Researchers measure reaction rates of second key atmospheric component
by Mike Janes
Researchers at the Combustion Research Facility, the University of Manchester, Bristol University, University of Southampton, and Hong Kong Polytechnic have successfully measured reaction rates of a second Criegee intermediate, CH3CHOO, and proved that the reactivity of the atmospheric chemical depends strongly on which way the molecule is twisted.
The measurements will provide further insight into hydrocarbon combustion and atmospheric chemistry. A paper describing the research findings titled “Direct Measurements of Conformer-Dependent Reactivity of the Criegee Intermediate CH3CHOO” is featured in the April 12 edition of Science magazine.
Criegee intermediates — carbonyl oxides — are considered to be pivotal atmospheric reactants, but only indirect knowledge of their reaction kinetics had previously been available. Last year, Sandia and its UK-based partners reported, for the first time, direct measurements of reactions of the smallest gas-phase Criegee intermediate using photoionization mass spectrometry.
That research was featured in the Jan. 13, 2012, edition of Science. See also the Jan. 27, 2012, issue of Sandia Lab News.
Sandia combustion chemist Craig Taatjes (8353), the lead author on the Science papers, says there are several significant aspects about the new research findings.
In particular, the measurements show that the reaction rate depends dramatically on whether the CH3CHOO is bent, with the CH3– and –OO ends pointing toward the same side, a conformation called “syn–” or more straightened, with the CH3– and –OO ends pointing away from each other, called “anti–”.
“Observing conformer-dependent reactivity represents the first direct experimental test of theoretical predictions,” says Craig. “The work will be of tremendous importance in validating the theoretical methods that are needed to accurately predict the kinetics for reactions of Criegee intermediates that still cannot be measured directly.”
In fact, says Craig, the latest results supply one of the most critical targets for such validation. Because of the large concentration of water in Earth’s atmosphere, Criegee concentrations — and, hence, the tropospheric implications of all Criegee intermediate reactions — depend on knowing the rate constant for reaction with water.
Although the reactions for most Criegee intermediates, including the syn- conformer of CH3CHOO, with water may simply be too slow to be measured by the research team’s methods, anti-CH3CHOO has been predicted to have a vastly enhanced reactivity with water. Craig and his colleagues confirmed this prediction and made the first experimental determination of the reaction rate of a Criegee intermediate with water. “A Criegee intermediate’s reaction with water determines what the concentration of these intermediates in the atmosphere is going to be. This is a significant benchmark,” he says.
Craig says one of the questions remaining after the first direct measurement of Criegee reactions was whether the remarkably fast reaction of CH2OO with SO2 was representative of other Criegee intermediates.
“This measurement of a second intermediate — which we found to react just about as fast with sulfur dioxide as the intermediate we measured last year — supports the notion that the reactions of all Criegee intermediates with SO2 will occur easily,” says Craig “It also confirms that Criegee intermediate reactions are likely to make a contribution to sulfate and nitrate chemistry in the troposphere.” This increase in reactivity, he says, provides additional evidence that Criegee intermediates will play a significant role in the oxidation of sulfur dioxide in the atmosphere.
Unraveling mysteries, complexities of Criegee intermediates
Hydrocarbons re-emitted into Earth’s troposphere, either naturally or by humans, are removed by many reactive atmospheric species. For unsaturated hydrocarbons — molecules with at least one C=C double bond — a prominent removal mechanism is reaction with ozone, called ozonolysis. It is accepted that ozonolysis produces other reactive species, including carbonyl oxides, which are known as Criegee intermediates. Rudolf Criegee, a German chemist, first proposed the mechanism of ozonolysis in the 1950s.
Because so much ozonolysis happens in the atmosphere, the reactions of Criegee intermediates are thought to be very important in a wide range of tropospheric processes like secondary organic aerosol formation and nighttime production of highly reactive OH radicals. As a result, the chemistry of these reactive Criegee intermediates has been the subject of intense investigation for decades, but without any direct measurement of their reaction rates until last year’s published work by Sandia and its collaborators.
The research was funded by DOE’s Office of Science and conducted using the Advanced Light Source at Lawrence Berkeley Laboratory, a scientific user facility also supported by the DOE Office of Science.
-- Mike Janes
Choosing future warfighting vehicles: Army Ground Combat Systems adopts Sandia tool to help in decision-making process
Imagine trying to solve this complex problem: You have to modernize a fleet of combat vehicles, such as tanks, tracked howitzers, and infantry fighting vehicles, choosing from among more than 50 ways to update them to meet future threats. Each modernization option can be configured differently to meet a variety of missions around the globe. You are constrained by fielding schedules and the costs of research and development, maintenance, and operations, and your budget can change without warning. A shift in the socio-political status of any country or the environment could have consequences that would require you to re-think your decision and, by the way, you’re planning 30 years into the future.
Are you scratching your head yet? This is the daunting task faced by analysts working for the US Army’s Program Executive Office Ground Combat Systems (PEO GCS), who help the nation’s top generals decide which Army vehicles to modernize for future wars.
Sandia, working closely with the Army and other contractors, has developed key components of a software tool to help the PEO GCS analyze countless what-if scenarios that can be manipulated as technology advances and the global environment, the federal budget, or other factors change. Sandia calls this advanced combination of modeling, simulation, and optimization decision support software the Capability Portfolio Analysis Tool (CPAT).
CPAT won the 2012 Military Operations Research Society’s Richard H. Barchi Prize, and its Sandia developers say senior Army leaders are expanding the use of the 2-year-old tool across a number of Army modernization programs.
The Sandia researchers envision adapting CPAT to help make a variety of complex decisions easier throughout the military and elsewhere.
“This has really revolutionized the way the Army thinks about things. It’s been a big shift in paradigm for how they do analysis,” says Liliana Shelton (6133), CPAT’s technical lead and a Sandia computer scientist. “About a year after we started from a blank sheet of paper, it started getting used by people once they saw the capability and the questions we could answer.”
Alan Nanco (6114), CPAT capability manager, says the tool that supports PEO GCS answers questions about ground combat vehicle modernization by combining optimization — mathematical formulae, software language, and a user interface that clarifies results — with a large number of choices that helps the Army leadership narrow millions of choices into a handful of options that best balance its goals while staying within budget, schedule, or other constraints.
“The beauty of the tool that we have developed in collaboration with the Army is it’s better to evaluate how you’re going to pick among such a huge array of options, if you have tools that will walk your equipment and your people through a scenario,” Alan says.
Growing partnership with Army
The analytic support CPAT provides grew out of a partnership between Sandia and the Army that started more than a decade ago. The Labs had been using modeling and simulation and systems-of-systems engineering to upgrade nuclear weapons systems by making choices of reliability, safety, and security, Alan says. The Defense Advanced Research Projects Agency teamed with the Army and wanted to use that expertise to support complex decisions for modernizing the Army’s combat systems to create “modular brigade combat teams,” Alan says.
For CPAT, Sandia worked closely with the Army to develop the structure of the models, the algorithms, the mathematical formulation for the optimization tool, and the software that makes CPAT user-friendly and displays the results so analysts can use them to brief decision-makers, Liliana says. Other contractors are responsible for data collection and feeding in assumptions made by the software.
Craig Lawton (6133), the lead for PEO GCS projects, says other contractors input specific requirements for each vehicle’s capabilities. Then, those capabilities are matched to each mission, and CPAT takes into account the operating, maintenance, and research and development costs.
Liliana adds: “These are all the decisions you have to balance when you do an optimization run.”
When PEO GCS calls Sandia, Liliana says she can get answers in days — a process that used to take weeks. The results are a variety of data and graphs that help analysts quickly compare what-if scenarios or choose the best path to modernize a vehicle or see where different choices fall in meeting the military’s long-term goals. (Eventually, Sandia envisions training Army systems analysts to use CPAT themselves.)
In the real world, most choices are trade-offs, Liliana says.
“You look at different levels of modernization because at different budgets, you might not be able to afford the gold-plated solution. There’s something in between, like a happy medium, that they can afford, so they can still improve the capability without breaking the bank,” she says.
As the situation changes over time, Sandia and its partners can input new information into the underlying assumptions to show how various changes have an impact on the entire system, she says.
In its two-plus years of existence, CPAT already has shown its value by correcting a misconception as to whether two certain military vehicles could be modernized at the same time.
“The tool reported differently and bucked conventional wisdom, leading to its success,” Craig says.
Other Sandia researchers working on the project include Stephen Henry, Matthew Hoffman, Hai Le, and Amanda Wachtel (all of 6133), Darryl Melander (9515), Gio Kao (5634), Jessica Mader (6923), and Robert Vander Meer (6114).
‘Sky’s the limit’ for CPAT applications
CPAT has been so successful that the assistant secretary of the Army for Acquisition, Logistics, and Technology asked that it be briefed to other Army PEOs. As a result, Sandia is working with other Army PEOs, such as Enterprise Information Systems, to apply it to their complex decision-making processes. Sandia has taken action to meet anticipated future demand for the tool, Craig says.
Eventually, CPAT could be adapted to other military branches or applied to entirely different, complex decision-making processes in other large organizations.
“The challenge is each organization has different things that they are managing. Conceptually you are making decisions about how you invest your money, but the details of what goes into it are very, very different,” Craig says, but he adds, “The sky’s the limit.”
-- Heather Clark
Sandia ranks high in Woman Engineer magazine’s top employers list
by Nancy Salem
Sandia moved from No. 18 to No. 4 on Woman Engineer magazine’s 22nd annual list of Top 20 Government Employers.
The list appears in the magazine’s spring 2013 issue. About 400 readers of Woman Engineer selected the US companies they would most like to work for or that they believe would provide a positive working environment for female engineers. The annual reader survey is mailed to randomly selected readers of the magazine.
The survey includes questions about age, gender, geographic location, resources for learning about job openings, annual salary, career discipline, and others. “We ask readers to list their top three companies or government agencies,” says Tamara Flaum-Dreyfuss, president and publisher of Equal Opportunity Publications Inc. “From that list, we weigh the answers based on their listing of first, second, and third choice.”
The top five finishers were NASA, US Department of Transportation, FBI, Sandia, and DOE. Last year Sandia was ranked 18 out of 20.
Pamela Hansen Hargan, VP of Human Resources and Communication Div. 3000, says the ranking reflects positively on Sandia. “It is an honor to be considered a top employer by the readers of Woman Engineer,” she says. “This type of branding is critical to attracting top talent such as the subscribers of this magazine.”
Recognition a powerful recruiting tool
Sheri Kennard (3555), who heads up student intern programs at the Labs, says the recognition is a powerful recruiting tool. “It shows we have a lot of diversity and a lot of opportunities at Sandia,” she says. “It acknowledges that this is a great place to work.”
Esther Hernandez (3010), Sandia’s chief diversity officer, says there is a consistent effort throughout the Labs to build a work environment where all individuals know they are important because they are valued, included, treated with respect and dignity, and are fully productive contributors to mission success.
“Sandia is an exceptional place to work,” she says. “I am delighted that we are viewed as an employer of choice by the readers of Woman Engineer.”
The magazine was launched in 1979 and is the country’s most widely read recruitment publication for women engineers. It is read by more than 56,000 student, entry-level, and professional women engineers, and goes to the placement offices of all 296 accredited engineering schools, and to student and professional associations and societies.-- Nancy Salem