Center on Airborne Organics

Annual Report 1995: Highlights

Sources and Control: Encouraging progress has been made on developing on the factors governing the formation and control of soot and on the sources of emissions of VOCs from engines. Professor Howard at MIT has developed a new sectional model for calculating molecular which treats kinetics of "molecules" with molecular weights covering eight order of magnitude and thus able to follow the transition from gas phase species to particle inception and growth. Data for testing such models has been obtained by Prof. Beér at MIT, who by examining soot formation under widely differing fuel/air ratios has provided a quantitative measure of the parallel roles of acetylene and PAH reactions in soot growth. In parallel, a novel method for minimizing soot as well as nitric oxide emissions by diesel engines is being pursued by Professors Pfeffer and Shaw from NJIT by finding the conditions which favor the soot reactions with nitric oxide over those with oxygen. For purposes of developing for mitigation of VOC precursors to tropospheric ozone Professors Heywood and Hochgreb from MIT have measured engine deposits in-situ, using a new electrical inductance probe and have shown that these deposits play a significant role in the escape of hydrocarbons from engines as a result of adsorption and consequent re-emission by the deposits. Kinetics of blends of oxygenates which pertain to the emissions from engines is being pursued by Professor Bozelli of NJIT. His study of the chemical kinetics of hydrocarbon/oxygenated fuel blends in complementary experimental and theoretical studies has provided the data needed for engine analysis with the surprising result that certain blends of methane and methanol have burning velocities exceeding that of the pure fuel.

Transport and Transformation: One of the lesser understood photochemical processes is that leading to the formation of organic aerosols. The yields of aerosols from hydrocarbons have been obtained, by Professors Seinfeld and Flagan in over 75 outdoor smog chamber experiments at Caltech, and the results are being analyzed using mechanisms developed in a controlled indoor smog chamber. These are being supported by the research of Professor Bozelli at NJIT by the study of aromatics with hydroxyl radicals in the presence of oxygen and nitrogen oxides. Detailed thermodynamic and kinetic pathways for the reactions are being developed that show promising agreement with experiments for the primary products of benzene photochemical reactions, that is an important first step in the aerosol formation mechanism.

Monitoring and Source Apportionment: The problem of obtaining analyses of the trace volatile organic compounds (VOCs) are being pursued by Professors Kebbekus and Mitra of NJIT. They have used selective membrane with canister sampling to concentrate the VOCs to multiples of the levels in the ambient. This has been achieved by reducing water vapor transport into the canister thus reducing a major constraint on the pressures that can be used in sampling without condensation. The mapping of the temporal and spatial distribution of the mutagenic activity in the LA basin has been carried out by Prof. Cass of Caltech utilizing bacterial and human cell mutations carried out at the MIT Center for Environmental Health Sciences. He has shown that the mutagenic activity correlates better with primary emissions from combustion products than with their photochemical transformation products., since the activity is highest near the sources than downwind and higher in winter than in summer. To complement the chemical signatures developed at Caltech for the extractable organic portion of the particles, Professors Vander Sande and Sarofim are generating quantitative measures of the physical and chemical structures of soots using high resolution electron microscopy. The methods show potential for use in both providing insights on the mechanisms of formation and signatures for use in source attribution studies.

Summer Symposia: The third annual Summer Symposium, scheduled with the Science Advisory Committee, meeting was organized by Professors John Heywood of MIT and Robert Sawyer of the University of California, Berkeley (also a member of the SAC) on "Effective Technologies for Reducing Vehicle Emissions." The Symposium brought together many of the key researchers and policy-makers to discuss the status of the emerging technologies for low emission vehicles. Like the first two symposia on the ozone in the North East and the prioritization of hazardous air pollutants, the 1995 Symposium provided opportunities for informal and sometimes spirited discussions between the participants in informal surroundings. The symposium planned for the summer of 1996 is on the next generation of air pollution instrumentation and that for 1997 on the health effects of fine particles.