Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Study Improves Accuracy of Models for Predicting Ozone Levels in Urban Areas

02.11.2010
Current computer models may underestimate levels of ground-level ozone

A team of scientists has, for the first time, completely characterized an important chemical reaction that is critical to the formation of ground-level ozone in urban areas. The team's results indicate that computer models may be underestimating ozone levels in urban areas during episodes of poor air quality (smoggy days) by as much as five to 10 percent.

Ground level ozone poses significant health hazards to people, animals and plants; is the primary ingredient of smog; and gives polluted air its characteristic odor. It is known that even small increases in ozone concentrations can lead to increases in death from respiratory problems. Because of the health hazards caused by ozone exposure, the research team's results may have regulatory implications.

The team's research, which was funded by the National Science Foundation (NSF), NASA and the California Air Resources Board CARB), appears in the October 29 issue of Science.

Big role of one reaction in predicting ozone in smoggy air

The reaction studied by the researchers plays an important role in controlling the efficiency of a sunlight-driven cycle of reactions that continuously generates ozone. In this reaction, a hydroxyl radical (OH) combines with nitrogen dioxide (NO2), which is produced from emissions generated by vehicles, various industrial processes and some biological processes.

When a hydroxyl radical and nitrogen dioxide collide, these molecules may stick together to form a stable byproduct known as nitric acid (HONO2). Because of the stability of nitric acid, its formation locks up hydroxyl radicals and nitrogen dioxide, and thereby prevents these molecules from contributing to ozone formation; this reaction thereby slows the formation of ozone.

Although scientists have long recognized the importance of the formation of nitric acid, they have, until now, been unable to agree on the speed, or "rate," at which hydrogen radicals and nitrogen dioxide combine to form this end product. "This reaction, which slows down ozone production, has been among the greatest sources of uncertainty in predicting ozone levels," said Mitchio Okumura of the California Institute of Technology--a member of the research team. This uncertainty has affected computer models that simulate air pollution chemistry.

An experimental challenge

Why is there so much uncertainty about the speed or rate of formation of nitric acid? In large part, because instead of combining to form a stable form of nitric acid, a hydroxyl radical may combine with nitrogen dioxide to form a less stable form of nitric acid (HOONO)--a snake-like molecule that quickly breaks apart in the atmosphere. This breakdown of the unstable form of nitric acid releases its hydroxyl radical back into the atmosphere where it may once again become available to form ozone; this breakdown therefore speeds the formation of ozone. Nevertheless questions about the existence, amount, speed and formation of the unstable form of nitric acid have, until now, complicated measurements of the speed or rate of the formation of the more stable form of nitric acid.

But through experiments conducted at the Jet Propulsion Laboratory (JPL) and at the California Institute of Technology using state-of-the-art techniques, Okumura and his colleague, Stanley P. Sander at JPL, led a team of researchers that accurately measured: 1) the overall speed at which hydroxyl radicals and nitrogen dioxide combine, or react, in given atmospheric conditions; 2) the ratio of stable nitric acid to unstable nitric acid that is formed under given atmospheric conditions.

In addition, new laser methods enabled researchers to directly detect the presence of the unstable form of nitric acid in microseconds. And with the help of companion calculations performed at Ohio State by Anne McCoy, they could quantify its yield as soon as it was formed.

The research team's experiments show that the stable form of nitric acid forms slower than previously believed. These results indicate that there is more OH available in polluted, ground-level air for the formation of ozone than previously believed, and thus probably more ozone in the atmosphere than previously predicted.

More ozone than previously believed

To demonstrate the significance of the new results, modelers on the research team led by Robert Harley and William Carter fed their newly quantified reaction rates and ratios into computer models to predict levels of ground-level ozone during the summer of 2010 in the Los Angeles Basin. Their results indicate that many current models have been underestimating ground-level ozone levels in the most polluted areas (where nitrogen dioxide is highest) by about 5 to 10 percent. The research team concluded that relatively small changes in the rates and proportions of reactions forming unstable and stable nitric acid could lead to small but significant changes in ground-level ozone levels.

The importance of the study

"The study illustrates the importance of developing new and improved experimental approaches that interrogate atmospheric systems at the molecular level with high accuracy," said Zeev Rosenweig, an NSF program officer. "This is imperative to reducing uncertainties in atmospheric model predictions."

"The determination of a more accurate value of the rate of nitric acid formation from a hydroxyl radical and nitrogen dioxide will be important in future air-quality modeling," said Anne B. McCoy, a member of the research team. "The research was made possible by bringing together several laboratories with different capabilities and expertise, including my lab at Ohio State, and labs at CalTech, JPL and Berkeley."

Regulatory implications

The ozone prediction models incorporated into the research team's study are similar to those used by regulatory agencies, such as the Environmental Protection Agency and the California Air Resources Board. Therefore, the team's results may have implications for future predictions of ground-level ozone used by regulatory agencies in developing air quality management plans.

Media Contacts
Lily Whiteman, National Science Foundation (703) 292-8310 lwhitema@nsf.gov
Jon Weiner, California Institute of Technology (626) 395-3226 jrweiner@caltech.edu
Co-Investigators
Mitchio Okumuro, California Institute of Technology (626) 395-6557 mo@caltech.edu

The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2010, its budget is about $6.9 billion. NSF funds reach all 50 states through grants to nearly 2,000 universities and institutions. Each year, NSF receives over 45,000 competitive requests for funding, and makes over 11,500 new funding awards. NSF also awards over $400 million in professional and service contracts yearly.

Lily Whiteman | EurekAlert!
Further information:
http://www.nsf.gov
http://nsf.gov/news/news_summ.jsp?cntn_id=117965&org=NSF&from=news

More articles from Ecology, The Environment and Conservation:

nachricht Successful calculation of human and natural influence on cloud formation
04.11.2016 | Goethe-Universität Frankfurt am Main

nachricht Invasive Insects Cost the World Billions Per Year
04.10.2016 | University of Adelaide

All articles from Ecology, The Environment and Conservation >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

Im Focus: MADMAX: Max Planck Institute for Physics takes up axion research

The Max Planck Institute for Physics (MPP) is opening up a new research field. A workshop from November 21 - 22, 2016 will mark the start of activities for an innovative axion experiment. Axions are still only purely hypothetical particles. Their detection could solve two fundamental problems in particle physics: What dark matter consists of and why it has not yet been possible to directly observe a CP violation for the strong interaction.

The “MADMAX” project is the MPP’s commitment to axion research. Axions are so far only a theoretical prediction and are difficult to detect: on the one hand,...

Im Focus: Molecules change shape when wet

Broadband rotational spectroscopy unravels structural reshaping of isolated molecules in the gas phase to accommodate water

In two recent publications in the Journal of Chemical Physics and in the Journal of Physical Chemistry Letters, researchers around Melanie Schnell from the Max...

Im Focus: Fraunhofer ISE Develops Highly Compact, High Frequency DC/DC Converter for Aviation

The efficiency of power electronic systems is not solely dependent on electrical efficiency but also on weight, for example, in mobile systems. When the weight of relevant components and devices in airplanes, for instance, is reduced, fuel savings can be achieved and correspondingly greenhouse gas emissions decreased. New materials and components based on gallium nitride (GaN) can help to reduce weight and increase the efficiency. With these new materials, power electronic switches can be operated at higher switching frequency, resulting in higher power density and lower material costs.

Researchers at the Fraunhofer Institute for Solar Energy Systems ISE together with partners have investigated how these materials can be used to make power...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

UTSA study describes new minimally invasive device to treat cancer and other illnesses

02.12.2016 | Medical Engineering

Plasma-zapping process could yield trans fat-free soybean oil product

02.12.2016 | Agricultural and Forestry Science

What do Netflix, Google and planetary systems have in common?

02.12.2016 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>