 So, we ended that panel very nicely on talking about, I think Barb talked about transformations and how we have one thing ending up as another thing and how do we think about that regulatory approach. So this next session and both our speaker and our panel, we're going to talk about transformations in indoor space and why that matters from indoor chemistry perspective. So I'd like to introduce Dr. Delphine Farmer, who is a professor of chemistry at Colorado State University. She runs a group studying atmospheric and indoor chemistry with a focus on mass spectrometry to study processes that control sources and sinks of organic gases and particles both indoors and outdoors. Important to this group, she together with Professor Nina Vance from University of Colorado led two of the, I call seminal indoor chemistry field campaigns in 2017 with the home come study and in 2022 with the CASA study. And she promises that there will be an overview article on the CASA study coming out any minute, promises. Most importantly, she's also a key contributor to training the next generation of indoor air chemistry experts and researchers, including my now colleague, Michael Link, and as highlighted by Vicki, she was one of the co-authors of this nasom report. She has a PhD in chemistry from the University of Colorado at Berkeley, was a postdoc fellow at NOAA, and she's been the recipient of the Arnold and Mabel Beckham Young Investigator Award and the 2002 AGU Ascent Award. And for Glensake, one of Delphine's nonchemistry passions is that she's also an incredible wildlife photographer. We'll turn it over to Delphine. Thank you, Dustin. I really appreciate the introduction. So I am delighted to talk to you today about our chemical perspective and a perspective from the National Academy's consensus report on chemistry in the indoor environment. And I adjusted my title slightly because I want to talk about the impacts of chemical transformations indoors, not just on the indoor environment, but also on the outdoor empire. But I wanted to start this talk with a collection of pictures and of diagrams. So the picture on the right really comes from that nasom report. I think you've seen it before. And it really shows that we have a complex set of sources in the indoor environment. The photographs on the left of this screen come from Colorado State University. And what they show, and I want you to look at this from a chemist's perspective. So just think about all of the different molecular surfaces, the interactions that a molecule can have in these different environments. You see different amounts of light, different qualities of light. You see different numbers of people. You see combustion sources and gas cooking. You see huge numbers of fabrics and potential products indoors. And so what I want to think about over the next 20 to 30 minutes is how this chemical complexity plays into what people think about in terms of exposure and health impacts and also what we think about in terms of air quality. All right. So indoor air is chemically complex. And I think both Vicki, Grassian and Barb Turpin made a spectacular case for that. This complexity really enables many reactions. And it really changes, I think, how we think about health and how we think about outdoor air quality. So the image on the left you've seen before this morning. But I really want to think about not just the chemicals that are in the environment and how we ingest or inhale or interact with them, but how chemical changes may shift their phase. So change the pathway of exposure. But chemical changes may also change the toxicity or potential toxicity of those compounds. From an outdoor air perspective, we're going to think about buildings. They're not Las Vegas, right? Something that happens in buildings does not stay in the buildings. It moves outdoors. And so that means that we have to think about what buildings are doing and the chemical transformation in buildings and also what's going to happen to those chemical compounds when they leave. Okay. So I wanted to start with thinking about some of the data from the home chem study. And I think you've heard illusions to this and I'm not going to go into huge detail on the study itself. But it suffices to say we took this little house at the University of Texas that Austin has and is very well characterized. And we thought about the chemistry indoors. So we managed to arm twist a huge number of collaborators from different institutions across the US and Canada to bring instruments and think about the chemistry that was happening in this house. And I had the student Jimmy Madela who did chemical ionization mass spec measurements. And he worked with several other research groups and numerous other students and post docs who'd collected chemical data. And he started to put it all together. And this is what he found. So on the X axis, we're going to have different types of situations in the house and out of the house. On the Y axis, we have the carbon mass concentration in the gas phase. So what you see is that outdoors, both in our study in purple, but in an array of other studies in the literature, we see a range of total carbon mass. The moment you go inside, I think this is probably clear from the previous talks we've had, that unoccupied house has a much higher level of carbon. So what this tells us is that homes and buildings are strong sources of organic carbon and they can be sources to the outdoor environment. To put this number in perspective, unoccupied, this innocuous little honkham house emitted the equivalent on a square meter basis of about half of an orange grove's worth of organic carbon. So that's a fair amount to start thinking about. We can start doing activity. So cleaning or cooking or in the extreme event, cooking events, giving dinner in June in Texas. This really shows that human activities can massively change the amount of carbon, but that means that we might be able to change the transformations that can occur as well. Of course, this is just mass. So this is what we've been thinking about concentrations, levels, carbon mass. But if we take all of the different types of organic compounds that we see indoors and we think about their chemistry, one of the simplest ways to do that is consider their rate constants with OH radicals or with ozone. And we can again sum up all of the compounds from this perspective. And on our various y-axis, we now have either OH reactivity in orange or ozone reactivity in blue. And you should see a couple of things. First off, all of this organic carbon is very, very reactive. It is fuel for chemical reactions. You also see that the reactivity does not necessarily follow the mass. And that is also important, because once we start thinking about chemical transformations, we need to start thinking about the chemical identity and resulting properties of those molecules. What I get out of this figure is this second bullet point. All of this carbon, all of this organic matter just in the gas phase. This is just a simple case, has a huge potential for chemical reactions and for secondary organic aerosol formation at any given time. There's just a huge amount of fuel. So this also suggests that we have very likely substantial effects as soon as this carbon gets outdoors, where we have large amounts of oxidants. Alternately, if we bring oxidants or other reaction initiators into the indoor environment, you have the potential for a large amount of chemistry. All right. Many reactions are possible and have been demonstrated to occur indoors. The National Academies Consensus Report divided all of these chemical transformations up into free classes. And I rather like this classification approach. So we're going to use that in this talk. The first sort of reaction process is that of partitioning. So phase partitioning is truly the movement of molecules across air, liquid and solid phases. And as Vicki noted earlier, that includes not only the building materials, but also indoor aerosols. And we'll look at a couple of case studies of both of those. And this is all going to occur as the chemical system, this complex chemical system of CSUs dorm rooms moves towards equilibrium. And I think, again, something you need to see in this picture is that we have a very high surface area to volume ratio indoors. And so this means that partitioning is very relevant. OK, the second class is going to be airborne chemical reactions. We can think about these with two large sources. One is oxidation, ozone being a very well-established oxidant. But hypochlorous acid from bleach, OH radicals and NO3 radicals are of emerging interest. They seem to be relevant under certain circumstances. And then we can think about fatalysis. And I just want to use this picture of the lovely engineering building that I do not get to work in on the CSU campus, but it's gorgeous. And you can see this combination of both natural light coming for windows as well as artificial light. And you have spatial gradients. And there's been some very nice modeling work that shows those spatial gradients impact chemistry. And then the third class is really surface involved chemical reactions. And you can think about this from a variety of different chemical reaction standpoints. I think one perspective and my perspective is that this is really multi-phase chemistry that occurs across interconnected gas, solid and liquid phases. And it encompasses because of those multiple components and all of those interactions that can occur on surfaces, a huge range of potential reactions, and these can occur on multiple timescales. So this is our picture. These reactions are all possible. They're all going to occur in these complex environments. And so what we're going to do is walk through a few examples that illustrate different points as to why these transformations really matter. All right, so we're going to start with phase partitioning. And you've seen this picture before. You can imagine any indoor environment is the one we are in right now. Chemicals are interacting between surfaces and the air. And that phase partitioning from indoor surface reservoirs to build up, whether they are things of compounds or carpets or other components we brought into the indoor environment, they really drive high indoor levels of different compounds. And Chen Wangsburg from Humkem really highlights this nicely. You can see that we have a high level of butyric acid. You open the windows and doors, the level goes down. As soon as you close the windows and doors, those levels bounce back up to where they were. And it's a seemingly inexhaustible indoor reservoir. So that's phase partitioning having an impact. A more recent example comes from the CASA project. And what this example shows is that this partitioning between surface reservoirs and the air is really dynamic. It changes with time. And so in this experiment, we borrowed this house and they didn't know what they were in for, but they let us add smoke. And so we added a wildfire smoke proxy. And you can see two examples of injections here. And you can see a time trace of one wildfire smoke VOC, hydroxymethylperforol, the various VOCs all behave similarly. And so what you can see is that we added the smoke. And then I felt really bad for NIST because we couldn't get those levels back down to where they were before. So that was even after several days. So we knew that we had built up surface reservoirs. So my postdoc, Jinan Lee, really started to think about this process and what we can imagine is that with wildfire smoke, you might bring in some of these molecules of HMF. And then over time, we can imagine what happens to them. And we're going to think about this relative to SF6, which is a beautiful tracer for building ventilation, beautiful except for its greenhouse warming potential. But that's a different gripe. All right, so we have this HMF that comes indoors and it decreases far more rapidly than ventilation alone. And so what we know is that the floors and the surfaces are removing those VOCs from the air. Then we see a slowdown of this process after a very specific time point. And we can imagine we're beginning to, again, move towards that chemical equilibrium. And at the same time, we're, of course, ventilating the air. And so we're constantly shifting this partitioning process and the equilibrium. And then after a given time, the floors stop being a thing and they start to become a source. So this enables wildfire smoke. VOCs to persist for hours, days, weeks, months after an event. The chemical structure controls that partitioning behavior. And that gives us a very useful tool to work with models to predict fate. And so we found some close connections and we were able to model this from a first principle spaces to think about saturation concentration, so vapor pressure of different compounds. And then we might think about the organic air partitioning. And that enables us to start to think about how much of these molecules end up on surfaces versus in the gas phase, where you might inhale them, versus going in ventilation, which certainly removes them from your space, but perhaps displaces those compounds to another space or to the outdoor environment. So thus partitioning certainly has a dynamic process and it has an effect. But I want to make the point that partitioning also occurs with aerosols, and this was brought up earlier, and that can enable, transport, and you exposure pathways. So this is a very nice example from a Swedish group that showed that if you took a chamber that you just made out of the vinyl flooring, cheap vinyl flooring, and you flow some aerosol particles of different composition through that chamber, what you see is that those aerosol particles pick up what should be really low volatility phthalates. And the phthalate esters that should stay in on flooring go quickly into the gas phase and immediately into the particle phase. And the rates depend on the chemical identity of the aerosols, but what this really tells us is that we have a mechanism through partitioning that means that the compounds that shouldn't be in the gas phase and shouldn't be inhalable can now move to a phase where they can transport to different regions of the house, but where they can also now contribute to exposure pathways like inhalation that weren't predicted to occur. All right, our third example of partitioning comes from cooking. And we're gonna go back to the home camp study where we cooked a huge amount of stir fry. And we found some very interesting things. So we found that with time, once you start cooking, you add some oil, you add some vegetables, you add some sauce, you make a huge amount of organic aerosol. My student, Matt Simpachi did this very nice experiment where he connected the aerosol measurement to different, at different temperatures, being able to look at what temperature do different components volvulize. We could use that data to work with a model. And what the model told us is that this cooking organic aerosol can undergo dilution-driven evaporation. And so you can imagine that that plume of cooking aerosol, as it moves and dilutes through the house, equilibrium is going to push components to the gas phase. We move it outdoors, even more components are gonna move to the gas phase. And we could quantify that. And in the case of home chem, once we moved those cooking particles outdoors, about 30 to 60% of the organic mass, which is most of the mass, would evaporate. And now we have gas phase components that can participate in atmospheric chemistry. So they can contribute to outdoor ozone and outdoor secondary organic aerosol formation. So when we put this together in terms of partitioning, hopefully you can see at this point, the partitioning really determines indoor concentrations of many compounds. It enables different exposure pathways. So you saw that from the smoke and the phthalates. And of course it impacts outdoor air. All right, next case, airborne chemical reactions. So here we might think about oxidation and fatalicin. And I think the point I wanna make here is the gas phase chemistry can create new chemical products. And those chemical products can have different health, outdoor air quality or even climate impacts. All right, this is a fantastic example. So ozone is a key ingredient of urban smog. And limonene is a lovely monoturping. It comes, you smell it every time you cut into a lemon and anytime you put a citrus scented product on yourself or you clean your floors with something citrus scented. So there's a lot of limonene around. And limonene, it looks like a simple molecule to a non-chemist, to a chemist who starts seeing two double bonds, lots of other sort of available carbons and hydrogens. And so there's been some recent work trying to figure out the oxidation mechanism of limonene. And so there's this lovely paper if you wanna understand this mechanism from Chen and Kierkegaard's group in Denmark and Paul Wemberg at Caltech. And this is one page on of about four pages of SI that shows what they think the mechanism is. I just snipped one because the point is that it is very complicated and that there are a lot of potential products. And from this one little snippet of the mechanism you should be able to see that we can generate chemical compounds that have lots of oxygens on them. You might not be able to read this but there are things with nine carbons and six oxygens, right? So that's pretty low volatility. And that type of compound can contribute to secondary organic aerosol, which of course is a key ingredient of PM 2.5 which we know from very, very clear and numerous studies has strong health effects. And of course this factor or PM 2.5 and the clarity of our understanding of its health effect have contributed to, I believe it was this week or last week's release from the EPA of new guidelines for PM 2.5 in the outdoor environment. So this is very well understood. Particles also happen to be very important short-lived climate forces. And so there's another reason to want to understand their sources. Not shown in again the snippet of the limonene oxidation mechanism but you can get toxic byproducts. Formaldehyde is one that is very well known and certainly comes out of this oxidation. And of course, another aspect anytime you take ozone and react it with one of those double bonds with an alkene you can generate OH radical. So you can generate more oxidants. So there's a lot of things that can happen. So the one case study I wanna show is one from originally, I think, considered by Charlie Weschler who thought about what happens when ozone interacts with skin, with humans. And there's this very simple experiment. You take a piece of glass wool and you expose it to ozone. You don't see any VOCs. You soil it with some skin oil and you add ozone and you see these huge emissions of different oxidized organic compounds. One is this ketone which will just abbreviate to six MHO. Turn the ozone off, these sort of VOCs slowly go away. So this is what can happen. Does it happen? So the Goldstein group out at Berkeley showed that indeed this happens and it happens ubiquitously and persistently. So you have an example from a real house in the Bay Area in California and indoor ozone tends to be very low. So people often tell me we couldn't possibly have ozonealysis reactions. But what this study shows is six MHO on the Y-axis, you can see that as soon as you increase the amount of ozone you get more of this compound and then you can see that if you have a party and you add more people to the house, you're going to also make more of this compound. So these ozonealysis products occur and they are observed indoors even if the ozone is low and perhaps contributing to that very low ozone. So we can see that airborne chemical reactions occur rapidly, ozonealysis is fast. They are ubiquitous and despite seemingly low ozone concentrations and of course they can generate toxic byproducts. Okay, our last set of types of chemical transformations indoors is of course the most complicated one and that is really surface-involved chemical reactions. And so these reactions can encompass a huge variety of different types of components. And so again, I'm gonna use a couple of examples. The first one is that of nicotine and this was alluded to earlier. If nicotine from cigarette smoking gets on a surface about just over 10 years ago, a very nice piece of work showed that it can undergo chemical reactions on surfaces. So what you see is the nicotine can actually react with nitrous acid that you heard Vicki talking about earlier and make a class of compounds called nitrosemines. Nitrosemines are known to be toxic and established to have health effects. And so this is the idea of pert-hance cigarette smoke is that you can do chemical reactions on surfaces and that will turn what was initially already toxic into something different and create a different exposure. Now, one thing that's really important to understand is that these reactions are not fast. These are not like ozone analysis. This evolved this chemical evolution on surfaces can occur over weeks or months. I believe a few months is often what people are studying when they're looking at these nitrosemines. So the temporal scales are distinct between indoor air and outdoor air. So reactions that we thought were unimportant in the environment can actually be really important indoors. All right, the other example we can think about in terms of this is one of bleach. So at home chem, we mopped the floors with just a commercial bleach containing solution. And what we found was that we would see this huge change in terms of the organic compounds and inorganic compounds that we were measuring. And what we figured out was that this was due to multi-phase chemistry. And you can see this chemistry initiating in the aqueous phase in that mopping solution. And so we would take hypochlorous acid. It interacts with a means and ammonia of varying forms making chloramines which are rather nasty compounds. And then those could then get out into the gas phase. But that wasn't all. We also could see that that partitioning of hypochlorous acid that would occur would enable gas phase reactions of varying forms. We could see evidence for secondary organic aerosol formation albeit very small amounts because you don't have much time for chemical reaction than gas phase indoors. But we could also see evidence for some photolysis and for some other chemistry. So overall surface chemistry here, you can see that it can mediate and it can change exposure in unexplored ways. And on temporal scales that we perhaps haven't considered from an outdoor ambient environmental chemistry perspective. So again, if we go to the summary, surface-involved chemical reactions mean occur because of large surface area to volume ratios and so we can drive health-relevant chemistry. But I think if you're looking at any of these pictures, one of the points I wanna make is that while the National Academy's report divided up these different types of reactions, none of them occur independently. They occur simultaneously and they interact with each other. And this is why I think Barb Turpin very nicely put it that you can't study simple reaction systems in the indoors without thinking about that broader context of the chemical complexity of both of those surfaces and the indoor environment because many things are happening at the same time. So we can glean some beautiful information about molecular properties and potential mechanisms but to place this in context, we need to think about real-world systems. Indoor air is a chemically complex multi-phase system and that enables again many potential transformations occurring on different timescales. So if we go back to this original picture in terms of reactivity based on different events that we had in home chem, what you can see is that the built environment contains a lot of reactive potential. That's fuel for oxidants, light and multi-phase reactions. If we go to this picture that Vicki showed in terms of sources and transformations and leading to health effect, we can start to think about these chemical transformations from this perspective. These reactions can impact exposure and health but I have added an extra arrow because I think we can't just think about indoor exposure and health. We have to think about how that transformation and transport goes to the outdoors, contributes to ozone, PM2.5, ultra-fine particles, other components because of course those components, PM2.5, ozone have very clearly well and well understood health effects. This of course also impacts air quality and again because ozone and PM2.5 or aerosols are short-lived climate forces they can have a climate effect as well. Adding any new reactive component indoors to this high-fuel system, my I think one very important point that you should take home from this is that should be done cautiously. There's a huge amount of reactive material here. The National Academy's report included recommendations for researchers and funders to engage across the disciplines. And you've heard about toxicologists needing to work with indoor chemists, needing to work with building scientists. I would also argue we could make that cross-disciplinary community a bit larger and we can think about material scientists and people designing products, people thinking about how humans actually use products, how we interact with the built environment. Also we can start thinking about a broader outdoor community. Free priorities noted in the National Academy's report that I think are particularly relevant when we think about transformation. Include the fifth recommendation was to understand indoor exposures to contaminants, including those that undergo subsequent transformation indoors. And I think we have a good system to think about this from ozone in the outdoor environment and from particulate matter in the outdoor environment where we can think about precursors. We need to develop novel methods to identify and quantify all of these different compounds, again, not just the primary emissions from a product but also their potential transformations and multi-generational products. And then finally, I think it is very important that we not forget that the buildings and the indoor environment impacts outdoor air quality. And so identifying indoor transformations that can then impact our outdoor air is finally very important. So with that, I would like to thank you for your time and I'll be delighted to take any questions. That was a great talk. It led me to wonder if you think that the indoor-generated reactive chlorine can make it outdoors, perhaps not as a gas because it'll be too sticky. But what are your thoughts about that? Yeah, I think that's a fantastic question. So there's been some recent hints that this may actually be occurring. Yoastick Out has shown some very interesting results that you can see chlorinated organic compounds in the air and LA. And when you start thinking about and you look at the chemical identity of those compounds that certainly looks like human sweat interacting with chlorine, which suggests gyms or hospitals or some other form of building sorts. And so I think that's the first hint of evidence. We know that chlorine in the outdoor environment is photochemically incredibly reactive. And so I think that it seems very likely that chlorine from indoor environments is a substantial source to urban outdoor air. The extent to which that occurs, I think we don't know because while we have evidence that you can generate chlorine aerosol and you can generate chlorine oxidation products and hypochlorous acid and Cl2 indoors, those have been the sort of lab in field studies of home chem and John Abbott's group has done some lovely work in labs. And so we know that the process and the mechanism can occur. But we have this problem that we don't understand on a survey basis, how much people use these sorts of compounds, what types of buildings use them, where they use them. So I think it's a fantastic question. And we don't have any other answer than mechanistically indoor chlorine should be impacting outdoor air. And that we see some hints that perhaps that's occurring, but it's a great open question. Thank you. I think Jeff was there first. Thanks, great talk. So I have a question that there might not be a good answer to it, but I'd be interested in your speculation. Obviously what's indoors takes a complicated pathway to get outdoors and different pathways and different buildings at different times. So how much do we know about the transformations that occur between inside and outside? Yeah, so I mean, I think you probably know more about this than I do, Jeff, because you have fought very deeply about how outdoor air comes in. And so maybe we can reverse that process in a back of the envelope way. We know a couple of things, though. So we know about how window opening impacts indoor outdoor exchange, air exchange. We know about how different types of HVAC systems are built. It's not quite, there are filters that are sometimes put in place in some buildings. And so we know that this exchange is occurring. The chemistry and the extent to which that occurs, I don't think we understand. I think one of the most interesting questions is what happens in terms of the cracks in buildings and how we know that around the edges of windows, we know that outdoor air seeps in and brings outdoor chemicals. I think it is reasonable to consider that indoor air gets out, but it's not going to be a one-to-one ratio because the pressures are different inside and outside. So I think it's a really interesting question and we don't have answers, but we again do have hints. So there was a study in New York City last summer and one of the postdocs in my group took air measurements in all sorts of different places, just different environments on Long Island near Maniola. And one thing that she found was evidence that we were seeing phthalates, we were seeing some of these other compounds associated with personal care products and we could look at them in residential areas versus in non-residential areas. And we think that there's enough evidence to at least suggest that some of that must be coming from the indoor environment based on timing and location. So I think there's evidence that this is occurring. How much? I think we need to reverse the way we've been thinking perhaps about indoor air in order to get at that question. So I think it's a fantastic question. I don't think there's a clean answer, but I wanna know the answer. Thanks. Okay, just because Brett's gonna be able to talk later, I'm gonna take one last question quickly from Vicky and then we're gonna move to the panel. Okay, two parts. One is not a question, but thank you for using that phrase tense toward equilibrium because Glenn and I actually, we sweated over that one statement. So thank you for using it and having it be of use to your research. But my question is, so remember I'm a surface chemist by training. So what the surface is matters to me. And I think I show in some of my work that it matters to everyone, but you didn't talk about that very much. You were very broad in your discussion of surfaces. What are we missing in that case? And how do we move forward? And what are some of your thoughts in that regard? Yeah, so unfortunately that was the slide I cut on a plane last night when I was trying to get this talk down to 30 minutes. So I think that's exactly the right question. As a chemist, we look at different surfaces and we know that the surface properties, you might think about the a hygroscopicity. So the ability of water to absorb onto the carpet is going to be different from the walls and from the glass. We know that, so that's gonna change surface films. And so that's gonna change the extent of aqueous chemistry. We know that the ability of different types of organic molecules to absorb and then to move through and into the pores of different surfaces is going to change, again, perhaps on the polarity and the other properties of those different surfaces. And so drywall is going to enable molecules to move further probably than glass. And so we know enough about chemistry from a fundamental perspective to, I absolutely agree. Say the surfaces, the actual identity of surfaces is going to matter. I don't think we have, I think actually on the simplest case, I don't think we actually even understand, for example, the porosity of this room, the extent to which that is driven by carpet versus drywall versus painted ceilings and wood. And so I think we need to understand in order to gain a larger context of how these different surfaces matter, I think we need to understand the properties, the simple surface properties of different indoor environments, which is an extremely not so simple problem for an analytical chemist to solve. But I think we also do need to think about those chemical reactions because I think material replacement and choice is one of the easiest things that a consumer can use to control their environment. But I don't think we as chemists yet have enough information to really give a comprehensive answer as to what those different types of chemistry are going to be. So yes, the surfaces clearly matter and clearly mitigate systems. The extent to which different surfaces are going to do that and how relevant different types of surfaces are in the indoor environment, I think we have yet to find out. Thank you, Delphine. That was an excellent talk. So I invite the second panelist to come up. Our next panel, we're going to look at one of the specific transformation case, which is looking at germicidal ultraviolet radiation as a means of pathogen reduction, transmission of viruses and other pathogens. I'm not saying that correctly. Anyways, so we're going to look at GUV and how it impacts the indoor air chemistry. And so I would like to start off just with a quick 20 seconds of who you are and why you know anything about GUV. Go ahead. So Delphine, there we go. Delphine Farmer, Colorado State University. I have not been sitting GUV specifically, like some of my colleagues on this panel, but I have obviously been thinking a lot about the types of chemical transformations that can occur in indoor environments. So I'll bring that perspective to this chat. Michael. I'm Michael Link. I'm a research scientist at NIST and over the past year, we've been developing a standard test method for the chemical assessment of air cleaning technologies. And one of the technologies was germicidal ultraviolet light with the peak emissions at 222 and 254 nanometers. So new opportunity to study some chemistry. Richard. Hello, yes, I'm Richard Williamson. I'm program director for FIUVC at Blueprint Biosecurity. We're a nonprofit and dedicated to pandemic prevention. And I'm currently working on a kind of detailed technical assessment of germicidal ultraviolet light. And what we expect it might be able to do for us in terms of reducing the transmission of respiratory pathogens. And also what are the challenges that we face in deploying this technology and understanding its potentially unintended consequences of which the chemistry is a very big part of that problem. And we have a special guest online today. Do some travel limitations, Paula? We can't hear you right now. You're muted. Did she get unmuted? OK, no, I'll try. All right, well, I'm truly disappointed that I'm not there in person. But despite all the medical countermeasures of vaccines and boosters and medicines, we don't have good indoor air quality. And so I have COVID, because we don't have enough ventilation, filtration, or disinfection. My day job is I am a contributing scholar at the Johns Hopkins Center for Health Security where I direct the work on indoor air policy, specifically to reduce the risk of catastrophic biological events, whether that's COVID or something else. So I'm delighted to be here today. And again, many people who already know me know that I spent two decades at the Sloan Foundation. And I was happy that the indoor chemistry program did so well and did really well even after I left. But the program was silent on bringing it. The program did not anticipate bringing in UV sources to stimulate chemistry. OK, so let's start off with just the basics simply. Why do we need to use UV devices indoors? Why can't we just use ventilation and filtration? So I'm going to point that to Richard and Paula to start off with. Sure, I'm happy to start with that. So to make this a concrete point rather than abstract one, so if my portable CO2 monitor is correct, about 1% of all the air that we're breathing in right now has been in someone else's lungs. And although this probability is probably slightly affected by the fact that people who get COVID don't come to these things, as Paula has not. But there's a very good chance among this group of people based on the prevalence at the moment, that one of us in here has a live COVID infection. And we certainly will, one of us probably has a live respiratory infection of some kind. And so the question becomes, OK, well, what do you need to do to prevent a transmission event from happening? And this is where you have to think about biological contaminants quite differently from chemical contaminants. Because with a chemical contaminant, you kind of think if you have a well-mixed room and you're introducing one air change per hour with clean air from outdoors or another source, then if you have some fixed level of contaminant, that will remove 67% of the contaminant. And if you do the second one, that removes 67% of what's remaining, which will be a much smaller total amount of contaminant, because you're already starting with 67% less. So in a kind of chemical contaminant world, that first air change is the most important one. It removes the highest quantity of contaminant. And that's also true of pathogens. The first one will remove the most. But the core question with a biological contaminant is how much do you need to remove in order to prevent transmission occurring because it reproduces? And that means that there will be further contaminants in other spaces that then reproduce and we get societal spread. And so to put that kind of concretely what you might need to do, let's say for the sake of argument that between ventilation in here and other sources of pathogen loss, that you have a kind of equivalent air exchange rate of 2 in here. And you looked at the viral or bacterial load, and you said, I need to get that down by 50% in order to prevent a transmission event happening here. So you'd have to introduce two more air changes into this room in order to achieve that. And you could readily achieve that with ventilation and filtration. You might notice it by hearing it, but it's eminently achievable. Now, what if you needed to reduce it by 90% in order to prevent that transmission event from occurring? You're going to need 20 air changes in this room in order to do that. And if we were doing that with any mechanism that required airflow, you would absolutely feel it. And you would definitely hear it. And germicide or ultraviolet light, whether that is using a kind of quite conventional technology that emits at a peak of 254 nanometers. And those are generally across the top of a room. If you came into here today by Dulles or by Reagan airports, you will be able to look up and see these devices emitting ultraviolet radiation coming across the top of the room, killing pathogen as it sort of circulates in the room. And then more recently, there is a new, there's far UBC, which is generally centered around 222 nanometer emitters, but it's kind of defined as a range. And what's different about those is that they could be potentially used across the whole room. It would be sort of safe for human eyes and skin, potentially to have direct exposure to that in a way that it would not be for conventional UV. And what's special about that is that this is a technology that potentially could deliver equivalent of 20 air changes per hour or something of that order of magnitude that could achieve that very, very large reduction in pathogen levels that are just not achievable with airflow-based technologies. Paul? All right, I'd like to, Richard gave a very good description, but basically, how can we clean the air? And that is using removal technologies rather than additive technologies because anything you add means we're going to breathe it in. So ventilation dilutes things out, but we know ventilation costs money in terms of you want to save money on your electric bill, you cut down on your ventilation. Filtration can be very effective, that it sometimes can be noisy. We probably need new research into new filter media, but filtration works very well. But we still need a little bit more, and that's where we come down to disinfection. And the sunlight kills germs, all right, great. UV light definitely kills germs, and that the traditional is at 254 nanometers, the sunlight nicks the DNA backbone and it can't reproduce. All right, so then Richard mentioned this new technique, this new moving down to 222, which shows a lot, a lot of promise. And it's very exciting, but it turns out that when these devices are deployed, all right, so when they're deployed in a room, we've got gas phase chemistry going on because we've, and oxygen reacts, it's photolyzable, turns into ozone at that wavelength. I'm also gonna put a reference in the chat. I don't think we'll have time to really go into this, but if we're thinking about respiratory aerosols, that's what we need the virus to be killed in, okay? Those are tiny particles generally, the virus is in the aqueous phase. I have done some poking around respiratory fluids that are 40 millimolar lactic acid. So I still don't know how, and hopefully people at Columbia will publish the work, but how the RUV kills the virus, okay? But it does, but what else does it do? So that's why I put a paper in the chat. Dear colleague Veronica Vida, she was also an advisor to the Sloan program, has been working in this field for years. And again, she, there's a paper there and hopefully she will be able to participate in future discussions of the indoor chemistry. So I know there's a lot to talk about, ozone generation, but there's a lot of other chemistry that can be generated by the RUV. Okay, thank you. I'd like to go to Michael and Delphine with a really quick question, and I didn't actually prep you on this one. How much time did you spend in your atmospheric chemistry training looking at the 222 nanometer wavelength? None. We spent a little bit of time thinking about stratospheric chemistry and atmospheric chemistry courses I took as a graduate student. And that's the, the close system, what we know about light in those low 200s wavelengths is really driven by our need to understand stratospheric chemistry, which I should say is a system dominated by organics and then otherwise long-lived compounds. So not the reactive organic carbon that we think about down here in the troposphere, but we're often thinking in the stratosphere about long-lived chlorinated compounds, N2O, CFCs, so chlorofluorocarbon, so other compounds like that. So, and that's the extent to which we think about the light level because that light's attenuated and we no longer see it when we get down here in the troposphere. So there's very little information at atmospheric pressure about what happens in those reactions. Okay, and so to build on that, what do we know about two-tonic, two-chemistry to date? I mean, we've done some intense research. What do we actually definitely know? And then we'll get into what we don't know in a second. Yeah, so echoing Paula, an unintended consequence of 222 nanometer light in particular is that it generates ozone. And we know we can model, we can measure. And so we have very high confidence in being able to predict those in production from this light. What we don't know, however, I'd like to break apart into three sections. One is the sources of reactivity for ozone reactions. The next is the actual byproducts that are formed if ozone reacts. And then the third is the time scales that these reactions can occur. Delphine brought up a really good point that in a lot of traditional outdoor atmospheric research, there isn't a very good characterization of the types of molecules that we see in indoor spaces. They're interactions with 222 nanometer light. So in addition to ozone, we might consider some of the reactivity of those molecules in this very unique circumstance. In terms of the chemical diversity of indoor spaces, there's a wide variety of ozone reactive molecules. And so Delphine and our talk showed some different human occupancy events that can lead to ozone reactive molecules. I think that there's some low hanging fruit in terms of identifying potentially problematic installations of this particular technology. One of those is in environments where you might expect a lot of consumer product emissions. So limonene was a really good example of a reactive molecule from consumer products. And when ozone reacts with these things in the gas phase, so these are the sources of reactivity, they can form gas phase byproducts as well as particulate phase byproducts. We know from laboratory chamber experiments and then also indoor air studies that when you form particulate matter indoors, you can form two general types. One is very, very small particles, these ultra fine particles that can penetrate deep into the lungs. And so they act physiologically a little bit differently than larger particles, which are consistent with the criteria pollutants that are regulated in the outdoor environment. And then finally, so these time scales. Ozone reactions are not particularly fast compared to say reactions with OH or halogen radicals in the gas phase. And so when you generate ozone in indoor space, being able to understand whether it reacts on surfaces or in the gas phase or is lost from the ventilation is really important to understanding what types of byproducts you might expect. And that's something that we don't know a lot about, represents a really important uncertainty when thinking about applying these in real indoor environments. Well, I led to just pointed out that we should be clarifying why we're looking at 222. Traditionally in the indoor space, we've used 254 as an upper room wavelength that's projected as Richard was talking about at the airports that you'll see. 222 is the wavelength that we're able to theoretically shine into the space. So what don't we know? What do we still need to figure out? So I can start with that. I think we don't know a lot about how the different types of organic and inorganic compounds that are present in indoor environments interact with 222 nanometer light, not just their absorption cross sections. So not just that first step of how much those molecules absorb. There's again some hints and indication that there's gonna be a lot of absorption. The lactic acid example that Paula mentioned is a good one. We know that nitrous acid, hypochlorous acid are going to photo-distribute, they're gonna absorb at 222 nanometers and they will likely dissociate. There are some other unknown stone that is what the next step of those dissociation products are. So just because you take, so HONO is easy, nitrous acid, you split it, you make an OH radical and an NO radical and then we can predict what some of those components will do. But lactic acid or some of the more complicated aldehydes and ketones and other strange compounds we find indoors, what they do next, I don't think we have a good handle on because a lot of the studies have been done either in pristine lab conditions or again under very outdoor or stratosphere relevant conditions that are not necessarily the same as indoor. So I think the unknowns, there are several of them but it's how much secondary organic aerosol are you gonna form in a real indoor environment? How many new particles? How many of those little ultra fine particles that Michael Link just mentioned? How many of those are we going to form and under what circumstances? How much additional oxidant? How many other OH radicals or NOx radicals or other surprises along the way are we going to generate that can do additional chemistry? And then another thing we don't know is how do things like different environmental parameters change that subsequent multi-generational chemistry? So how much those changing the humidity in an indoor environment change that chemistry? I think questions like that, for atmospheric chemists will tell you there are always surprises in terms of things like the temperature dependence of different chemical reactions. You might think that all chemical reactions increase in rate with temperature, that's actually not true. So we're going to have surprises along the way and I think that's what makes it very difficult to predict and just use simple models to think about what's happening. So I think there are a lot of unknowns. Go one more for Michael. What role the surfaces have to play in our unknowns in the chemistry related to GOV? Yeah, so I guess that goes back to the question of what types of by-products are formed. And if we're considering the formation of say particulate matter, if we expect ozone to react with some chemical in the gas phase, it'll form these vapors that can stick to surfaces as Vicki has talked about. And the competition between that surface loss of those condensable vapors with condensing onto pre-existing aerosol that may exist in a space can determine if and how much particulate matter by-product would be formed from a GOV222 installation. But additionally, the role of ozone surface chemistry is something that has a lot of unknowns associated with it in terms of by-product formation. And in addition to all of the kind of chemical complexity that we've talked about extensively today, a really big factor here, which you have to know in order to weigh up, should we be using this technology or not, is what are the health effects of those by-products and specifically which by-products are causing those health effects? So to bring that to life a bit, and so the most widely cited study about the hazards of ozone is a kind of outdoor ozone epidemiology paper, which found that for every increase in 10-parts a billion of outdoor ozone, you get a 2% increase in all-cause mortality, which is a very, very large number. And especially given that 10-parts a billion is well within the variation that you see across a country like the United States, and 2% is a very big number, given that we're talking about all-cause mortality. But the question is what's actually driving that number? So outdoor ozone is gonna be linked to indoor ozone levels through the fact that it's infiltrating outdoors, from outdoors through ventilation. It's going to be lost to a reaction by-products primarily with surfaces, but a little bit also with organic carbons in the air. And so the question is, we're observing this variation in outdoor ozone in the country and we can see through the epidemiological modeling, like what's the expected health outcomes of that? But are those health outcomes driven by the time we spend outside where we've got high ozone levels, so it's a higher ozone level, so it's that exposure to kind of 20, 30, 40 plus parts a billion of ozone that is causing that health effect? Is it the fact that we're spending the vast majority of our time indoors and indoor ozone might be to the mid-single digits? And it's that sort of cumulative exposure of the low levels of ozone that is driving that health effect? Or is it the reaction by-products of that ozone that we are inhaling, ingesting, dermally uptaking that are causing that effect? And which one of those is true has extremely profound implications for the cost-benefit kind of analysis of this technology and for how you go about mitigating that impact? I think there's a number of assumptions in this that have not been examined. I think there's quite a common view that we assume that the harmful by-products are in aerosols. That might not be true. The vast majority of reactions of ozone take place on surfaces and we will come into contact with our skin and ingestion and all that. We know various different ways of intaking your potential toxin. So I think it's probably likely that it's true that the vast majority of the harm comes through our true roots, but we don't actually know. If you look at the difference between the mode of harm for particulate matter or at least outdoor particulate matter, PM 2.5, which we know a lot more about, ozone harms appear to be more tend to have more effects on the respiratory system, particulate matter more on the cardiovascular system, which suggests that there could be a difference in the mechanisms of those, or it could be that the indoor particulate matter is different outdoor particulate matter and indoor PM causes problems in the respiratory system as opposed to the cardiovascular system because of the different chemical nature of the makeup. We don't know any of these things. And so if you want to deploy GV to suppress pathogen transmission and you want to mitigate whatever the sort of byproducts that it creates, do you need to remove particulate matter? Do you need to scrub ozone? Do you need to clean surfaces? I don't know the answer to that question. I don't think anyone here does either. And so if you do know the answer to that question, please come up to the mic. And so if we think about, and a number of the people on this panel are engineers and many people here are engineers and the finding that GV has these unintended consequences should be the start of the investigation of how do we best combine the technologies that we have ventilation, filtration, GV to deliver like the overall best outcome in terms of removing chemical contaminants, including those that are already present and also suppressing pathogen transmission. And that's kind of how I see the goal of what we've got to do. So to build upon that, we definitely know that there's biological benefits for GV reducing pathogen transfer. So when we're putting these in indoor spaces and we have ozone generation in that space, how do we compare that chemistry that we're increasing? Because we know the ozone's initiating some chemistry. How do we compare that chemistry from the chemistry that's coming from outdoors? So we have ozone coming in the building through the ventilation system, through infiltration. How do we put those two in context so that we can appropriate the appropriate amount of risk associated with adding GV to a space as opposed to just there is some added risk of just bringing in extra ozone when you increase your ventilation. I think this is a really good place for bringing in models. I mean, we actually know a fair amount about things like indoor outdoor air exchange. We know a fair amount about rate constants for ozone with different types of compounds. There are different techniques to think about that both indoors and outdoors. So I think there is actually a fair amount of information for thinking about how much ozone you're going to bring in from an outdoor environment based on just based off of simple models. So I think that's the problem that's distractible. I think some of these other questions are a little more challenging. Michael? Yeah, experimentally, since we talked about models, experimentally, Charlie wrote a paper last year called Ozone Loss as a Surrogate for Biproduct Formation. And it's wonderful. And one of the things that these GV technologies, the 222 has allowed us to do is to run these devices in indoor spaces. And like Richard highlighted is that they'll form maybe four or five PPB of ozone in the gas phase. And we can, after we turn off the lights, we can watch that ozone go away. And so we can measure where that ozone is actually going, whether it's reacting on surfaces or in the gas phase. And so being able to characterize the ozone reactivity of different spaces, I think is potentially a good experimental approach. So building on that and different, what types of spaces should we be concerned about? And is there potential spaces that we may not want to apply this technology? Well, let me say a bit about where we positively should be thinking about the most impactful spaces or we could be applying it and where the risk reward is gonna look better just because the reward is gonna look better. And so a very big driver of infection transmission is not just the, we think of the basic reproductive number, but it's the variance within that number and how very, very small numbers of infections drive like a very large proportion of the subsequent infections. And the key question is, well, okay, so where do those infections happen? Where do the, as we colloquially call them, kind of super spreading events happen? And identifying those places and figuring out where do we get the best bang for our buck where we prevent the most infections was also creating the minimal amount of exposure is the kind of key question here. The one thing I would say on that point and I'm not certain about this, so this is just my current working hypothesis is that kind of public spaces are much more important for this purpose than homes. And this is important from a chemical standpoint because homes are vastly better chemically, they're still not well enough chemically characterized, but they're vastly better chemically characterized than the places that we might think of as potential kind of high risk transmission situations. If we take the review of that Michael mentioned of ozone is indoor sources and looking at just what we know about ozone decay loss, indoor outdoor ozone kind of concentration ratios, the vast majority of that literature is focused on residences and maybe like a little bit in schools and that's pretty much everything that we have. And so it's quite possible that what we should be caring about is places like this or offices or restaurants. So I don't know the answer to the question, but we don't have the kind of chemical characterization of the spaces where we think actually the technology could potentially be the most impactful. Yeah, I'm just gonna follow on because that is exactly what I've been thinking about this problem is that this is not a problem of your home, this is a problem of hospitals and other areas where people are gonna be concentrated. And I think if we think about risk, the risk of transmission on a population level and where that occurs, if you're worried, obviously depends on what types of diseases you're worried about. If you're worried about tuberculosis, you might choose different types of environments from where you might be worried about measles outbreaks because in one of them you're much more worried about childcare and daycare facilities than you might be worried about hospital wards or prisons or other areas where people are adults or congregating. So different diseases are gonna have different answers. And I think the challenge and the big unknown exactly as you say, Richard, is that we don't know enough about the potential reactivity, the absorption cross sections effectively, the ozone reaction rates in those other environments. We as a community used homes as a starting point for many reasons, but I think there are really important questions to ask about spaces where we might be first deploying these technologies. So I wanna vote for airports and particularly airport club lounges. I can't say for sure I got my coat there, but I spent a lot of time in airports and lounges. It wasn't some auditoriums, but the thing is, air quality is invisible unless you have your CO2 meter and then are you taking your mask off and so on. So I think that there are some where public spaces where people are congregating are definitely a first place to consider. I also, again, we don't have time to sort of go into the other photo chemistry that takes place, but Veronica's paper there, I think that needs to be added to the mix. But in the end, we're gonna have to make some decisions as to, and again, is the next COVID around the bend? All right, I work in a center for health security that's always tracking virus outbreaks. Right now there's one in a military school in the country of Columbia. All right, so is something else on the horizon? So we need to understand what tools we have on the toolbox. And then if another pandemic comes in six months, people aren't gonna say, well, we're gonna wait for six months and we're gonna wait till we get the research done and we're gonna wait till somebody funds it, they're gonna have to make decisions with the information we have are currently available. That said, we do need to scope out a research agenda of where are the gaps so that we know when to deploy technologies and when not to. So anyway, I remain a fan of UV and I am a huge fan of indoor chemistry and I think together the fields will come together and we'll know what to do, but we're gonna have to make decisions. That's a transition to my last question. So what do we need to do to prepare for the next pandemic and what role does the precautionary principle to play in that preparation? I think also I was saying as an environmental chemist, I'm certainly a strong advocate of the precautionary principle, which really just as before you bring in something you need to understand it and to consider the unintended consequences. And many of them, again, we have some evidence for it, we can think about these problems. That said, pandemic kills people and so you have to think about the balance of when you need to use technology and when you don't. And so I think what the precautionary principle will tell you is that if you don't need to use a new technology or a new product, then consider the unintended consequences and don't. But now is absolutely the time to be considering the other side and considering the potential benefits but also understanding enough of the science. And I hope it's clear from this panel that there are huge unanswered questions about how, for example, 222 nanometer ultraviolet light interacts with the air in the surfaces indoors. And so I think there's an opportunity and I think there is a great need to consider that, that so that we can make an educated guess in the future. I mean, I just echo the point about the precautionary principle where it's easy, depending on what framing you come from to just kind of take one side of the equation and ignore the other and we can't do that. Certainly in the long term, not only would I, it would obviously just be bad to introduce a technology that does more harm than good, but a lot of the things that keeps me awake at night is not the idea that UV couldn't stop a pandemic, although there's definitely, I'm not certain that it can. But the thing that actually probably keeps me more awake at night is that we actually do implement this technology. It gets some use and then we discover something later that we didn't fully understand and then we don't have it when it actually comes around, when we actually need it. And this isn't exactly at all what's happened with Upper Room UV, which has been around for a long time, but this is a technology that has been around for a long time and we haven't used it, even though it was there as a tool in the toolkit. And so to make, not just make kind of the right sort of objective rational decision, but to make sure that the deployment or something like this goes well with like societal acceptance, means doing some work to assure people that we understand why it does what it does. So it sounds like we need classroom Kim before the next pandemic. There's been a lot of great questions online, but I'm gonna leave the last question to Catherine here in the room as she's been on a lot of the biological testing for these devices. Well, you all teed up the question I was gonna ask perfectly. I'm curious, you obviously focused a lot on the unintended consequences and the costs related to using this technology. I'm wondering who you look to and where the data comes from for quantifying the benefit because obviously to be able to make those informed cost benefit decisions, we need to know about the benefit as well. So just curious about how you think about balancing both of those things. And that's a fantastic question. And one of the things here is that we don't just have a GUV problem with trying to assess like what does this amount of pathogen disinfection or pathogen low reduction or whatever achieve. We have this problem with ventilation. We have this problem with filtration. We have the problem with vaccines. We have this problem with masks. We, this is just an intrinsically extremely challenging problem to study. And we are basically kind of going off the germ theory of disease pretty much and kind of saying like, we assume that it's good if we remove pathogen from the air and that has some like relationship with the quantity of infections that happen and we can try and quantify how many virus particles people emit and how many you need to breathe in in order to get infected. But this is an area with like very high uncertainty. And we don't have to my knowledge a good randomized controlled trial of basically anything that is extremely convincing in how it suppresses transmission not because these things don't work but because it's an extremely challenging question to study for reasons that I'd be happy to chew your ear off if you're here in the room and why that's the case. So it's a great question because we are basically reduced to modeling and to try to understand like, what does four air changes an hour get us? What does this power of UV get us? What does wearing N95 masks get us? We don't have any better way of doing that at the moment than just trying to do some kind of parametric modeling. I'd just like to end up here on the comment that there's a lot of research that obviously needs to be done. And I know Lou Rendowski at CDC is pushing to do a major effort at this massive field campaigns to see if we can evaluate this from both the biological chemical and practical deployment. And so I urge all of my federal colleagues here to figure out how we can move this research forward because it's great to say we need to do it but we also need to fund it both internally in the federal government and externally. So hopefully we can work as a group to try and figure out the best ways that we can advance this technology and other technologies that improve the indoor air quality and help make indoor spaces healthier. So I'd like to say one more point. If you are a funder, can you just please tell us what you would want to know in order to spend money on this problem? Like what would you want to see in terms of understanding the impact that it has that would convince you that like this is something that is worth investing resource into? There are many, there's many uncertainties, there are many things that we could investigate but I think there is, there could just be more understanding of what do different government agencies, what do different foundations just want to see in the data to decide that like this is something that is worth investing time and money in. So if you are one of those people I would love you to think about that question. So for those in the room I don't want to hold up any longer. We will be reconvening here shortly before two o'clock for our next panel or next presentation on exposures. We'll talk about exposures after lunch. So please make return back to the room shortly before two o'clock. Our lunch is right next door.