Single Particle Characterization Source Apportionment And Aging Effects Of Ambient Aerosols In Southern California

Download Single Particle Characterization Source Apportionment And Aging Effects Of Ambient Aerosols In Southern California full books in PDF, epub, and Kindle. Read online Single Particle Characterization Source Apportionment And Aging Effects Of Ambient Aerosols In Southern California ebook anywhere anytime directly on your device. Fast Download speed and no annoying ads. We cannot guarantee that every ebooks is available!

Single Particle Characterization, Source Apportionment, and Aging Effects of Ambient Aerosols in Southern California

Author : Laura Grace Shields
Publisher : ProQuest
ISBN 13 : 9780549598473
Total Pages : 230 pages
Book Rating : 4.5/5 (984 download)

DOWNLOAD NOW!

Book Synopsis Single Particle Characterization, Source Apportionment, and Aging Effects of Ambient Aerosols in Southern California by : Laura Grace Shields

Download or read book Single Particle Characterization, Source Apportionment, and Aging Effects of Ambient Aerosols in Southern California written by Laura Grace Shields and published by ProQuest. This book was released on 2008 with total page 230 pages. Available in PDF, EPUB and Kindle. Book excerpt: Composed of a mixture of chemical species and phases and existing in a variety of shapes and sizes, atmospheric aerosols are complex and can have serious influence on human health, the environment, and climate. In order to better understand the impact of aerosols on local to global scales, detailed measurements on the physical and chemical properties of ambient particles are essential. In addition, knowing the origin or the source of the aerosols is important for policymakers to implement targeted regulations and effective control strategies to reduce air pollution in their region. One of the most ground breaking techniques in aerosol instrumentation is single particle mass spectrometry (SPMS), which can provide online chemical composition and size information on the individual particle level. The primary focus of this work is to further improve the ability of one specific SPMS technique, aerosol time-of-flight mass spectrometry (ATOFMS), for the use of identifying the specific origin of ambient aerosols, which is known as source apportionment. The ATOFMS source apportionment method utilizes a library of distinct source mass spectral signatures to match the chemical information of the single ambient particles. The unique signatures are obtained in controlled source characterization studies, such as with the exhaust emissions of heavy duty diesel vehicles (HDDV) operating on a dynamometer. The apportionment of ambient aerosols is complicated by the chemical and physical processes an individual particle can undergo as it spends time in the atmosphere, which is referred to as "aging" of the aerosol. Therefore, the performance of the source signature library technique was investigated on the ambient dataset of the highly aged environment of Riverside, California. Additionally, two specific subsets of the Riverside dataset (ultrafine particles and particles containing trace metals), which are known to cause adverse health effects, were probed in greater detail. Finally, the impact of large wildfires on the ambient levels of particulate matter in Southern California is discussed. The results of this work provide insight into single particles impacting the Southern California region, the relative source contributions to this region, and finally an examination of how atmospheric aging influences the ability to perform source apportionment.

Anthropogenic Particulate Source Characterization and Source Apportionment Using Aerosol Time-of-flight Mass Spectrometry

Author : Stephen Mark Toner
Publisher :
ISBN 13 :
Total Pages : 288 pages
Book Rating : 4.:/5 (19 download)

DOWNLOAD NOW!

Book Synopsis Anthropogenic Particulate Source Characterization and Source Apportionment Using Aerosol Time-of-flight Mass Spectrometry by : Stephen Mark Toner

Download or read book Anthropogenic Particulate Source Characterization and Source Apportionment Using Aerosol Time-of-flight Mass Spectrometry written by Stephen Mark Toner and published by . This book was released on 2007 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt: Methods of measuring the chemical and physical properties of aerosols as well as proper source apportionment of ambient particles are necessary to provide insight as to the roles they play in the environment and their impact on human health. In addition, the ability to apportion ambient particles quickly and accurately will be very helpful for environmental and health agencies and for monitoring and enforcing emission standards by allowing such agencies to determine the primary source of aerosols in their monitoring areas. The goal of this dissertation is to provide a new approach for aerosol source apportionment using aerosol time-of-flight mass spectrometry (ATOFMS) single particle data. This goal was accomplished by determining unique mass spectral signatures for specific aerosol sources and by developing these signatures into a source signature library in which ambient ATOFMS data can be matched and apportioned. The creation of the source signature library (SSL) began with the characterization of specific sources themselves. Heavy duty diesel vehicle (HDDV) emissions were characterized using ATOFMS from a dynamometer study. The particle types detected for HDDVs were compared to those from a previous dynamometer study of gasoline powered light duty vehicles (LDV) to see if HDDV and LDV particles can be distinguished. A SSL was then created for the HDDV and LDV emissions to test the ability to properly apportion between the two sources on ambient ATOFMS data collected next to a major freeway using a SSL matching technique. This work demonstrated that the two sources are readily distinguishable in a fresh emission environment, and that the matching method is a valid means for apportioning ATOFMS data. The SSL was then extended for multiple specific sources as well as for non-source specific particles and was used to apportion the same freeway study particles; showing that the source matching method is able to accurately distinguish different particle sources and that there can be a large contribution from sources other than vehicles near a major freeway. Lastly, the SSL matching method was used to apportion ambient aerosols for two major non-US cities to show that the SSL matching technique is applicable to worldwide ambient ATOFMS data.

Extending the Physicochemical Characterization of Aerosol Particles in California

Author : Melanie Dorothy Zauscher
Publisher :
ISBN 13 : 9781267513793
Total Pages : 218 pages
Book Rating : 4.5/5 (137 download)

DOWNLOAD NOW!

Book Synopsis Extending the Physicochemical Characterization of Aerosol Particles in California by : Melanie Dorothy Zauscher

Download or read book Extending the Physicochemical Characterization of Aerosol Particles in California written by Melanie Dorothy Zauscher and published by . This book was released on 2012 with total page 218 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aerosols affect the radiative balance of earth, alter cloud formation, and adversely impact human health. Knowledge of the physicochemical properties of particles, which can rapidly change, is essential to predict and mitigate their negative impacts. Hence, in-situ measurements of single-particle composition and physical properties are needed. Aerosol time-of-flight mass spectrometry (ATOFMS), which measures the size-resolved chemical mixing state of individual particles, was used to study aerosols at different locations in California. Soot particles internally mixed with soluble ammonium, nitrate, and sulfate transported from the Central Valley were found to be a major source of cloud condensation nuclei in the Sierra Nevada during winter 2010, never identified before. These aged soot particles may be affecting regional cloud microphysics and potentially precipitation. Rapid aging of biomass burning aerosols during intense urban fires were analyzed for the first time via single-particle mass spectrometry throughout the 2007 San Diego Wildfires. Furthermore, estimated size-resolved mass concentrations of particulate matter during the wildfires showed for the first time that particles

Determination of the spatial and temporal variability of size-resolved PM2.5 composition and mixing state in multiple regions in California

Download Determination of the spatial and temporal variability of size-resolved PM2.5 composition and mixing state in multiple regions in California PDF Online Free

Author : Kimberly Prather
Publisher : California Air Resources Board
ISBN 13 :
Total Pages : 318 pages
Book Rating : 4./5 ( download)

DOWNLOAD NOW!

Book Synopsis Determination of the spatial and temporal variability of size-resolved PM2.5 composition and mixing state in multiple regions in California by : Kimberly Prather

Download or read book Determination of the spatial and temporal variability of size-resolved PM2.5 composition and mixing state in multiple regions in California written by Kimberly Prather and published by California Air Resources Board. This book was released on 2009-12-01 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: Final report for California Air Resources Board contract 04-336. For an abstract and link to full text, please see: http://www.arb.ca.gov/research/single-project.php?row_id=64974

Dissertation Abstracts International

Author :
Publisher :
ISBN 13 :
Total Pages : 800 pages
Book Rating : 4.F/5 ( download)

DOWNLOAD NOW!

Book Synopsis Dissertation Abstracts International by :

Download or read book Dissertation Abstracts International written by and published by . This book was released on 2008 with total page 800 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Analysis of Atmospheric Aerosol Processes Using Single Particle Mass Spectrometry

Author : Jeffrey Robert Whiteaker
Publisher :
ISBN 13 :
Total Pages : 644 pages
Book Rating : 4.3/5 (121 download)

DOWNLOAD NOW!

Book Synopsis Analysis of Atmospheric Aerosol Processes Using Single Particle Mass Spectrometry by : Jeffrey Robert Whiteaker

Download or read book Analysis of Atmospheric Aerosol Processes Using Single Particle Mass Spectrometry written by Jeffrey Robert Whiteaker and published by . This book was released on 2002 with total page 644 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Chemical Characterization and Source Apportionment of Atmospheric Aerosols in Urban and Rural Regions

Author : Caroline Parworth
Publisher :
ISBN 13 : 9780355594157
Total Pages : 0 pages
Book Rating : 4.5/5 (941 download)

DOWNLOAD NOW!

Book Synopsis Chemical Characterization and Source Apportionment of Atmospheric Aerosols in Urban and Rural Regions by : Caroline Parworth

Download or read book Chemical Characterization and Source Apportionment of Atmospheric Aerosols in Urban and Rural Regions written by Caroline Parworth and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aerosols, or particulate matter (PM), can affect climate through scattering and absorption of radiation and influence the radiative properties, precipitation efficiency, thickness, and lifetime of clouds. Aerosols are one of the greatest sources of uncertainty in climate model predictions of radiative forcing. To fully understand the sources of uncertainty contributing to the radiative properties of aerosols, measurements of PM mass, composition, and size distribution are needed globally and seasonally. To add to the current understanding of the seasonal and temporal variations in aerosol composition and chemistry, this study has focused on the quantification, speciation, and characterization of atmospheric PM in urban and rural regions of the United States (US) for short and long periods of time. In the first two chapters, we focus on 1 month of aerosol and gas-phase measurements taken in Fresno, CA, an urban and agricultural area, during the National Aeronautics and Space Administration's (NASA) field study called DISCOVER-AQ. This air quality measurement supersite included a plethora of highly detailed chemical measurements of aerosols and gases, which were made at the same time as similar aircraft column measurements of aerosols and gases. The goal of DISCOVER-AQ is to improve the interpretation of satellite observations to approximate surface conditions relating to air quality, which can be achieved by making concurrent ground- and aircraft-based measurements of aerosols and gases. We begin in chapter 2 by exploring the urban aerosol and gas-phase dataset from the NASA DISCOVER-AQ study in California. Specifically, we discuss the chemical composition and mass concentration of water-soluble PM2.5 that were measured using a particle-into-liquid sampler with ion chromatography (PILS-IC) in Fresno, California from January 13–February 10, 2013. This data was analyzed for ionic inorganic species, organic acids and amines. Gas-phase species including HNO3 and NH3 were collected with annular denuders and analyzed using ion chromatography. Using the thermodynamic E-AIM model, inorganic particle water mass concentration and pH were calculated for the first time in this area. Organic particle water mass concentration was calculated from [kappa]-Köhler theory. In chapter 3 further analysis of the aerosol- and gas-phase data measured during DISCOVER-AQ was performed to determine the effectiveness of a local residential wood burning curtailment program in improving air quality. Using aerosol speciation and concentration measurements from the 2013 winter DISCOVER-AQ study in Fresno, CA, we investigate the impact of residential wood burning restrictions on fine particulate mass concentration and composition. Key species associated with biomass burning in this region include K+, acetonitrile, black carbon, and biomass burning organic aerosol (BBOA), which represents primary organic aerosol associated with residential wood burning. Reductions in acetonitrile associated with wood burning restrictions even at night were not observed and most likely associated with stagnant conditions during curtailment periods that led to the buildup of this long-lived gas. In chapter 4 we transition to the rural aerosol dataset from the DOE SGP site. We discuss the chemical composition and mass concentration of non-refractory submicron aerosols (NR-PM1) that were measured with an aerosol chemical speciation monitor (ACSM) at the DOE SGP site from November 2010 through June 2012. Positive matrix factorization (PMF) was performed on the measured organic aerosol (OA) mass spectral matrix using a newly developed rolling window technique to derive factors associated with distinct sources, evolution processes, and physiochemical properties. The rolling window approach captured the dynamic variations of the chemical properties of the OA factors over time. Three OA factors were obtained including two oxygenated OA (OOA) factors, differing in degrees of oxidation, and a BBOA factor. Sources of NR-PM1 species at the SGP site were determined from back trajectory analyses. NR-PM1 mass concentration was dominated by organics for the majority of the study with the exception of winter, when NH4N33 increased due to transport of precursor species from surrounding urban and agricultural regions and also due to cooler temperatures. Chapter 5 is a continuation of chapter 4, where we will explore the use of the multilinear engine (ME-2) as a factor analysis technique, which is an algorithm used for solving the bilinear model called positive matrix factorization (PMF). The importance of ME-2 and its potential application on the long-term aerosol chemical speciation monitor (ACSM) data collected from the Department of Energy (DOE) Southern Great Plains (SPG) site will be discussed. ME-2 was performed on 19 months of OA mass spectral data obtained from the ACSM at the SGP site. Evaluation of ME-2 results are presented, followed by comparison of ME-2 factor results with corresponding OACOMP factor results reported in chapter 4. We show that ME-2 can determine a biomass burning organic aerosol (BBOA) factor during periods when OACOMP cannot. (Abstract shortened by ProQuest.)

Characterization of Ambient Aerosol Source and Processes During CalNex 2010 with Aerosol Mass Spectrometry

Author : José Luis Jiménez
Publisher :
ISBN 13 :
Total Pages : 124 pages
Book Rating : 4.:/5 (318 download)

DOWNLOAD NOW!

Book Synopsis Characterization of Ambient Aerosol Source and Processes During CalNex 2010 with Aerosol Mass Spectrometry by : José Luis Jiménez

Download or read book Characterization of Ambient Aerosol Source and Processes During CalNex 2010 with Aerosol Mass Spectrometry written by José Luis Jiménez and published by . This book was released on 2013 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Source Profiling and Apportionment of Airborne Particles

Author : Philip Joseph Silva
Publisher :
ISBN 13 :
Total Pages : 904 pages
Book Rating : 4.3/5 (121 download)

DOWNLOAD NOW!

Book Synopsis Source Profiling and Apportionment of Airborne Particles by : Philip Joseph Silva

Download or read book Source Profiling and Apportionment of Airborne Particles written by Philip Joseph Silva and published by . This book was released on 2000 with total page 904 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Single Particle Perspective on the Southern California Ozone Study

Author : Sylvia Harriet Pastor
Publisher :
ISBN 13 :
Total Pages : 1244 pages
Book Rating : 4.3/5 (121 download)

DOWNLOAD NOW!

Book Synopsis Single Particle Perspective on the Southern California Ozone Study by : Sylvia Harriet Pastor

Download or read book Single Particle Perspective on the Southern California Ozone Study written by Sylvia Harriet Pastor and published by . This book was released on 2003 with total page 1244 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Studies of Ambient Organic and Inorganic Aerosol in Southern California

Author : Joseph James Ensberg
Publisher :
ISBN 13 :
Total Pages : 494 pages
Book Rating : 4.:/5 (878 download)

DOWNLOAD NOW!

Book Synopsis Studies of Ambient Organic and Inorganic Aerosol in Southern California by : Joseph James Ensberg

Download or read book Studies of Ambient Organic and Inorganic Aerosol in Southern California written by Joseph James Ensberg and published by . This book was released on 2014 with total page 494 pages. Available in PDF, EPUB and Kindle. Book excerpt: The negative impacts of ambient aerosol particles, or particulate matter (PM), on human health and climate are well recognized. However, owing to the complexity of aerosol particle formation and chemical evolution, emissions control strategies remain difficult to develop in a cost effective manner. In this work, three studies are presented to address several key issues currently stymieing California's efforts to continue improving its air quality. Gas-phase organic mass (GPOM) and CO emission factors are used in conjunction with measured enhancements in oxygenated organic aerosol (OOA) relative to CO to quantify the significant lack of closure between expected and observed organic aerosol concentrations attributable to fossil-fuel emissions. Two possible conclusions emerge from the analysis to yield consistency with the ambient organic data: (1) vehicular emissions are not a dominant source of anthropogenic fossil SOA in the Los Angeles Basin, or (2) the ambient SOA mass yields used to determine the SOA formation potential of vehicular emissions are substantially higher than those derived from laboratory chamber studies. Additional laboratory chamber studies confirm that, owing to vapor-phase wall loss, the SOA mass yields currently used in virtually all 3D chemical transport models are biased low by as much as a factor of 4. Furthermore, predictions from the Statistical Oxidation Model suggest that this bias could be as high as a factor of 8 if the influence of the chamber walls could be removed entirely. Once vapor-phase wall loss has been accounted for in a new suite of laboratory chamber experiments, the SOA parameterizations within atmospheric chemical transport models should also be updated. To address the numerical challenges of implementing the next generation of SOA models in atmospheric chemical transport models, a novel mathematical framework, termed the Moment Method, is designed and presented. Assessment of the Moment Method strengths and weaknesses provide valuable insight that can guide future development of SOA modules for atmospheric CTMs. Finally, regional inorganic aerosol formation and evolution is investigated via detailed comparison of predictions from the Community Multiscale Air Quality (CMAQ version 4.7.1) model against a suite of airborne and ground-based meteorological measurements, gas- and aerosol-phase inorganic measurements, and black carbon (BC) measurements over Southern California during the CalNex field campaign in May/June 2010. Results suggests that continuing to target sulfur emissions with the hopes of reducing ambient PM concentrations may not the most effective strategy for Southern California. Instead, targeting dairy emissions is likely to be an effective strategy for substantially reducing ammonium nitrate concentrations in the eastern part of the Los Angeles Basin.

Single Particle Analysis of Transient Variations Occurring in Atmospheric Aerosols

Author : Christopher Alan Noble
Publisher :
ISBN 13 :
Total Pages : 1230 pages
Book Rating : 4.3/5 (121 download)

DOWNLOAD NOW!

Book Synopsis Single Particle Analysis of Transient Variations Occurring in Atmospheric Aerosols by : Christopher Alan Noble

Download or read book Single Particle Analysis of Transient Variations Occurring in Atmospheric Aerosols written by Christopher Alan Noble and published by . This book was released on 1999 with total page 1230 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Interpretation of Mass Spectra

Author : Fred Warren McLafferty (Chemiker, USA)
Publisher :
ISBN 13 : 9780805370485
Total Pages : 278 pages
Book Rating : 4.3/5 (74 download)

DOWNLOAD NOW!

Book Synopsis Interpretation of Mass Spectra by : Fred Warren McLafferty (Chemiker, USA)

Download or read book Interpretation of Mass Spectra written by Fred Warren McLafferty (Chemiker, USA) and published by . This book was released on 1973 with total page 278 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Single Particle Characterization of Soil and Dust Particulate Matter in the Urban and Marine Environments

Author : Keith Robert Coffee
Publisher :
ISBN 13 :
Total Pages : 604 pages
Book Rating : 4.3/5 (121 download)

DOWNLOAD NOW!

Book Synopsis Single Particle Characterization of Soil and Dust Particulate Matter in the Urban and Marine Environments by : Keith Robert Coffee

Download or read book Single Particle Characterization of Soil and Dust Particulate Matter in the Urban and Marine Environments written by Keith Robert Coffee and published by . This book was released on 2002 with total page 604 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Air Quality in the Mexico Megacity

Author : L. Molina
Publisher : Springer Science & Business Media
ISBN 13 : 9401004544
Total Pages : 401 pages
Book Rating : 4.4/5 (1 download)

DOWNLOAD NOW!

Book Synopsis Air Quality in the Mexico Megacity by : L. Molina

Download or read book Air Quality in the Mexico Megacity written by L. Molina and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 401 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this book, experts in atmospheric sciences, human health, economics, social and political sciences contribute to an integrated assessment of the complex elements needed to structure air quality policy in the 21st century. The analysis is developed through a case study of the Mexico City Metropolitan Area - one of the world's largest megacities in which air pollution grew unchecked for decades. The international research team is led by Luisa T. and Mario J. Molina, Nobel Laureate in Chemistry. Improvements in Mexico City's air quality in the last decade testifies to the power of determined and enlightened policy making, and throws into relief the tough problems that remain to be solved. The volume's first six chapters, including the contributions of over 50 distinguished scholars from Mexico and the US, outline the fundamental areas of knowledge policy makers must accommodate. The message is that only good science and well-chosen technologies can direct the way to corrective regulatory measures; but without strong commitment from government, no amount of science or technology can help.

Particulate Matter Science for Policy Makers

Author : Peter H. McMurry
Publisher : Cambridge University Press
ISBN 13 : 9780521842877
Total Pages : 652 pages
Book Rating : 4.8/5 (428 download)

DOWNLOAD NOW!

Book Synopsis Particulate Matter Science for Policy Makers by : Peter H. McMurry

Download or read book Particulate Matter Science for Policy Makers written by Peter H. McMurry and published by Cambridge University Press. This book was released on 2004-11-29 with total page 652 pages. Available in PDF, EPUB and Kindle. Book excerpt: Particulate Matter Science for Policy Makers: A NARSTO Assessment was commissioned by NARSTO, a cooperative public-private sector organization of Canada, Mexico and the United States. It is a concise and comprehensive discussion of the current understanding by atmospheric scientists of airborne particulate matter (PM). Its goal is to provide policy makers who implement air-quality standards with this relevant and needed scientific information. The primary audience for this volume will be regulators, scientists, and members of industry, all of whom have a stake in effective PM management. It will also inform exposure and health scientists, who investigate causal hypotheses of health impacts, characterize exposure, and conduct epidemiological and toxicological studies.

New Insights Into Single-particle Mixing State Using Aircraft Aerosol Time-of-flight Mass Spectrometry

Author : Kerri Anne Pratt
Publisher :
ISBN 13 : 9781109365450
Total Pages : 387 pages
Book Rating : 4.3/5 (654 download)

DOWNLOAD NOW!

Book Synopsis New Insights Into Single-particle Mixing State Using Aircraft Aerosol Time-of-flight Mass Spectrometry by : Kerri Anne Pratt

Download or read book New Insights Into Single-particle Mixing State Using Aircraft Aerosol Time-of-flight Mass Spectrometry written by Kerri Anne Pratt and published by . This book was released on 2009 with total page 387 pages. Available in PDF, EPUB and Kindle. Book excerpt: Atmospheric aerosols strongly influence the energy balance of the Earth and the hydrological cycle by scattering and absorbing radiation and acting as cloud condensation and ice nuclei. The climate and human health impacts of aerosols are strongly dependent on particle size, chemical composition, and mixing state. During transport in the atmosphere, aerosol particles undergo physical and chemical transformations (atmospheric aging) through heterogeneous reactions with trace gases and gas-particle partitioning of semivolatile species. The size-resolved chemical composition of individual particles may be examined in real-time using aerosol time-of-flight mass spectrometry (ATOFMS). A smaller ATOFMS with increased data acquisition capabilities was developed for aircraft-based studies. Particle volatility was examined through ground-based measurements during the Study of Organic Aerosols in Riverside, CA (SOAR), and vertical mixing state profiles and cloud residues were examined through flight-based measurements during the Ice in Clouds Experiment - Layer Clouds (ICE-L). An automated thermodenuder (TD) was coupled to the aircraft (A)-ATOFMS to provide the first real-time, individual-particle size and volatility-resolved chemical composition measurements. This work provided insight into the volatility of secondary species, as well as the sources and chemistry of ambient particle cores. Seasonal differences in the volatility of amine species were attributed to the formation of aminium sulfate and nitrate salts in the summer. Oligomeric species were detected in real-time for the first time in individual ambient aerosol particles; increased oligomer ion intensities were associated with increased particle acidity and heating. During ICE-L, vertical profiles of particle types, such as soot, mixed with secondary species, such as sulfuric acid, were examined. For cloud sampling, a counterflow virtual impactor was utilized in series with the A-ATOFMS to examine the residues of cloud droplets and ice crystals. This resulted in the first in-situ detection of biological particles in high altitude ice clouds influenced by long-range transported dust. Playa salts were observed to serve as cloud condensation nuclei and were preferentially observed as residues of large droplets.