Developing Models of Aerosol Representation to Investigate Composition, Evolution, Optical Properties, and CCN Spectra Using Measurements of Size-resolved Hygroscopicity PDF Download
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Author: Roberto Gasparini Publisher: ISBN: Category : Languages : en Pages :
Book Description
A Differential Mobility Analyzer/Tandem Differential Mobility Analyzer (DMA/TDMA) was used to measure size distributions, hygroscopicity, and volatility during the May 2003 Aerosol Intensive Operational Period at the Central Facility of the Atmospheric Radiation Measurement Southern Great Plains site. Hygroscopic growth factor distributions for particles at eight dry diameters ranging from 0.012 [mu]m to 0.600 [mu]m were measured. These measurements, along with backtrajectory clustering, were used to infer aerosol composition and evolution. The hygroscopic growth of the smallest and largest particles analyzed was typically less than that of particles with dry diameters of about 0.100 [mu]m. Condensation of secondary organic aerosol on nucleation mode particles may be responsible for the minimal growth observed at the smallest sizes. Growth factor distributions of the largest particles typically contained a non-hygroscopic mode believed to be composed of dust. A model was developed to characterize the hygroscopic properties of particles within a size distribution mode through analysis of the fixed-size hygroscopic growth measurements. This model was used to examine three cases in which the sampled aerosol evolved over a period of hours or days. Additionally, size and hygroscopicity information were combined to model the aerosol as a population of multi-component particles. With this model, the aerosol hygroscopic growth factor f(RH), relating the submicron scattering at high RH to that at low RH, is predicted. The f(RH) values predicted when the hygroscopic fraction of the aerosol is assumed to be metastable agree better with measurements than do those predicted under the assumption of crystalline aerosol. Agreement decreases at RH greater than 65%. This multi-component aerosol model is used to derive cloud condensation nuclei (CCN) spectra for comparison with spectra measured directly with two Desert Research Institute (DRI) CCN spectrometers. Among the 1490 pairs of DMA/TDMA-predicted and DRI-measured CCN concentrations at various critical supersaturations from 0.02-1.05%, the sample number-weighted mean R2 value is 0.74. CCN concentrations are slightly overpredicted at both the lowest (0.02-0.04%) and highest (0.80-1.05%) supersaturations measured. Overall, this multi-component aerosol model based on size distributions and size-resolved hygroscopicity yields reasonable predictions of the humidity-dependent optical properties and CCN spectra of the aerosol.
Author: Roberto Gasparini Publisher: ISBN: Category : Languages : en Pages :
Book Description
A Differential Mobility Analyzer/Tandem Differential Mobility Analyzer (DMA/TDMA) was used to measure size distributions, hygroscopicity, and volatility during the May 2003 Aerosol Intensive Operational Period at the Central Facility of the Atmospheric Radiation Measurement Southern Great Plains site. Hygroscopic growth factor distributions for particles at eight dry diameters ranging from 0.012 [mu]m to 0.600 [mu]m were measured. These measurements, along with backtrajectory clustering, were used to infer aerosol composition and evolution. The hygroscopic growth of the smallest and largest particles analyzed was typically less than that of particles with dry diameters of about 0.100 [mu]m. Condensation of secondary organic aerosol on nucleation mode particles may be responsible for the minimal growth observed at the smallest sizes. Growth factor distributions of the largest particles typically contained a non-hygroscopic mode believed to be composed of dust. A model was developed to characterize the hygroscopic properties of particles within a size distribution mode through analysis of the fixed-size hygroscopic growth measurements. This model was used to examine three cases in which the sampled aerosol evolved over a period of hours or days. Additionally, size and hygroscopicity information were combined to model the aerosol as a population of multi-component particles. With this model, the aerosol hygroscopic growth factor f(RH), relating the submicron scattering at high RH to that at low RH, is predicted. The f(RH) values predicted when the hygroscopic fraction of the aerosol is assumed to be metastable agree better with measurements than do those predicted under the assumption of crystalline aerosol. Agreement decreases at RH greater than 65%. This multi-component aerosol model is used to derive cloud condensation nuclei (CCN) spectra for comparison with spectra measured directly with two Desert Research Institute (DRI) CCN spectrometers. Among the 1490 pairs of DMA/TDMA-predicted and DRI-measured CCN concentrations at various critical supersaturations from 0.02-1.05%, the sample number-weighted mean R2 value is 0.74. CCN concentrations are slightly overpredicted at both the lowest (0.02-0.04%) and highest (0.80-1.05%) supersaturations measured. Overall, this multi-component aerosol model based on size distributions and size-resolved hygroscopicity yields reasonable predictions of the humidity-dependent optical properties and CCN spectra of the aerosol.
Author: Yong Seob Lee Publisher: ISBN: Category : Languages : en Pages :
Book Description
This dissertation describes the use of measured aerosol size distributions and size-resolved hygroscopic growth to examine the physical and chemical properties of several particle classes. The primary objective of this work was to investigate the optical and cloud forming properties of a range of ambient aerosol types measured in a number of different locations. The tool used for most of these analyses is a differential mobility analyzer / tandem differential mobility analyzer (DMA / TDMA) system developed in our research group. To collect the data described in two of the chapters of this dissertation, an aircraft-based version of the DMA / TDMA was deployed to Japan and California. The data described in two other chapters were conveniently collected during a period when the aerosol of interest came to us. The unique aspect of this analysis is the use of these data to isolate the size distributions of distinct aerosol types in order to quantify their optical and cloud forming properties. I used collected data during the Asian Aerosol Characterization Experiment (ACE-Asia) to examine the composition and homogeneity of a complex aerosol generated in the deserts and urban regions of China and other Asian countries. An aircraft-based TDMA was used for the first time during this campaign to examine the size-resolved hygroscopic properties of the aerosol. The Asian Dust Above Monterey (ADAM-2003) study was designed both to evaluate the degree to which models can predict the long-range transport of Asian dust, and to examine the physical and optical properties of that aged dust upon reaching the California coast. Aerosol size distributions and hygroscopic growth were measured in College Station, Texas to investigate the cloud nucleating and optical properties of a biomass burning aerosol generated from fires on the Yucatan Peninsula. Measured aerosol size distributions and size-resolved hygroscopicity and volatility were used to infer critical supersaturation distributions of the distinct particle types that were observed during this period. The predicted cloud condensation nuclei concentrations were used in a cloud model to determine the impact of the different aerosol types on the expected cloud droplet concentration. RH-dependent aerosol extinction coefficients were also calculated.
Author: Eric P. Shettle Publisher: ISBN: Category : Aerosols Languages : en Pages : 100
Book Description
Aerosol models have been developed for the lower atmosphere. These models are representative of conditions found in rural, urban, and maritime air masses. The changes in the aerosol properties with variations in the relative humidity are discussed. To describe the aerosol optical properties in the extreme of 100 percent relative humidity, several fog models are presented. For each model the coefficients for extinction, scattering, and absorption, the angular scattering distribution, and other optical parameters have been computed for wavelengths between 0.2 and 40 microns. These aerosol models are presented together with a review of their experimental basis. The optical properties of these models are discussed and some comparisons of the model with experimental measurements are presented.
Author: Muhammad Altaf Publisher: ISBN: Category : Languages : en Pages :
Book Description
The Earths atmosphere is composed of a wide variety of gas phase species and particulate matter that have a large impact on our climate. Though our understanding of the climate system has improved significantly over the past few decades, the impact of aerosol particles remains uncertain. Aerosol particles can affect climate through the absorption and scattering of radiation (aerosol direct effect) and by serving as cloud condensation nuclei (aerosol indirect effect). It is known that aerosol particles cause a net cooling effect on the planet, but the magnitude of cooling is unclear and remains under investigation. A large part of this uncertainty is due to an incomplete understanding of the complex physical and chemical properties of aerosol particles such as composition, morphology, and phase state.In this dissertation, we focus on investigating the role of particle size and composition in determining morphology. We have discovered that for some organic aerosol systems, particle morphology depends on size, where small particles are homogeneous and large particles are phase separated. To explore the origins of this size dependent behavior, we have worked with a model organic aerosol system, poly(ethylene glycol)-400 mixed with ammonium sulfate. We have used cryogenic-transmission electron microscopy to probe the effect of phase separation mechanism on particle morphology by varying the organic aerosol composition. Our results suggest that a size dependent morphology occurs due to an activated process, where the presence or absence of an activation barrier to phase separation controls the resulting morphology.We have also explored the kinetics and thermodynamics of the phase separation process that results in a size dependent morphology by varying the experimental drying rates. Drying rates that span over four orders of magnitude were investigated. We have observed that at the fastest drying rates, the size of the transition region where both phase separated and homogeneous morphologies exist is on the order of ~100 nm. At the slowest drying rates, the transition region shifts to smaller diameters and the width narrows to ~3 nm. Our results suggest that a size dependent morphology persists to the slowest drying rates. Thus, we conclude that an underlying thermodynamic effect results in this size dependent behavior, rather than solely a kinetic phenomenon.To determine the atmospheric implications of a size dependent morphology, we have used a cloud condensation nuclei counter to probe the effect of a homogeneous vs. a phase separated morphology on cloud condensation nuclei (CCN) activity. We have found that the activation diameters differ for particles which have the same composition, but varying morphology. Since aerosol optical properties are a sensitive measure of particle structure, we have studied the morphology-resolved optical properties of organic aerosol using cavity ring-down spectroscopy. Our spectroscopy data indicate that the optical properties of core-shell and partially engulfed particles are approximately equal, but different than the prediction for homogeneous particles. By accurately parametrizing aerosol particle morphology, optical properties, and CCN activity we will be able to better predict heterogeneous chemistry in the atmosphere, in addition to the aerosol direct and aerosol indirect effects which play a critical role in constraining climate forcing.
Author: Panel on Aerosol Radiative Forcing and Climate Change Publisher: National Academies Press ISBN: 0309588871 Category : Science Languages : en Pages : 180
Book Description
This book recommends the initiation of an "integrated" research program to study the role of aerosols in the predicted global climate change. Current understanding suggest that, even now, aerosols, primarily from anthropogenic sources, may be reducing the rate of warming caused by greenhouse gas emissions. In addition to specific research recommendations, this book forcefully argues for two kinds of research program integration: integration of the individual laboratory, field, and theoretical research activities and an integrated management structure that involves all of the concerned federal agencies.
Author: National Academies of Sciences, Engineering, and Medicine Publisher: National Academies Press ISBN: 0309443458 Category : Science Languages : en Pages : 53
Book Description
One of the most significant and uncertain aspects of climate change projections is the impact of aerosols on the climate system. Aerosols influence the climate indirectly by interacting with nearby clouds leading to small changes in cloud cover, thickness, and altitude, which significantly affect Earth's radiative balance. Advancements have been made in recent years on understanding the complex processes and atmospheric interactions involved when aerosols interact with surrounding clouds, but further progress has been hindered by limited observations. The National Academies of Sciences, Engineering, and Medicine organized a workshop to discuss the usefulness of the classified observing systems in advancing understanding of cloud and aerosol interactions. Because these systems were not developed with weather and climate modeling as a primary mission objective, many participants said it is necessary for scientists to find creative ways to utilize the data. The data from these systems have the potential to be useful in advancing understanding of cloud and aerosol interactions. This publication summarizes the presentations and discussions from the workshop.
Author: Richard Herbert Moore Publisher: ISBN: Category : Atmospheric aerosols Languages : en Pages :
Book Description
Atmospheric aerosols are known to exert a significant influence on the Earth's climate system; however, the magnitude of this influence is highly uncertain because of the complex interaction between aerosols and water vapor to form clouds. Toward reducing this uncertainty, this dissertation outlines a series of laboratory and in-situ field measurements, instrument technique development, and model simulations designed to characterize the ability of aerosols to act as cloud condensation nuclei (CCN) and form cloud droplets. Specifically, we empirically quantify the mixing state and thermodynamic properties of organic aerosols (e.g., hygroscopicity and droplet condensational uptake coefficient) measured in polluted and non-polluted environments including Alaska, California, and Georgia. It is shown that organic aerosols comprise a substantial portion of the aerosol mass and are often water soluble. CCN measurements are compared to predictions from theory in order to determine the error associated with simplified composition and mixing state assumptions employed by current large-scale models, and these errors are used to constrain the uncertainty of global and regional cloud droplet number and albedo using a recently-developed cloud droplet parameterization adjoint coupled with the GMI chemical transport model. These sensitivities are important because they describe the main determinants of climate forcing. We also present two novel techniques for fast measurements of CCN concentrations with high size, supersaturation, and temporal resolution that substantially improve the state of the art by several orders of magnitude. Ultimately, this work represents a step toward better understanding how atmospheric aerosols influence cloud properties and Earth's climate.
Author: Roberto Gasparini
Author: Roberto Gasparini
Author: 
Author: Yong Seob Lee
Author: Eric P. Shettle
Author: Muhammad Altaf
Author: Panel on Aerosol Radiative Forcing and Climate Change
Author: 
Author: National Academies of Sciences, Engineering, and Medicine
Author: Alan P. Waggoner
Author: Richard Herbert Moore