There is growing evidence that fine airborne particulates could play the most important role in determining health effects. The aim of this work was to investigate the number concentration and size distributions of particulates in the exhausts of diesel vehicles (mainly buses) of different ages and make, operating under different loads. Particlesizing instruments used were the Scanning Mobility Particle Sizer (SMPS) and Aerodynamic Particle Sizer (APS). The average particle number concentration of the exhausts was in the range (0.7-3.9) × 10 7 cm -3 in the SMPS range (0.0075-0.304 µm) and (0.3-32) × 10 3 cm -3 in the APS range (0.5-30 µm). In most cases, particle number concentrations increased with the increased power output from the engine and, in both SMPS and APS ranges, varied significantly within each group of vehicles, but the differences between the groups were small. For individual vehicles, there was no relation between emissions in the smaller and larger particle ranges. Emission characteristics did not appear to be correlated with engine model or age. The implications of these findings to particle emission testing and control as well as to exposure and risk analysis are discussed.

[1] Two secondary organic aerosol (SOA) formation modules have been implemented into a global chemical transport model (Model for Ozone And Related chemical Tracers, Version 2) to estimate the global distribution of SOA and to compare between methods. The first SOA model is based on bulk smog chamber yields while the second uses the gas to particle partitioning theory to predict SOA concentrations. Maximum SOA concentrations using the bulk yield method were found to vary up to 10 mg/m 3 with concentrations peaking over the southeast United States, Europe, South America, central Africa, and southern Asia. Maximum SOA concentrations were found over the Northern Hemisphere (NH) and tropics in June while SOA concentrations in the tropics remained high through December. SOA production was found to be dependant on oxidant availability rather than volatile organic compound emissions in South America and Asia. Using the partitioning model, SOA concentrations peaked at 10 mg/m 3 over South America in September related to organic carbon aerosol availability. The partitioning model produced significantly less SOA during the NH summer, and SOA production was found to be dependant on organic carbon primary aerosol and oxidant availability for South America and Asia. The total annual global production of SOA was calculated to be 24.6 Tg/yr using the bulk yield method and 15.3 Tg/yr using the partitioning method.

Particulate emissions from 11 gasoline-powered and 2 liquefied petroleum (LPG)-powered passenger vehicles were characterized during the Accelerated Simulation Mode driving cycles on a chassis dynamometer. The test fleet consisted of 10 catalyst-equipped vehicles operated with unleaded gasoline (5 Ford Falcons and 5 Holden Commodores), 2 LPG-powered vehicles (both Ford Falcons), and 1 older type noncatalyst vehicle operated with leaded gasoline. Particulate characterization included determination of total particulate number concentration and size distribution using the scanning mobility particle sizer (SMPS) and the aerodynamic particle sizer (APS). The average particle number concentrations in the SMPS range for all modes was lower for Ford Falcons and somewhat higher for Commodores, with values of 1.5 × 10 4 and 4.1 × 10 4 cm -3 , respectively. This difference is significant and was observed for all modes. The number concentration levels were higher for the LPG-fueled cars (8.4 × 10 4 cm -3 ) and for the leaded gasoline-powered vehicle (7.9 × 10 5 cm -3 ). There was not a significant variation in particle count median diameter in the SMPS and the APS ranges, either for different operating conditions of the vehicles investigated or between different vehicle groups. The observed size distributions were bimodal with average values of CMD ranging from 39.1 to 60.2 nm in the SMPS range and from 0.9 to 1.4 µm in the APS range. The results obtained from this study can be used as a firstorder estimation toward emission inventories for vehicle groups included in the investigations.

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A set of chemical reactions is postulated to account for the formation of the macrocyclic porphin structure, basic to the pyrrole derivatives chlorophyll, protoporphyrin, heme and bilirubin, important in photosynthesis, respiration and digestion. A set of equations is given for the prebiotic synthesis of porphin derivatives from the simple molecules; cyanoacetylene, diacetylene, carbon monoxide and ammonia that have been detected in space. A number of isomers of hydrogenated porphin arise which may lose hydrogen to give ultimately porphin and its dehydrogenated derivative. The reactions, while not unique, provide a pathway which has been shown to be feasible from the overall enthalpy changes in the ZKE approximation at the HF and MP2/6-31G* level.