Atmospheric oxidation capacity in the summer of Houston 2006: Comparison with summer measurements in other metropolitan studies

Both similarities and differences in summertime atmospheric photochemical oxidation appear in the comparison of four field studies: TEXAQS2000 (Houston, 2000), NYC2001 (New York City, 2001), MCMA2003 (Mexico City, 2003), and TRAMP2006 (Houston, 2006). The compared photochemical indicators are OH and HO₂ abundances, OH reactivity (the inverse of the OH lifetime), HO_x budget, OH chain length (ratio of OH cycling to OH loss), calculated ozone production, and ozone sensitivity. In terms of photochemical activity, Houston is much more like Mexico City than New York City. These relationships result from the ratio of volatile organic compounds (VOCs) to nitrogen oxides (NO_x), which are comparable in Houston and Mexico City, but much lower in New York City. Compared to New York City, Houston and Mexico City also have higher levels of OH and HO₂, longer OH chain lengths, a smaller contribution of reactions with NO_x to the OH reactivity, and NO_x-sensitivity for ozone production during the day. In all four studies, the photolysis of nitrous acid (HONO) and formaldehyde (HCHO) are significant, if not dominant, HO_x sources. A problematic result in all four studies is the greater OH production than OH loss during morning rush hour, even though OH production and loss are expected to always be in balance because of the short OH lifetime. The cause of this discrepancy is not understood, but may be related to the under-predicted HO₂ in high NO_x conditions, which could have implications for ozone production. Three photochemical indicators show particularly high photochemical activity in Houston during the TRAMP2006 study: the long portion of the day for which ozone production was NO_x-sensitive, the calculated ozone production rate that was second only to Mexico City's, and the OH chain length that was twice that of any other location. These results on photochemical activity provide additional support for regulatory actions to reduce reactive VOCs in Houston in order to reduce ozone and other pollutants.     

Nocturnal NO3 radical chemistry in Houston,TX

Radical chemistry in the nocturnal urban boundary layer is dominated by the nitrate radical, NO₃, which oxidizes hydrocarbons and, through the aerosol uptake of N₂O₅, indirectly influences the nitrogen budget. The impact of NO₃ chemistry on polluted atmospheres and urban air quality is, however, not well understood, due to a lack of observations and the strong impact of vertical stability of the boundary layer, which makes nocturnal chemistry highly altitude dependent.Here we present long-path DOAS observations of the vertical distribution of the key nocturnal species O₃, NO₂, and NO₃ during the TRAMP experiment in Summer 2006 in Houston, TX. Our observations confirm the altitude dependence of nocturnal chemistry, which is reflected in the concentration profiles of all trace gases at night. In contrast to other study locations, NO₃ chemistry in Houston is dominated by industrial emissions of alkenes, in particular of isoprene, isobutene, and sporadically 1,3-butadiene, which are responsible for more than 70% of the nocturnal NO₃ loss. The nocturnally averaged loss of NO_x in the lowest 300 m of the Houston atmosphere is ～0.9 ppb h^?1, with little day-to-day variability. A comparison with the daytime NO_x loss shows that NO₃ chemistry is responsible for 16–50% of the NO_x loss in a 24-h period in the lowest 300 m of the atmosphere. The importance of the NO₃ + isoprene/1,3-butadiene reactions implies the efficient formation of organic nitrates and secondary organic aerosol at night in Houston.     

Interaction of nitrogen dioxide (NO2) with a monolayer of oleic acid at the air–water interface – A simple proxy for atmospheric aerosol

The reactions between atmospheric oxidants and organic amphiphiles at the air–water interface of an aerosol droplet may affect the size and critical supersaturation required for cloud droplet formation. We demonstrate that no reaction occurs between gaseous nitrogen dioxide (1000 ppm in air) and a monolayer of an insoluble amphiphile, oleic acid (cis-9-octadecenoic acid), at the air–water interface which removes material from the air–water interface. We present evidence that the NO₂ isomerises the cis-9-octadecenoic (oleic) acid to trans-9-octadecenoic (elaidic) acid. The study presented here is important for future and previous studies of (1) the reaction between the nitrate radical, NO₃, and thin organic films as NO₂ is usually present in high concentrations in these experimental systems and (2) the effect of NO₂ air pollution on the unsaturated fatty acids and lipids found at the air–liquid surface of human lung lining fluid.     

The Anthropocene: From Global Change to Planetary Stewardship

Over the past century, the total material wealth of humanity has been enhanced. However, in the twenty-first century, we face scarcity in critical resources, the degradation of ecosystem services, and the erosion of the planet's capability to absorb our wastes. Equity issues remain stubbornly difficult to solve. This situation is novel in its speed, its global scale and its threat to the resilience of the Earth System. The advent of the Anthropence, the time interval in which human activities now rival global geophysical processes, suggests that we need to fundamentally alter our relationship with the planet we inhabit. Many approaches could be adopted, ranging from geoengineering solutions that purposefully manipulate parts of the Earth System to becoming active stewards of our own life support system. The Anthropocene is a reminder that the Holocene, during which complex human societies have developed, has been a stable, accommodating environment and is the only state of the Earth System that we know for sure can support contemporary society. The need to achieve effective planetary stewardship is urgent. As we go further into the Anthropocene, we risk driving the Earth System onto a trajectory toward more hostile states from which we cannot easily return.     

Traffic exposure in a population with high prevalence type 2 diabetes – Do medications influence concentrations of C-reactive protein?

Type 2 Diabetes (T2D) and particulate air pollution are associated with inflammatory dysregulation. We assessed the modifying effects of diabetes medications on the association of C-reactive protein (CRP), a marker of inflammation, and traffic exposure in adults with T2D (n = 379). CRP concentrations were significantly positively associated with residence ≤100 m of a roadway, >100 m and ≤200 m of a roadway and increased traffic density for individuals using insulin. For individuals using oral hypoglycemic medications (OHAs), CRP was significantly negatively associated with residence >100 m - ≤200 m of a roadway and multiple roadway exposure in an interaction model. Among people with diabetes, individuals on insulin appear to be most vulnerable to the effects of traffic exposure. Disease severity among insulin users may promote the pro-inflammatory response to traffic exposure, though diabetes medications may also modify the response. Possible anti-inflammatory effects of OHAs with traffic exposure merit further evaluation.     

Mitochondrial DNA sequence variation in spiny lobsters: population expansion,panmixia, and divergence

To investigate population differentiation in a comparative and historical context, segments of the mitochondrial cytochrome c oxidase subunit I gene and the control region were sequenced in Panulirus argus from nine sites along approximately 1,500 km of the Northern Caribbean Sea (n = 326) and analyzed with respect to available panulirid data. A mismatch analysis and Fu’s F _S test uncovered a signature of historical population expansion around the time of the Last Glacial Maximum. Significant population structure was not detected in the area. The data supported a hypothesis of panmixia resulting from ongoing larval transport by ocean currents and historical population expansion. Despite high intraspecific divergence levels at COI within Panulirus argus and several other Panulirus species, genetic species identification through DNA barcoding was feasible using either a modified distance threshold or a character-based approach.     

When is an invasive not an invasive? Macrofossil evidence of doubtful native plant species in the Galápagos Islands

The Galápagos Islands are globally renowned for their ecological value and as a world symbol of scientific discovery; however the native biodiversity of this unique region is currently under threat. One of the primary concerns is the detrimental impact of approximately 750 nonnative plants introduced over the last 500 years of human presence in the archipelago. In addition to these known introduced species, there are an additional 62 vascular plants classified as "doubtful natives," where native status remains unclear. To help address the questions of provenance regarding these doubtfully native species and their impact on highland ecosystems over the past 500-1000 years, we analyzed plant macrofossils in sedimentary records. Appropriate species classification (native or introduced) was determined using baseline data of species presence on the islands. We confirmed that six plants (Ageratum conyzoides, Solanum americanum, Ranunculus flagelliformis, Brickellia diffusa, Galium canescens, and Anthephora hermaphrodita) once considered doubtful natives or introduced are actually native to the Galápagos flora. These results have relevance not just for the Galápagos but also many other oceanic islands in demonstrating the application of palaeobotanical data to conserving and restoring native biodiversity.     

Gravity currents in two-layer stratified media

An analytical, experimental and numerical study of boundary gravity currents propagating through a two-layer stratified ambient of finite vertical extent is presented. Gravity currents are supposed to originate from a lock-release apparatus; the (heavy) gravity current fluid is assumed to span the entire channel depth, H, at the initial instant. Our theoretical discussion considers slumping, supercritical gravity currents, i.e. those that generate an interfacial disturbance whose speed of propagation matches the front speed, and follows from the classical analysis of Benjamin (J Fluid Mech 31:209?C248, 1968). In contrast to previous investigations, we argue that the interfacial disturbance must be parameterized so that its amplitude can be straightforwardly determined from the ambient layer depths. Our parameterization is based on sensible physical arguments; its accuracy is confirmed by comparison against experimental and numerical data. More generally, measured front speeds show positive agreement with analogue model predictions, which remain strictly single-valued. From experimental and numerical observations of supercritical gravity currents, it is noted that this front speed is essentially independent of the interfacial thickness, ??, even in the limiting case where ?? = H so that the environment is comprised of a uniformly stratified ambient with no readily discernible upper or lower ambient layer. Conversely, when the gravity current is subcritical, there is a mild increase of front speed with ??. Our experiments also consider the horizontal distance, X, at which the front begins to decelerate. The variation of X with the interface thickness and the depths and densities of the ambient layers is discussed. For subcritical gravity currents, X may be as small as three lock lengths whereas with supercritical gravity currents, the gravity current may travel long distances at constant speed, particularly as the lower layer depth diminishes.     

Reduction of ferrate(VI) and oxidation of cyanate in a Fe(VI)-TiO2-UV-NCO- system

The aqueous photocatalytic degradation of cyanate (NCO(-)), which is a long-lived neurotoxin formed during the remediation of cyanide in industrial waste streams, was studied in the ferrate(VI)-UV-TiO2-NCO(-) system. Kinetics measurements of the photocatalytic reduction of ferrate(VI) were carried out as a function of [NCO(-)], [ferrate(VI)], [O(2)], light intensity (I(o)), and amount of TiO2 in suspensions at pH 9.0. The photocatalytic reduction rate of ferrate(VI) in the studied system can be expressed as -d[Fe(VI)]/dt=kI(o)(0.5) [NCO(-)] [TiO2]. The rate of photocatalytic oxidation of cyanate with ferrate(VI) was greater than the rate in the analogous system without ferrate(VI). The possibility of involvement of reactive ferrate(V) species for this enhancement was determined by studying the reactivity of ferrate(V) with NCO(-) in a homogeneous solution using a premix pulse radiolysis technique. The rate constant for the reaction of ferrate(V) and NCO(-) in alkaline medium was estimated to be (9.60+/-0.07) x 10(2) M(-1) s(-1), which is much slower than the ferrate(VI) self-decomposition reaction (k approximately 10(7) M(-1) s(-1)). An analysis of the kinetic data in the Fe(VI)-UV-TiO2-NCO(-) system suggests that ferrate(V) is not directly participating in the oxidation of cyanate. Possible reactions in the system are presented to explain results of ferrate(VI) reduction and oxidation of cyanate.     

Genes and song: genetic and social connections in fragmented habitat in a woodland bird with limited dispersal

Understanding the processes leading to population declines in fragmented landscapes is essential for successful conservation management. However, isolating the influence of disparate processes, and dispersal in particular, is challenging. The Grey Shrike-thrush, Colluricincla harmonica, is a sedentary woodland-dependent songbird, with learned vocalizations whose incidence in suitable habitat patches falls disproportionally with decline in tree cover in the landscape. Although it has been suggested that gaps in tree cover might act as barriers to its dispersal, the species remains in many remnants of native vegetation in agricultural landscapes, suggesting that it may have responded to habitat removal and fragmentation by maintaining or even increasing dispersal distances. We quantified population connectivity of the Grey Shrike-thrush in a system fragmented over more than 120 years using genetic (microsatellites) and acoustic (song types) data. First, we tested for population genetic and acoustic structure at regional and local scales in search of barriers to dispersal or gene flow and signals of local spatial structuring indicative of restricted dispersal or localized acoustic similarity. Then we tested for effects of habitat loss and fragmentation on genetic and acoustic connectivity by fitting alternative models of mobility (isolation-by-distance [the null model] and reduced and increased movement models) across treeless vs. treed areas. Birds within -5 km of each other had more similar genotypes and song types than those farther away, suggesting that dispersal and song matching are limited in the region. Despite restricted dispersal detected for females (but not males), populations appeared to be connected by gene flow and displayed some cultural (acoustic) connectivity across the region. Fragmentation did not appear to impact greatly the dispersal of the Grey Shrike-thrush: none of the mobility models fit the genetic distances of males, whereas for females, an isolation-by-distance model could not be rejected in favor of the models of reduced or increased movement through treeless gaps. However, dissimilarities of the song types were more consistent with the model of reduced cultural connectivity through treeless areas, suggesting that fragmentation impedes song type sharing in the Grey Shrike-thrush. Our paper demonstrates that habitat fragmentation hinders important population processes in an Australian woodland bird even though its dispersal is not detectably impacted.