{"id":6215,"date":"2019-02-18T21:53:55","date_gmt":"2019-02-19T02:53:55","guid":{"rendered":"http:\/\/spaceandplanetarynewswire.com\/?p=6215"},"modified":"2019-02-18T21:53:55","modified_gmt":"2019-02-19T02:53:55","slug":"sandia-research-investigates-how-organic-reactions-affect-earths-atmosphere","status":"publish","type":"post","link":"https:\/\/spaceandplanetarynewswire.com\/?p=6215","title":{"rendered":"Sandia Research Investigates How Organic Reactions Affect Earth\u2019s Atmosphere"},"content":{"rendered":"
Formaldehyde and methanol time profiles from the methylperoxy self- and hydroxyl reactions. Comparison of the contributions from 13CH3OO self-reaction and reaction of 13CH3OO with OH in producing methanol in the photolysis experiments at P\u2009=\u200930\u2009Torr. a CH3OO self-reaction (photolysis of 13CH3I in the presence of O2) compared to a kinetic model employing literature rate coefficients and directly measured reactant concentrations, wall loss and two fits to the photolytic depletion. b Measurements at the same conditions as (a) except with the addition of H2O2. The contribution from 13CH3OO self-reaction is represented by the signal from another product at m\/z\u2009=\u200964, 13CH3OO13CH3 (formed only by the self-reaction), scaled using directly measured branching fractions of the self-reaction. The additional, rapidly formed 13CH3OH arises from the reactions of 13CH3OO with OH and 13CH3O with HO2. The temporal resolution of the methanol and CH3OOCH3 signals is here reduced by a factor of five to more clearly show the amplitudes<\/figcaption><\/figure>\n

Volatile organic compounds can be found in the air \u2014 everywhere. A wide range of sources, including from plants, cooking fuels and household cleaners, emit these compounds directly. They also can be formed in the atmosphere through a complex network of photochemical reactions.<\/p>\n

Researchers at Sandia National Laboratories and colleagues from other institutions investigated the reactions of hydroxyl and methylperoxy radicals to understand their impact on the atmosphere\u2019s ability to process pollutants.<\/p>\n

This work, which was published in Nature Communications<\/a><\/em>, showed that the reactions can impact levels of a key chemical marker used to assess the understanding of the processing and abundances of pollutants. This ultimately helps our understanding of how both nature and human activity affect the chemical composition of the atmosphere.<\/p>\n

Recent studies in this area had indicated that the reaction of methylperoxy with the hydroxyl radical occurs more rapidly than previously thought, and so this reaction could change the current understanding of chemistry in both low-temperature combustion and the Earth\u2019s atmosphere.<\/p>\n

The hydroxyl radical, an important molecule in combustion and atmospheric chemistry, initiates the oxidation, or processing, of fuel and pollutant molecules. When this radical reacts with fuel molecules in the presence of oxygen, a new class of radicals \u2014 known as peroxy radicals \u2014 is formed. In the Earth\u2019s atmosphere, when the hydroxyl radical reacts with methane (which is both a greenhouse gas and the most abundant hydrocarbon), methylperoxy is created.<\/p>\n

Impacts to combustion<\/strong><\/p>\n

Dino Vournas Rebecca Caravan, Sandia National Laboratories postdoctoral appointee, adjusts the Sandia Multiplexed Photoionization Mass Spectrometer that was used to conduct research on volatile organic compounds<\/figcaption><\/figure>\n

Rebecca Caravan, a Sandia postdoctoral appointee and lead researcher of the collaborative new effort, said investigating the subsequent reactions of peroxy radicals is critical to understanding low-temperature combustion because the peroxy radical\u2019s fate determines to what extent fuel will undergo autoignition. The researchers wanted to understand how the reaction of hydroxyl and methylperoxy radicals could impact this \u2014 for example, whether autoignition could be inhibited due to the removal of reactive radicals and the production of relatively unreactive chemicals.<\/p>\n

\u201cDetermining the impact of any specific reaction within any given environment requires knowing both how fast the reaction occurs and the products of the reaction,\u201d she said. \u201cCarefully quantifying the products is often the more difficult task. A relatively small change in in these reactions can significantly change the magnitude and even the direction of the impact a reaction has in a given environment.\u201d<\/p>\n

Recent theoretical work indicated that a possible product of the hydroxyl radical and methylperoxy reaction could be methanol and oxygen. These products would have significant affect on our understanding of the chemistry in Earth\u2019s troposphere \u2014 the part of the atmosphere between zero to 10 kilometers (6 miles), which contains around 75 percent of the atmosphere\u2019s mass.<\/p>\n

Caravan said that methanol has long been significantly underpredicted in the troposphere by atmospheric modelers. Because methanol can be formed from multiple sequences of oxidation reactions in the troposphere, understanding how chemical reactions contribute to the levels of methanol in the atmosphere sheds light on how the atmosphere processes hydrocarbons emitted by both nature and human activity, therefore helping us understand the influence of both on the chemical composition of the atmosphere.<\/p>\n

Sandia combustion chemist Craig Taatjes, the principal investigator of this research effort, said, \u201cWe recognized that our fundamental measurements of methanol yield from the hydroxyl radical and methylperoxy reaction could have an impact on modeled atmospheric methanol abundance, so we brought in modeler colleagues who could focus on those consequences of our investigations.\u201d<\/p>\n

International collaboration<\/strong><\/p>\n

The discrepancy between modeled and measured methanol is particularly significant in the remote troposphere \u2014 regions with relatively limited influence from human activity.<\/p>\n

Dwayne Heard, professor of atmospheric chemistry at the University of Leeds in the United Kingdom, said an understanding of these regions is needed before human changes can be understood.<\/p>\n

\u201cWe know that changes in man-made emissions are leading to a warming of the atmosphere and a deterioration in the quality of the air that we breathe,\u201d Heard said. \u201cHowever, set against this are natural, dominant processes that occur everywhere \u2014 for example, over the oceans where there is relatively little influence from humans.\u201d<\/p>\n

Studies of radical-radical chemistry are complicated; the multiple side reactions need to be understood along with the reaction of interest. To tackle this, researchers from Sandia and NASA\u2019s Jet Propulsion Laboratory employed the world-renowned capabilities at Sandia\u2019s Combustion Research Facility<\/a> and the Advanced Light Source<\/a> at Lawrence Berkeley National Laboratory.<\/p>\n

The researchers relied on the Sandia Multiplexed Photoionization Mass Spectrometer instruments developed by Sandia researchers David Osborn and Lenny Sheps. The team also used the tunable vacuum ultraviolet ionizing radiation from the Chemical Dynamics beamline at the Advanced Light Source to observe and characterize the chemistry and reaction products.<\/p>\n

The researchers then worked to interpret their experimental observations via models and calculations. They examined the role of longer timescale chemistry on the reaction products by collaborating with partners at the University of Lille in France, who used their atmospheric simulation chamber. Additional team members at the University of Bristol in the United Kingdom used a global chemical model to assess the experimental results on the troposphere.<\/p>\n

\u201cIt was a highly collaborative, international project with each party bringing their own world-class capabilities,\u201d said Caravan.<\/p>\n

The Sandia team was funded by the Department of Energy\u2019s Basic Energy Sciences Office. The co-authors of the paper were supported by NASA and British and French agencies.<\/p>\n

Impact on the atmosphere<\/strong><\/p>\n

Because of this collaborative effort, it is now understood that in the troposphere around 25 percent of methylperoxy radicals are removed by the fast reaction with the hydroxyl radical, meaning that fewer peroxy radicals undergo other reactions known to lead to methanol. To counterbalance that, the methanol yield from the reaction of hydroxyl radicals with methylperoxy would need to be about 15 percent, but the authors\u2019 measure yields in the range 6-9 percent.<\/p>\n

The implications of this result on the understanding of tropospheric methanol are significant. The hydroxyl radical and methylperoxy reaction fails to resolve the discrepancy between higher measured and lower modeled methanol abundances; in fact, this discrepancy is now exacerbated. Methanol in remote regions is now underpredicted by around a factor of 1.5 in global models of the atmosphere.<\/p>\n

\u201cThis work highlights our incomplete understanding of key tropospheric chemical reactivity. We are missing significant reactions, opening the door to further investigation,\u201d Caravan said.<\/p>\n

Alexander Archibald, a Cambridge University professor and an expert in the field, says the experiments led by Caravan demonstrate that methanol has additional secrets to reveal.<\/p>\n

\u201cWhile the reaction between methylperoxy radicals and hydroxyl radicals may not be a major source of methanol, models still underestimate the amount of methanol,\u201d said Archibald. \u201cThe exciting work that Caravan and co-workers have performed closes one chapter in the story, but the book remains unfinished. Further work is required to help complete our understanding of this important compound in the atmosphere.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"

Volatile organic compounds can be found in the air \u2014 everywhere. A wide range of sources, including from plants, cooking fuels and household cleaners, emit these compounds directly. They also can be formed in the atmosphere through a complex network of photochemical reactions. Researchers at Sandia National Laboratories and colleagues from other institutions investigated the…<\/p>\n","protected":false},"author":71,"featured_media":7406,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ngg_post_thumbnail":0,"fifu_image_url":"https:\/\/media.springernature.com\/lw900\/springer-static\/image\/art%3A10.1038%2Fs41467-018-06716-x\/MediaObjects\/41467_2018_6716_Fig1_HTML.png","fifu_image_alt":"Sandia Research Investigates How Organic Reactions Affect Earth\u2019s Atmosphere","footnotes":""},"categories":[207],"tags":[],"class_list":["post-6215","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-research"],"_links":{"self":[{"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/posts\/6215","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/users\/71"}],"replies":[{"embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=6215"}],"version-history":[{"count":1,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/posts\/6215\/revisions"}],"predecessor-version":[{"id":6217,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/posts\/6215\/revisions\/6217"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=\/wp\/v2\/media\/7406"}],"wp:attachment":[{"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=6215"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=6215"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/spaceandplanetarynewswire.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=6215"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}