Relationships between analytical methods utilized as tools in the evaluation of landfill waste stability

In this study, the refuse from 12 landfills of various ages ranging from fresh refuse to material 11 years old was collected, and changes in the bio-stability parameters were determined. The parameters measured included cellulose, lignin, biochemical methane potential (BMP) and volatile solids, along with plastics. These parameters, along with the cellulose to lignin ratio were compared to determine which were most indicative of the bio-stability of the refuse. Lignin and volatile solids measurements were affected by plastics in refuse samples. Plastics increased both lignin and volatile solids measurements by approximately 10%. Cellulose and volatile solids measurements correlated well with age, each other, and with BMP measurements and were therefore considered the best parameters to determine stability. Data for the Riverbend landfill, a landfill with a moisture content of 48%, which is similar to that of bioreactor landfills, showed that degradation was nearly complete after 5 years as indicated by low values for cellulose and BMP.     

Urban Transitions: On Urban Resilience and Human-Dominated Ecosystems

Urbanization is a global multidimensional process paired with increasing uncertainty due to climate change, migration of people, and changes in the capacity to sustain ecosystem services. This article lays a foundation for discussing transitions in urban governance, which enable cities to navigate change, build capacity to withstand shocks, and use experimentation and innovation in face of uncertainty. Using the three concrete case cities—New Orleans, Cape Town, and Phoenix—the article analyzes thresholds and cross-scale interactions, and expands the scale at which urban resilience has been discussed by integrating the idea from geography that cities form part of “system of cities” (i.e., they cannot be seen as single entities). Based on this, the article argues that urban governance need to harness social networks of urban innovation to sustain ecosystem services, while nurturing discourses that situate the city as part of regional ecosystems. The article broadens the discussion on urban resilience while challenging resilience theory when addressing human-dominated ecosystems. Practical examples of harnessing urban innovation are presented, paired with an agenda for research and policy.     

Formation of oxidized products from the reaction of gaseous phenanthrene with the OH radical in a reaction chamber

The reaction of gas phase phenanthrene (Phen) with the OH radical in the presence of NO_x was studied in a reaction chamber. A number of oxidation products were identified by two dimensional gas chromatography–time of flight mass spectrometry (GC × GC–TOFMS). Identified products included 9-fluorenone, 1,2-naphthalic anhydride, 2,2′-diformylbiphenyl, dibenzopyranone, 1, 2, 3, 4 and 9-phenanthrols, 2, 3, 4 and 9-nitrophenanthrenes, 1,4-phenanthrenequinone, 9,10-phenanthrenequinone, and 2- and 4-nitrodibenzopyranones. This is the first study to identify 1,2-naphthalic anhydride and 1,4-phenanthrenequinone as products of the gas phase reaction of Phen with the OH radical. Eight more products were tentatively identified by their mass spectral fragmentation patterns and based on the typical OH radical initiated photochemical reaction mechanisms of simple aromatic compounds and naphthalene. In the reaction chamber, particle formation of products as a function of irradiation time was measured. Phenanthrenequinones, phenanthrol, nitrophenanthrene and nitrobenzopyranone were observed predominantly in the particle phase. This implies that these oxidized products formed from the reaction of Phen with the OH radical in the chamber would be associated with particles in the atmosphere and may, therefore, have an impact on human health. Possible pathways for the formation of these products are suggested and discussed.     

Characterizing changes in surface ozone levels in metropolitan and rural areas in the United States for 1980–2008 and 1994–2008

In this analysis, we characterize urban and rural ozone (O₃) trends across the US for the periods 1980–2008 (29 years) and 1994–2008 (15 years) using three exposure metrics, which summarize daily O₃ concentrations to reflect different ways O₃ may affect human health and vegetation. We observe that a statistically significant trend at a specific monitoring site, using one exposure metric, does not necessarily result in a similar trend using the other two metrics. The two most common trends among the monitoring sites are either a continuation of negative trending over the 29-year period or a shift from negative to no trend status, indicating a leveling off of the trending. Very few sites exhibit statistically significant increases in the exposure indices. In characterizing the statistically significant changes in the distribution of hourly average O₃, we observe subtle statistically significant changes in the lower part of the distribution (i.e., below 50 ppb) that are not necessarily captured by the trending patterns associated with the three exposure metrics. Using multisite data from 12 metropolitan cities, we find that as the frequency of higher hourly average concentrations is reduced, the lower hourly average concentrations also move upward toward the mid-level values. The change in the number of the hourly average concentrations in the lower range is consistent with decreased NO scavenging. We recommend assessing possible subtle shifts in O₃ concentrations by characterizing changes in the distribution of hourly average concentrations by month. Identifying statistically significant monthly changes in the mid- and low-level hourly average concentrations may provide important information for assessing changes in physical processes associated with global climate change, long-range transport, and the efficacy of models used for emission and risk reductions. Our results indicate that it is important to investigate the change in the trending pattern with time (e.g., moving 15-year trending) in order to assess how year-to-year variability may influence the trend calculation.     

Role of back diffusion and biodegradation reactions in sustaining an MTBE/TBA plume in alluvial media

A methyl tert-butyl ether (MTBE) / tert-butyl alcohol (TBA) plume originating from a gasoline spill in late 1994 at Vandenberg Air Force Base (VAFB) persisted for over 15 years within 200 feet of the original spill source. The plume persisted until 2010 despite excavation of the tanks and piping within months after the spill and excavations of additional contaminated sediments from the source area in 2007 and 2008. The probable history of MTBE concentrations along the plume centerline at its source was estimated using a wide variety of available information, including published details about the original spill, excavations and monitoring by VAFB consultants, and our own research data. Two-dimensional reactive transport simulations of MTBE along the plume centerline were conducted for a 20-year period following the spill. These analyses suggest that MTBE diffused from the thin anaerobic aquifer into the adjacent anaerobic silts and transformed to TBA in both aquifer and silt layers. The model reproduces the observation that after 2004 TBA was the dominant solute, diffusing back out of the silts into the aquifer and sustaining plume concentrations much longer than would have been the case in the absence of such diffusive exchange. Simulations also suggest that aerobic degradation of MTBE or TBA at the water table in the overlying silt layer significantly affected concentrations of MTBE and TBA by limiting the chemical mass available for back diffusion to the aquifer.     

Regional source identification using Lagrangian stochastic particle dispersion and HYSPLIT backward-trajectory models

The main objective of this study was to investigate the capabilities of the receptor-oriented inverse mode Lagrangian Stochastic Particle Dispersion Model (LSPDM) with the 12-km resolution Mesoscale Model 5 (MM5) wind field input for the assessment of source identification from seven regions impacting two receptors located in the eastern United States. The LSPDM analysis was compared with a standard version of the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) single-particle backward-trajectory analysis using inputs from MM5 and the Eta Data Assimilation System (EDAS) with horizontal grid resolutions of 12 and 80 km, respectively. The analysis included four 7-day summertime events in 2002; residence times in the modeling domain were computed from the inverse LSPDM runs and HYPSLIT-simulated backward trajectories started from receptor-source heights of 100, 500, 1000, 1500, and 3000 m. Statistics were derived using normalized values of LSPDM- and HYSPLIT-predicted residence times versus Community Multiscale Air Quality model-predicted sulfate concentrations used as baseline information. From 40 cases considered, the LSPDM identified first- and second-ranked emission region influences in 37 cases, whereas HYSPLIT-MM5 (HYSPLIT-EDAS) identified the sources in 21 (16) cases. The LSPDM produced a higher overall correlation coefficient (0.89) compared with HYSPLIT (0.55-0.62). The improvement of using the LSPDM is also seen in the overall normalized root mean square error values of 0.17 for LSPDM compared with 0.30-0.32 for HYSPLIT. The HYSPLIT backward trajectories generally tend to underestimate near-receptor sources because of a lack of stochastic dispersion of the backward trajectories and to overestimate distant sources because of a lack of treatment of dispersion. Additionally, the HYSPLIT backward trajectories showed a lack of consistency in the results obtained from different single vertical levels for starting the backward trajectories. To alleviate problems due to selection of a backward-trajectory starting level within a large complex set of 3-dimensional winds, turbulence, and dispersion, results were averaged from all heights, which yielded uniform improvement against all individual cases.     

Formed-in-place Polyelectrolyte Complex Membranes for Atrazine Recovery from Aqueous Media

A permeable system composed of a polyelectrolyte complex (PEC) membrane formed by alternated deposition of chitosan (CHI) and carboxymethylcellulose (CMC) onto a porous solid substrate was investigated. The films, with thicknesses not superior to 20 nm, were obtained by a self-assembly technique, i.e., by direct dipping of chemically cleaned porous glass membranes, into concentrated polymeric precursor solutions. The resulting depositions have irregular structures and reduce the initial membrane permeability, especially for higher flux velocities. Concerning filtration tests for herbicide removal in aqueous medium, the chitosan deposition attained better results. A tentative model of binding involving hydrogen bonding and/or charge-transfer to nonspecific sites available dynamically as a function of the conformational estate of the deposited polymers is proposed for polysaccharide-herbicide interactions.     

Heading for the hills: climate-driven community relocations in the Solomon Islands and Alaska provide insight for a 1.5 °C future

Whilst future air temperature thresholds have become the centrepiece of international climate negotiations, even the most ambitious target of 1.5 °C will result in significant sea-level rise and associated impacts on human populations globally. Of additional concern in Arctic regions is declining sea ice and warming permafrost which can increasingly expose coastal areas to erosion particularly through exposure to wave action due to storm activity. Regional variability over the past two decades provides insight into the coastal and human responses to anticipated future rates of sea-level rise under 1.5 °C scenarios. Exceeding 1.5 °C will generate sea-level rise scenarios beyond that currently experienced and substantially increase the proportion of the global population impacted. Despite these dire challenges, there has been limited analysis of how, where and why communities will relocate inland in response. Here, we present case studies of local responses to coastal erosion driven by sea-level rise and warming in remote indigenous communities of the Solomon Islands and Alaska, USA, respectively. In both the Solomon Islands and the USA, there is no national government agency that has the organisational and technical capacity and resources to facilitate a community-wide relocation. In the Solomon Islands, communities have been able to draw on flexible land tenure regimes to rapidly adapt to coastal erosion through relocations. These relocations have led to ad hoc fragmentation of communities into smaller hamlets. Government-supported relocation initiatives in both countries have been less successful in the short term due to limitations of land tenure, lacking relocation governance framework, financial support and complex planning processes. These experiences from the Solomon Islands and USA demonstrate the urgent need to create a relocation governance framework that protects people’s human rights.     

The relationship of place to substance use and perceptions of risk and safety in urban adolescents

Geographic and substance use data were collected from 301 urban adolescents to compare the perceived and observed risk and safety associated with their home and activity space locations (routine locations). The geographic characteristics of the neighborhood surrounding each location was summarized according to features theorized to be risky, such as criminal activity and alcohol sales, and features theorized to be safe, such as recreation centers and churches. Data on socioeconomic status, derived from U.S. Bureau of the Census data, were also used to characterize locations. Adolescents' homes were typically perceived as safe despite observed measures of risk such as density of crimes and proximity to alcohol outlets. This held for both substance users and non-users. Differences in geographic characteristics for safe and risky activity spaces were observed for both substance users and non-users, with non-users appearing to be more sensitive to the presence of risky characteristics in the environment than substance users. Results highlight the need and provide a methodology to collect fine-grained activity space data instead of relying only on home residence when attempting to represent place and health behaviors with urban youth.