A study of emissions from a Euro 4 light duty diesel vehicle with the European particulate measurement programme

The California Air Resources Board, CARB, has participated in a program to quantify particulate matter (PM) emissions with a European methodology, which is known as the Particulate Measurement Programme (PMP). The essence of the PMP methodology is that the diesel PM from a Euro 4 vehicle equipped with a Diesel Particulate Filter (DPF) consists primarily of solid particles with a size range greater than 23 nm. The PMP testing and the enhanced testing performed by CARB have enabled an increased understanding of both the progress that has been made in PM reduction, and the future remaining challenges for new and improved DPF-equipped diesel vehicles. A comparison of measured regulated emissions and solid particle number emissions with the results obtained by the PMP participating international laboratories was a success, and CARB’s measurements and standard deviations compared well with the other laboratories. Enhanced measurements of the influence of vehicle conditioning prior to testing on PM mass and solid particle number results were performed, and some significant influences were discovered. For example, the influence of vehicle preconditioning on particle number results was significant for both the European and USA test driving cycles. However, the trends for the cycles were opposite with one cycle showing an increase and the other cycle showing a decrease in particle number emissions. If solid particle size distribution and total particle numbers are to be used as proposed in PMP, then a greater understanding of the quality and errors associated with measurement technologies is advisable.In general, particle counting instruments gave results with similar trends, but cycle-to-cycle testing variation was observed. Continuous measurements of particle number concentrations during test cycles have given detailed insight into PM generation. At the present time there is significant variation in the capabilities of the particle counting instruments in terms of particle size and concentration.Current measurements show the existence of a large number of volatile and semi-volatile particles of yet-to-be-resolved chemical composition in diesel exhaust, especially during DPF regeneration, and these particles are not included in the PMP methodology because they are smaller than 20 nm. It will be very challenging to improve our understanding of this class of diesel particulate matter.     

Persistent elevated nitrate in a riparian zone aquifer

Streamside vegetated buffer strips (riparian zones) are often assumed to be zones of ground water nitrate (NO3(-)) attenuation. At a site in southwestern Ontario (Zorra site), detailed monitoring revealed that elevated NO3(-) -N (4-93 mg L(-1)) persisted throughout a 100-m-wide riparian floodplain. Typical of riparian zones, the site has a soil zone of recent river alluvium that is organic carbon (OC) rich (36 +/- 16 g kg(-1)). This material is underlain by an older glacial outwash aquifer with a much lower OC content (2.3 +/- 2.5 g kg(-1). Examination of NO3(-), Cl(-), SO4(2-), and dissolved organic carbon (DOC) concentrations; N/Cl ratios; and NO3(-) isotopic composition (delta15N and delta18O) provides evidence of four distinct NO3(-) source zones within the riparian environment. Denitrification occurs but is incomplete and is restricted to a narrow interval located within ~0.5 m of the alluvium-aquifer contact and to one zone (poultry manure compost zone) where elevated DOC persists from the source. In older ground water close to the river discharge point, denitrification remains insufficient to substantially deplete NO3(-). Overall, denitrification related specifically to the riparian environment is limited at this site. The persistence of NO3(-) in the aquifer at this site is a consequence of its Pleistocene age and resulting low OC content, in contrast to recent fluvial sediments in modern agricultural terrain, which, even if permeable, usually have zones enriched in labile OC. Thus, sediment age and origin are additional factors that should be considered when assessing the potential for riparian zone denitrification.     

Use of dimethyl sulfoxide as solubilization agent in the detection of 2,3,7,8-TCDD by radioimmunoassay

Immunoassays are potentially valuable tools for use in screening environmental samples for a broad range of contaminants, such as polychlorinated dibenzo-p-dioxins (PCDDs). The performance of the radioimmunoassay (RIA) for PCDDs was characterized using 4 solubilization systems: Cutscum, Triton, horse serum, and dimethyl sulfoxide (DMSO). The DMSO based assay appeared to perform best at low 2,3,7,8-TCDD levels. The effects of assay incubation time and hapten storage conditions on the DMSO based assay were assessed. The separation of bound from unbound radioactivity was accelerated without adversely affecting assay performance. Further assay development through the use of an alternative labelled hapten is considered.     

Nitrogen regulation of the climate-carbon feedback: evidence from a long-term global change experiment

Modeling studies have shown that nitrogen (N) strongly regulates ecosystem responses and feedback to climate warming. However, it remains unclear what mechanisms underlie N regulation of ecosystem-climate interactions. To examine N regulation of ecosystem feedback to climate change, we have conducted a warming and clipping experiment since November 1999 in a tallgrass prairie of the Great Plains, USA. Infrared heaters were used to elevate soil temperature by an average of 1.96 degrees C at a depth of 2.5 cm from 2000 to 2008. Yearly biomass clipping mimicked hay or biofuel feedstock harvest. We measured carbon (C) and N concentrations, estimated their content and C:N ratio in plant, root, litter, and soil pools. Warming significantly stimulated C storage in aboveground plant, root, and litter pools by 17%, 38%, and 29%, respectively, averaged over the nine years (all P < 0.05) but did not change soil C content or N content in any pool. Plant C:N ratio and nitrogen use efficiency increased in the warmed plots compared to the control plots, resulting primarily from increased dominance of C4 plants in the community. Clipping significantly decreased C and N storage in plant and litter pools (all P < 0.05) but did not have interactive effects with warming on either C or N pools over the nine years. Our results suggest that increased ecosystem nitrogen use efficiency via a shift in species composition toward C4 dominance rather than plant N uptake is a key mechanism underlying warming stimulation of plant biomass growth.     

Comparison of methods used to calculate typical threshold values for potentially toxic elements in soil

The environmental quality of land can be assessed by calculating relevant threshold values, which differentiate between concentrations of elements resulting from geogenic and diffuse anthropogenic sources and concentrations generated by point sources of elements. A simple process allowing the calculation of these typical threshold values (TTVs) was applied across a region of highly complex geology (Northern Ireland) to six elements of interest; arsenic, chromium, copper, lead, nickel and vanadium. Three methods for identifying domains (areas where a readily identifiable factor can be shown to control the concentration of an element) were used: k-means cluster analysis, boxplots and empirical cumulative distribution functions (ECDF). The ECDF method was most efficient at determining areas of both elevated and reduced concentrations and was used to identify domains in this investigation. Two statistical methods for calculating normal background concentrations (NBCs) and upper limits of geochemical baseline variation (ULBLs), currently used in conjunction with legislative regimes in the UK and Finland respectively, were applied within each domain. The NBC methodology was constructed to run within a specific legislative framework, and its use on this soil geochemical data set was influenced by the presence of skewed distributions and outliers. In contrast, the ULBL methodology was found to calculate more appropriate TTVs that were generally more conservative than the NBCs. TTVs indicate what a “typical” concentration of an element would be within a defined geographical area and should be considered alongside the risk that each of the elements pose in these areas to determine potential risk to receptors.     

Polybrominated diphenyl ethers and their methoxylated and hydroxylated analogs in Brown Bullhead (Ameiurus nebulosus) plasma from Lake Ontario

Polybrominated diphenyl ethers (PBDEs), methoxylated PBDEs (MeO-PBDEs) and hydroxylated PBDEs (OH-PBDEs) were detected and quantified in Brown Bullhead (Ameiurus nebulosus) from Lake Ontario. Samples were collected in 2006 from three different locations near the city of Toronto: Frenchman’s Bay, Toronto Island, and Tommy Thompson Park. A total of 117 plasma samples were pooled into 19 samples, separating males and females by site of capture. Pooled samples were analyzed for 36 PBDEs, 20 MeO-PBDEs and 20 OH-PBDEs, but only six PBDEs, five MeO- and eight OH-compounds were confirmed against standards currently available. These peaks were quantified as “identified” peaks, while peaks matching ion ratios but not matching the retention time of the available standards were quantified as “unidentified” peaks. Both “identified” and “unidentified” concentrations were combined to obtain a total concentration. No significant variations were obtained for total PBDE concentrations, ranging from 3.33 to 9.02 ng g^?1 wet weight. However, OH- and MeO-PBDE totals ranged over 1 order of magnitude among the samples (not detected – 3.57 ng g^?1 wet weight for OH-PBDEs and not detected ?0.10 ng/g wet weight for MeO-PBDE). The results of this study suggested that these compounds are ubiquitous in biota. Source estimation of MeO- and OH-PBDEs in freshwater fish were discussed. Considering that up to date no freshwater sources for MeO- or OH-PBDEs have been reported, concentrations found should be mainly related to bioaccumulation from anthropogenic sources, although other sources could not be dismissed.     

Grouping Lakes for Water Quality Assessment and Monitoring: The Roles of Regionalization and Spatial Scale

Regionalization frameworks cluster geographic data to create contiguous regions of similar climate, geology and hydrology by delineating land into discrete regions, such as ecoregions or watersheds, often at several spatial scales. Although most regionalization schemes were not originally designed for aquatic ecosystem classification or management, they are often used for such purposes, with surprisingly few explicit tests of the relative ability of different regionalization frameworks to group lakes for water quality monitoring and assessment. We examined which of 11 different lake grouping schemes at two spatial scales best captures the maximum amount of variation in water quality among regions for total nutrients, water clarity, chlorophyll, overall trophic state, and alkalinity in 479 lakes in Michigan (USA). We conducted analyses on two data sets: one that included all lakes and one that included only minimally disturbed lakes. Using hierarchical linear models that partitioned total variance into within-region and among-region components, we found that ecological drainage units and 8-digit hydrologic units most consistently captured among-region heterogeneity at their respective spatial scales using all lakes (variation among lake groups = 3% to 50% and 12% to 52%, respectively). However, regionalization schemes capture less among-region variance for minimally disturbed lakes. Diagnostics of spatial autocorrelation provided insight into the relative performance of regionalization frameworks but also demonstrated that region size is only partly responsible for capturing variation among lakes. These results suggest that regionalization schemes can provide useful frameworks for lake water quality assessment and monitoring but that we must identify the appropriate spatial scale for the questions being asked, the type of management applied, and the metrics being assessed.