Research▼Watch Miniaturized sulfur dioxide analyzer
PHOTODISC
Researchers in Japan and the United States have developed an inexpensive miniaturized sulfur dioxide (SO2) analyzer that can run on a 12-volt automotive battery. The new device could help developing countries monitor atmospheric SO2 levels and can be easily deployed in the field to monitor SO2 emissions from natural sources like volcanoes.
Alarmingly high concentrations of sulfur dioxide have been observed near erupting volcanoes. A new field-portable device could make monitoring volcanic emissions easier.
Although anthropogenic emissions of SO2 have been regulated for several decades, many developing countries cannot afford control technologies and still burn fossil fuels with high sulfur content. Natural emissions of SO2 also contribute to high levels of the respiratory irritant in the atmosphere. Commercially available SO2 analyzers are typically bulky and require large volumes of solution to absorb the collected gas. Such devices can take up to one hour to accumulate
the gas into solution, and they require ac power supplies, which are not easy to find in the field. To overcome these limitations, Kei Toda of Kumamoto University in Japan, and colleagues developed a smaller, less costly SO2 analyzer that does not require an ac power supply. In the new device, SO2 diffuses through a porous polypropylene membrane and absorbs into 800 nanoliters of a dilute sulfuric acid solution containing 2-propanol and hydrogen peroxide. SO2 is oxidized to sulfuric acid, and the resulting change in conductivity is measured by microfabricated electrodes integrated into the gas collection device. Under optimized conditions, the new SO2 analyzer can detect as little as 0.7–1.0 parts per billion (by volume) in about 1.5 minutes. Compared with commercial SO2 analyzers, the new device offers better temporal resolution and therefore much more accurately measures quickly changing atmospheric concentrations. The researchers believe that this general approach could be used to monitor numerous other air pollutants. (Anal. Chem. 2002, 74, 5890–5896)
Surprise reactions yield atmospheric aerosols A previously unrecognized category of chemical reactions appears to play a major role in aerosol formation in the atmosphere. In laboratory studies, researchers at the University of North Carolina at Chapel Hill found that when inert, seed aerosols coated with an inorganic acid, such as H2SO4, were introduced into an atmosphere containing aliphatic aldehydes, organic aerosol formation increased by as much as fivefold over experiments with acid-free aerosols. These findings should improve predictive models for aerosol formation, hazy conditions, and climate change. Secondary organic aerosols have been linked to health effects and
blamed for reduced visibility in scenic areas, and they are believed to generate a net cooling effect in the troposphere. The U.S. EPA regulates aerosols under the National Ambient Air Quality Standards and is under pressure to toughen those standards to include finer particles. Researchers already know that terpenes from natural vegetation and aromatic hydrocarbons from anthropogenic sources are precursors to organic aerosols. Myoseon Jang and colleagues in Richard Kamens’s laboratory recognized that photooxidation reactions of volatile organic compounds yield large amounts of multifunctional organic carbonyls. Using Teflon film reaction chambers, they were able to demonstrate that particles coated with 2–5% H2SO4—a value characteristic of diesel soot—underwent acid-catalyzed heterogeneous reactions with these volatile carbonyls to form organic aerosols. In fact, they report a rich chemistry of new reactions involving species such as di- and tricarbonyls, multifunctional conjugated carbonyls, and alcohols. Increasing relative humidity also affected the reactions by retarding aerosol growth. The researchers say that standard analytical methods used to study atmospheric reactions tend to miss the aldehyde role, because the reaction products can easily convert back to their original starting material during the sample preparation. They found greater success with infrared spectroscopy techniques. This new class of reactions is not limited to urban areas. The researchers show that there is sufficient acid in undeveloped locations to promote the carbonyl reactions. Infrared spectra collected in the relatively isolated Smoky Mountains, an area famous for its natural haze, showed evidence of the acidcatalyzed reactions. (Science 2002, 298, 814–817)
JANUARY 1, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 15 A
