Spatial and temporal variablity of nonmethane hydrocarbon mixing ratios and their relation to photochemical lifetime

The relationship between temporal and spatial variability of C2-C8 nonmethane hydrocarbon mixing ratios and their HO lifetimes (τ) is presented for samples collected during the 1993 North Atlantic Regional Experiment (NARE) and from other urban and remote sites. The C2-C4 alkanes, acetylene and benzene typically define a trend of the form slnx=Aτ-b where slnx is the standard deviation of the ln of the mixing ratio. The relationship extended over a wider range of hydrocarbons in winter. The exponent b ranged in value from 0.2±0.023 for winter urban data where C2-C8 hydrocarbons defined a strongly correlated trend, to 0.56±0.15 for C2-C4 hydrocarbons at a coastal site in Nova Scotia during NARE. The trends are significantly different from that given by the Junge relationship [Junge, 1974]. Data from the Azores do not display such a trend and were likely influenced by local emissions. Variance trends are a useful analytical tool for examining the validity of hydrocarbon measurements

Trace gas mixing ratio variability versus lifetime in the troposphere and stratosphere: Observations

Several archived data sets have been reviewed to examine the relationship between mixing ratio variability and lifetime for hydrocarbon and halocarbon species in the troposphere and stratosphere. The dependence on lifetime was described by the power law relationship slnX = Aτ-b, where slnX is the standard deviation of the In of the mixing ratios, A is a proportionality coefficient, and b is an exponent that relates to the dominance of sink terms in the regional variability budget. At the Harvard forest ground site, winter and summer data displayed the same lifetime dependence, τ-0.18, which was significantly weaker than the τ-0.5 dependence of remote tropospheric data, indicating that source terms dominated regional variability at Harvard. In addition, the ratio of summer to winter slnX values was found to be similar for all species except ethane, averaging 1.54 ± 0.04. This ratio is consistent with a factor of 11 seasonal change in the species lifetimes, given a τ-0.18 lifetime dependence. Stratospheric data displayed a stronger lifetime dependence than tropospheric trends, indicating a more dominant role for sink terms in describing spatial variability in this region of the atmosphere. We show that a unique power law relationship between slnX ratios for two species Xi and Xj and the kinetic slope of ln(Xi) versus ln(Xj) correlation plots is found to hold in both observations and theory. Thus knowledge of the coefficient b allows for a clearer understanding of the relationship between observed slopes of ln(Xi) versus ln(Xj) correlation plots and the ratio of the species lifetimes. Copyright 1999 by the American Geophysical Union

Evidence for strong, widespread chlorine radical chemistry associated with pollution outflow from continental Asia

The chlorine radical is a potent atmospheric oxidant, capable of perturbing tropospheric oxidative cycles normally controlled by the hydroxyl radical. Significantly faster reaction rates allow chlorine radicals to expedite oxidation of hydrocarbons, including methane, and in polluted environments, to enhance ozone production. Here we present evidence, from the CARIBIC airborne dataset, for extensive chlorine radical chemistry associated with Asian pollution outflow, from airborne observations made over the Malaysian Peninsula in winter. This region is known for persistent convection that regularly delivers surface air to higher altitudes and serves as a major transport pathway into the stratosphere. Oxidant ratios inferred from hydrocarbon relationships show that chlorine radicals were regionally more important than hydroxyl radicals for alkane oxidation and were also important for methane and alkene oxidation (>10%). Our observations reveal pollution-related chlorine chemistry that is both widespread and recurrent, and has implications for tropospheric oxidizing capacity, stratospheric composition and ozone chemistry

Structural Alterations in a Component of Cytochrome c Oxidase and Molecular Evolution of Pathogenic Neisseria in Humans

Three closely related bacterial species within the genus Neisseria are of importance to human disease and health. Neisseria meningitidis is a major cause of meningitis, while Neisseria gonorrhoeae is the agent of the sexually transmitted disease gonorrhea and Neisseria lactamica is a common, harmless commensal of children. Comparative genomics have yet to yield clear insights into which factors dictate the unique host-parasite relationships exhibited by each since, as a group, they display remarkable conservation at the levels of nucleotide sequence, gene content and synteny. Here, we discovered two rare alterations in the gene encoding the CcoP protein component of cytochrome cbb3 oxidase that are phylogenetically informative. One is a single nucleotide polymorphism resulting in CcoP truncation that acts as a molecular signature for the species N. meningitidis. We go on to show that the ancestral ccoP gene arose by a unique gene duplication and fusion event and is specifically and completely distributed within species of the genus Neisseria. Surprisingly, we found that strains engineered to express either of the two CcoP forms conditionally differed in their capacity to support nitrite-dependent, microaerobic growth mediated by NirK, a nitrite reductase. Thus, we propose that changes in CcoP domain architecture and ensuing alterations in function are key traits in successive, adaptive radiations within these metapopulations. These findings provide a dramatic example of how rare changes in core metabolic proteins can be connected to significant macroevolutionary shifts. They also show how evolutionary change at the molecular level can be linked to metabolic innovation and its reversal as well as demonstrating how genotype can be used to infer alterations of the fitness landscape within a single host

Prostate-specific antigen velocity in a prospective prostate cancer screening study of men with genetic predisposition.

This corrects the article DOI: 10.1038/bjc.2017.429

Isoprene suppression of new particle formation in a mixed deciduous forest

Production of new particles over forests is an important source of cloud condensation nuclei that can affect climate. While such particle formation events have been widely observed, their formation mechanisms over forests are poorly understood. Our observations made in a mixed deciduous forest with large isoprene emissions during the summer displayed a surprisingly rare occurrence of new particle formation (NPF). Typically, NPF events occur around noon but no NPF events were observed during the 5 weeks of measurements. The exceptions were two evening ultrafine particle events. During the day, sulfuric acid concentrations were in the 106 cm-3 range with very low preexisting aerosol particles, a favorable condition for NPF to occur even during the summer. The ratio of emitted isoprene carbon to monoterpene carbon at this site was similar to that in Amazon rainforests (ratio >10), where NPF events are also very rare, compared with a ratio <0.5 in Finland boreal forests, where NPF events are frequent. Our results suggest that large isoprene emissions can suppress NPF formation in forests although the underlying mechanism for the suppression is unclear. The two evening ultrafine particle events were associated with the transported anthropogenic sulfur plumes and ultrafine particles were likely formed via ion-induced nucleation. Changes in landcover and environmental conditions could modify the isoprene suppression of NPF in some forest regions resulting in a radiative forcing that could have influence on the climate. © 2011 Author(s)

Isoprene suppression of new particle formation in a mixed deciduous forest

Production of new particles over forests is an important source of cloud condensation nuclei that can affect climate. While such particle formation events have been widely observed, their formation mechanisms over forests are poorly understood. Our observations made in a mixed deciduous forest with large isoprene emissions during the summer displayed a surprisingly rare occurrence of new particle formation (NPF). Typically, NPF events occur around noon but no NPF events were observed during the 5 weeks of measurements. The exceptions were two evening ultrafine particle events. During the day, sulfuric acid concentrations were in the 106 cm-3 range with very low preexisting aerosol particles, a favorable condition for NPF to occur even during the summer. The ratio of emitted isoprene carbon to monoterpene carbon at this site was similar to that in Amazon rainforests (ratio >10), where NPF events are also very rare, compared with a ratio <0.5 in Finland boreal forests, where NPF events are frequent. Our results suggest that large isoprene emissions can suppress NPF formation in forests although the underlying mechanism for the suppression is unclear. The two evening ultrafine particle events were associated with the transported anthropogenic sulfur plumes and ultrafine particles were likely formed via ion-induced nucleation. Changes in landcover and environmental conditions could modify the isoprene suppression of NPF in some forest regions resulting in a radiative forcing that could have influence on the climate. © 2011 Author(s)

In-canopy gas-phase chemistry during CABINEX 2009: Sensitivity of a 1-D canopy model to vertical mixing and isoprene chemistry

Vegetation emits large quantities of biogenic volatile organic compounds (BVOC). At remote sites, these compounds are the dominant precursors to ozone and secondary organic aerosol (SOA) production, yet current field studies show that atmospheric models have difficulty in capturing the observed HOx cycle and concentrations of BVOC oxidation products. In this manuscript, we simulate BVOC chemistry within a forest canopy using a one-dimensional canopy-chemistry model (Canopy Atmospheric CHemistry Emission model; CACHE) for a mixed deciduous forest in northern Michigan during the CABINEX 2009 campaign. We find that the base-case model, using fully-parameterized mixing and the simplified biogenic chemistry of the Regional Atmospheric Chemistry Model (RACM), underestimates daytime in-canopy vertical mixing by 50-70% and by an order of magnitude at night, leading to discrepancies in the diurnal evolution of HO x, BVOC, and BVOC oxidation products. Implementing observed micrometeorological data from above and within the canopy substantially improves the diurnal cycle of modeled BVOC, particularly at the end of the day, and also improves the observation-model agreement for some BVOC oxidation products and OH reactivity. We compare the RACM mechanism to a version that includes the Mainz isoprene mechanism (RACM-MIM) to test the model sensitivity to enhanced isoprene degradation. RACM-MIM simulates higher concentrations of both primary BVOC (isoprene and monoterpenes) and oxidation products (HCHO, MACR+MVK) compared with RACM simulations. Additionally, the revised mechanism alters the OH concentrations and increases HO 2. These changes generally improve agreement with HO x observations yet overestimate BVOC oxidation products, indicating that this isoprene mechanism does not improve the representation of local chemistry at the site. Overall, the revised mechanism yields smaller changes in BVOC and BVOC oxidation product concentrations and gradients than improving the parameterization of vertical mixing with observations, suggesting that uncertainties in vertical mixing parameterizations are an important component in understanding observed BVOC chemistry. © 2012 Author(s)