RESEARCH WATCH

Air Airborne particles. The relationship was determined between particle mass (examined using a tapered ele­ment oscillating microbalance) and the number of ambient air particles in the submicrometer size range (ex­amined using a scanning mobility particle sizer). (Morawska, L.; John­son, G.; Ristovski, Z. D.; Agranovski, V. "Relation Between Particle Mass and Number for Submicrometer Air­borne Particles," Atmos. Environ. 1999, 33(13), 1983-1990)

Atmospheric aerosols. Hydroxy-methanesulfonate (HMS), a product of the heterogeneous reaction be­tween S(IV) and HCHO, was mea­sured in aerosol samples, indicating it can exist outside of clouds. (Dixon, R. W.; Aasen, H. "Measurement of Hydroxymethanesulfonate in Atmo­spheric Aerosols," Atmos. Environ. 1999, 33(13), 2023-2029)

VOC reactivity. VOC reactivity fac­tors were determined from smog chamber experiments and compared with those derived from a reactivity factor model. (Kelly, N. A.; Chang, T. Y. "An Experimental Investigation of Incremental Reactivities of Volatile Organic Compounds," Atmos. Envi­ron. 1999, 33(13), 2101-2110)

Assessment Aquatic humic substances. Humic substances from open ocean, coastal, estuarine, and fluvial environments were characterized and compared on the basis of their thermogravimetric properties. (Esteves, V I.; Duarte, A. C. "Thermogravimetric Properties of Aquatic Humic Substances," Mar. Chem. 1999, 63(3-4), 225-233)

Gulf War illnesses. In determining from published epidemiological litera­ture whether evidence for a causal association exists between Gulf War service and illness in U.S. veterans, 11 published studies were analyzed using standardized epidemiological

criteria for assessing causality. (Joel-lenbeck, L. M.; Landrigan, E J.; Larson, E. L. "Gulf War Veterans' Illnesses: A Case Study in Causal Inference," Envi­ron. Res. 1998, 79(2), 71-81)

Source apportionment Degradation of chiral pesticides often takes place enantioselectively, yielding nonra-cemic residues. The distinct enantiomeric signatures of these residues can be used as markers to follow environmental transport and fate processes. T. F. Bidleman and R. L Falconer derived a relationship for estimating the contribution of chiral com­pounds from two different sources, A and B, in an A-B mixture. The apportionment equation that they developed requires only the enantiomer ratios of the two sources and the resultant mixture. The authors report that ER values can be determined with high precision and are not affected by analytical method recoveries or by abiotic processes that take place during transport. These advantages make ERs especially attractive for source apportionment. (Environ. Sci. Technol., this isiue, pp. 2299-2301)

Chemistry Chemisorption. Models describing the sorption of pollutants are com­pared, with results indicating that chemisorption processes could be rate limiting in the sorption step. (Ho, Y. S.; McKay, G. "A Comparison of Chemisorption Kinetic Models Applied to Pollutant Removal on Var­ious Sorbents," Process Saf. Environ. Prot. 1998, 76(B4), 332-340)

PCDD/DF chemistry. Mechanisms for formation and destruction of polychlorinated dioxins and furans (PCDDs, PCDFs) were determined by analyzing the behavior of fly ash in various incinerator environments. (Weber, R.; Sakurai, T; Hagenmaier, H. "Formation and Destruction of PCDD/PCDF During Heat Treatment of Fly Ash Samples From Fluidized Bed Incinerators," Chemosphere 1999, 38(11), 2633-2642)

PCDD/PCDF formation. Character­istic PCDF isomer distribution pat­terns found in samples from fluid-ized-bed incinerators were explained by a difference in the mechanism of formation due to a difference in fly ash composition. (Weber, R.; Hagen­

maier, H. "PCDD/PCDF Formation in Fluidized Bed Incineration," Che­mosphere 1999, 38(11), 2643-2654)

Silver-sulfur compounds. X-ray and nuclear magnetic resonance data revealing the chains and networks formed by silver and sulfur atoms in inorganic and organic complexes are reviewed. (Bell, R. A.; Kramer, J. R. "Structural Chemistry and Geochem­istry of Silver-Sulfur Compounds: A Critical Review," Environ. Toxicol. Chem. 1999, 28(1), 9-22)

Climate Archival CO2. Antarctic ice core records show that carbon dioxide concentrations increased by 80-100 ppmv 600 ± 400 yr after the warming of the last three deglaciations. (Fischer, H.; Wahlen, M.; Smith, J.; Mastroianni, D.; Deck, B. "Ice Core Records of Atmospheric CO, Around the Last Three Glacial Terminations," Science 1999, 283(5408), 1712-1714)

Carbon cycle. The ice-core record of atmospheric COz concentrations over the Holocene epoch shows that the global carbon cycle has not been in steady state during the past 11,000 years. (Indermuhle, A., et al. "Holocene Carbon-Cycle Dynamics Based on C0 2 Trapped in Ice at Tay­lor Dome, Antarctica," Nature 1999, 398(6723), 121-126)

JULY 1, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 2 8 3 A