We present an overview of the background, scientific goals, and execution of the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC) project of April 2008. We then summarize ...airborne measurements, made in the troposphere of the Alaskan Arctic, of aerosol particle size distributions, composition, and optical properties and discuss the sources and transport of the aerosols. The aerosol data were grouped into four categories based on gas-phase composition. First, the background troposphere contained a relatively diffuse, sulfate-rich aerosol extending from the top of the sea-ice inversion layer to 7.4 km altitude. Second, a region of depleted (relative to the background) aerosol was present within the surface inversion layer over sea-ice. Third, layers of dense, organic-rich smoke from open biomass fires in southern Russia and southeastern Siberia were frequently encountered at all altitudes from the top of the inversion layer to 7.1 km. Finally, some aerosol layers were dominated by components originating from fossil fuel combustion. Of these four categories measured during ARCPAC, the diffuse background aerosol was most similar to the average springtime aerosol properties observed at a long-term monitoring site at Barrow, Alaska. The biomass burning (BB) and fossil fuel layers were present above the sea-ice inversion layer and did not reach the sea-ice surface during the course of the ARCPAC measurements. The BB aerosol layers were highly scattering and were moderately hygroscopic. On average, the layers produced a noontime net heating of ~0.1 K day−1 between 3 and 7 km and a slight cooling at the surface. The ratios of particle mass to carbon monoxide (CO) in the BB plumes, which had been transported over distances >5000 km, were comparable to the high end of literature values derived from previous measurements in wildfire smoke. These ratios suggest minimal precipitation scavenging and removal of the BB particles between the time they were emitted and the time they were observed in dense layers above the sea-ice inversion layer.
Meridional transport from the tropics redistributes ozone and water vapor at middle and high latitudes. In situ measurements of water vapor, CH4, and N2O, acquired aboard the NASA ER‐2 aircraft ...during January−March 2000 in a campaign to survey the Arctic vortex, are used to examine transport into the lowermost stratosphere in the context of middle‐ and high‐latitude ozone declines observed over the last several decades. Analysis of tracer‐tracer correlations of H2O + 2*CH4 and N2O indicates that rapid, poleward isentropic transport from the lower tropical stratosphere coupled with diabatic descent between the subtropical and polar jet streams delivers very young air to the high‐latitude lowermost stratosphere during winter, while descent of older air from the vortex and subsequent transport to lower latitudes is very limited. From middle to late winter, mixing ratios of H2O + 2*CH4 decrease by about 1 ppmv immediately outside the vortex, consistent with rapid transport of the winter phase of the seasonal cycle in water vapor to high latitudes from the lower tropical stratosphere. No evidence of isentropic mixing from the upper tropical troposphere survives in the high‐latitude lowermost stratosphere except below 350 K, where markedly higher water vapor mixing ratios indicate mixing from the extratropical troposphere. All of these transport processes pose dynamical and chemical consequences for ozone. Transport from the lower tropical stratosphere (1) exports ozone‐poor air to midlatitudes and the subvortex region and (2) distributes elevated water vapor to high latitudes, potentially enhancing halogen‐catalyzed ozone destruction through heterogeneous processing in the polar vortex.
A large fraction of atmospheric aerosols are derived from organic compounds with various volatilities. A National Oceanic and Atmospheric Administration (NOAA) WP-3D research aircraft made airborne ...measurements of the gaseous and aerosol composition of air over the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico that occurred from April to August 2010. A narrow plume of hydrocarbons was observed downwind of DWH that is attributed to the evaporation of fresh oil on the sea surface. A much wider plume with high concentrations of organic aerosol (>25 micrograms per cubic meter) was attributed to the formation of secondary organic aerosol (SOA) from unmeasured, less volatile hydrocarbons that were emitted from a wider area around DWH. These observations provide direct and compelling evidence for the importance of formation of SOA from less volatile hydrocarbons.
The determination of sediment and nutrient loads is typically based on the collection and analysis of grab samples. The frequency and regularity of traditional sampling may not provide representation ...of constituent loading, particularly in systems with flashy hydrology. At two sites in the Little Bear River, Utah, continuous, high-frequency turbidity was used with surrogate relationships to generate estimates of total phosphorus and total suspended solids concentrations, which were paired with discharge to estimate annual loads. The high frequency records were randomly subsampled to represent hourly, daily, weekly, and monthly sampling frequencies and to examine the effects of timing, and resulting annual load estimates were compared to the reference loads. Higher frequency sampling resulted in load estimates that better approximated the reference loads. The degree of bias was greater at the more hydrologically responsive site in the upper watershed, which required a higher sampling frequency than the lower watershed site to achieve the same level of accuracy in estimating the reference load. The hour of day and day of week of sampling impacted load estimation, depending on site and hydrologic conditions. The effects of sampling frequency on the determination of compliance with a water quality criterion were also examined. These techniques can be helpful in determining necessary sampling frequency to meet the objectives of a water quality monitoring program. PUBLICATION ABSTRACT
We use a global chemical transport model (GEOS‐Chem) to interpret aircraft curtain observations of black carbon (BC) aerosol over the Pacific from 85°N to 67°S during the 2009–2011 HIAPER ...(High‐Performance Instrumented Airborne Platform for Environmental Research) Pole‐to‐Pole Observations (HIPPO) campaigns. Observed concentrations are very low, implying much more efficient scavenging than is usually implemented in models. Our simulation with a global source of 6.5 Tg a−1 and mean tropospheric lifetime of 4.2 days (versus 6.8 ± 1.8 days for the Aerosol Comparisons between Observations and Models (AeroCom) models) successfully simulates BC concentrations in source regions and continental outflow and captures the principal features of the HIPPO data but is still higher by a factor of 2 (1.48 for column loads) over the Pacific. It underestimates BC absorbing aerosol optical depths (AAODs) from the Aerosol Robotic Network by 32% on a global basis. Only 8.7% of global BC loading in GEOS‐Chem is above 5 km, versus 21 ± 11% for the AeroCom models, with important implications for radiative forcing estimates. Our simulation yields a global BC burden of 77 Gg, a global mean BC AAOD of 0.0017, and a top‐of‐atmosphere direct radiative forcing (TOA DRF) of 0.19 W m−2, with a range of 0.17–0.31 W m−2 based on uncertainties in the BC atmospheric distribution. Our TOA DRF is lower than previous estimates (0.27 ± 0.06 W m−2 in AeroCom, 0.65–0.9 W m−2 in more recent studies). We argue that these previous estimates are biased high because of excessive BC concentrations over the oceans and in the free troposphere.
Key Points
A global distribution of BC is simulated in GEOS‐Chem
Results imply more efficient BC removal than is usually included in models
Previous estimates of DRF from BC were biased high due to excessive remote BC
Stratospheric H2O, CH4, and H2 measured during the 1999/2000 Arctic winter are used to examine the total hydrogen budget and to quantify hydration and dehydration within the Arctic polar vortex. The ...mean volume mixing ratio of equivalent water, H2Oeq = H2O + 2*CH4, was found to be 7.38 ± 0.11 ppmv in the vortex and 7.35 ± 0.10 ppmv in the extravortex and vortex edge regions, implying insignificant net loss of H2O from the 50–90 hPa layer of the Arctic stratosphere. However, isolated occurrences of hydration and dehydration were observed on several flights. In particular, an average dehydration of 0.31 ppmv was encountered for 440 km along the NASA ER‐2 aircraft flight path on 27 January 2000 (0.63 ppmv maximum dehydration). Diabatic back‐trajectory calculations indicate that this dehydrated air parcel may have encountered temperatures below the ice frost point two weeks earlier. In addition to these isolated events, measurements of equivalent water indicated a decrease with altitude throughout the lower stratospheric vortex and vortex edge. Potential causes of this altitude dependence are quantified.
Miscommunications are a leading cause of serious medical errors. Data from multicenter studies assessing programs designed to improve handoff of information about patient care are lacking.
We ...conducted a prospective intervention study of a resident handoff-improvement program in nine hospitals, measuring rates of medical errors, preventable adverse events, and miscommunications, as well as resident workflow. The intervention included a mnemonic to standardize oral and written handoffs, handoff and communication training, a faculty development and observation program, and a sustainability campaign. Error rates were measured through active surveillance. Handoffs were assessed by means of evaluation of printed handoff documents and audio recordings. Workflow was assessed through time-motion observations. The primary outcome had two components: medical errors and preventable adverse events.
In 10,740 patient admissions, the medical-error rate decreased by 23% from the preintervention period to the postintervention period (24.5 vs. 18.8 per 100 admissions, P<0.001), and the rate of preventable adverse events decreased by 30% (4.7 vs. 3.3 events per 100 admissions, P<0.001). The rate of nonpreventable adverse events did not change significantly (3.0 and 2.8 events per 100 admissions, P=0.79). Site-level analyses showed significant error reductions at six of nine sites. Across sites, significant increases were observed in the inclusion of all prespecified key elements in written documents and oral communication during handoff (nine written and five oral elements; P<0.001 for all 14 comparisons). There were no significant changes from the preintervention period to the postintervention period in the duration of oral handoffs (2.4 and 2.5 minutes per patient, respectively; P=0.55) or in resident workflow, including patient-family contact and computer time.
Implementation of the handoff program was associated with reductions in medical errors and in preventable adverse events and with improvements in communication, without a negative effect on workflow. (Funded by the Office of the Assistant Secretary for Planning and Evaluation, U.S. Department of Health and Human Services, and others.).
We compared the version 5 Microwave Limb Sounder (MLS), version 3 Polar Ozone and Aerosol Measurement III (POAM III), version 6.0 Stratospheric Aerosol and Gas Experiment II (SAGE II), and NASA ER‐2 ...aircraft measurements made in the Northern Hemisphere in January–February 2000 during the SAGE III Ozone Loss and Validation Experiment (SOLVE). This study addresses one of the key scientific objectives of the SOLVE campaign, namely, to validate multiplatform satellite measurements made in the polar stratosphere during winter. This intercomparison was performed by using a traditional correlative analysis (TCA) and a trajectory hunting technique (THT). TCA compares profiles colocated within a chosen spatial‐temporal vicinity. Launching backward and forward trajectories from the points of measurement, the THT identifies air parcels sampled at least twice within a prescribed match criterion during the course of 5 days. We found that the ozone measurements made by these four instruments agree most of the time within ±10% in the stratosphere up to 1400 K (∼35 km). The water vapor measurements from POAM III and the ER‐2 Harvard Lyman α hygrometer and Jet Propulsion Laboratory laser hygrometer agree to within ±0.5 ppmv (or about ±10%) in the lower stratosphere above 380 K. The MLS and ER‐2 ClO measurements agree within their error bars for the TCA. The MLS and ER‐2 nitric acid measurements near 17‐ to 20‐km altitude agree within their uncertainties most of the time with a hint of a positive offset by MLS according to the TCA. We also applied the Atmospheric and Environmental Research, Inc. box model constrained by the ER‐2 measurements for analysis of the ClO and HNO3 measurements using the THT. We found that: (1) the model values of ClO are smaller by about 0.3–0.4 (0.2) ppbv below (above) 400 K than those by MLS and (2) the HNO3 comparison shows a positive offset of MLS values by ∼1 and 1–2 ppbv below 400 K and near 450 K, respectively. Our study shows that, with some limitations (like HNO3 comparison under polar stratospheric cloud conditions), the THT is a more powerful tool for validation studies than the TCA, making conclusions of the comparison statistically more robust.
Most structure‐based drug discovery methods utilize crystal structures of receptor proteins. Crystal engineering, on the other hand, utilizes the wealth of chemical information inherent in ...small‐molecule crystal structures in the Cambridge Structural Database (CSD). We show that the interaction surfaces and shapes of molecules in experimentally determined small‐molecule crystal structures can serve as effective tools in drug discovery. Our description of the shape and interaction propensities of molecules in their crystal structures can be used to screen them for specific binding compatibility with protein targets, as demonstrated through the high‐throughput profiling of around 138 000 small‐molecule structures in the CSD and a series of drug–protein crystal structures. Electron‐density‐based intermolecular boundary surfaces in small‐molecule crystal structures and in target‐protein pockets are utilized to identify potential ligand molecules from the CSD based on 3D shape and intermolecular interaction matching.
Crystal clear: Highly efficient profiling of intermolecular interactions and molecular shape in crystal structures led to a new drug‐discovery approach that combines small‐molecule crystallography and protein crystallography to identify potential ligand molecules from the Cambridge Structural Database.
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