Diesel exhaust particles (DEP) are a major constituent of ambient air pollution and are associated with various adverse health effects, posing a major safety and public health concern in ambient and occupational environments. The effects of DEP from various biodiesel blends on biological systems was investigated using glutathione (GSH) as a marker of possible oxidative effects, based on the decrease in the concentration of GSH at physiological pH. The fluorophoric agent 2,3-naphthalenedicarboxaldehyde (NDA) was used as a selective probe of GSH in the presence of any likely interferents via fluorescence detection. Three different polar solvents (acetonitrile, methanol and water) were used to extract DEP generated during the combustion of different biodiesel blends (5%–99%). Oxidation of GSH to the disulfide (GSSG) was confirmed using electrospray ionization mass spectrometry.A decrease in the concentration of GSH was observed in the presence of DEP extracts from all of the biodiesel blends studied, with reaction rates that depend on the biodiesel blend. Interestingly the reactivity peaked at 50% biodiesel (B50) rather than decreasing monotonically with increased biodiesel content, as was expected. Organic solvent DEP extracts showed wider variations in reactivity with GSH, with methanol extracts giving the largest decrease in GSH concentrations. This may imply a more organic nature of the oxidants in the biodiesel exhaust. It is therefore important to consider ways of reducing concentrations of organic components in biodiesel exhaust that can cause different toxic activity before any blend is offered as a preferred alternative to petroleum diesel fuel.

Extensive aerosol optical properties, particle size distributions, and Aerodyne quadrupole aerosol mass spectrometer measurements collected during TRAMP/TexAQS 2006 were examined in light of collocated meteorological and chemical measurements. Much of the evident variability in the observed aerosol-related air quality is due to changing synoptic meteorological situations that direct emissions from various sources to the TRAMP site near the center of the Houston-Galveston-Brazoria (HGB) metropolitan area. In this study, five distinct long-term periods have been identified. During each of these periods, observed aerosol properties have implications that are of interest to environmental quality management agencies. During three of the periods, long range transport (LRT), both intra-continental and intercontinental, appears to have played an important role in producing the observed aerosol. During late August 2006, southerly winds brought super-micron Saharan dust and sea salt to the HGB area, adding mass to fine particulate matter (PM2.5) measurements, but apparently not affecting secondary particle growth or gas-phase air pollution. A second type of LRT was associated with northerly winds in early September 2006 and with increased ozone and sub-micron particulate matter in the HGB area. Later in the study, LRT of emissions from wildfires appeared to increase the abundance of absorbing aerosols (and carbon monoxide and other chemical tracers) in the HGB area. However, the greatest impacts on Houston PM2.5 air quality are caused by periods with low-wind-speed sea breeze circulation or winds that directly transport pollutants from major industrial areas, i.e., the Houston Ship Channel, into the city center.

A pulsed cavity ring-down transmissometer is shown here to be capable of sensitively measuring the aerosol extinction coefficient at two wavelengths (lambda = 532, 1064 nm) simultaneously. This instrument can be coupled with a nephelometer (yielding a measurement of the 530 nm scattering coefficient of the same aerosol) and a particle counter to allow the in situ measurement of extensive and intensive optical properties and particle number concentrations of aerosols. From the scattering and extinction coefficient measurements, the aerosol absorption coefficient can be calculated and the intensive properties single scattering albedo and extinction Angstrom exponent can be determined. In this report, the pulsed cavity-ring down transmissometer (CRDT) is validated through a series of laboratory experiments. Agreement between the extinction coefficients from the cavity ring-down transmissometer and the scattering coefficient from the nephelometer is demonstrated for purely scattering sub-micron particles. Then agreement between measured extinction and Mie theory is demonstrated when using size-selected particles of measured number concentration. The agreement with Mie theory ranges from excellent (less than 1% deviation) to marginal (12%) depending on the particle size and composition. Similar deviations from Mie theory have been observed (Baynard et al. 2007) and we suggest that they could be due to the influence of multiply charged particles in the size-selection (DMA) process. The 95% confidence level limits of detection and quantitation for the extinction measurement by the CRD transmissometer are estimated to be b(ext) = 4.0 Mm(-1) and 13.4 Mm(-1), respectively (Skoog et al. 2004).