A wide range of estimates exists for the radiative forcing of the aerosol effect on cloud albedo. We argue that a component of this uncertainty derives from the use of a wide range of observational ...scales and platforms. Aerosol influences cloud properties at the microphysical scale, or the "process scale", but observations are most often made of bulk properties over a wide range of resolutions, or "analysis scales". We show that differences between process and analysis scales incur biases in quantification of the albedo effect through the impact that data aggregation and computational approach have on statistical properties of the aerosol or cloud variable, and their covariance. Measures made within this range of scales are erroneously treated as equivalent, leading to a large uncertainty in associated radiative forcing estimates. Issues associated with the coarsening of observational resolution particular to quantifying the albedo effect are discussed. Specifically, the omission of the constraint on cloud liquid water path and the separation in space of cloud and aerosol properties from passive, space-based remote sensors dampen the measured strength of the albedo effect. We argue that, because of this lack of constraints, many of these values are in fact more representative of the full range of aerosol-cloud interactions and their associated feedbacks. Based on our understanding of these biases we propose a new observationally-based and process-model-constrained, method for estimating aerosol-cloud interactions that can be used for radiative forcing estimates as well as a better characterization of the uncertainties associated with those estimates.
Values for Mie‐equivalent aerosol asymmetry parameter (g) were derived using a variety of methods from the large suite of measurements (in situ and remote from surface and aircraft) made in Oklahoma ...during the 2003 aerosol Intensive Operations Period (IOP). Median values derived for dry asymmetry parameter at 550 nm ranged between 0.55 and 0.63 over all instruments and for all derivation methods, with the exception of one instrument which did not measure over the full size range of optically important aerosol. Median values for the “wet” asymmetry parameter (i.e., asymmetry parameter at humidity conditions closer to ambient) were between 0.59 and 0.72. Values for g derived for surface and airborne in situ measurements were highly correlated, but in situ and remote sensing measurements both at the surface and aloft did not agree as well because of vertical inhomogeneity of the aerosol. Radiative forcing calculations suggest that a 10% decrease in g would result in a 19% reduction in top of atmosphere radiative forcing for the conditions observed during the IOP. Comparison of the different methods for deriving g suggests that in computing the asymmetry parameter, aerosol size is the most important parameter to measure; composition is less important except for how it influences the hygroscopic growth (i.e., size) of particles.
Emissions of SO2 in the United States have declined since the early 1990s, resulting in a decrease in aerosol sulfate mass in the Southeastern U.S. of −4.5(±0.9)% yr−1 between 1992 and 2013. Organic ...aerosol mass, the other major aerosol component in the Southeastern U.S., has decreased more slowly despite concurrent emission reductions in anthropogenic precursors. Summertime measurements in rural Alabama quantify the change in aerosol light extinction as a function of aerosol composition and relative humidity. Application of this relationship to composition data from 2001 to 2013 shows that a −1.1(±0.7)% yr−1 decrease in extinction can be attributed to decreasing aerosol water mass caused by the change in aerosol sulfate/organic ratio. Calculated reductions in extinction agree with regional trends in ground‐based and satellite‐derived aerosol optical depth. The diurnally averaged summertime surface radiative effect has changed by 8.0 W m−2, with 19% attributed to the decrease in aerosol water.
Key Points
Aerosol sulfate mass has decreased faster than organic mass in the SE U.S.Aerosol water mass has decreased due to decreasing sulfate/organic ratioAerosol extinction and radiative forcing have changed due to composition changes
The Department of Energy's Atmospheric Radiation Measurement (ARM) program sponsored a large aerosol intensive observation period (AIOP) to study aerosol during the month of May 2003 around the ...Southern Great Plains (SGP) Climate Research Facility (CRF) in north central Oklahoma. Redundant measurements of aerosol optical properties were made using different techniques at the surface as well as in vertical profile with sensors aboard two aircraft. One of the principal motivations for this experiment was to resolve the disagreement between models and measurements of diffuse horizontal broadband shortwave irradiance at the surface, especially for modest aerosol loading. This paper focuses on using the redundant aerosol and radiation measurements during this AIOP to compare direct beam and diffuse horizontal broadband shortwave irradiance measurements and models at the surface for a wide range of aerosol cases that occurred during 30 clear‐sky periods on 13 days of May 2003. Models and measurements are compared over a large range of solar‐zenith angles. Six different models are used to assess the relative agreement among them and the measurements. Better agreement than previously achieved appears to be the result of better specification of input parameters and better measurements of irradiances than in prior studies. Biases between modeled and measured direct irradiances are in the worst case 1%, and biases between modeled and measured diffuse irradiances are less than 1.9%.
The largest uncertainty in the radiative forcing of climate change over the industrial era is that due to aerosols, a substantial fraction of which is the uncertainty associated with scattering and ...absorption of shortwave (solar) radiation by anthropogenic aerosols in cloud-free conditions (IPCC, 2001). Quantifying and reducing the uncertainty in aerosol influences on climate is critical to understanding climate change over the industrial period and to improving predictions of future climate change for assumed emission scenarios. Measurements of aerosol properties during major field campaigns in several regions of the globe during the past decade are contributing to an enhanced understanding of atmospheric aerosols and their effects on light scattering and climate. The present study, which focuses on three regions downwind of major urban/population centers (North Indian Ocean (NIO) during INDOEX, the Northwest Pacific Ocean (NWP) during ACE-Asia, and the Northwest Atlantic Ocean (NWA) during ICARTT), incorporates understanding gained from field observations of aerosol distributions and properties into calculations of perturbations in radiative fluxes due to these aerosols. This study evaluates the current state of observations and of two chemical transport models (STEM and MOZART). Measurements of burdens, extinction optical depth (AOD), and direct radiative effect of aerosols (DRE – change in radiative flux due to total aerosols) are used as measurement-model check points to assess uncertainties. In-situ measured and remotely sensed aerosol properties for each region (mixing state, mass scattering efficiency, single scattering albedo, and angular scattering properties and their dependences on relative humidity) are used as input parameters to two radiative transfer models (GFDL and University of Michigan) to constrain estimates of aerosol radiative effects, with uncertainties in each step propagated through the analysis. Constraining the radiative transfer calculations by observational inputs increases the clear-sky, 24-h averaged AOD (34±8%), top of atmosphere (TOA) DRE (32±12%), and TOA direct climate forcing of aerosols (DCF – change in radiative flux due to anthropogenic aerosols) (37±7%) relative to values obtained with "a priori" parameterizations of aerosol loadings and properties (GFDL RTM). The resulting constrained clear-sky TOA DCF is −3.3±0.47, −14±2.6, −6.4±2.1 Wm−2 for the NIO, NWP, and NWA, respectively. With the use of constrained quantities (extensive and intensive parameters) the calculated uncertainty in DCF was 25% less than the "structural uncertainties" used in the IPCC-2001 global estimates of direct aerosol climate forcing. Such comparisons with observations and resultant reductions in uncertainties are essential for improving and developing confidence in climate model calculations incorporating aerosol forcing.
Abstract
This work is motivated by previous studies of transatlantic transport of Saharan dust and the observed quasi-static nature of coarse mode aerosol with a volume median diameter (VMD) of ...approximately 3.5 μm. The authors examine coarse mode contributions from transpacific transport of dust to North American aerosol properties using a dataset collected at the high-elevation Storm Peak Laboratory (SPL) and the nearby Atmospheric Radiation Measurement (ARM) Mobile Facility. Collected ground-based data are complemented by quasi-global model simulations and satellite and ground-based observations. The authors identify a major dust event associated mostly with a transpacific plume (about 65% of near-surface aerosol mass) in which the coarse mode with moderate (~3 μm) VMD is distinct and contributes substantially to total aerosol volume (up to 70%) and scattering (up to 40%). The results demonstrate that the identified plume at the SPL site has a considerable fraction of supermicron particles (VMD ~3 μm) and, thus, suggest that these particles have a fairly invariant behavior despite transpacific transport. If confirmed in additional studies, this invariant behavior may simplify considerably parameterizations for size-dependent processes associated with dust transport and removal.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Pearl River Delta (PRD) region in southeastern China is one of the most polluted industrial and metropolitan areas in the world. We report single‐particle measurements of the refractory black ...carbon (rBC) component in ambient aerosol in the region, and we interpret the results to improve understanding of the importance of rBC for radiative forcing in this region and others like it. A Single‐Particle Soot Photometer (SP2) provided rBC mass loadings, size distributions, and mixing state information. Average rBC loadings are approximately an order of magnitude higher than those measured near Houston, Texas, a major U.S. metropolitan area. The rBC in the PRD is also more often internally mixed with nonrefractory materials than is rBC around Houston. Localized atmospheric heating from rBC solar absorption reached an average rate of 0.4 K d−1. A one‐dimensional discrete ordinates radiative transfer (DISORT) model coupled with the average measured rBC is used to illustrate the potential local contribution of rBC mass and associated scattering aerosol to the radiative forcing. Solar energy deposition rates in the atmosphere at the sampling site due to rBC absorption are estimated to have an average value of 17 W m−2 and be largest in the first 1 km above the ground. These results indicate that rBC has significant potential to influence local meteorology and climate parameters in the PRD region.
Key Points
We performed black carbon measurements in China
A single‐particle soot photometer was used to determine black carbon properties
Solar energy deposition rates due to the black carbon were estimated
As demand for nurse practitioners in all types of intensive care units continues to increase, ensuring successful integration of these nurses into adult and pediatric general and specialty intensive ...care units poses several challenges. Adding nurse practitioners requires strategic planning to define critical aspects of the care delivery model before the practitioners are hired, develop a comprehensive program for integrating and training these nurses, and create a plan for implementing the program. Key strategies to ensure successful integration include defining and implementing the role of nurse practitioners, providing options for orientation, and supporting and training novice nurse practitioners. Understanding the importance of appropriate role utilization, the depth of knowledge and skill expected of nurse practitioners working in intensive care units, the need for a comprehensive training program, and a commitment to continued professional development beyond orientation are necessary to fully realize the contributions of these nurses in critical care.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, OILJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK, VSZLJ
At our institution, the most common cohort of individuals having computed tomography colonography (CTC) are those that require primary screening for colorectal cancer and were unable to tolerate or ...failed optical colonoscopy (OC). CTC is an efficient method for detecting polyps, masses, flat-lesions, and overt colorectal cancer, serving as a viable alternative to colonoscopy. This study follows patients with negative CTC results to evaluate the number of clinically significant lesions that may have been potentially missed by CTC. We suspect this number will be exceedingly low given the high sensitivity of this technique.
All patients with negative CTC screening (n = 509) in the Eastern Health Medical Health Region, located in Newfoundland and Labrador, Canada were included. An electronic medical record review was undertaken, encompassing provider, colonoscopy, imaging, and histopathology reports. Subjects were also checked through the Newfoundland Cancer Clinic Registry Database. All incidents of colorectal cancer were recorded.
The study cohort comprised 509 subjects. These subjects were followed for an average of 7.88 years. Two colorectal adenocarcinomas in this cohort were identified representing a crude cancer incidence rate of 0.49 cancers per 1000 patient years, and a rate of 0.39% following a normal CTC.
Colorectal cancer presenting clinically is rare in the 7.88 years following a negative CTC, suggesting CTC is equally effective for colorectal screening compared to OC. Furthermore, current guidelines that recommend interval CTC screening every 5 years is conservative, and interval screening can likely be recommended over a longer time frame.
Dans notre établissement, parmi les individus qui se soumettent à une coloscopie virtuelle (ou coloscopie par tomodensitométrie, CTDM), la cohorte la plus courante se compose de ceux nécessitant un premier dépistage de cancer colorectal et qui ne peuvent pas tolérer une coloscopie optique ou n'ont pas réussi à passer cet examen. La CTDM est une méthode efficace de détection des polypes, masses, lésions planes et cancers colorectaux manifestes, servant de solution alternative utile à la coloscopie conventionnelle. Lors de cette étude, des patients présentant des résultats négatifs à un examen de CTDM ont été suivis pour évaluer le nombre de lésions d'importance clinique qui n'auraient pas été détectées par CTDM. Notre hypothèse était que ce nombre serait excessivement faible en raison de la forte sensibilité de cette technique.
Tous les patients dont le dépistage par CTDM était négatif (n = 509) dans les services de santé de la région Eastern Health, à Terre-Neuve-et-Labrador, au Canada, ont été inclus dans l’étude. Une revue des dossiers médicaux électroniques a été réalisée, en tenant compte des rapports de professionnels de la santé, de coloscopie, d'imagerie et d'histopathologie. Une recherche sur les sujets a également été effectuée dans la base de données des archives cliniques sur le cancer de Terre-Neuve (Newfoundland Cancer Clinic Registry Database). Tous les cas de cancer colorectal ont été relevés.
Cette étude de cohorte comportait 509 sujets qui ont fait l'objet d'un suivi pendant une durée moyenne de 7,88 ans. Deux adénocarcinomes colorectaux ont été identifiés dans cette cohorte, ce qui représente un taux brut de cancers de 0,49 pour 1 000 patients-années et un taux de 0,39 % suite à un CTDM normal.
Le cancer colorectal à présentation clinique est rare au cours des 7,88 ans consécutifs à un examen de CTDM négatif, ce qui suggère que l'efficacité de cette technique pour le dépistage du cancer colorectal est équivalente à celle de la coloscopie optique. De plus, les directives en vigueur qui préconisent des intervalles de dépistage par CTDM de 5 ans sont conservatrices et la recommandation de recourir à des échéances plus longues entre les examens de dépistage est possible.
A three‐dimensional (3D) atmospheric radiative transfer model that explicitly represents surface albedo heterogeneity is tested against a one‐dimensional model and surface irradiance observations in ...a polar region where land cover heterogeneity is high. For observations located near high latitude coastlines, the contrast between the highly absorbing ocean and reflective snow surface creates spatial heterogeneity, or a 3D effect, around the observation site. The resulting effect on radiation at the sensor should be taken into account when using a solar radiative transfer model to interpret measurements. This assessment shows that better closure is obtained with a three‐dimensional model (≤5%) versus a plane‐parallel model (≤7%). The importance of the surface 3D effect increases with aerosol or cloud optical depth and with surface albedo contrast. The model used here can be implemented at any surface site given the surrounding land cover properties.
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