to that odor threshold and, guess what? You still may have odor.

And I want to be clear, there may not exist a quantifiable level, because of the ratio and the subjective nature of the odor itself. I mean, if you look at the odor detection threshold literature for things that we know smell, they’re wild, they’re all over the place. So it’s a challenge. Our approach with Byers is we think we can remove enough of those molecules, now that we know what they are, and we target our engineering systems to capture those optimally. We can get it to a place where you don't have to worry about it at all. And that’s really the only way: zero tolerance. Now for the problem. You can have a perfectly enclosed greenhouse, you can have a carbon system that’s capturing all the odor, and all you have to do is open the door and then all of a sudden a little whiff may get out. But that small amount – we’re talking parts per trillion – is all you need to instigate an odor. So nothing’s perfect either. But if the controls are working as we design them, then we can say that we’re mitigating odor nearly completely.

AG: We want to basically get to the point where the neighbors aren’t complaining. That’s kind of the goal for the client. On the other hand, you could imagine, well just throw everything you got there. Cover the floor of that greenhouse with carbon scrubbers, right? But obviously you don’t want to do that either. Beyond just the cost is just the amount of electricity going into that. It’s not going to be a sustainable industry if we do that. So that’s why it really is about optimizing.

LBM: There’s an awful lot to consider, isn’t there? Circling back to something you said a few minutes ago, Alex, about how cannabis VOCs can mix with anthropogenic emissions – I’m curious, can that mixing produce anything unique?

AG: Yeah, so that’s where you’ll produce ozone and particles, so the major components of smog. And that’s not just cannabis, but emissions from pine trees and oaks and everything else.

LBM: And would there be a greater risk, say, if the greenhouse were next to a highway?

WV: That’s exactly right. I ran two models, one in Denver and one in Santa Barbara County in California. Denver is high desert; not a lot of volatiles are coming from plants. Most of it’s from cars. Santa Barbara County is [full of] national forests, ocean of volatiles that are coming from plants. You put the same cannabis emissions in downtown Denver, you’ll get some ozone because there’s not a lot of volatiles already there. There’s plenty of anthropogenic nitrogen oxides, what we call NOx. And so if only it had more volatiles, it could make more ozone. And that’s exactly the case in Denver, and that was the paper that I published. But if you do the same amount of emissions, and you put that industry in Santa Barbara County, you’re adding a drop of VOCs into an ocean of VOCs that are already there; it's making a negligible increase. That area’s starved for nitrogen oxides; if it only had more nitrogen oxides, it would make more ozone because there’s an ocean of VOCs there. So adding the cannabis industry in Santa Barbara County makes negligible differences on air quality; adding it to Denver makes an impact.

Dr. William Vizuete and Dr. Alex Guenter, chief scientific officer and senior scientist, respectively, at Byers Scientific, were speaking to Leo Bear-McGuinness. Questions and responses have been edited for clarity.