Guidance for the Performance Evaluation of Three-Dimensional Air Quality Modeling Systems for Particulate Matter and Visibility

ABSTRACT

Guidance for the performance evaluation of three-dimensional air quality modeling systems for particulate matter and visibility is presented. Four levels are considered: operational, diagnostic, mechanistic, and probabilistic evaluations. First, a comprehensive model evaluation should be conducted in at least two distinct geographical locations and for several meteorological episodes. Next, streamlined evaluations can be conducted for other similar applications if the comprehensive evaluation is deemed satisfactory. In all cases, the operational evaluation alone is insufficient, and some diagnostic evaluation must always be carried out. Recommendations are provided for designing field measurement programs that can provide the data needed for such model performance evaluations.     

Emission Factors for High-Emitting Vehicles Based on On-Road Measurements of Individual Vehicle Exhaust with a Mobile Measurement Platform

ABSTRACT

Fuel-based emission factors for 143 light-duty gasoline vehicles (LDGVs) and 93 heavy-duty diesel trucks (HDDTs) were measured in Wilmington, CA using a zero-emission mobile measurement platform (MMP). The frequency distributions of emission factors of carbon monoxide (CO), nitrogen oxides (NO_x), and particle mass with aerodynamic diameter below 2.5 μm (PM_2.5) varied widely, whereas the average of the individual vehicle emission factors were comparable to those reported in previous tunnel and remote sensing studies as well as the predictions by Emission Factors (EMFAC) 2007 mobile source emission model for Los Angeles County. Variation in emissions due to different driving modes (idle, low- and high-speed acceleration, low- and high-speed cruise) was found to be relatively small in comparison to intervehicle variability and did not appear to interfere with the identification of high emitters, defined as the vehicles whose emissions were more than 5 times the fleet-average values. Using this definition, approximately 5% of the LDGVs and HDDTs measured were high emitters. Among the 143 LDGVs, the average emission factors of NO_x, black carbon (BC), PM_2.5, and ultrafine particle (UFP) would be reduced by 34%, 39%, 44%, and 31%, respectively, by removing the highest 5% of emitting vehicles, whereas CO emission factor would be reduced by 50%. The emission distributions of the 93 HDDTs measured were even more skewed: approximately half of the NO_x and CO fleet-average emission factors and more than 60% of PM_2.5, UFP, and BC fleet-average emission factors would be reduced by eliminating the highest-emitting 5% HDDTs. Furthermore, high emissions of BC, PM_2.5, and NO_x tended to cluster among the same vehicles.

IMPLICATIONS This study presents the characterization of on-road vehicle emissions in Wilmington, CA, by sampling individual vehicle plumes. Approximately 5% of the vehicles were high emitters, whose emissions were more than 5 times the fleet-average values. These high emitters were responsible for 30% and more than 50% of the average emission factors of LDGVs and HDDVs, respectively. It is likely that as the overall fleet becomes cleaner due to more stringent regulations, a small fraction of the fleet may contribute a growing and disproportionate share of the overall emissions. Therefore, long-term changes in on-road emissions need to be monitored.     

Monitoring and modelling of siloxanes in a sewage treatment plant in the UK

Monitoring of cyclic volatile methylsiloxanes (cVMS) carried out at Anglian Water’s Broadholme sewage treatment plant (STP) is described. The method deployed used headspace gas chromatography/mass spectrometry (HS-GC/MS) and the addition of isotopically labelled cVMS to correct for partitioning in samples containing high levels of particulate and dissolved organic carbon. The method was capable of measuring cVMS in raw sewage samples, with recoveries of 80%, 85% and 71% respectively, for D₄, D₅ and D₆. The limit of quantification was 0.2 μg L⁻¹ for all three substances. Recoveries close to 100% were observed for all cVMS spiked into treated effluent (LOQ = 0.01 μg L⁻¹). Despite the volatile nature of cVMS and its ubiquitous presence in the ambient atmosphere, the methods deployed showed excellent recoveries, reproducibility and quantification limits. A distinct diurnal variation in cVMS concentration, probably linked with the use of personal care products was observed for raw sewage but not in treated sewage effluent. The estimated per capita consumption of D₅ (∼2.7 mg cap⁻¹ d⁻¹) derived for the population served by this plant was significantly lower than that derived in the Environment Agency (UK) risk assessment (11.6 mg cap⁻¹ d⁻¹). The cVMS were highly removed during sewage treatment with efficiencies greater than 98%. The methods and findings of this pilot study can be used as the basis for future studies on the fate of cVMS substances in STPs.     

Biologically directed environmental monitoring, fate, and transport of estrogenic endocrine disrupting compounds in water: A review

Endocrine disrupting compounds (EDCs) are contaminants that may be hormonally active at low concentrations and are emerging as a major concern for water quality. Estrogenic EDCs (e-EDCs) are a subclass of EDCs that, when organisms are exposed to them, function as estrogens. Given that there are numerous e-EDCs that can negatively affect humans and wildlife, general screening techniques like biologically based assays (BBAs) may provide major advantages by estimating the total estrogenic effects of many e-EDCs in the environment. These techniques may potentially be adapted for field portable biologically directed sampling and analyses. This article summarizes available BBAs used to measure estrogenic e-EDCs in the environmental samples and also presents results relating to fate and transport of e-EDCs. Estrogenic EDCs appear to be almost ubiquitous in the environment, despite low solubility and high affinity of organic matter. Potential transport mechanisms may include: (1) transport of more soluble precursors, (2) colloid facilitated transport, (3) enhanced solubility through elevated pH, and (4) the formation of micelles by longer-chain ethoxylates. Due to their persistent and ubiquitous nature, source control strategies for e-EDCs may reduce influent concentration to wastewater treatment plants so that the post treatment effluent will decrease concentrations to estrogenically inactive levels. Alternatively if source reduction is not possible, then more testing is needed on tertiary treatment technologies and treatment efficiencies for e-EDCs. There is still a need for research on remediation and restoration approaches for habitats disturbed by elevated e-EDC concentrations.     

Persistent toxic substances in soils and waters along an altitudinal gradient in the Laja River Basin, Central Southern Chile

In this study the levels and distribution of some persistent toxic substances (PTS) were investigated in soils, superficial water, and snow along an altitudinal gradient in the Laja River Basin (South Central Chile). The principal objective was to establish the basin's contamination status. The working hypothesis was that PTS levels and distribution in the basin are dependent on the degree of anthropogenic intervention. Fifteen PAHs, seven PCBs congeners, and three organochlorine pesticides were studied in superficial soil and water samples obtained along the altitudinal gradient and from a coastal reference station (Lleu-Lleu River). Soil samples were extracted using accelerated solvent extraction with acetone/cyclohexane (1:1) for PAHs and organochlorine compounds. Contaminants were extracted from water and snow samples by liquid-liquid extraction (LLE). PAH and organochlorine compound quantification was carried out by HPLC with fluorescence detection and GC-MS, respectively. PCBs in soils presented four different profiles in the altitudinal gradient, mainly determined by their chlorination degree; these profiles were not observed for the chlorinated pesticides. In general, the detected levels for the analyzed compounds were low for soils when compared with soil data from other remote areas of the world. Higher summation operator PAHs levels in soils were found in the station located at 227 masl (4243 ng g-1 TOC), in a forestry area and near a timber industry, where detected levels were up to eight times higher than the other sampling sites. In general, PAH levels and distribution seems to be dependent on local conditions. No pesticides were detected in surface waters. However, congeners of PCBs were detected in almost all sampling stations with the highest levels being found in Laja Lake waters, where 1.1 ng/l were observed. This concentration is two times higher than values reported for polluted lakes in the Northern Hemisphere. The presence of organochlorine compound in snow sampled at the highest elevation point of the basin is indicative of the transport and atmospheric deposition phenomena of alpha-HCH, gamma-HCH and PCB 52, with values being similar to the levels reported in Canadian snow samples. We conclude that environmental PTS substance levels are in general relatively low, although PAHs may be of concern in some areas of the basin.     

Pharmaceuticals in the river Elbe and its tributaries

Medicinal drugs were found to be ubiquitous in the river Elbe, its tributary the river Saale and in other tributaries at their points of entry into the Elbe. The distribution of concentration peaks along the investigated river stretches provides an indication that they are mainly due to the emission of treated waste water from municipal sewage treatment works. This leads to the conclusion that medicinal substances can be regarded as faecal indicators for water pollution caused by human activity. The main substances found in the Elbe in 1998 were diclofenac, ibuprofen and carbamazepine as well as various antibiotics and lipid regulators in the concentration range of <20-140 ng/l. The more thorough investigations carried out in 1999 and 2000 show that in addition to the drugs (phenazone, isopropyl-phenazone and paracetamol) metabolite concentrations contributed significantly to the total concentration of pharmaceuticals in the Elbe. The metamizole metabolites N-acetyl-4-aminoantipyrine (AAA) and N-formyl-4-aminoantipyrine (FAA) were found in concentrations from <20 to 939 ng/l. A multivariate statistical analysis revealed a high correlation in respect of the distribution of persistent substances. The metoprolol distribution throughout the Saale demonstrated that the tributaries cause either an increase (Weisse Elster, Unstrut, Ilm) or a reduction (Wipper, Bode) in the concentration, depending on the respective load of waste water. Wide scale sampling in Saxony during 2002 showed the ubiquitous occurrence of carbamazepine in surface waters. The ecotoxicological effects of this contamination cannot be assessed at present. This is due to the fact that no legal framework in respect of these medicinal drugs for human consumption has been established and therefore little research and no risk assessment has been carried out. Therefore it is urgently necessary to include at least the quantitatively most significant substances in the new assessment concept of the EC White Paper.     

Metals Associated with Suspended Sediments in Lakes Erie and Ontario, 2000–2002

Sediment traps were deployed in the three major basins of Lake Erie, and the central (Mississauga) basin of Lake Ontario, and refurbished seasonally over the period 2000–2002. In Lake Ontario, sediment down-flux rates and corresponding contaminant down-flux rates were highest in winter during periods of unstratified thermal conditions, and generally increased with depth due to the influence of resuspended bottom sediments during all sampling periods. Lake Ontario suspended sediments exhibited the highest concentrations of metals; concentrations of mercury and lead frequently exceeded guideline values for bottom sediments. Contaminant levels in Lake Ontario suspended sediments were similar to concentrations in bottom sediments in the same area. There was a spatial trend toward higher suspended sediment metals concentrations from the eastern basin to the western basin of Lake Erie, which is similar to the trend in bottom sediment contamination. In the eastern basin of Lake Erie, which is the deepest area of the lake, there was no trend in down-flux rate with depth in 2001; however, down-flux rates increased with depth in 2002. Suspended sediments in the western basin of Lake Erie were determined to be largely resuspended bottom sediments; all western basin samples collected in the study exceeded the guideline value for mercury (0.486 μg/g).     

Aerosol number size distributions within the exhaust plume of a diesel and a gasoline passenger car under on-road conditions and determination of emission factors

A new setup has been developed and built to measure number size distributions of exhaust particles and thermodynamic parameters under real traffic conditions. Measurements have been performed using a diesel and a gasoline passenger car driving with different speeds and engine conditions. Significant number of nucleation mode particles was found only during high load conditions, i.e. high car and engine speeds behind the diesel car. The number concentration of soot mode particles varied within a factor of two for different engine conditions while the concentration of nucleation mode particles varied up to two orders of magnitude. The results show that roadside measurements are still quite different from those behind the tailpipe. Beside dilution transformation processes within the first meter behind the tailpipe also play an important role, such as nucleation and growth. Emission factors were calculated and compared with those obtained by other studies. Emission factors for particles larger than 25 nm (primary emissions) varied within 1.1 × 10¹⁴ km^?1 and 2.7 × 10¹⁴ km^?1 for the diesel car and between 0.6 × 10¹² km^?1 and 3.5 × 10¹² km^?1 for the gasoline car. The advantage of these measurements is the exhaust dilution under atmospheric conditions and the size-resolved measurement technique to divide into primary emitted and secondary formed particles.     

Inhibition of metamorphosis in tadpoles of Xenopus laevis exposed to polybrominated diphenyl ethers (PBDEs)

Tadpoles of the African clawed frog, Xenopus laevis were exposed, beginning at stage 50, to a commercial pentabromodiphenyl ether mixture (DE-71) through the diet. Subsequent experiments were conducted using a single intraperitoneal injection at stage 58 with limited quantities of two purified brominated diphenyl ether (BDE) congeners, BDE47 and BDE99 and DE-71 to determine the relative potency of these BDE congeners within the commercial mixture. Significant inhibition of tail resorption, delayed metamorphosis and impacts on skin pigmentation were observed in Xenopus exposed to DE-71 in the diet at nominal doses of 1000 and 5000 microgg(-1) of food. The estimated time required for 50% of the tadpoles to complete metamorphosis was significantly lengthened in Xenopus exposed to a dietary concentration of 1 microg DE-71 per gram of food. Analysis of PBDEs (sum of 32 congeners) in Xenopus from the treatment with 5000 microgg(-1) of DE-71 indicated that the frogs accumulated an average of 1030 microgg(-1) (wet weight) of PBDEs. In the intraperitoneal injection trials, similar inhibitory responses were observed in Xenopus injected with DE-71 at a nominal dose of 60 microg per tadpole, or injected with BDE47 at a nominal dose of 100 microg per tadpole. No responses were observed in Xenopus injected with BDE99 at doses up to 100 microg per tadpole. Complete inhibition of metamorphosis was observed only in the highest DE-71 dietary treatment. The results of this study are consistent with a mechanism of action of PBDEs involving competitive inhibition of binding of thyroid hormones to transporter proteins, although the mechanism cannot be definitively determined from this study. The observed effects may have occurred through other mechanisms, including sublethal toxicity. The doses used in this study are greater than the levels of PBDEs to which anurans are exposed in the environment, so further studies are required to determine whether exposure to PBDEs at environmentally relevant concentrations can affect frog metamorphosis.     

The detection of drowsiness using a driver monitoring system

Abstract

Objective: Drowsiness is a major cause of driver impairment leading to crashes and fatalities. Research has established the ability to detect drowsiness with various kinds of sensors. We studied drowsy driving in a high-fidelity driving simulator and evaluated the ability of an automotive production-ready driver monitoring system (DMS) to detect drowsy driving. Additionally, this feature was compared to and combined with signals from vehicle-based sensors.

Methods: The National Advanced Driving Simulator was used to expose drivers to long, monotonous drives. Twenty participants drove for about 4?h in the simulator between 10 p.m. and 2 a.m. They were allowed to use cruise control and traffic was sparse and semirandom, with both slower- and faster-moving vehicles. Observational ratings of drowsiness (ORDs) were used as the ground truth for drowsiness, and several dependent measures were calculated from vehicle and DMS signals. Drowsiness classification models were created that used only vehicle signals, only driver monitoring signals, and a combination of the 2 sources.

Results: The model that used DMS signals performed better than the one that used only vehicle signals; however, the combination of the two performed the best. The models were effective at discriminating low levels of drowsiness from moderate to severe drowsiness; however, they were not effective at telling the difference between moderate and severe levels. A binary model that lumped drowsiness into 2 classes had an area under the receiver operating characteristic (ROC) curve of 0.897.

Conclusions: Blinks and saccades have been shown to be predictive of microsleeps; however, it may be that detection of microsleeps and lane departures occurs too late. Therefore, it is encouraging that the model was able to distinguish mild from moderate drowsy driving. The use of automation may make vehicle-based signals useless for characterizing driver states, providing further motivation for a DMS. Future improvements in impairment detection systems may be expected through a combination of improved hardware, physiological measures from unobtrusive sensors and wearables, and the intelligent integration of environmental variables like time of day and time on task.