Traffic generated non-exhaust particulate emissions from concrete pavement: A mass and particle size study for two-wheelers and small cars

This study aimed to understand the non-exhaust (NE) emission of particles from wear of summer tire and concrete pavement, especially for two wheelers and small cars. A fully enclosed laboratory-scale model was fabricated to simulate road tire interaction with a facility to collect particles in different sizes. A road was cast using the M-45 concrete mixture and the centrifugal casting method. It was observed that emission of large particle non exhaust emission (LPNE) as well as PM₁₀ and PM_2.5 increased with increasing load. The LPNE was 3.5 mg tire⁻¹ km⁻¹ for a two wheeler and 6.4 mg tire⁻¹ km⁻¹ for a small car. The LPNE can lead to water pollution through water run-off from the roads. The contribution of the PM₁₀ and PM_2.5 was smaller compared to the LPNE particles (less than 0.1%). About 32 percent of particle mass of PM₁₀ was present below 1 μm. The number as well as mass size distribution for PM₁₀ was observed to be bi-modal with peaks at 0.3 μm and 4–5 μm. The NE emissions did not show any significant trend with change in tire pressure.     

Evaluation of methods for the physical characterization of the fine particle emissions from two residential wood combustion appliances

The fine particle emissions from a U. S. certified non-catalytic wood stove and a zero-clearance fireplace burning Quercus rubra L. (northern red oak) and Pseudotsuga menziesii (Douglas fir) cordwood each at two different moisture levels were determined. Emission testing was performed using both time-integrated and continuous instrumentation for total particle mass, particle number, particle size distribution, and fixed combustion gases using an atmospheric wind tunnel, full-flow laboratory dilution tunnel, and dilution stack sampler with a comparison made between the three dilution systems and two sampling filter types. The total mass emission factors (EFs) for all dilution systems and filter media are extremely variable ranging from <1 to 55 g kg⁻¹ of dry wood depending on the combination of appliance type, wood species and moisture content, filter medium, and dilution system. For Teflon filter sampling of stove emissions in the wind tunnel, the total mass EFs varied from 2 to 8 g kg⁻¹ of dry fuel depending on wood type whereas the equivalent fireplace emissions burning wet oak averaged 11 g kg⁻¹. A substantial number of ultrafine particles in the accumulation size range were also observed during all tests as determined by an Electrical Low Pressure Impactor (ELPI) and Scanning Mobility Particle Sizer. The PM-2.5 (particles ≤2.5 μm in aerodynamic diameter) fractions determined from the ELPI electrometer data ranged from 93 to 98% (mass) depending on appliance type as reported previously by Hays et al. (Aerosol Science, 34, 1061, 2003).     

Exposure of acid aerosol for schoolchildren in metropolitan Taipei

Metropolitan Taipei, which is located in the subtropical area, is characterized by high population and automobile densities. For convenience, most primary schools are located near major roads. This study explores the exposure of acid aerosols for schoolchildren in areas in Taipei with different traffic densities. Acid aerosols were collected by using a honeycomb denuder filter pack sampling system (HDS). Experimental results indicated that the air pollutants were significantly correlated with traffic densities. The ambient air NO₂, SO₂, HNO₃, NO₃⁻, SO₄²⁻, and aerosol acidity concentrations were 31.3 ppb, 4.7 ppb, 1.3 ppb, 1.9 μg m⁻³, 18.5 μg m⁻³, and 49.5 nmol m⁻³ in high traffic density areas, and 6.1 ppb, 1.8 ppb, 0.9 ppb, 0.7 μg m⁻³, 8.8 μg m⁻³ and 14.7 nmol m⁻³ in low traffic density areas. The exposure levels of acid aerosols for schoolchildren would be higher than the measurements because the sampling height was 5 m above the ground. The SO₂ levels were low (0.13–8.03 ppb) in the metropolitan Taipei. However, the SO₄²⁻ concentrations were relatively high, and might be attributed to natural emissions of sulfur-rich geothermal sources. The seasonal variations of acid aerosol concentrations were also observed. The high levels of acidic particles in spring time may be attributed to the Asian dust storm and low height of the mixture layer. We conclude that automobile contributed not only the primary pollutants but also the secondary acid aerosols through the photochemical reaction. Schoolchildren were exposed to twice the acid aerosol concentrations in high traffic density areas compared to those in low traffic density areas. The incidence of allergic rhinitis of schoolchildren in the high traffic density areas was the highest in spring time. Accompanied by high temperature variation and high levels of air pollution in spring, the health risk of schoolchildren had been observed.     

Biogeochemistry of two types of permeable reactive barriers, organic carbon and iron-bearing organic carbon for mine drainage treatment: Column experiments

Permeable reactive barriers (PRBs) are an alternative technology to treat mine drainage containing sulfate and heavy metals. Two column experiments were conducted to assess the suitability of an organic carbon (OC) based reactive mixture and an Fe⁰-bearing organic carbon (FeOC) based reactive mixture, under controlled groundwater flow conditions. The organic carbon mixture contains about 30% (volume) organic carbon (composted leaf mulch) and 70% (volume) sand and gravel. The Fe⁰-bearing organic carbon mixture contains 10% (volume) zero-valent iron, 20% (volume) organic carbon, 10% (volume) limestone, and 60% (volume) sand and gravel. Simulated groundwater containing 380 ppm sulfate, 5 ppm As, and 0.5 ppm Sb was passed through the columns at flow rates of 64 (the OC column) and 62 (the FeOC column) ml d^− 1, which are equivalent to 0.79 (the OC column) and 0.78 (the FeOC column) pore volumes (PVs) per week or 0.046 m d^− 1 for both columns. The OC column showed an initial sulfate reduction rate of 0.4 µmol g (OC)^− 1 d^− 1 and exhausted its capacity to promote sulfate reduction after 30 PVs, or 9 months of flow. The FeOC column sustained a relatively constant sulfate reduction rate of 0.9 µmol g (OC)^− 1 d^− 1 for at least 65 PVs (17 months). In the FeOC column, the δ³⁴S values increase with the decreasing sulfate concentration. The δ³⁴S fractionation follows a Rayleigh fractionation model with an enrichment factor of 21.6‰. The performance decline of the OC column was caused by the depletion of substrate or electron donor. The cathodic production of H₂ by anaerobic corrosion of Fe probably sustained a higher level of SRB activity in the FeOC column. These results suggest that zero-valent iron can be used to provide an electron donor in sulfate reducing PRBs. A sharp increase in the δ¹³C value of the dissolved inorganic carbon and a decrease in the concentration of HCO₃⁻ indicate that hydrogenotrophic methanogenesis is occurring in the first 15 cm of the FeOC column.     

Concentrations and elemental composition of particulate matter in the Buenos Aires underground system

Total suspended particulate (TSP) samples have been collected at six stations in the C and B lines of the Buenos Aires underground system and, almost simultaneously, at six ground level sites outside and nearby the corresponding underground stations, in the Oct 2005/Oct 2006 period. All these samples were analyzed for mass and elemental Fe, Cu, and Zn concentrations by using the Particle Induced X-ray Emission (PIXE) technique. Mostly, TSP concentrations were found to be between 152 μg m⁻³ (25% percentile) and 270 μg m⁻³ (75% percentile) in the platform of the stations, while those in outside ambient air oscillated from 55 μg m⁻³ (25% percentile) to 137 μg m⁻³ (75% percentile). Moreover, experimental results indicate that TSP levels are comparable to those measured for other underground systems worldwide. Statistical results demonstrate that subway TSP levels are about 3 times larger on average than those for urban ambient air. The TSP levels inside stations and outdoors are poorly correlated, indicating that TSP levels in the metro system are mainly influenced by internal sources.Regarding metal concentrations, the most enriched element in TSP samples was Fe, the levels of which ranged from 36 (25% percentile) to 86 μg m⁻³ (75% percentile) in Line C stations, while in Line B ones they varied between 8 μg m⁻³ (25% percentile) and 46 μg m⁻³ (75% percentile). As a comparison, Fe concentrations in ambient air oscillated between 0.7 μg m⁻³ (25% percentile) and 1.2 μg m⁻³ (75% percentile). Other enriched elements include Cu and Zn. With regard to their sources, Fe and Cu have been related to processes taking place inside the subway system, while Zn has been associated with outdoor vehicular traffic. Additionally, concerns about possible health implications based on comparisons to various indoor air quality limits and available toxicological information are discussed.     

Experiments probing the influence of air exchange rates on secondary organic aerosols derived from indoor chemistry

Reactions between ozone and terpenes have been shown to increase the concentrations of submicron particles in indoor settings. The present study was designed to examine the influence of air exchange rates on the concentrations of these secondary organic aerosols as well as on the evolution of their particle size distributions. The experiments were performed in a manipulated office setting containing a constant source of d-limonene and an ozone generator that was remotely turned “on” or “off” at 6 h intervals. The particle number concentrations were monitored using an optical particle counter with eight-channels ranging from 0.1–0.2 to>2.0 μm diameter. The air exchange rates during the experiments were either high (working hours) or low (non-working hours) and ranged from 1.6 to>12 h⁻¹, with intermediate exchange rates. Given the emission rates of ozone and d-limonene used in these studies, at an air exchange rate of 1.6 h⁻¹ particle number concentration in the 0.1–0.2 μm size-range peaked 1.2 h after the ozone generator was switched on. In the ensuing 4.8 h particle counts increased in successive size-ranges up to the 0.5–0.7 μm diameter range. At higher air exchange rates, the resulting concentrations of total particles and particle mass (calculated from particle counts) were smaller, and at exchange rates exceeding 12 h⁻¹, no excess particle formation was detectable with the instrument used in this study. Particle size evolved through accretion and, in some cases, coagulation. There was evidence for coagulation among particles in the smallest size-range at low air exchange rates (high particle concentrations) but no evidence of coagulation was apparent at higher air exchange rates (lower particle concentrations). At higher air exchange rates the particle count or size distributions were shifted towards smaller particle diameters and less time was required to achieve the maximum concentration in each of the size-ranges where discernable particle growth occurred. These results illustrate still another way in which ventilation affects human exposures in indoor settings. However, the ultimate effects of these exposures on health and well being remain to be determined.     

Effects of field-applied composted cattle manure and chemical fertilizer on ammonia and particulate ammonium exchanges at an upland field

The present study aimed to investigate the NH₃ volatilization loss from field-applied compost and chemical fertilizer and evaluate the atmosphere–land exchange of NH₃ and particulate NH₄⁺ (pNH₄) at an upland field with volcanic ash soil (Andosol) in Hokkaido, northern Japan. Two-step basal fertilization was conducted on the bare soil surface. First, a moderately fermented compost of cattle manure was applied by surface incorporation (mixing depth, 0–15 cm) at a rate of 117 kg N ha⁻¹ as total nitrogen (T-N) corresponding to 9.9 kg N ha⁻¹ as ammoniacal nitrogen (NH₄–N). Twelve days later, a chemical fertilizer containing 10% (w/w) of NH₄–N as a mixture of ammonium sulfate and ammonium phosphates was applied by row placement (cover depth, 3 cm) at a rate of 100 kg N ha⁻¹ as NH₄–N. The study period was divided into the first-half, beginning after the compost application (CCM period), and the second-half, beginning after the chemical fertilizer application (CF period). The mean air concentrations of NH₃ and pNH₄ (1.5 m height) were 7.6 and 3.0 μg N m⁻³, respectively, in the CCM period; the values were 3.7 and 3.9 μg N m⁻³, respectively, in the CF period. The composition ratios of NH₃ to the sum of NH₃ and pNH₄ (1.5 m height) were 72% and 49% in the CCM and CF periods, respectively. The NH₃ volatilization loss from the compost was 0.8% of the applied T-N (or 9.3% of the applied NH₄–N) and that from the chemical fertilizer was near zero. Excluding the period immediately after the compost application, the upland field acted as a net sink for NH₃ and pNH₄.     

The algal toxicity of silver engineered nanoparticles and detoxification by exopolymeric substances

In this study, we report that silver ions (Ag⁺) from the oxidative dissolution of silver engineered nanoparticles (Ag-ENs) determined the EN toxicity to the marine diatom Thalassiosira weissflogii. Most of the Ag-ENs formed non-toxic aggregates (>0.22 μm) in seawater. When the free Ag⁺ concentration ([Ag⁺]_F) was greatly reduced by diafiltration or thiol complexation, no toxicity was observed, even though the Ag-ENs were better dispersed in the presence of thiols with up to 1.08 × 10⁻⁵ M Ag-ENs found in the <0.22 μm fraction, which are orders of magnitude higher than predicted for the natural aquatic environment. The secretion of polysaccharide-rich algal exopolymeric substances (EPS) significantly increased at increasing [Ag⁺]_F. Both dissolved and particulate polysaccharide concentrations were higher for nutrient-limited cells, coinciding with their higher Ag⁺ tolerance, suggesting that EPS may be involved in Ag⁺ detoxification.     

Estimates of AOT ozone indices from time-integrated ozone data and hourly air temperature measurements in southwest Sweden

Surface ozone concentration and surface air temperature was measured hourly at three coastal sites, four low elevation inland sites and two high elevation inland sites in southwestern Sweden. Diurnal ozone concentration range (DOR) and diurnal temperature range (DTR) were strongly correlated, both spatially and temporally, most likely because both depended on atmospheric stability. Accumulated ozone exposure above a threshold concentration of x nmol mol⁻¹ (AOTx) was estimated from time-integrated ozone concentration (as from diffusive sampling) and measures of ozone concentration variability. Two methods both estimated 24-h AOTx with high accuracy (modelling efficiencies >90% for x ≤ 40 nmol mol⁻¹). Daytime (08:00–20:00) AOTx could not be equally well estimated. Estimates were better for lower AOT thresholds. Diffusive ozone concentration sampling, combined with hourly temperature monitoring, could be a valuable complement to ozone concentration monitoring with continuous instruments.     

A new direct thermal desorption-GC/MS method: Organic speciation of ambient particulate matter collected in Golden, BC

Particulate matter having an aerodynamic diameter less than 2.5 μm (PM2.5) is thought to be implicated in a number of medical conditions, including cancer, rheumatoid arthritis, heart attack, and aging. However, very little chemical speciation data is available for the organic fraction of ambient aerosols. A new direct thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) method was developed for the analysis of the organic fraction of PM2.5. Samples were collected in Golden, British Columbia, over a 15-month period. n-Alkanes constituted 33–98% by mass of the organic compounds identified. PAHs accounted for 1–65% and biomarkers (hopanes and steranes) 1–8% of the organic mass. Annual mean concentrations were: n-alkanes (0.07–1.55 ng m⁻³), 16 PAHs (0.02–1.83 ng m⁻³), and biomarkers (0.02–0.18 ng m⁻³). Daily levels of these organics were 4.89–74.38 ng m⁻³, 0.27–100.24 ng m⁻³, 0.14–4.39 ng m⁻³, respectively. Ratios of organic carbon to elemental carbon (OC/EC) and trends over time were similar to those observed for PM2.5. There was no clear seasonal variation in the distribution of petroleum biomarkers, but elevated levels of other organic species were observed during the winter. Strong correlations between PAHs and EC, and between petroleum biomarkers and EC, suggest a common emission source – most likely motor vehicles and space heating.     

Volcanic sulphate and arctic dust plumes over the North Atlantic Ocean

High time resolution aerosol mass spectrometry measurements were conducted during a field campaign at Mace Head Research Station, Ireland, in June 2007. Observations on one particular day of the campaign clearly indicated advection of aerosol from volcanoes and desert plains in Iceland which could be traced with NOAA Hysplit air mass back trajectories and satellite images. In conjunction with this event, elevated levels of sulphate and light absorbing particles were encountered at Mace Head. While sulphate concentration was continuously increasing, nitrate levels remained low indicating no significant contribution from anthropogenic pollutants. Sulphate concentration increased about 3.8 μg m⁻³ in comparison with the background conditions. Corresponding sulphur flux from volcanic emissions was estimated to about 0.3 TgS yr⁻¹, suggesting that a large amount of sulphur released from Icelandic volcanoes may be distributed over distances larger than 1000 km. Overall, our results corroborate that transport of volcanogenic sulphate and dust particles can significantly change the chemical composition, size distribution, and optical properties of aerosol over the North Atlantic Ocean and should be considered accordingly by regional climate models.     

Determination of soil content in chlordecone (organochlorine pesticide) using near infrared reflectance spectroscopy (NIRS)

Chlordecone is a toxic organochlorine insecticide that was used in banana plantations until 1993 in the French West Indies. This study aimed at assessing the potential of near infrared reflectance spectroscopy (NIRS) for determining chlordecone content in Andosols, Nitisols and Ferralsols from Martinique. Using partial least square regression, chlordecone content conventionally determined through gas chromatography–mass spectrometry could be correctly predicted by NIRS (Q² = 0.75, R² = 0.82 for the total set), especially for samples with chlordecone content <12 mg kg⁻¹ or when the sample set was rather homogeneous (Q² = 0.91, R² = 0.82 for the Andosols). Conventional measures and NIRS predictions were poorly correlated for chlordecone content >12 mg kg⁻¹, nevertheless ca. 80% samples were correctly predicted when the set was divided into three or four classes of chlordecone content. Thus NIRS could be considered a time- and cost-effective method for characterising soil contamination by chlordecone.     

Particle size distributions and health-related exposures of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) of sinter plant workers

This study measured particle size distributions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in two workplace atmospheres of the sintering grate and rough roll shredder in a sintering plant, and to assess their workers’ health-related exposures. We found that the PCDD/F concentration of the sintering grate (site A = 14.47 pg m⁻³) was lower than that of the rough roll shredder (site B = 17.20 pg m⁻³). Particle size distributions of PCDD/Fs were in the form of the unimodal with the mass median aerodynamic diameter (MMAD) of 4.74 μm and 5.23 μm, and geometric standard deviation (σ_g) of 3.15 and 2.15 for the site A and B, respectively. The above results suggest that the workplace of the site A had a less fraction of coarse particles than that of the site B. The estimated PCDD/F concentrations of the inhalable fraction (11.0 pg m⁻³) and thoracic fraction (8.89 pg m⁻³) of the site A were lower than those of the site B (12.4 and 9.39 pg m⁻³, respectively). But to the contrary the estimated respirable fraction of the site A (5.05 pg m⁻³) was slightly higher than that of the site B (4.93 pg m⁻³). Our results clearly indicate the importance to conduct particle size segregating samplings for assessing human PCDD/F exposures.     

An assessment of indoor air quality in recent Mexican immigrant housing in Commerce City, Colorado

An indoor air quality assessment was conducted on 100 homes of recent Mexican immigrants in Commerce City, Colorado, an urban industrial community north of Denver. Head of households were administered a family health survey, filled out an activity diary, and participated in a home inspection. Carbon monoxide (CO) and carbon dioxide (CO₂) were measured for 24 h inside the main living area and outside of the homes. Harvard Impactors were used to collect 24-h samples of PM_2.5 at the same locations for gravimetric analysis. Dust samples were collected by vacuuming carpeting and flooring at four locations within the home and analyzed by ELISA for seven allergens. Mean indoor and outdoor PM_2.5 levels were 27.2 and 8.5 μg m⁻³, respectively. Indoor PM_2.5 and CO₂ were elevated in homes for which the number of hours with door/window open was zero compared to homes in which the number of hours was high (>15 h). Indoor PM_2.5 levels did not correlate with outdoor levels and tended to increase with number of inhabitants, and results indicate that the source of indoor particles were occupants and their activities, excluding smoking and cooking. Mean indoor CO₂ and CO levels were 1170 and 2.4 ppm, respectively. Carbon monoxide was higher than the 24-h National Ambient Air Quality Standard in 3 of the homes. The predominant allergens were cat (Fel d 1) and mouse (Mus m 1) allergens, found in 20 and 34 homes, respectively.     

Assessment of traffic-related air pollution in the urban streets before and during the 2008 Beijing Olympic Games traffic control period

In order to investigate the air quality and the abatement of traffic-related pollution during the 2008 Olympic Games, we select 12 avenues in the urban area of Beijing to calculate the concentrations of PM₁₀, CO, NO₂ and O₃ before and during the Olympic traffic controlling days, with the OSPM model.Through comparing the modeled results with the measurement results on a representative street, the OSPM model is validated as sufficient to predict the average concentrations of these pollutants at street level, and also reflects their daily variations well, i.e. CO presents the similar double peaks as the traffic flow, PM₁₀ concentration is influenced by other sources. Meanwhile, the model predicts O₃ to stay less during the daytime and ascend in the night, just opposite to NO₂, which reveals the impact of photochemical reactions. In addition, the predicted concentrations on the windward side often exceed the leeward side, indicating the impact of the special street shape, as well as the wind.The comparison between the predicted street concentrations before and during the Olympic traffic control period shows that the overall on-road air quality was improved effectively, due to the 32.3% traffic flow reduction. The concentrations of PM₁₀, CO and NO₂ have reduced from 142.6 μg m⁻³, 3.02 mg m⁻³ and 118.7 μg m⁻³ to 102.0 μg m⁻³, 2.43 mg m⁻³ and 104.1 μg m⁻³. However, the different pollutants show diverse changes after the traffic control. PM₁₀ decreases most, and the reduction effect focusing on the first half-day even clears the morning peak, whereas CO and NO₂ have even reductions to minify the daily fluctuations on the whole. Opposite to the other pollutants, ozone shows an increase of concentration. The average reduction rate of PM₁₀, CO, NO₂ and O₃ are respectively 28%, 19.3%, 12.3% and −25.2%. Furthermore, the streets in east, west, south and north areas present different air quality improvements, probably induced by the varied background pollution in different regions around Beijing, along with the impact of wind force. This finding suggests the pollution control in the surrounding regions, not only in the urban area.     

Modeling traffic air pollution in street canyons in New York City for intra-urban exposure assessment in the US Multi-Ethnic Study of atherosclerosis and air pollution

We evaluated the Danish AirGIS air quality and exposure model system using air quality measurement data from New York City in the Multi-Ethnic Study of Atherosclerosis and Air Pollution (MESA Air). Measurements were used from three US EPA Air Quality System (AQS) monitoring stations and a comprehensive MESA Air measurement campaign including about 150 different locations and about 650 samples of about 2 week measurements of NO_x, NO₂ and PM_2.5. AirGIS is a deterministic exposure model system based on the dispersion models Operational Street Pollution Model (OSPM) and the Urban Background Model (UBM). The UBM model reproduced the annual levels within 1–26% depending on station and pollutant at the three urban background EPA monitor stations, and generally reproduced well the seasonal and diurnal variation. The full model with OSPM and UBM reproduced the MESA Air measurements with a correlation coefficient of r² = 0.51 for NO_x, r² = 0.28 for NO₂ and r² = 0.73 for PM_2.5.     

Variation of particle number and mass concentration in various size ranges of ambient aerosols in Eastern Germany

There is an ongoing debate on the question which size fraction of particles in ambient air may be responsible for short-term responses of the respiratory system as observed in several epidemiological studies. However, the available data on ambient particle concentrations in various size ranges are not sufficient to answer this question.Therefore, on 180 days during the winter 1991/92 daily mean size distributions of ambient particles were determined in. Erfurt, a city in Eastern Germany. In the range 0.01–0.3 μm particles were classified by an electrical mobility analyzer and in the range 0.1–2.5 μm by an optical particle counter. From the derived size distributions, number and mass concentrations were calculated.The mean number concentration over this period of time was governed by particles smaller than 0.1 μm (72%), whereas the mean mass concentration was governed by particles in the size range 0.1–0.5 pm (83%). The contribution of particles larger than 0.5 μm to the overall number concentration was negligible and so was the contribution of particles smaller than 0.1 μm to the overall mass concentration. Furthermore, total number and mass concentrations in the range 0.01–2.5 μm were poorly correlated.The results suggest that particles larger than 2.5 μm (or even larger than 0.5 μm) are rare in the European urban environment so that the inhalation of these particles is probably not relevant for human health. Since particle number and mass concentrations can be considered poorly correlated variables, more insight into health-related aspects of particulate air pollution will be obtained by correlating respiratory responses with mass and number concentrations of ambient particles below 0.5 μm.     

Spatial gradients and source apportionment of volatile organic compounds near roadways

Concentrations of 55 volatile organic compounds (VOCs) (C₂–C₁₂) are reported near a highway in Raleigh, NC. Thirty-minute samples were collected at eight locations, ranging from approximately 10–100 m perpendicular from the roadway. The highest concentrations of VOCs were generally measured closest to the roadway, and concentrations decreased exponentially with increasing distance from the roadway. The highest mean concentration for individual VOCs were for ethylene (3.10 ppbv) (mean concentration at x = 13 m), propane (2.27 ppbv), ethane (1.91 ppbv), isopentane (1.54 ppbv), toluene (0.95 ppbv), and n-butane (0.89 ppbv). Concentrations at the nearest roadway location (x = 13 m) were generally between 2.0 and 1.5 times those from the farthest roadway location (x = 92 m). The data were apportioned into four source categories using the EPA Chemical Mass Balance Model (CMB8.2): motor vehicle exhaust, compressed natural gas, propane gas, and evaporative gasoline. The majority of the VOCs resulted from motor vehicle exhaust (67 ± 12%) (% of total VOC at x = 13 m ± S.D.). Compressed natural gas, propane gas, and evaporative gasoline accounted for approximately 15%, 7% and 1% of the total VOC emissions, respectively, at x = 13 m.     

Microbial characterization of nitrification in a shallow, nitrogen-contaminated aquifer, Cape Cod, Massachusetts and detection of a novel cluster associated with nitrifying Betaproteobacteria

Groundwater nitrification is a poorly characterized process affecting the speciation and transport of nitrogen. Cores from two sites in a plume of contamination were examined using culture-based and molecular techniques targeting nitrification processes. The first site, located beneath a sewage effluent infiltration bed, received treated effluent containing O₂ (> 300 µM) and NH₄⁺ (51–800 µM). The second site was 2.5 km down-gradient near the leading edge of the ammonium zone within the contaminant plume and featured vertical gradients of O₂, NH₄⁺, and NO₃⁻ (0–300, 0–500, and 100–200 µM with depth, respectively). Ammonia- and nitrite-oxidizers enumerated by the culture-based MPN method were low in abundance at both sites (1.8 to 350 g^− 1 and 33 to 35,000 g^− 1, respectively). Potential nitrifying activity measured in core material in the laboratory was also very low, requiring several weeks for products to accumulate. Molecular analysis of aquifer DNA (nested PCR followed by cloning and 16S rDNA sequencing) detected primarily sequences associated with the Nitrosospira genus throughout the cores at the down-gradient site and a smaller proportion from the Nitrosomonas genus in the deeper anoxic, NH₄⁺ zone at the down-gradient site. Only a single Nitrosospira sequence was detected beneath the infiltration bed. Furthermore, the majority of Nitrosospira-associated sequences represent an unrecognized cluster. We conclude that an uncharacterized group associated with Nitrosospira dominate at the geochemically stable, down-gradient site, but found little evidence for Betaproteobacteria nitrifiers beneath the infiltration beds where geochemical conditions were more variable.     

Dissecting the spatial scales of mercury accumulation in Ontario lake sediment

Total mercury concentration was analyzed in 171 lakes from pre-industrial (>30 cm depth; Hg_{pre-industrial}) and present-day sediments (0.5–1 cm; Hg_present-day). Numerous hot or cold spots of sediment mercury enrichment (Hg EF; Hg_{pre-industrial}/Hg_present-day) were evident as determined by local tests of autocorrelation, although in most cases, the maximum correlation among sites was not the nearest neighbor, indicating a strong influence of watershed characteristics. Hg EF was correlated with the area of open water (ha) (r = 0.91, p = 0.035), mine tailings (r = 0.94, p = 0.019), and organic deposits in surficial geology of the watershed (r = −0.91, p = 0.034). Through use of local rather than global regression coefficients, R² increased from 0.20 (p = 0.005) to 0.60 (p = 0.013). A broad spatial pattern (>500 km) observed only in Hg_{pre-industrial} was best explained by mean annual precipitation (shared variance = 3.5%), while finer spatial patterns only observed in Hg_present-day and Hg EF were best explained by pH (average shared variance = 10.8%).