Interpretation of Secondary Organic Aerosol Formation from Diesel Exhaust Photooxidation in an Environmental Chamber

Secondary organic aerosol (SOA) formation from diesel exhaust was investigated using an environmental chamber. Particle volume measurement based solely on mobility diameter underestimated the SOA formation from diesel exhaust due to the external void space of agglomerate particles. Therefore, particle mass concentration and fractal-like dimension was determined from the particle effective density as a function of particle mass using an aerosol particle mass analyzer and scanning mobility particle sizer (APM–SMPS). Continuous aging of aerosol measured by an increase of atomic ratio (O/C) underscored the importance of multigenerational oxidation of low-volatile organic vapors emitted from diesel engine as a possible significant source of ambient oxygenated SOA. Higher particle effective densities were observed when raw exhaust was injected into a full bag as opposed to filling a bag with diluted exhaust using an ejector diluter. This suggests that the dilution method, in addition to dilution ratio, may impact the evaporation of semivolatile species. This study demonstrates the critical need to evaluate particle mass when evaluating SOA formation onto fractal particles such as diesel exhaust.     

Evaluation of the European PMP Methodologies during On-Road and Chassis Dynamometer Testing for DPF Equipped Heavy-Duty Diesel Vehicles

This study evaluated the UN-ECE Particle Measurement Programme (PMP) protocol for the measurement of solid particle number emissions under laboratory and on-road conditions for two passive diesel particle filters (DPF)–equipped medium and heavy-heavy duty diesel vehicles. The PMP number emissions were lower than the European light-duty certification value (9.6 × 10¹¹ #/mi) for all standardized cycles, but exceeded this value during some higher load on-road driving conditions. Particle number measurements were generally less variable than those of the PM mass for the on-road testing, but had comparable or greater variability than PM mass for the laboratory measurements due to outliers. These outliers appear to be real events that are not apparent with integrated filter methods. The particle number measurements for the low cut point CPCs (3–7 nm) below the PMP system were approximately an order of magnitude higher than those for the PMP-compliant CPC (23 nm), indicating the presence of a large fraction of solid sub-23 nm particles. Although such particles are defined as solid by the PMP method, their actual state is unknown. Nucleation particles with a large sulfate contribution formed under a variety of conditions when the exhaust temperature near the DPF exceeded a “critical” temperature, typically >300°C.     

Review: Epidemiological Basis for Particulate Air Pollution Health Standards

There are now more than 150 published epidemiologic studies of health effects of particulate air pollution and dozens of related literature reviews. This article explores the basic inferences currently being drawn from the literature regarding the epidemiologic evidence particulate pollution induced health effects. Although there is not a complete consensus of opinion, most reviewers conclude that the overall epidemiologic evidence suggests that particulate air pollution, especially fine combustion-source pollution common to many urban and industrial environments, is an important risk factor for cardiopulmonary disease and mortality. Most of the epidemiological effort has focused on effects of acute exposure, but effects of chronic exposure may be more important in terms of overall public health relevance. Some reviewers contend that long-term, repeated exposure likely increases the risk of chronic respiratory disease and the risk of cardiorespiratory mortality. There is more general (but still not unanimous) agreement that short-term exposures to particulate pollution can exacerbate existing cardiovascular and pulmonary disease and increase the number of persons in a population who become symptomatic, require medical attention, or die.     

Toxicity of Dangerous Prey: Variation of Tetrodotoxin Levels Within and Among Populations of the Newt Taricha granulosa

The ability to identify and accurately measure traits at the phenotypic interface of potential coevolutionary interactions is critical in documenting reciprocal evolutionary change between species. We quantify the defensive chemical trait of a prey species, the newt Taricha granulosa, thought to be part of a coevolutionary arms race. Variation in newt toxicity among populations results from variation in levels of the neurotoxin tetrodotoxin (TTX). Individual variation in TTX levels occurs within populations. Although TTX exists as a family of stereoisomers, only two of these (TTX and 6-epi-TTX) are likely to be sufficiently toxic and abundant to play a role in the defensive ecology of the newt.     

Conditions for HCN synthesis and catalyst activation over Pt–Rh gauzes

We have examined different processing conditions for the synthesis of HCN by the ammoxidation of methane over woven Pt–Rh gauzes in an autothermal bench scale reactor. Compared to the conventional air processes, the HCN yield can be improved 10–15% by preheating the reactant gases, and HCN throughput can be increased 140% by removing N₂ from the feed stream. We were able to attain operation in a high pressure bench scale reactor, and HCN yields were maintained above 0.60 up to 3.5 atm at 300% of the throughput achievable at 1 atm.

We also investigated activation of the Pt–Rh gauze catalyst which occurs through facet and pit formation on the metal surface. A high temperature treatment reduced activation times from 30 to 3 h. Pits on the catalyst surface resulted from increased temperatures and NH₃ in the reactant gas, but HCN processing conditions were necessary for the catalyst to achieve best performance.     

Hydrogen-donating mechanism of rosmariquinone, an antioxidant found in rosemary

Rosmariquinone (RQ), an ortho-quinone diterpenoid found in rosemary, was shown to act as a hydrogen-donating antioxidant. The proposed mechanism is based on the isolation of the catechol intermediate arucadiol (AD) in methyl oleate test systems. AD was also observed in a bulk soybean oil oxidation experiment, which supports the observation that RQ is converted to AD during oxidation of the oil. Because AD was found in both light-induced oxidation and autoxidation test systems, the antioxidant mechanism proceeds in a similar manner. The antioxidant activities of RQ and AD were not significantly different in the autoxidation experiments, while AD was a significantly better (P<0.05) antioxidant than RQ in the light-induced oxidation.     

Hydrogen-donating mechanism of rosmariquinone, an antioxidant found in rosemary

Rosmariquinone (RQ), an ortho-quinone diterpenoid found in rosemary, was shown to act as a hydrogen-donating antioxidant. The proposed mechanism is based on the isolation of the catechol intermediate arucadiol (AD) in methyl oleate test systems. AD was also observed in a bulk soybean oil oxidation experiment, which supports the observation that RQ is converted to AD during oxidation of the oil. Because AD was found in both light-induced oxidation and autoxidation test systems, the antioxidant mechanism proceeds in a similar manner. The antioxidant activities of RQ and AD were not significantly different in the autoxidation experiments, while AD was a significantly better (P<0.05) antioxidant than RQ in the light-induced oxidation.     

Structure and Activity of the Thermophilic Tryptophan-6 Halogenase BorH

Flavin-dependent halogenases carry out regioselective aryl halide synthesis in aqueous solution at ambient temperature and neutral pH using benign halide salts, making them attractive catalysts for green chemistry. BorH and BorF, two proteins encoded by the biosynthetic gene cluster for the chlorinated bisindole alkaloid borregomycin A, are the halogenase and flavin reductase subunits of a tryptophan-6-halogenase. Quantitative conversion of l -tryptophan (Trp) to 6-chlorotryptophan could be achieved using 1.2 mol % BorH and 2 mol % BorF. The optimal reaction temperature for Trp chlorination is 45 °C, and the melting temperatures of BorH and BorF are 48 and 50 °C respectively, which are higher than the thermal parameters for most other halogenases previously studied. Steady-state kinetic analysis of Trp chlorination by BorH determined parameters of k_cat=4.42 min⁻¹, and K_M of 9.78 μm at 45 °C. BorH exhibits a broad substrate scope, chlorinating and brominating a variety of aromatic substrates with and without indole groups. Chlorination of Trp at a 100 mg scale with 52 % crude yield, using 0.2 mol % BorH indicates that industrial scale biotransformations using BorH/BorF are feasible. The X-ray crystal structure of BorH with bound Trp provides additional evidence for the model that regioselectivity is determined by substrate positioning in the active site, showing C6 of Trp juxtaposed with the catalytic Lys79 in the same binding pose previously observed in the structure of Thal.