Atmospheric Chemistry of Greenhouse Gases: Sources & Climate Impact

[00:00:15]Yes. Uh you are audible.

[00:00:17]>> Okay.

[00:00:18]>> And uh now we can start. So good evening to all and actually uh Dr. Apologize Dr. I cannot uh put my camera on because uh there is no camera in the in my desktop.

[00:00:34]So Mr. Ajo is Dr. Aar is one of one of my batchmate in in the Kolkatar University when we were studying MSE in Raja Science College. So I am fortunate to have him here within us and I would like like to request Nilmadob Mukharji one of the research scholar in the department of industrial and applied chemistry to just introduce give the introduction.

[00:01:12]>> Am I audible Maharaj?

[00:01:14]>> Yes. Yes.

[00:01:14]>> Okay.

[00:01:23]Respected principal Maharaj Swami Maharan Maharaj respected coordinator Maharaj Swami indust Maharaj revered monastic members of Ramak Krishna Mission Vidya Mandra Buru M and estim esteemed faculty dear fellow students and others good evening to all and good morning to Dr. Oprah, it is my privilege and honor to welcome you all to today's seminar on atmospheric chemistry of greenhouse gases. We are especially honored to have with us Dr. Oprah Chtobadhai, a scientist in the patron lab at the University of Rochester. His re research focuses on the intricate chemistry of our atmosphere addressing critical issues in air quality and climate change. His specific interests include the global methane budget, hydroxil radical abundance in both past and present atmospheres, gas kinetics, photochemistry, spectroscopy, ice core studies, and atmospheric monitoring.

[00:02:28]Before joining the University of Rochester, Dr. Chtoadai served as a research scientist at the NOAA chemical science laboratory and the cooperative institute of for research in environmental science university of Colorado Boulder from 2018 to 2023. He received his PhD in physical chemistry from the Indian association for the cultivation of science in 2018. His outstanding contributions to science have been recognized with several pastriious honors including the researcher development grant 2022 from the royal society of chemistry UK, the Newton international fellowship award 2018 jointly from the Royal Society UK and ACRB India, the international travel grant from the government of India and two best poster presentation awards at the national symposium on radiation and photochemistry in 2013 and 2015. 15. Dr. Chtobadada is an active member of leading scientific organization including the American Geoysical Union and the Royal Society of Chemistry reflecting his commitment to advancing global research collaboration. In the esteemed presence of rever principal Maharaj and Swami Indrashanji Maharaj, it is indeed a privilege to welcome such an accomplished scientist whose work bridge breous research and environmental responsibility. Without further delay, I humbly invite Dr. Apurajio Chtoades to deliver his work talk. Thank you.

[00:04:01]>> Um, thank you for your kind introduction. Uh, okay. Yeah. Uh thank you very much for inviting me. Um I I have uh um given a presentation few years back in one of the uh seminars organized by uh by Rama Ramakrishna mission. So it's indeed a great pleasure and uh I'm I'm excited to see lot of students. Um yeah I'll be talking about atmospheric chemistry of greenhouse gases. Um I was told and I I can see there are a lot of students. So I would like to um keep it um uh as descriptive as possible. Don't want to uh use too many research terms uh so that it is um understandable to everybody. Uh uh here is a little bit of my my background. I did my undergraduate and post-graduate studies from the University of Kolkata. uh in particular I did my BSc from the Sepurand Institution College and then my MSE from the Raja Science College. Yeah. So and then I did my PhD from the Indian association for the cultivation of science and worked at Noah and currently at University of Rochester. Uh so here is the outline of my talk. Um I'll talk about my research interest. I'll go through some basics of atmospheric chemistry. I think it is it is not yet a regular subject in in in our bachelor's or masters curriculum. So I'll give some basics uh in in particular I'll talk about climate and greenhouse gases. uh then regarding my research work I'll I'll I'll present my selected work from Noah particularly on the atmospheric chemistry of hogenated gases and then I'll talk about my uh a glimpse of my current and future research at the University of Rochester um in in atmospheric chemistry of methane.

[00:05:56]Okay. So let's talk about our atmosphere. Um this is a image of our atmosphere's atmosphere. This image was taken from the International Space Station. Uh this the air glow that uh that that makes our different layers of our atmosphere visible. Uh so our atmosphere is uh like um uh we call it um skin of an apple. It's very thin uh but yet a very important blanket. uh it acts as a blanket to protect our planet from from harmful radiation uh from sunlight and also helps to maintain our uh earth's temperature. So it's it's very important. If we look at earth the diameter of our our planet is about about 12,000 kilometer. uh on the other hand the atmosphere extends to only 50 to 100 kilometers. So it's it's very thin and uh here are some of the um here are the layers of the atmosphere and the layers are actually the layers are based on the temperature. Uh the the lowermost uh atmosphere is the troposphere where we live. As you go height uh in altitude the temperature uh goes down. Uh then there is stratosphere uh in in here the temperature goes up with with with altitude. Uh stratosphere also uh is home for the ozone layer. The the famous ozone layer that protects our uh planet from the harmful ultraviolet radiation of sunlight. And there are some upper atmospheres but mainly the the most of the mass of atmosphere is within the troposphere and stratosphere.

[00:07:55]Okay. So now let's let's talk about atmospheric chemistry. What is atmospheric chemistry? It is the study of the chemical and physical processes that affect the chemical composition of the atmosphere. So what is the chemical composition of the atmosphere? uh mo I think most of you know that atmospheric atmosphere is composed of mainly nitrogen and oxygen gases uh little bit of argon and all other gases combined are only 0.1%.

[00:08:28]Uh and they are known as stress gases because of this extremely low abundance.

[00:08:33]uh but these trace gases are responsible for major atmospheric events. Uh for example, carbon dioxide, methane and other greenhouse gases are responsible for climate change.

[00:08:46]Gases like ozone, nitrogen oxides, volatile organic compounds are responsible for air pollution. Volatile organic compounds are we in S we call VOCC's. These are compounds organic compounds which are volatile. For example, um some common examples are acetone, methanol, some of the chemicals that you that you use regularly. Uh also, uh hydrocarbons, they they're very important for air pollution. And there are other compounds which are also kind of viosis like hogenated compounds, chlorofluorocarbons etc. They are responsible for ozone replacement. So this only.1% of the constituent uh gases they are actually responsible for the major events that that happen in the atmosphere and we'll we'll see some of the examples.

[00:09:37]Here is the structure of the atmospheric chemistry research. We can divide it um uh we we can think it as a three-lex tool where the components of this tool are um field studies, laboratory studies and atmospheric modeling. In field studies we measure these uh different atmospheric chemicals uh using either from aircraft campaign or balloons or or or just just field campaign um from satellite also. And the laboratory studies is where we measure or study the chemistry of this this this u uh these components and uh atmospheric modeling is that we want to model and understand what we are observing is the in the field whether it makes sense or not based on the chemistry. So laboratory study actually bridge between field studies and atmospheric modeling. Okay. So these are fundamental sciences that we apply in societal issues such as air quality, climate and ozone. Um now one thing I want to mention here is um that atmospheric chemistry is a very multi-disiplinary research field. We we we have contributions from uh chemists, physicists and engineers.

[00:10:59]uh so anybody can can basically come to this field and and contribute.

[00:11:05]Okay. Now let's look in more details about the atmospheric processes.

[00:11:10]We can divide our planet in u in in different boxes like this uh both horizontally and vertically.

[00:11:20]Let's take uh one of these boxes. Let's take it here. Uh so as I said uh our our main objective here is to understand uh the the the factor that is affecting the abundance of a an atmospheric chemical.

[00:11:37]Uh and let's take an example of a VOC that that I just said VC the volatile organic compound. So we want to understand in this atmospheric box what are the factors that affect the abundance of this VC. Uh so it is guided by mainly two terms. One is the sources and the sinks. Uh the sources are are mainly emission emission from different sources. Uh there are also chemical production chemical reactions that is um that is generating this VOC and the losses are chemical loss that is by chemical reaction or deposition to the surface or or or to clouds maybe rains.

[00:12:18]Uh so these are the different factors that uh uh that control or determine the concentration of of use in the in this box and there are several other box. So there will be transport there will be air flowing from one box to the other and from from this box to to the other box. So this this is methodology. uh so you also take into account of that but what I want to learn want you to learn from this particular slide is that the basic takeaway is different sources and syncs determine the atmospheric abundance of of a VOC and we want to understand these sources and syncs so let's look at uh what are the sources particularly the emissions so the emission of VOCC's could be either from natural sources such as um biogenic emission biomass mining, volcanic eruptions or by anthropogenic sources. Anthro means man.

[00:13:17]So man-made whatever is not natural whatever we we we are doing the man-made sources such as um um industrial sources, cooking fire or veular sources which is basically fossil fossil source.

[00:13:32]Uh so after being emitted into the atmosphere this viosis undergo chemistry or chemical transformation and our atmosphere is is a is has a oxidative behavior. So it it's it's an oxidizing environment. So they are being oxidized mainly by hydroxil radical or O. O is the primary atmospheric oxidant. it uh it reacts with almost all of the VOCC's and other chemicals that are in the atmosphere. Uh for that reason it is also called the atmospheric detergent.

[00:14:08]It helps us cleaning the atmosphere from this uh from this bad pollutants and and other other compounds. So hydroxil radical in the atmosphere is actually produced by photochemistry of ozone. In presence of sunlight ozone dissociates to produce o singlet D which reacts with water vapor to produce hydroxil radicals. So the these hydroxil radicals react with VOC to and in this reaction other organic radicals are being formed.

[00:14:37]As you know radicals are are not stable species. They they they instantaneously react with other other chemicals and and form stable end products. But what what we want to understand here is the is that what is the rate of this reaction.

[00:14:53]This is important here because this determines the atmospheric lifetime. If the rate is uh really really fast then the atm that that chemical will not survive long in the in the atmosphere.

[00:15:07]Uh if the rate is slow then it will survive for long. And this atmospheric lifetime can be uh it's in the range of few hours to thousands of years and and uh that is really important how long a chemical is surviving in the atmosphere and that determines a lot of important atmospheric phenomena.

[00:15:29]So uh this is the formula that we use to to to determine atmospheric lifetime. We need the uh rate constant and the concentration of O which is known. O concentration is pretty low. It's about 10 ^ six um molecules per cc.

[00:15:48]There are other oxidants as well. O is the main oxygen. But there is a chlorine atom which is particularly important in coastal region. There is nitrate radical which is important particularly for the nighttime chemistry. Ozone itself is a oxidant. Um osinc mainly in the stratosphere and of course direct photo dissociation.

[00:16:09]So atmospheric oxidation chemistry has a critical impact on on major atmospheric events such as climate change, air quality and also deflation as I said.

[00:16:20]Okay, we will be focusing today mainly on the climate. So let let's let's look at earth's energy balance.

[00:16:28]Uh here are the um uh black body cards um for for radiation coming from sun. Um you you can you can you can um think or consider sun as as a as a black body.

[00:16:43]And uh I think some of you who who who know the introduction of quantum mechanics know that uh this black body radiation card was was um explained by Max Plank. uh but and it was a revolutionary um invention that uh that uh that energy can only be received or emitted by uh by packets in energy h new and uh the the uh how much uh what wavelength black body is emitting is related to its temperature sun's temperature is really high uh about I think more than 5,000 Kelvin so it emits uh in the um in the visible and ultraviolet region earth's temperature then then we get the energy from sunlight uh and earth also emits but earth's temperature is much lower about 25°C so it emits at um at um in in the infrared region and we also know the steepen boltsman law where it says that energy flux is proportional to temperature fourth power of temp absolute temperature. Uh so we uh we know that the intensity of sun is actually really high. This is scaled by a factor of 10^ minus 6. So these are these are just a basic physics quantum mechanics and very well known very well known right now. uh so from this uh energy balance uh we can calculate how what should be the energy of earth and the mean temperature at earth's surface should be -8° C from this energy balance so it would be or earth should be a frozen planet um there should not be any life but the observed mean temperature of earth is actually about plus 15° C so why is this difference.

[00:18:44]Um this is because of the natural greenhouse effect. The energy that earth is emitting some of that energy is trapped in the atmosphere trapped by greenhouse gases such as carbon dioxide, water vapor and methane. Uh they absorb this terrestrial infrared radiation that that's been trapped in their internal vibrational modes. For example, here there here are some molecular vibrations of um water vapor.

[00:19:11]uh and that is the reason why our earth's temperature is much much higher.

[00:19:17]Um so uh do you think that u I I talked about this earth's mean temperature but is it really constant? Uh that's the question. It has been constant for quite long. Uh this is this figure is from IPCC. Uh this is um this figure uh is uh the change in global service temperature relative to uh 1850 1900 which is about about pre-industrial. So if we if you look at the this this plot uh for the last 2,000 years almost from 2,000 years arts energy was very sterile. It was it was it was very stable within the last 100 and 150 years. It has skyrocketed. It is it is going high like anything. And why why why this happened? This is because of the extreme use of greenhouse gases such as CO2, methane, NO during this period. uh the concentration of these greenhouse gases also increased uh mainly due to uh due to anthropogenic activities. Um and if you look at the the the concentrations here still low in parts per million parts per million means one parts per 10 to the^ six molecule.

[00:20:50]So it's still really really low but it it makes a big difference. So here are the u how much uh different gases contribute to this warming. Uh of course we have carbon dioxide that that that that contributes um close to a one degree centigrade of of temperature change. Uh methane of course as I said there are nitrous oxide hogenated gases. uh but we are in in my research we are mainly interested in methane and hogenated gases. Uh so let's now uh talk about some of my research work uh from Noah which was um related to the hogenated gases. We uh in in the past in the uh 60s7s chlorophyllarbons one of the hogenated compounds were being regularly used as refrigerants and also in other other applications.

[00:21:48]But it was discovered that they destroy stratosphere ozone layer uh by a uh by a catalytic cycle. So in the in the upper atmosphere CFCs are uh photograded by UV radiation of sunlight and and and generate chlorine atom and this chlorine then uh is involved in a catalytic cycle and destroy ozone and uh from from one CL atom many molecules of ozone can be destroyed. It is a catalytic cycle and it was destroying ozone layer which was observed. Because of that reason the CFCs were banned by an international agreement known as Montreal protocol.

[00:22:30]After CFCs are banned the new compounds that come to the market are hydro fluorocarbons or HFCs. They do not contain chlorine. So they do not destroy ozone layer which is good but they are greenhouse gases. Here I have shown the on on on the red curve is arts radiation. Uh now you see the dips here.

[00:22:50]Why is that? Because because of this natural venos gases such as this is the um um absorption of carbon dioxide. This is ozone. But there are some windows which are transparent to infrared. And uh if you have a new gas which absorbs here then you will have uh more energy will be trapped. And in fact HFC is absorbed in this atmospheric window as you can see. So they are greenhouse gases. They they are making our uh temperature earth temperature high.

[00:23:21]Because of that in the recent kegali amendment of the Montreal protocol it was decided that HFC's will be phased down. So what are the new compounds? Now the new generation refrigerants are hydrofluorolifins or HFOs and partflipins or PFOS. So, but we want to know these are new compounds. Uh we don't know a lot about them. So, we want to know are they uh will they are they causing less warming? Uh are they good for environment? Um so that's that's the objective of our of our work u providing experimentally measured climate metrics of new generation replacement compounds uh to help in environmental policym. I have studied one of these compounds um at at Noah and uh this is part fluorohptin one of the pfos and I worked actually with a with a with a with a actual commercial compound this a proposed refrigerant um and the complexity of this commercial sample is that it it is a mixture it comes as a mixture of different stereo isomers uh that is E and Z isomers Centrons as you can you can So 85% is E isomer, 11% is Z isomer and this this this mixture I mean makes it complex as as you'll see. So the research objective uh that we had is first measuring and and and key a key climate metrics known as global warming potential or GWP. It is a simple measure of how much warning compound can cause and it is expressed in in relative terms. We we uh it is expressed with respect to CO2. Uh so we um consider the GWB value of CO2 is one and we want to understand uh what is in comparison how how much more warming another chemical can cause and there are two factors that that uh that contribute here. One is the radiative efficiency that is how much uh um how much uh uh energy it absorbs and so it depend we need to know the infrared spect spectrum of that from that we we we know how much how much uh energy it it is it can trap.

[00:25:46]So it is done by by by studying infrared spectra and second is atmospheric lifetime. So if a chemical is survives for long then it will it will absorb energy for a long time. Uh so and for that we want to measure O reaction kinetics.

[00:26:05]So this this these two term uh if we know these two terms then we'll be able to estimate GWP of this compound. And the second is we also want to know atmospheric degradation mechanism that is what is going to be the fate of this compound in the atmosphere.

[00:26:21]Okay. So let's start with spectroscopy uh invert spectroscopy.

[00:26:27]Uh in this plot uh this um this this black curve is uh is the um measured infrared absorption spectrum of of this compound this mixture. Uh now the E and Z isomers they absorb in in in in pretty same same region in in infrared. It's difficult to uh separate them. So we took little help of theory density functional theory and these are the theoretically predicted infrared spectra for Z isomer and E isomer and we we compared them with experiment. The uh plot in gray here is coming from theory and the black is from experiment. They they agree pretty well to each other.

[00:27:13]Now from that we can estimate the radiative efficiency. uh you can uh by just um uh estimating the area of under this carb. So the relative efficiency for the E isomer and Z isomer is 0.12 and.19.

[00:27:30]What does it mean? It does mean that uh the the uh unit is what per meter squared per parts per billion. Which means that if you inject one parts per billion of this compound then the um amount of energy it will trap or amount of uh amount of energy disruption it will cause is.1 watt per meter squared. So u we do see there is large infrared absorption uh cross-section in this atmospheric window.

[00:28:07]Uh so next part is what is the light time? Uh for lifetime we need to measure the kinetics. Um to do that we we use a technique um known as pulse laser photosis laser induced fluosense or plif.

[00:28:24]Uh so first um so we want to uh study reaction of this compound with hydroxil radical. Now hydroxil radical radical is not stable. So we need to generate that. We generate that from hydrogen peroxide by doing laser photosis at 248 nanometer. For that purpose we use a an eximal laser emitting at 248 nanometer. Now this these lasers are pulseed meaning they the 10 energy laser. So it will give 10 pulses per second. So this this laser generates hydroxil and then we have a probe laser. This is 282 nanometer. This comes from India pumped diler.

[00:29:12]uh what it does is uh it excites hydroxil radical electronically and then then it flues and we collect that fluosense light the laser using a photo multiplier tube. So essentially the the intensity of this fluosense is proportional to the concentration of your hydroxil radical. Okay. So this is the hydroxil radical part. U and so we flow both the this H2O2 and our compound through this cell. Um and these are other spectroscopic setups. Um we have a UV spectroscopy setup here and FTR spectroscopy. This is to monitor the concentration of of of uh of of our compound.

[00:29:59]Uh so let's look at the kinetic results.

[00:30:03]We do this under the condition of pseudofosal reaction condition. This is a biollecular reaction but we keep our compound the heptine in much excess with respect to weight so that we can we can have pseudo order condition which is easy to handle. Uh and you can see here um the pseudo plots. These are uh O intensities at different um uh concentration of our our reacting compound. Uh so as you increase the concentration of park heptine you see the uh steeper carbs um the O um decays much faster. From that we can get this pseudo first order rate constant which I have plotted here as a function of uh the our compound which is also known as second order plot and from the slope of this plot uh you can determine the red constant uh it's pretty pretty straightforward um standard kinetics.

[00:31:03]So the rate constant that we got is 3.9 10 ^ minus3 cm cube molecule inverse second inverse. Um now the issue here is that as I said again this is the mixture compound. So the so the this rate constant that we are getting is um characteristic of the mixture not the individual studio is uh how can we get that um uh in individual reactivities. For that purpose we use another another technique which is a relative rate technique. In this technique what we do is we determine the rate constant of of our compound um with respect to a known compound. Uh we call those references like u these are the two references we have used their rate coefficient is already known.

[00:31:56]Uh so if we react our compound and the reference both at the same time with hydroxil radical and see how they degrade with time then from the relative uh decay of both compounds from this equation if we know the rate coefficient for our reference then we'll we'll know the rate coefficient of of our compound.

[00:32:19]Okay. So uh the way we do it again we use XMR laser photosis but we we use a different radical generation scheme here. We actually photoized ozone in presence of uh water vapor uh and circulated this reaction mixture between this photo reactor and the FTI cell. FPR is not used for kinetics because it cannot differentiate the stereo isomer as well. But what we used for that purpose here is a GCMS gas chromatography mass spectrometry or we also used ECD detector. This can separate these compounds as you can see here. Um this is the E isomer and Z isomer both are separated along with some other other other impurities.

[00:33:10]Okay, let's uh look at the relative rate um data. Uh so here is the data relative rate plot for EI isomer and Z isomer.

[00:33:18]Clearly they they they differ in their reactivities um about by a factor of about 1.5. Uh the the the rate constant for E isomer is 3.6US3 for G it is 2.2 10 ^US3.

[00:33:33]So based on that we can estimate the lifetime. So the EI isomer lifetime is 33 days. So it it survives about around 33 days. Uh GI is 56 days. Uh so how does it compare with the the other method from PLF we got 3.9US3 and from this if we if we estimate the recent for the composite mixture it will be 3.43 10us3. Both methods gave us um u rate constant which are pretty comparable to each other uh which gives us lot of confidence. Okay. So we have the spectroscopy data and we also have the kinetic data.

[00:34:18]So now what is the GWP? uh the GWP uh is and we we uh we we estimate for for some amount of time for example for 100 years how much how much warming it will will do for 100 year time horizon the GWPV values values are about two and five so in comparison to CO2 if if we are if we have made um same amount then the uh the warming will be two times and five times than CO2. Uh so what do you mean by these numbers? Are they large or small?

[00:34:58]What is that? Uh we can compare it uh with um uh with um uh I think I probably don't have that information here but if you look at the typical HFC's they are they are in hundreds to even thousands.

[00:35:15]So so and this is much lower than that.

[00:35:19]uh so it it is low by industrial standards. So these are these are good and the reason is that uh the lifetime is much longer uh much shorter uh if if you think about HFC's their lifetimes are really large uh because because of that the GWP is high.

[00:35:40]Okay. So GWP is good but can you safely say that we we can use this compound? Um the answer is we need to know more details. We need to know the atmospheric degradation mechanism. That is what is the atmospheric fate of this compounds in the atmosphere.

[00:35:57]Uh so this compound reacts with hydroxil radical. The hydroxil radical reacts with this double bond here. There is no hydrogen. So only possible to react with this double bond. then it it produces a free radical that reacts with oxygen and form um peroxy radicals. The peroxy radicals react with um nitric oxide or other peroxid radicals to form aloxxy radical and they degrade to form fluocarbon. So these are the two fluorocarbonals uh expected as a atmospheric degradation product and we did measure those in the infrared spectrum. We did measure this this these compounds as as the uh as the reaction product in close to 100% yield. Uh now these fluorocarbonils are of concern because it is known that heterogeneous loss of fluocarbon could form fluorocaroxilic acids. Now fluorocarbocyic acids are toxic compounds. U but how much um that how much fluocarily acid will be formed we don't know yet. We need to do more more measurements for that. But it it makes us concerned because um although the GWP is low uh it could form toxic compounds in the atmosphere. Uh so we need to know the complete atmospheric fate of of a compound that that's what we I want to uh I want to say here. Another such example is the atmospheric chemistry of triphoracetylate or CF3 CHO. uh triflloro acid diide is a is a is is a major reaction product from HFC's and also HFOs and uh it has been really recently postulated that CF3 CHO can fertilize in the atmosphere and form trifluromthane or or fluoroform or HFC23. Now this would be a big problem because the GWB value of this compound is huge 12,700.

[00:38:05]Uh uh so it has um drawn some recent attention of of the scientists. Um so if if you look at the CF3 CHV spectrum there are basically three degradation channels possible. uh it can have the radical channels to form this radicals or the molecular channel or al also known as the roaming pathway that's what what we are interested in um as I said u there is a claim of production of CHF3 from CF3 CHO but we need experimental verification of that it was it was detected in the short wavelength but not in the longer wavelength where were where where uh I I to describe this figure more in more details. This is the UV spectrum of this compound and this headed area is the UV light that we get from sunlight in the troposphere. And if you look at the wavelength, it is from about 290 nanometer. Uh the shorter wavelengths are uh already absorbed by ozone. Uh so in this region nobody detected this this compound from from from the photo photochemistry that that's that's that's uh what we want to do. Uh that's the motivation of the study.

[00:39:30]Uh so and it it is also became important because recently when atmospheric chemist the modelers modeled it. These the modeled HFC23 emission. Uh the uh red circles here are the estimates based on atmospheric measurement and these uh black um squares are based on uh global industry reporting. Recently there is a big mismatch. So uh something is going wrong either uh there is um inaccurate um reporting or this these compounds are make uh are actually responsible for that from from this from this chemistry.

[00:40:15]So we want to understand whether this chemistry is responsible for it or not.

[00:40:19]So we are one of the first groups that detected CHF3 as a product of uh actctinic photosis that is 308 nanometer photosis of uh of this compound uh at atmospheric pressure and to to to do that um we used a GCMS detection with laser photosis and the quantum that we measured is 3 10 ^ minus 4 which is pretty low um so as I said previously nobody detected it but the estimates that were based on the measurement upper limits are in the range of uh 0.02 to 0.003.

[00:40:55]So what we actually measured is um um about one to two orders of magnitude less than that. Um and we we did measurements at different wavelengths, different pressures. You can you can you can you can get you can you can draw stmer plot from that as well. Uh so basically is it making a difference? No.

[00:41:18]the contribution from this chemistry if if we if we plug that into the model this is contributing really less. So CF save is uh which initially claimed but which we from our measurement it is clear that it is not significant atmospheric source of HFC23 uh which means that there is there is some other other thing going on and we don't know what's going on right now.

[00:41:44]Okay. So this is the summary of this um this part of my talk. We we we measured the atmospheric lifetime and and uh uh GWB values of of these proposed refrigerants. Uh and the basic takeaway is that we need to know the complete uh fate of atmospheric fate of these replacement compounds. Uh okay let's uh talk a little bit uh about my current and future research at University of Rochester. I'll not go into details but just just few uh glimpses. So here I'm I'm I'm working on atmospheric methane. Methane as you already know is the second strongest greenhouse gas after CO2. Its GW value is 27 for 100 year time horizon. That is it's 27 times more stronger uh with respect to CO2. um in in in in uh as as a greenhouse gas. Uh and the good thing is that its atmospheric lifetime is about 9 years. For CO2, it's hundred to thousands of years. So which means that if we can um if we can decrease the concentration of methane uh then within 9 years we'll we should see the effects.

[00:42:59]That's why methane is a prime target for fast mitigation of warming. But unfortunately methan is increasing. Um this is the uh methan data from Noah from 1990s is it was it was increasing uh in in there was a phase between 202 and 2007 when it was stable and people thought that oh it's it's it's probably going down but no it's again started going up and the grow growth rate is even faster in recent years.

[00:43:32]So the primary question is that yeah we know it methan is coming both from natural sources as well as anthropogenic sources but how much are the contribution of these different sources that is the question how how do we know that we can measure methan in the atmosphere but how do we know whether how much it is coming from natural sources how much is coming from man-made activities how do we know that so a a really fascinating build here is the isotope chemistry. Uh isotope ratios are natural markers for different sources and things. Uh so let's take an example of carbon isotopes. So you know carbon has uh two major stable isotopes 12c and 13c. 12c is about 99% 13 C is about 1% and there is also radioisotope 14C which is really less the abundance is really really low. Now the thing is that um the isotop ratio that is 12c by 13 C that is different in different sources. U is ratio is um reported in delta values which is I mean um it's probably a new term to to to you um these ratios are really low. So they for accuracy they are uh reported uh or measured with respect to a reference. Here the reference is PDB. Um uh uh so and and it is um expressed in terms of per mill that is in 2,000 you see here this so these numbers are so low that you need to convert it in into per mill. So basically if your uh 13C con content is high then your delta value will be high.

[00:45:22]If your 13C value is low delta value will be low. Um so if we look at different sources that is let's say microwwell sources or natural sources and fossil fuel which is which is man-made. If we look at the delta numbers they are distinctly different.

[00:45:36]Uh for micro it is about minus60 per mill for fossil it is about minus30 minus 40 per mill biomass burning is even even higher minus 30 minus 20 something like that. So this is ratios are different in different sources. So from that measurement we can determine how much is coming from from which sources. So if we do a balance of these different sources um based on their uh their their amounts the the average value of delta C for methan for our atmosphere should be something around - 53 per mill but it is not the case in in atmosphere the measured uh delta value is about minus 47 so it is slightly different and this difference comes from chemistry uh We call it fractionation is removal particularly it is the kinetic isotope effect because uh this methane is being degraded by let's say hydroxy radical mainly. Now hydroxide radical reacts with these different isotopes at different rates which is the kinetic isotope effect.

[00:46:47]Um because of that uh there is a change.

[00:46:52]Now the problem currently we have is that this is this is a small ratio. This is a small quantity 13 CKIO and it it is uncertain uh it's it's not very well known. Uh and that creates a problem because what atmospheric modelers do they they take all these numbers and and optimize the model based on that they attribute how much um methane is coming from different sources.

[00:47:18]So if we look at the numbers um these are the two uh currently accepted numbers uh of 13C KI 1.0039 by Soros and co-workers from NPI mains and um 1.0054 from Canrell and co-workers from ENKR.

[00:47:37]Uh first of all these are very uh close numbers uh it's probably.1% different.

[00:47:43]Um what NASA JPL recommended is the source value 1.0039 but they also made the error bar larger uh to also accommodate this number as a as a chance.

[00:47:57]Now the small difference make a big difference in in in in source um attribution. So if uh currently the the the estimate is that the fossil um fossil source um contribute about 173 terag per year of methane.

[00:48:17]Uh if you if you take this number if you take the 1.0054 number it will change the emission from 173 to 131 big change 20 about 25% change. uh same with for the for the natural it will change from 374 to 414. So a very small difference in measured uh ki value translate to a big uncertainty in in the uh in in the in the source of uh this uh uh to the different sources.

[00:48:50]Um so we and it is highlighted in recent literature. For example, this this paper says it is also crucial to determine the KI values of methan sync processes more precisely by conducting more laboratory experiments.

[00:49:04]Uh and that's what we want to do. Uh we need more high confidence KI measurements. uh one of our projects have been recently funded by NSF National Science Foundation where we'll be measuring this and uh and I'm the PI of that project and uh this is the uh we we'll use a similar photois scheme here we'll do a laser photosis production of radical we'll use multiple radical precursors because the two studies that I said the one used hydrogen peroxide another study used ozone as the O source uh so we'll see whether that made any change or not. Uh we'll also do temperature and pressure pressure dependent studies particularly uh we don't have uh any measurements at low temperature. Um and we'll we'll process this in a in a in a using using spectroscopy methods. So it will be a process free gas measurement. So we are currently we're in process of building the state-of-the-art experimental apparatus at the University of Rochester. It will be similar to the Noah reactor that I I I worked with. Uh um so the plans are to measure this different KIS 13 CKI for O also for chlorine. We'll also measure the dotarium kinetic isotop effects and we'll measure the KIS at at this large temperature range. So we hope that this new experimental data will likely improve the uh model estimations of isotopic data and our understanding of atmospheric methane sinks and the overall budget.

[00:50:40]Okay. Uh now let's talk about some field studies. I I talked more mostly on on laboratory studies. U so let's talk about the radiocarbon. uh the radiocarbon potency carbon is also also very useful in in in in this case fossil methane is anient um carbon is isolated for in from the atmosphere for millions of years. So you know for is radioactive with a high half life of 5,730 years. So uh there will be no 14y in fossil methan right uh because they they would be already degraded. But if we look at natural sources there will be 14C content. So if we can measure forcy uh then we can get a better idea of of how much is coming from which source. Uh to do that we we we measure um we collect air samples from different parts of the world. Um and then this is the schematic of our measurement and we do a some measurement in at our lab uh at the University of Rochester. do some sample processing and we send our samples for radiocarbon measurements at Australian um nuclear facility at MSTO. Uh so these are the uh regions where we do the measurements. We have um Barrow in Alaska, Monaloa, Hawaii, uh American Summer. These are the baseline stations like u far from pollutants so that we can get the u get the base amount of of methane. uh Barbados, um Iania, Canary Island and Bearingham, New Zealand. So we have some in the um northern hemisphere, some in the southern hemisphere.

[00:52:26]Uh and uh I actually um went to Baralaska last year to to install one of our systems. This is the gas manifold that that we use. It is um it is automated. We can do sampling from here online. And this is the canister where we where we fill our air samples.

[00:52:45]uh and air is collected from a tower. I took we took a picture of of the new laboratory from that tower. Um so after collection we we we we measure these samples at our in our laboratory at University of Rochester. We use a pic ring down spectrometer to to measure carbon monoxide, methane, carbon dioxide. greenhouse gases. Then we do measure the stabiliz and D uh using aodine tildas instrument.

[00:53:15]Then we do a process the sample for radiocarbon measurements.

[00:53:20]As you probably saw radiocarbon um concentration is really really low. So we first have to uh separate out methane from anything else uh CO2. Uh so we have different uh different different traps to to to separate out methane from from others. Then we combust methane to CO2 and then we isolate them in the flame cell. Here uh I I'll show you a really cool video where So this is the flame tubes are now the methan symbol is trapped and we we send those to um anto this is their accelerator mass spectrometer. this uh this really high power mass spectrometers are required to measure this very small amount of radio carbons.

[00:54:28]So this uh this campaign is ongoing. We hope to get some results soon. Um I think I have little bit more time. Um I I I'll just just talk a little bit about past atmosphere. So this is all about present atmosphere. How do we know what was the mitten concentration uh 200 years back? Nobody measured at that time. Uh so one way to measure it uh there there are ears from from that time which are trapped inside inside ice u uh in in in Antarctica or Greenland. Uh so if we can extract those um air from from ice then we we can get a sense of how much methane or other compounds were there 200 years or maybe thousand years ago.

[00:55:13]uh so if you look at uh the data as I said earlier it methan started increasing during pre-industrial uh but we want to know how much is uh due to fossil and how much is due to due to uh due to other sources like agriculture and waste uh and we can do it by by uh using isotopes uh so we are we are going to do a campaign next year at Greenland we'll be the site is called southeast system. It is high elevation about 3,000 m very cold mean annual temperature of minus 21° C which is good because it it it preserves the gas as well extremely high accumulation rate 1 m ice um per per year uh so we'll we'll drill um and get ISIS from about 80 to 230 m if you can drill up to 230 m then it's equivalent to the year of 1850 50 uh then we'll melt those we we need really large amount of eyes uh we we'll melt those and extract air from there and then then that that air will be measured in the laboratory for isotopes uh so yeah that's it I would like to mention a little bit about the scopes in atmospheric chemistry is probably still not a popular field in India as I said it's a multi multi-disiplinary research field as I said uh almost anybody from any science science discipline can come and contribute. uh of course there are scopes in academics but but there is there is big scope in industry for example the exam the the uh compound that I talked about the uh partins these are proposed refrigerants so you need to know their chemistry uh and of course policy you can you can also contribute to the policy um yeah I think I'm I'm on time uh yeah thank you very much for listening and you can ask your questions now Yes.

[00:57:11]>> Yes, I can hear you.

[00:57:12]>> Thank you sir. Very much actually very useful presentations and nice presentation also. I'm asking a question regarding the taking the sample of air.

[00:57:23]Uh so I think uh I heard that the migratory birds that they are coming so many long so long and also the many countries and the feathers of the migratory birds are taken and also the air sample can be how it is fruitful or it is helpful actually I am asking that >> uh I'm not very aware of that particular application but if if the feathers is taken uh there there will be some some signatures there but not air. Uh I I don't exactly know what which signature the scientist collect in that case.

[00:58:02]There there should be some some signature.

[00:58:07]>> Okay. Okay.

[00:58:09]>> Yes sir. Good evening sir. Uh I'm Aratri Sen from Kolata. I studying in class 11.

[00:58:15]So uh you have explained very well sir.

[00:58:17]I could understand only a bit of 25% I can say and sir if I want to go deeper into this subject uh how should I approach this and what book should I read if you just say >> uh yeah you you were um a class 11 student so I I don't know about any any any school level textbook but a college level textbook there is a very popular book that we study uh uh that is called introduction to atmospheric chemistry by Daniel Jacob uh that's freely available um over internet you can probably try uh try try um try that but yeah for for school level there should be some book I'm not very aware of that uh but now yeah the resources are online resources are really helpful so you can >> um you can search those but yeah feel free to reach out to me I I I can give you some resources.

[00:59:20]>> Thank you so much sir.

[00:59:22]>> Good evening sir. Uh nice lecture I have learned the many of things of the basic of atmospheric chemistry and greenhouse gases. So sir I have a little question that we know the photochemical smoke or oxidizing smoke that is span peroxy acetile nitrate.

[00:59:50]So it is very much harmful to the ecosystem for the as it is an oxidizing agent. So in artificially or any laboratory technique that how the scientist can control the pan formation for the reduction of this oxidizing agent.

[01:00:23]Sir any >> your your specific question is uh if I understand well how can you u in the in the laboratory how can you uh synthesize pan and and and control its uh it its concentration is that right >> exactly sir >> okay so pan or paroxy acidal nitrate it it is important mainly from air quality perspective uh not very related to it's it's related climate and alcohol are very related but yeah pan is really an exciting compound it's paroxy acetyl nitrate so if you think about acetone if you fertilize you'll get a paroxy acetyl radical and then it reacts with nitrogen dioxide to to form peroxy acetyl nitrate and uh so what you can do is you can actually in the lab you can generate it in the similar way The way we we we did our experiments here. If you take um acetone or or any other compound like bacile which has this acetyl moy and you if you fertilize at right wavelength you can if you can dissociate the right chemical bond you'll you'll have acetal radical then if you also have nitrogen dioxide in your system then they will combine to each other to form pan. uh you can you can change the concentration all con control the concentrations in different ways uh by changing the concentration of your source gas that is if you take acetone then acetone uh if you also you can vary nitrogen dioxide one thing about pan is that there is it's it's also the lifetime is dependent the on on on on the temperature it's it's at high temperature it dissociates uh so and and That's that's how it transports nitrogen dioxide. It's a transporting agent of NOx.

[01:02:26]It goes to the upper troposphere where it's it's it's cold, it's more stable, then it transports to other region and there it can dissociate. No. So uh it's a really important compound in the in the in the in the atmosphere particularly from air quality perspective and yes you we we can do it we can synthesize it and and control it in the laboratory by by the way I I mentioned you can also vary photosis energy or or to to to control the information.

[01:02:57]>> Okay sir. Thank you sir. Thank you.

[01:03:00]>> Good evening sir. uh thank you for this uh lecture you have shared with us and uh from this I have learned a lot and I understood that I have to learn a lot more. So my question is that you you people have collected the air sample from the ice sheets the older air samples uh but through the years of this freezing and all that it might the air quality which was earlier was present might get disrupted. No means the concentration or the quality might get disrupted. So how can we get the original or the proper sample for the research? So the eyes are a um are buried under under so they they do not get the um effect of I mean the the the upper layers of ice do get some effect particularly when there is melting but if we go to first of all we have not collected that uh we we are uh this campaign will be next year but the idea is that we will go deeper I think uh what I said will drill up to let's say from 80 to 230 m. So if we go that deep 80 to 230 m uh at at at at uh at that level uh the changing environment outside doesn't doesn't make an impact because air cannot diffuse through that deep. So that's why that uh that pristine uh environment of of of past artists preserved there. So that's that that's that's that that's why we are uh going to get those. So um but of course uh if your question is whether after ex after after extracting whether that will make any difference after extract extracting we of getting the ice we take extreme care we we mel those inside inside the vacuum chamber so that it's not it's isolated from from our current atmosphere.

[01:05:10]Am I am am I am I am I clear or did you have any any distinct question about it?

[01:05:16]>> No sir. Thank you sir. Thank you.

[01:05:19]>> Good evening sir. Thank you for your giving lecture. Uh I have a little question. Um in this lecture you told uh tell us that uh you are collecting samples of CH4. Is there a way to control is there a way to control the formation of CH4 in um atmosphere?

[01:05:38]>> Uh okay. So good question. We we need to understand the different sources. First of all, as I said, um natural sources, we we probably cannot control how much is coming from uh from from plants or from soil. But we can definitely control the atmos anthropogenic sources. For example, a big source is fossil fuel, the the vehicular emission. If we can if we can limit the use of fossil fuel, of course we we should uh we we can limit methane and other greenhouse gases and that uh so far there there there has been some effort uh by different countries uh but but still it is increasing as you saw. So probably our effort is not good enough as of now or there is a change in natural emission as well. If if natural emission gets higher we cannot really know about it and that's an that's a that's a open question right now actually we we have been doing lot of research about this recent increase in atmosphere uh whether it is how much is coming from natural and how much is coming from from from manmade but yes our from our part if we can if we can limit the um limit the uh man-made sources like vehicular emission industrial emission and then we can we we can definitely uh limit it and that's that's been the on ongoing um science talks or policy talks throughout the world. How how how can we do that or what policies should we should we adopt to do that?

[01:07:12]>> Okay sir. Thank you.

[01:07:14]>> Come >> sir thank you for your time that you have given to us. My question is can we find a replacement for CFCs or HFC's before uh it is too late for our environment?

[01:07:28]>> Yeah, that's that's a good question. Uh as I said currently we are um the the new generation compounds are HFOs but as you saw it it's it's uh it's much better than HFC's uh and CFCs of course but uh but still it might have harmful effect to our environment. it might be better for our climate but over for overall climate air quality it might not be the good solution. So yeah uh some research is uh going on um on that if you can find the replacement compounds and um yeah that's that's a that that is an active active part of research um in this field and yeah hopefully scientists will be able to get synthesize something that's what we we hope but the these compounds also need to have the right thermmochemical properties to to act as a refrigerant. Uh so it's it's tricky.

[01:08:25]>> Thank you sir.

[01:08:28]>> Sir as you mentioned that methane is the second largest greenhouse gas. Is there any decay process of methane just like CO2 is absorbed by tree.

[01:08:38]>> Okay. So for methane the major process is as I said hydroxy radical that's the major degradation process but hydroxy radical is present in the atmosphere uh naturally also its abundance is 10 to six okay so that's the main process there is some a a little amount is um is deposited into soil that's probably 5% 10% but the major part is oh uh there there there has been a lot of talk going on actually uh can We synthetically degrade methane uh by for example if we can have lot of hydroxy radicals in the atmosphere uh yeah we can but whenever we do part of our nature um by introducing synthetic things we have to be very careful. We have to know first understand well what could be the other effects or side effects. uh but there is an active active um research going on in this in this case the if we can inject some oxidants or or some other materials that that can absorb methane u that's an active area and and very active area and very recent area that if we can if we can somehow destroy methane by by reaction or absorption then then it will be it will be helpful but but we have to know the full picture. We have to know if we do something to our environment system, synthetically, artificially, what is going to be the overall effect. But it's it's an active area of research right now.

[01:10:16]>> Yes. Am I audible?

[01:10:18]>> Yes, I can hear you.

[01:10:22]>> So I have a personal question that uh what is the placement opportunity in this particular field or what is the career opportunity? Uh can you explain?

[01:10:33]>> Yeah, I I I said uh my last slide but I didn't explain a lot. Uh like like like every every field you definitely have academic opportunities. Uh particularly I think that in India I think uh there is not many atmospheric chemists um particularly in the laboratory studies who work in this in this area. So uh definitely uh we should have more atmospheric chemists working in atmospheric chemistry in our country. Uh so there should be but still there is not a lot of lot of lot of opportunities but I do hope that uh the the opportunity is um in in next few years the opportunities become more more available. uh but uh regarding the industry there is definitely uh some big big um opportunities uh I don't exactly know about how the condition is in India but here in in US uh the the chemical companies they are actively looking at uh this this refrigerants uh to to to synthesis uh chemical which is uh which is better for our climate. So if you are let's say synthetic chemist you can definitely uh contribute to that that's and if you are a physical chemist like me then you can you can you can u characterize those compounds um and and and assess whether that's that's good for our climate and environment or not.

[01:12:02]So uh in there there are definitely a lot of industrial opportunities here. uh and the other thing that I didn't mention well is policy uh this the science policy is is really important in this respect and all of these things came up dur during during our conversation that u um can we make a policy to to reduce this emissions? Yes.

[01:12:30]But but uh that that um that involves um not only science but also uh but also government etc. So you you can also it's probably not yet very common but in India but if you if you you can also be a policy person uh in in this in this area. So um I think there are there are scopes uh um I I I I'm not in India right now so I don't have a sense of how much exactly the scope in India but here at least in US uh there is there are a lot of scopes um another field that I didn't describe well is atmospheric modeling um because I do not do modeling but atmospheric modelers are also they they they're uh uh the they their job opportunities are really high uh because because um they can model at at what if if you do uh the model the future scenarios. So so uh they they make valuable impact. So uh in my opinion there are opportunities not only in academics but also in in in in industry as well as in policy. uh but um um yeah but hopefully in India also this different opportunities will will be more available in in in future I I hope >> sir can I ask you a question >> yes >> uh sir I'm a teacher of humanities and I could not understand 90% of your lecture but uh what I have understood that our children if they are interested to go for the studies is how can we inspire them for this because as just now you told that there are no such in opportunities right now in India as my son is also there in this seminar and he's listening to you and he only asked for this deeper knowledge and you have uh mentioned a book sir suggested a book so as a teacher as a mother I just wanted to know uh a suggestion I wanted from you that how can we inspire our children for this awareness this topic because it is very difficult topic and since it is not that much popular in India, how can we inspire children and can add it in the curriculum? What do you suggest sir as a scientist or should we add it in the curriculum of CBSC and other boards so that the children can learn it from at early age? That is my question sir.

[01:15:04]>> Yeah definite definitely the these things should be added into the curriculum. I'm not very well aware of recent curriculum also I I do not say I I didn't say that there is no opportunity there are opportunities uh I I know some some laboratories in in at at least in the undergraduate and post-graduate level I know some some laboratories uh who who work in atmospheric chemistry for example there is a a group at Muhali who they do a lot of measurements there is a group at IIT Madras they do do laboratory studies is uh but what I am saying is that it should be there should be more people who should be working on this important topic for example we we see a lot of biohysicsist um but this environmental scientist science should be should should also be um uh given given preference u uh so regarding the regarding the curriculum yes first of all um I I don't know about current current co course details but what I recall from from my time when I was a student of uh there there was no such course of atmospheric chemistry it definitely should be included in in in bachelor's and and and and mast's level in in chemistry uh and uh and uh and and in in school level I think you probably they probably uh get some idea about like greenhouse gases and air pollutants but uh there there should be more uh in in more structured way like uh what are the actual molecular mechanisms so uh of of let's say uh light absorption or or infrared light absorption etc. So um yeah I I think that from the perspective of I mean uh who who are who are in charge of um creating these uh curriculums uh I I think we can uh the educators they can um talk to them in in in more uh details and and ask them uh I mean convince them that this is important uh um this not only important just just from the perspective of of of of of science but also from from our um from our country because India particularly is air poll in air pollution we we're not doing good we so so if we can if we can if if the educators can convince the people who are in charge of the mentoring the syllabuses and curriculums then that will be then then everybody will get an opportunity to learn about these things so I I think I think that that should be done if if if it has not done already because as I said I don't know about the current syllabuses and courses. What I said is uh from uh 10 20 years back when when I was a student.

[01:18:05]>> Thank you so much sir. Thank you.

[01:18:07]>> Thank you so uh so much to Dr. Aaraj.

[01:18:14]Now uh I formally am giving the vote of thanks.

[01:18:20]So it is my good privilege. Am I audible?

[01:18:24]>> Yes.

[01:18:26]>> It is my proud privilege on behalf of the organizing committee Ramish Vidam Mandira to propose the vote of thanks for today's enlightening seminar on atmospheric chemistry of greenhouse gases. So first and foremost I extend our heartfelt gratitude to our esteemed speaker Dr. Aparaj a distinguished scientist from the USA.

[01:18:48]Your lucid explanations, deep insight and thoughtprovoking analysis have not only enriched our understanding of the complex chemistry of greenhouse gases but have also inspired us to give more critically about about the climate changes and its mitigation. I also take the opportunity to thank our respected dignitaries and our principal Maharaj who has given us this opport opportunity to conduct the seminar.

[01:19:21]A sincere thanks to the placement and career counseling sale technical st support support staff were present in the seminar and volunteers for the meticulous planning and smooth coordination without which this seminar would not have been possible.

[01:19:38]Finally, I am grateful to all the participants for your keen interest, active engagement and thoughtful questions which made today's session truly interactive and impactful.

[01:19:49]Let us carry forward the knowledge we have gained today and work together towards a sustainable and environmentally conscious future. Thank you all once again. Thank you the to to the to our resource person and thank you again all. We now conclude the session. I also want to uh thank thank you everybody uh particularly Jit Maharaj who is my dear friend and um also everybody uh all all the participants here all the students and of course the president Maharaj and all all um all of the um members of Ramak Krishna mission uh thank you very much >> okay So we can expect him in the near future also.

[01:20:41]Sure. Yes. It will be my great privilege. Yes. Yes. Thank you so much.

[01:20:46]Thank you.

[01:20:48]Bye.