appears today<\/a> in\u00a0the\u00a0Journal of Advances in Modeling Earth Systems (JAMES).\u00a0The study\u2019s MIT co-authors include Jian Guan and Paolo Giani, along with Robert Pincus, Nicole Neumann, George Milly, and Clare Singer of Lamont-Doherty Earth Observatory and the Columbia Climate School, and Brian Medeiros at the National Center for Atmospheric Research.<\/p>\nA natural neutralizer<\/p>\n
The hydroxyl radical, known chemically as OH, is made up of one oxygen atom and one hydrogen atom, along with an unpaired electron. This configuration makes the molecule extremely reactive. Like a chemical vacuum cleaner, OH easily pulls an electron or hydrogen atom away from other molecules, breaking them down into weaker, more water-soluble forms. In this way, OH reduces a vast range of chemicals, including some air pollutants, pathogens, and ozone. And changes in OH are a powerful lever on methane.<\/p>\n
\u201cFor methane, the reaction with OH is considered the most important loss pathway,\u201d Zhu says. \u201cAbout 90 percent of the methane that\u2019s removed from the atmosphere is due to the reaction with OH.\u201d<\/p>\n
Indeed, it\u2019s thanks to reactions with hydroxyl radical that methane can only stick around in the atmosphere for about a decade \u2014 far shorter than carbon dioxide, which can linger for 1,000 years or longer. But even as OH breaks down methane already in the atmosphere, more methane continues to accumulate. Rising methane concentrations, in addition to human-derived emissions of carbon dioxide, are driving global warming, and it\u2019s unclear how OH\u2019s methane-clearing power will keep up.<\/p>\n
\u201cThe questions we\u2019re exploring here are: What are the main processes that control OH concentrations? And how will OH respond to climate change?\u201d Fiore says.<\/p>\n
An aquaplanet\u2019s air<\/p>\n
For their study, the researchers developed a new model to simulate levels of OH in the atmosphere under a current global climate scenario, compared to a future warmer climate. Their model, dubbed \u201cAquaChem,\u201d is an expansion of a simplified model that is part of a suite of tools developed by the Community Earth System Model (CESM) project. The model that the team chose to build off is one that represents the Earth as a simplified \u201caquaplanet,\u201d with an entirely ocean-covered surface.<\/p>\n
Aquaplanet models allow scientists to study detailed interactions in the atmosphere in response to changes in surface temperatures, without having to also spend computing time and energy on simulating complex dynamics between the land, water, and polar ice caps.<\/p>\n
To the aquaplanet model, Zhu added an atmospheric chemistry component that simulates detailed chemical reactions in the atmosphere consistent with the applied surface temperatures. The chemical reactions that she modeled represent those that are known to affect OH concentrations.<\/p>\n
OH is primarily produced when ozone interacts with sunlight in the presence of water vapor. For instance, scientists have found that OH levels can vary depending certain anthropogenic and natural emissions, all of which Zhu incorporated separately and together into the AquaChem model in order to isolate the impact of each process on OH.<\/p>\n
The emissions in particular include carbon monoxide, methane, nitrogen oxides, and volatile organic compounds (VOCs), some of which are emitted through human practices, and others that are given off by natural processes. One type of naturally-derived VOCs are \u201cbiogenic\u201d emissions \u2014 gases, such as isoprene, that some plants and trees emit through tiny pores called stomata during transpiration.<\/p>\n
Into the AquaChem model, Zhu plugged in data that were available for each type of emissions from the year 2000 \u2014 a year that is generally considered to represent the current climate in a simplified form.\u00a0She set the aquaplanet\u2019s sea surface temperatures to\u00a0the zonal annual mean of\u00a0that year, and found that\u00a0the model accurately reproduced the\u00a0major sensitivities of OH chemistry to the underlying chemical processing as simulated in a more complex chemistry-climate model.<\/p>\n
Then, Zhu ran the model under a second, globally warming scenario. She set the planet\u2019s sea surface temperatures to warm by 2 degrees Celsius (a warming that is likely to occur unless global anthropogenic carbon emissions are mitigated). The team looked at how this warming would affect the various types of emissions and chemical processes, and how these changes would ultimately affect levels of OH in the atmosphere.<\/p>\n
In the end, they found the two biggest drivers of OH levels were rising water vapor and biogenic emissions. They found that global warming would increase the amount of water vapor to the atmosphere, which in turn would boost production of OH by 9 percent. However, this same degree of warming would also increase biogenic emissions such as isoprene, which reacts with and breaks down OH, bringing down its levels by 6 percent.<\/p>\n
The team recognizes that there are many other factors that affect the response of isoprene emissions to surface warming. Rising CO2, not considered in this study, may dampen this temperature-driven response. Of all the factors that can shift OH levels under global warming, the researchers caution that biogenic emissions are the most uncertain, even though they appear to have a large influence. Going forward, the scientists plan to update AquaChem to continue studying how biogenic emissions, as well as other processes and climate scenarios, could sway OH concentrations.<\/p>\n
\u201cWe know that changes in atmospheric OH, even of a few percent, can actually matter for interpreting how methane might accumulate in the atmosphere,\u201d Zhu says. \u201cUnderstanding future trends of OH will allow us to determine future trends of methane.\u201d<\/p>\n
This work was supported, in part, by\u00a0Spark Climate Solutions and\u00a0the National Oceanic and Atmospheric Administration.\u00a0<\/p>\n","protected":false},"excerpt":{"rendered":"Methane is a powerful greenhouse gas that is second only to carbon dioxide in driving up global temperatures.…\n","protected":false},"author":2,"featured_media":362030,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7],"tags":[163639,163635,163638,43297,163637,61,60,39287,37080,163636,82],"class_list":["post-362029","post","type-post","status-publish","format-standard","has-post-thumbnail","category-science","tag-aquaplanet","tag-arlene-fiore","tag-atmospheric-detergent","tag-climate-modeling","tag-hydroxyl-radical","tag-ie","tag-ireland","tag-methane-emissions","tag-mit-eaps","tag-qindan-zhu","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts\/362029","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/comments?post=362029"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/posts\/362029\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/media\/362030"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/media?parent=362029"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/categories?post=362029"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ie\/wp-json\/wp\/v2\/tags?post=362029"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}