Increased absorption by coarse aerosol particles over the Gangetic–Himalayan region

Each atmospheric aerosol type has distinctive light-absorption characteristics related to its physical/chemical properties. Climate models treat black carbon as the main light-absorbing component of carbonaceous atmospheric aerosols, while absorption by some organic aerosols is also considered, particularly at ultraviolet wavelengths. Most absorbing aerosols are assumed to be < 1 μm in diameter (sub-micron). Here we present results from a recent field study in India, primarily during the post-monsoon season (October–November), suggesting the presence of absorbing aerosols sized 1–10 μm. Absorption due to super-micron-sized particles was nearly 30% greater than that due to smaller particles. Periods of increased absorption by larger particles ranged from a week to a month. Radiative forcing calculations under clear-sky conditions show that super-micron particles account for nearly 44% of the total aerosol forcing. The origin of the large aerosols is unknown, but meteorological conditions indicate that they are of local origin. Such economic and habitation conditions exist throughout much of the developing world. Hence, large absorbing particles could be an important component of the regional-scale atmospheric energy balance

Process-Scale Modeling of Elevated Wintertime Ozone in Wyoming.

Measurements of meteorological variables and trace gas concentrations, provided by the Wyoming Department of Environmental Quality for Daniel, Jonah, and Boulder Counties in the state of Wyoming, were analyzed for this project. The data indicate that highest ozone concentrations were observed at temperatures of -10 C to 0 C, at low wind speeds of about 5 mph. The median values for nitrogen oxides (NOx) during these episodes ranged between 10 ppbv and 20 ppbv (parts per billion by volume). Measurements of volatile organic compounds (VOCs) during these periods were insufficient for quantitative analysis. The few available VOCs measurements indicated unusually high levels of alkanes and aromatics and low levels of alkenes. In addition, the column ozone concentration during one of the high-ozone episodes was low, on the order of 250 DU (Dobson unit) as compared to a normal column ozone concentration of approximately 300-325 DU during spring for this region. Analysis of this observation was outside the scope of this project. The data analysis reported here was used to establish criteria for making a large number of sensitivity calculations through use of a box photochemical model. Two different VOCs lumping schemes, RACM and SAPRC-98, were used for the calculations. Calculations based on this data analysis indicated that the ozone mixing ratios are sensitive to (a) surface albedo, (b) column ozone, (c) NOx mixing ratios, and (d) available terminal olefins. The RACM model showed a large response to an increase in lumped species containing propane that was not reproduced by the SAPRC scheme, which models propane as a nearly independent species. The rest of the VOCs produced similar changes in ozone in both schemes. In general, if one assumes that measured VOCs are fairly representative of the conditions at these locations, sufficient precursors might be available to produce ozone in the range of 60-80 ppbv under the conditions modeled

Future atmospheric methane concentrations in the context of the stabilization of greenhouse gas concentrations

Abstract. Tropospheric CH 4 concentration depends, according to modeled tropospheric processes, on many factors, including emissions of CH 4 as well as NO x and CO. Illustrative analyses of the relation between emissions and CH 4 concentration give some guidance on the role of CH 4 in the stabilization of greenhouse gas concentrations. The contribution of CH 4 to radiative forcing at the time of stabilization is expected to be modest, provided CH 4 and CO emissions do not go far beyond current rates. However, in cases leading to stabilization the potential mitigation of increases in radiative forcing by methane control could be comparable to that of CO 2 control over the next century. Whether or not this potential is realized will depend partially on the cost of deep reductions of CH 4 , NO x , CO, or CO 2 emissions over the next century, which is not known

Medical applicant general practice experience and career aspirations: a questionnaire study

Background: Increasing access to general practice work experience placements for school students is a strategy for improving general practice recruitment, despite limited evidence and concerns surrounding equity of access to general practice experiences. Aims: To examine the association between undertaking general practice experience and the perceptions of general practice as an appealing future career among prospective medical applicants. To identify socioeconomic factors associated with obtaining general practice experience. Design & setting: Cross-sectional questionnaire study in the UK. Method: Participants were UK residents aged ≥16 years and seriously considering applying to study medicine in 2019/2020. They were invited to take part via the University Clinical Aptitude Test (UCAT). Questionnaire data were analysed using a linear regression of general practice appeal on general practice experience, adjusting for career motivations and demographics, and a logistic regression of general practice experience on measures of social capital and demographics. Results: Of 6391 responders, 4031 were in their last year of school. General practice experience predicted general practice appeal after adjusting for career motivation and demographics (b = 0.37, standard error [SE] = 0.06, P<0.00001). General practice experience was more common among students at private (odds ratio [OR] = 1.65, 95% confidence interval [CI] = 1.31 to 2.08, P<0.0001) or grammar schools (OR = 1.33, 95% CI = 1.02 to 1.72, P = 0.03) and in the highest socioeconomic group (OR = 1.62, 95% CI = 1.28 to 2.05, P<0.0001), and less likely among students of ‘other’ ethnicity (OR = 0.37, 95% CI = 0.20 to 0.67, P = 0.0011). Conclusion: Having general practice experience prior to medical school was associated with finding general practice appealing, which supports its utility in recruitment. Applicants from more deprived backgrounds were less likely to have had a general practice experience, possibly through lack of accessible opportunities

Extraction of Accurate Biomolecular Parameters from Single-Molecule Force Spectroscopy Experiments

The atomic force microscope (AFM) is able to manipulate biomolecules and their complexes with exquisite force sensitivity and distance resolution. This capability, complemented by theoretical models, has greatly improved our understanding of the determinants of mechanical strength in proteins and revealed the diverse effects of directional forces on the energy landscape of biomolecules. In unbinding experiments, the interacting partners are usually immobilized on their respective substrates via extensible linkers. These linkers affect both the force and contour length (Lc) of the complex at rupture. Surprisingly, while the former effect is well understood, the latter is largely neglected, leading to incorrect estimations of Lc, a parameter that is often used as evidence for the detection of specific interactions and remodeling events and for the inference of interaction regions. To address this problem, a model that predicts contour length measurements from single-molecule forced-dissociation experiments is presented that considers attachment position on the AFM tip, geometric effects, and polymer dynamics of the linkers. Modeled data are compared with measured contour length distributions from several different experimental systems, revealing that current methods underestimate contour lengths. The model enables nonspecific interactions to be identified unequivocally, allows accurate determination of Lc, and, by comparing experimental and modeled distributions, enables partial unfolding events before rupture to be identified unequivocally

Large-eddy simulation sensitivities to variations of configuration and forcing parameters in canonical boundary-layer flows for wind energy applications

The sensitivities of idealized large-eddy simulations (LESs) to variations of model configuration and forcing parameters on quantities of interest to wind power applications are examined. Simulated wind speed, turbulent fluxes, spectra and cospectra are assessed in relation to variations in two physical factors, geostrophic wind speed and surface roughness length, and several model configuration choices, including mesh size and grid aspect ratio, turbulence model, and numerical discretization schemes, in three different code bases. Two case studies representing nearly steady neutral and convective atmospheric boundary layer (ABL) flow conditions over nearly flat and homogeneous terrain were used to force and assess idealized LESs, using periodic lateral boundary conditions. Comparison with fast-response velocity measurements at 10 heights within the lowest 100&thinsp;m indicates that most model configurations performed similarly overall, with differences between observed and predicted wind speed generally smaller than measurement variability. Simulations of convective conditions produced turbulence quantities and spectra that matched the observations well, while those of neutral simulations produced good predictions of stress, but smaller than observed magnitudes of turbulence kinetic energy, likely due to tower wakes influencing the measurements. While sensitivities to model configuration choices and variability in forcing can be considerable, idealized LESs are shown to reliably reproduce quantities of interest to wind energy applications within the lower ABL during quasi-ideal, nearly steady neutral and convective conditions over nearly flat and homogeneous terrain.</p

Ganges Valley Aerosol Experiment: Science and Operations Plan

The Ganges Valley region is one of the largest and most rapidly developing sections of the Indian subcontinent. The Ganges River, which provides the region with water needed for sustaining life, is fed primarily by snow and rainfall associated with Indian summer monsoons. Impacts of changes in precipitation patterns, temperature, and the flow of the snow-fed rivers can be immense. Recent satellite-based measurements have indicated that the upper Ganges Valley has some of the highest persistently observed aerosol optical depth values. The aerosol layer covers a vast region, extending across the Indo-Gangetic Plain to the Bay of Bengal during the winter and early spring of each year. The persistent winter fog in the region is already a cause of much concern, and several studies have been proposed to understand the economic, scientific, and societal dimensions of this problem. During the INDian Ocean EXperiment (INDOEX) field studies, aerosols from this region were shown to affect cloud formation and monsoon activity over the Indian Ocean. This is one of the few regions showing a trend toward increasing surface dimming and enhanced mid-tropospheric warming. Increasing air pollution over this region could modify the radiative balance through direct, indirect, and semi-indirect effects associated with aerosols. The consequences of aerosols and associated pollution for surface insolation over the Ganges Valley and monsoons, in particular, are not well understood. The proposed field study is designed for use of (1) the ARM Mobile Facility (AMF) to measure relevant radiative, cloud, convection, and aerosol optical characteristics over mainland India during an extended period of 9–12 months and (2) the G-1 aircraft and surface sites to measure relevant aerosol chemical, physical, and optical characteristics in the Ganges Valley during a period of 6–12 weeks. The aerosols in this region have complex sources, including burning of coal, biomass, and biofuels; automobile emissions; and dust. The extended AMF deployment will enable measurements under different regimes of the climate and aerosol abundance—in the wet monsoon period with low aerosol loading; in the dry, hot summer with aerosols dispersed throughout the atmospheric column; and in the cool, dry winter with aerosols confined mostly to the boundary later and mid-troposphere. Each regime, in addition, has its own distinct radiative and atmospheric dynamic drivers. The aircraft operational phase will assist in characterizing the aerosols at times when they have been observed to be at the highest concentrations. A number of agencies in India will collaborate with the proposed field study and provide support in terms of planning, aircraft measurements, and surface sites. The high concentration of aerosols in the upper Ganges Valley, together with hypotheses involving several possible mechanisms with direct impacts on the hydrologic cycle of the region, gives us a unique opportunity to generate data sets that will be useful both in understanding the processes at work and in providing answers regarding the effects of aerosols on climate in a region where the perturbation is the highest

Brown carbon: a significant atmospheric absorber of solar radiation?

Several recent observational studies have shown organic carbon aerosols to be a significant source of absorption of solar radiation. The absorbing part of organic aerosols is referred to as "brown" carbon (BrC). Using a global chemical transport model and a radiative transfer model, we estimate for the first time the enhanced absorption of solar radiation due to BrC in a global model. The simulated wavelength dependence of aerosol absorption, as measured by the absorption Ångström exponent (AAE), increases from 0.9 for non-absorbing organic carbon to 1.2 (1.0) for strongly (moderately) absorbing BrC. The calculated AAE for the strongly absorbing BrC agrees with AERONET spectral observations at 440–870 nm over most regions but overpredicts for the biomass burning-dominated South America and southern Africa, in which the inclusion of moderately absorbing BrC has better agreement. The resulting aerosol absorption optical depth increases by 18% (3%) at 550 nm and 56% (38%) at 380 nm for strongly (moderately) absorbing BrC. The global simulations suggest that the strongly absorbing BrC contributes up to +0.25 W m−2 or 19% of the absorption by anthropogenic aerosols, while 72% is attributed to black carbon, and 9% is due to sulfate and non-absorbing organic aerosols coated on black carbon. Like black carbon, the absorption of BrC (moderately to strongly) inserts a warming effect at the top of the atmosphere (TOA) (0.04 to 0.11 W m−2), while the effect at the surface is a reduction (−0.06 to −0.14 W m−2). Inclusion of the strongly absorption of BrC in our model causes the direct radiative forcing (global mean) of organic carbon aerosols at the TOA to change from cooling (−0.08 W m−2) to warming (+0.025 W m−2). Over source regions and above clouds, the absorption of BrC is higher and thus can play an important role in photochemistry and the hydrologic cycle