Proton Transfer Reaction Ion Trap Mass Spectrometer (PTR-ITMS): Next Generation Aircraft Instrumentation for Gas Phase Organic Analysis
PI: Michael Alexander, PNNL
Knowledge of the impacts of volatile organic compounds (VOCs) on aerosol formation and evolution in the troposphere is limited by our ability to make selective, high time resolution measurements of key species from airborne platforms. Current technologies lack the sensitivity to measure boundary layer concentrations of these species (<10 ppt at one second time resolution) and their oxidation products from aircraft platforms. Real-time measurements of key volatile organic species are a critical component in understanding gas-particle partitioning and the interaction of primary and secondary aerosols (POA and SOA) with organic species and their oxidation products. Recent evidence shows that VOCs play an important role in the nucleation process where new aerosols are formed. New climate models will require improved measurements of the gas-phase organic species correlated with real-time measurements of aerosol size distributions, composition, and optical properties. Proton transfer reaction mass spectrometry (PTR-MS) is a chemical ionization (CI) method that has been successfully deployed on aircraft with a demonstrated sensitivity of close to 100 ppt for a single species with 1 second time resolution. Current PTR-MS instruments are limited in both time resolution and sensitivity by the use of a linear, sequential scanning quadrupole mass spectrometer. The use of proton transfer from H3O+ as a CI reagent also has limitations that result from ions of the same mass but different identity (isobaric interferences). We propose to develop a more sensitive and selective direct sampling mass spectrometer by coupling the H3O+ ionization source to an ion trap mass spectrometer (ITMS). This PTR-ITMS instrument will allow simultaneous, multiple ion detection with the time resolution and sensitivity required for the new aircraft studies. The use of an ITMS will also allow resolution of isobaric interferences using real-time MS-MS analysis. Finally, the PTR-ITMS will incorporate the use of CI agents other than H3O+ to further increase selectivity for key organic species.
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Atmospheric Formation, Transformation, and Radiative Forcing of Secondary Organic Aerosols
PI: Cynthia Atherton, LLNL
This project will use IMPACT (Integrated Massively Parallel Atmospheric
Chemical Transport model), a global, three-dimensional chemistry-transport-deposition
model (Rotman et al., 2004). The model simulates the emissions, advection, diffusion,
wet scavenging (rainout, washout, and re-evaporation), dry deposition, convection,
gravitational settling, photolysis and chemical reactions governing gaseous and aerosol
species. IMPACT’s domain, the troposphere, stratosphere, and the climatically critical
tropopause region, requires roughly 100 species and 300 photochemical reactions. The
IMPACT model is “driven” by meteorological information from either a general
circulation model (GCM) or actual assimilated meteorological data. Using general
circulation model meteorology allows us to examine climatologically average
atmospheres (past, present, future). Using assimilated meteorological data allows us to
compare model results directly with field campaign measurements for a particular time
period. The model has been run at horizontal grid resolutions of 1˚ x 1˚, 2˚x 2.5˚, and 4˚ x 5˚
(latitude x longitude) with 25 to 55 vertical levels.
Currently IMPACT predicts the distributions of five major aerosols components
(sulfate, organic carbon, black carbon, dust, and seasalt), with the sixth component,
nitrate, to be added shortly (Chuang et al., 2002b). IMPACT includes a radiation package
that includes shortwave, near-IR, and longwave radiation (Grant et al., 1997; Grant et al.,
1999), as well as parameterizations of aerosol optical properties to calculate the direct
radiative forcing and heating/cooling rates by aerosols and greenhouse gases. In addition,
parameterizations of drop concentrations have been implemented to calculate the first
indirect aerosol effect (Chuang et al., 1997, 2002a). An aerosol microphysics sectional
based module (Zhang and Wexler, 2002) is being implemented into the IMPACT model
that will allow more realistic simulations of aerosol size distributions and mixing.
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The Effects of Cloud Processes on the Optical Properties of Aerosols
PI: Carl Berkowitz, PNNL
Previous research has shown that there is significant mass transport from the boundary layer to the free troposphere associated with shallow fair-weather cumuli and cumuli with more vertical development. Anticipating a similar redistribution of aerosol particulate matter, we argue that aerosol activation, aqueous-phase chemistry, and scavenging associated with cumulus transport will induce significant changes not only to the particulate matter (PM) size and mass distribution but to intrinsic aerosol optical properties as well. We will conduct a research program to address three questions relevant to this topic: 1) what is the vertical and horizontal variability in aerosol absorption and scattering over regions occupied primarily by cumuliform clouds? 2) what are the differences in these properties below and above cumulus clouds? and 3) what is the variability and magnitude of derived quantities such as the aerosol single scattering albedo and aerosol extinction below and above these clouds? We will address these questions by completing the following tasks:
an aircraft field program to characterize aerosols processed by cumuliform clouds downwind of an urban area producing fresh aerosols,
development and use of a detailed aerosol-process model to analyze results from the field program, and
the addition of parameterized aerosol physics and chemistry to an existing cumulus parameterization suitable for inclusion in regional-scale models.
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Instrumentation and Deployment in Support of ASP Field Studies
PI: Rich Coulter, ANL
We support Atmospheric Science Program (ASP) field studies of the radiative effects of aerosols and their life cycles (1) by deploying instrumentation during intensive field campaigns to determine the basic chemical state of the atmosphere and the vertical and horizontal physical structure of the planetary boundary layer and (2) by measuring near-surface meteorological parameters such as wind, temperature, and aerosol fields to approximately 20 km above the surface and generating data necessary to estimate boundary layer heights in real time (or near real time). Ground-based instrumented sites use surface towers, radar wind profilers-radio
acoustic sounding systems, sodars, lidars, and balloon-borne instruments. Basic chemical measurements made in the field include carbon monoxide, ozone, and aerosol loadings. The organic molecular constituents of aerosols can be measured at Argonne with a mass spectrometer. We are deploying a multifilter rotating shadowband radiometer and other radiometers to determine photolytic radiation fields and aerosol column densities during daytime hours, with a mobile facility housing the needed electronics and instrumentation. The data we gather are made available to the ASP Science Team and the wider community. Our efforts are coordinated with other ASP efforts.
Key Words: aerosols, aerosol field studies, aerosol optical depths, atmospheric characterization,
Instrumentation.
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Aerosol Cloud Interactions: Field Studies and Interpretation
PI: Peter Daum, BNL
The primary focus of this proposal is to provide an enhanced scientific basis for specifying the relationship between aerosol chemical and physical properties and their properties as cloud condensation nuclei (CCN); CCN and cloud droplet microphysics; and, between cloud droplet microphysics and the initiation of drizzle in warm clouds. Aerosol activation, droplet formation, and drizzle production will be studied using the Department of Energy (DOE) G-1 aircraft as the primary measurement platform. The intention is to make measurements in diverse environments containing the major categories of aerosols that need to be represented in General Circulation
Models (GCMs). Because of the necessity to separately identify anthropogenic impacts, the studies will start with urban, industrial, and power plant aerosol sources. The selection of proposed field venues also includes marine and biogenic organic environments. To make optimum use of the G-1 aircraft, it is proposed that aerosol/CCN studies be done during clear-air flights designed to investigate aerosol direct radiative effects. Separate field studies are proposed for the in-cloud work. In recognition of the fact that computational constraints dictate a compact description of aerosol composition and cloud microphysics, the focus is on determining the essential features of aerosols that need to be incorporated into GCMs to predict aerosol indirect effects.
Keywords: aerosols, cloud condensation nuclei, cloud microphysics, radiation fields, indirect effects.
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Field Studies of the Evolution of Aerosols Downwind of an Urban Area: The Roles of Black Carbon and Meteorological Processes on Aerosol Radiative Effects
PI: Chris Doran, PNNL
We hypothesize that the shift from an externally mixed state to an internally mixed one will result in significant modifications to the optical properties of aerosols as they age and are advected downstream from an urban source. We propose to use field and laboratory measurements, analyses, and mesoscale modeling to study those modifications and their radiative impact. We will examine and characterize the changes in aerosol light scattering, absorption, optical depths, and surface radiative fluxes in an urban plume as it is advected between two sites downwind of an urban area and separated by 100 to 200 km with travel times of 3 to 12 hours. We will conduct a detailed analysis of the meteorological conditions during the field campaign to identify what aspects of the observed changes in aerosol properties are attributable to factors such as transport, diffusion and dilution, and relative humidity effects. We will then ascertain what aspects must be attributed to modifications in the chemical and microphysical properties of the aerosols, e.g., their mixing state. In particular, we will use three methods to study the evolution of the specific absorption of black carbon (BC) and attempt to relate it to the aging and mixing state of those aerosols. A key component of our proposal is to organize and conduct a field measurement campaign to facilitate studies of the life cycles of aerosols, by us and others, over the desired distance and time scales. The field measurements will be supplemented by a laboratory study to help characterize the chemical behavior of atmospheric soot and the times required for significant changes in its mixing state as it ages, and to relate those changes to changes in the specific absorption.
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Synthesis of Field Observations and Multi-Scale Modeling of Aerosol Evolution and Its Impact on Radiative Forcing from Urban to Regional Scales
PI: Jerome Fast, PNNL
In collaboration with national laboratory and university researchers in the Atmospheric Sciences Program (ASP), an advanced fully-coupled meteorology-chemistry-aerosol model, PNNL’s version of Weather Research and Forecasting (WRF)-chem, will be used to simulate the mass, size distribution, composition, physical characteristics, and optical properties of particulates as well as aerosol direct and indirect forcing over urban to regional scales. Our analyses will integrate the findings of ASP field observations and modeling developments to address issues of importance to the ASP mission that include: quantifying the uncertainties associated with urban to regional-scale predictions of anthropogenic particulates as they are transported from urban sources and mixed into the regional-scale environment with precursor trace gases, natural particulates, and particulates from other anthropogenic sources; examining how those uncertainties affect the estimates of direct and indirect forcing; determining whether urban to regional-scale variations in aerosol radiative forcing are significant in terms of global climate modeling; and identifying which key processes resolved by urban to regional-scale simulations need to be better represented in global climate models. Our comprehensive approach that synthesizes data analysis and modeling will elucidate aerosol-chemistry-cloud-radiation feedback mechanisms. Our analysis will utilize measurements obtained during future ASP field campaigns, including ASP’s participation in FY 2004 summer’s Northeast Air Quality Study-International Transport and Chemical Transformation (NEASQ-ITCT) field campaign. Improved aerosol parameterizations will be tested and evaluated within our modeling framework. Since our version of WRF-chem is based on a community model, improved aerosol treatments can be easily disseminated to other ASP scientists and to the larger aerosol and climate scientific community.
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Determining Aerosol Mean Residence Times and Black Carbon Washout Rates with Natural Radionuclides
PI: Jeff Gaffney, ANL
The impacts on climate and radiative balance of aerosols depend on their tropospheric lifetimes, their compositions and sizes, and related optical properties. Carbonaceous aerosols are less hygroscopic than fine inorganic aerosols and therefore have potentially longer lifetimes. The ability of carbonaceous aerosols to take up water increases with time as the carbon surfaces are oxidized in the atmosphere. Currently, carbonaceous aerosols are treated in climate models as if their wet removal rates were similar to those for inorganic aerosols. A better understanding of the lifetimes and removal rates of carbonaceous aerosols is required to determine the overall impact of tropospheric aerosols on radiative balance. We are using natural radionuclide tracers, including 210Pb, 7Be, 40K, and 14C, to determine the lifetimes and sources of fine atmospheric aerosols,
particularly the carbonaceous aerosols, in air samples size-fractionated by cascade impactors.
As lead scientist for the ASP’s Megacity Aerosol Experiment in Mexico City (MAX-Mex),
planned for February-March 2006. This effort will be collaborative with the Megacity Impacts on Regional and Global Environments (MIRAGE) study. MIRAGE (http://mirage-ex.acd.ucar.edu) is a project of the National Center for Atmospheric Research (NCAR) and the National Science Foundation (NSF). Future Accomplishments: In FY 2006 we will complete laboratory development of carbon separations and studies on the distribution and stability of radionuclides attached to carbonaceous soots. Our experiments on aging of soot use 7Be and 210Pb and daughters as tracers, with the oxidant ozone and ultraviolet light generating hydroxyl radical.
In FY 2005 and FY 2006 we will lead and organize the MAX-Mex field study. MAX-Mex will focus on the export of aerosols and precursor pollutants from Mexico City and the effects on regional-scale air quality and climate, particularly measurement of black carbon aerosol effects and removal of black carbon by rainfall and aging processes (including changing hygroscopicity of the black carbon aerosols and secondary organic aerosols). We will continue to work with Mario and Luisa Molina and with ASP Science Team members toward collaboration with the MIRAGE study in Mexico City in February-March 2006 and will be completing a science plan for that effort. Preliminary plans are on the ASP web site (http://www.asp.bnl.gov/MAXMex.
html). Relationships to Other Projects: Our field work will involve ground- and aircraft-based measurements and will entail collaboration on black carbon, organic, and secondary organic aerosols with Pacific Northwest and Brookhaven National Laboratories, other ASP participants, various organizations involved in the North American Research Strategy for Tropospheric Ozone, and organizations specific to the field study areas. Extensive interactions occur with MIT; the University of California, San Diego; the University of Chicago; New Mexico Tech in Socorro, New Mexico; the University of Illinois at Chicago; and other universities. We will also collaborate with Aerodyne Research, Inc., in the MAX-Mex 2006 effort.
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Superparameterization of Aerosol Transport, Transformation, and Removal by Clouds
PI: Stephen Ghan, PNNL
Although we understand the basic physics of direct and indirect effects quite well now, and have applied much of that understanding to global aerosol models, there remains a major source of uncertainty: the poor representation of the influence of clouds on subgrid pollutant (primary aerosols, secondary aerosols, and precursor gases for secondary aerosols) transport, transformation, and removal in global models. This source of uncertainty has remained elusive and will continue to be elusive unless a bold step is taken. We propose to use grid cell mean statistics from cloud resolving models (CRMs) embedded within each global model grid cell to drive a physically-based treatment of pollutant processing by clouds. For example, the grid cell mean cloud mass flux can be used to treat vertical transport of pollutants, the mean updraft velocity can be used to determine the aerosol activation, the mean cloud fraction and in-cloud water content can be used to treat aqueous chemistry, and the mean precipitation fraction and precipitation rate can be used to treat precipitation scavenging. We call this the Explicit Cloud-Parameterized Pollutants (ECPP) approach. The method will be tested first using a single column model driven by statistics derived from cloud-resolving simulations of pollutant transport, transformation, and removal by clouds for a limited domain. It will be further tested using CRMs embedded within each grid cell of a regional circulation model, with pollutant processes either embedded within the CRMs or parameterized using the ECPP method. When the ECPP is mature it will be applied to a global climate model already running with embedded CRMs.
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Soft X-Ray Spectromicroscopy of Black Carbon Aerosols
PI: Mary K. Gilles, LBNL
Direct measurements of the mixing state of black carbon are necessary for improved modeling of black carbon radiative properties. The technique to map near edge x-ray absorption fine structure spectroscopy (NEXAFS) onto single carbonaceous aerosol particles will be developed. Mapping techniques currently used in multicomponent polymer systems will be extended to investigate the distribution of black carbon in individual aerosol particles. The ultimate goal is determination of the distribution of black, organic and inorganic carbon along with nitrogen and oxygen functional groups with a spatial resolution of 35 nm. Chemical maps of the carbon will be used to determine the mixing state of the carbonaceous particles. For selected particles, metals (and their oxidation states) or sulfur spectra may also be acquired and mapped. The variation in NEXAFS spectra of atmospheric samples will also be measured. Studies on the variation of NEXAFS (C and O edges) spectra of atmospheric samples will be compared with black carbon surrogates (n-hexane soot,
Palas soot etc.). Field samples are an important part of this project and will be provided by several collaborators. Collaborative participation in laboratory field studies (Pt. Reyes and MAX-Mex) are with Alex Laskin (PNNL) who will be performing TEM measurements. The results of this research will lead to soot characterization, determination of mixing states, and insight into atmospheric aging, improving our ability to model their radiative influence.
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Research Aircraft Facility
PI: John Hubbe, PNNL
The Research Aircraft Facility is dedicated to fulfilling DOE and national goals related to understanding atmospheric processes of concern to the National Energy Policy Act and the global environment. It is pivotal to DOE's investigation of aerosol and cloud chemical, physical and optical properties; radiative transfer; atmospheric chemistry; and transport processes. A Grumman Gulfstream-159 (G-1) twin-engine turboprop aircraft instrumented for aerosol, cloud, gaseous chemistry, and atmospheric physics and dynamics investigations, is funded to serve the DOE atmospheric sciences community with up to 250 flying hours annually. It provides a low- to mid-troposphere measurement capability; safely and reliably penetrates weather systems under a variety of conditions; and has sufficient range, payload, and electrical power required for long-term service to DOE as an airborne atmospheric research laboratory.
Future accomplishments depend heavily on internal DOE planning for the use of the facility in its major programs. By providing researchers access to the aircraft facility, DOE encourages the application of new concepts and specialized equipment to obtain airborne measurements that enhance our understanding of atmospheric processes and the global environment. Field campaigns and other users of the Research Aircraft Facility are sanctioned by the DOE Atmospheric Science Program and its Steering Committee.
Key Words: aircraft, measurements, atmospheric research, chemistry, cloud physics, aerosols, facility, infrastructure
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Field Studies on the Life Cycle of Aerosols and their Direct Radiative Impacts
PI: Larry Kleinman, BNL
The Department of Energy (DOE) G-1 aircraft will be used as the primary measurement platform in a series of field campaigns directed at obtaining a process-level understanding of aerosol production in diverse chemical and meteorological environments. Broadly speaking, the goal is to understand the processes controlling ambient levels of aerosols and their properties to the extent needed to predict their direct effect on the radiation balance of the atmosphere. Properties that are important include size distribution, chemical composition, light scattering, light absorption, and hygroscopicity. A focus of the proposed field work will be on the time evolution of aerosol properties downwind of various source regions to gain an understanding of the important processes that control aerosol properties, and the effects that these source regions have on modifying the properties of background aerosol. Measurements will be used to elucidate the processes responsible for creating cloud condensation nuclei. The activities will include the planning and execution of field campaigns, followed by data analysis. Proposed venues
include the Midwest United States (US), Houston, Texas, and Mexico City, Mexico. By providing information that links emissions with the concentration and optical properties of ambient aerosols, the direct radiative impact of these aerosols can be predicted, which will allow a more accurate assessment of the effects of increasing greenhouse gasses on climate.
Keywords: atmospheric aerosols, direct radiative effect, aerosol composition, aerosol microphysics
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Process-Scale Modeling of ASP Field Experiments
PI: V. Rao Kotomarthi, ANL
We use models -- from process-scale (zero- and one-dimensional) models of aerosol formation and removal to comprehensive three-dimensional (3-D) models of aerosol formation, transport, and removal — to analyze Atmospheric Science Program (ASP) field measurements in urban and regional-scale air masses. We focus on the production of radiatively important aerosols from chemical precursors, their spatial and temporal distributions in the planetary boundary layer, and their aging and removal. We investigate organic precursors to radiatively important aerosols, yield factors for secondary aerosol production, constraints from measured black carbon loadings on lifetimes and emissions, urban contributions to the regional aerosol background, effects of
aging on aerosol radiative properties and lifetimes, and effects of precursor gases and aged aerosols on chemical compositions of cloud water and rainwater. We evaluate models of aerosol microphysics and transport for inclusion in global climate models. We analyze data from ASP field campaigns, organize data sets for use with process-scale and 3-D models, and make the data sets available to ASP investigators and others. Our analysis of ASP field data will benefit the DOE climate change initiative and foster both development of suitable aerosol process models for use in global-scale climate change models and the independent development of regionalscale
climate models.
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Electron Microscopy and Microprobe Studies of Field-Collected Atmospheric Aerosols
PI: Alexander Laskin, PNNL
The scope of this research program is to characterize the chemical and physical properties of field-collected atmospheric aerosols to establish the quantitative relations between the composition of aerosols and their optical and hygroscopic properties. This project employs an array of EMSL hosted analytical methods for chemical and microscopy characterization of aerosol samples collected during the ASP defined field studies.
These techniques are capable of providing outstanding specificity and detail on particle surface and inner composition, chemistry, morphology, phase and internal structure, hygroscopic properties of individual aerosol particles as well as time-resolved mass loads of non-volatile aerosols. Analysis of aerosol samples is carried out in conjunction with the available in-situ data from the sampling sites. We also use the in situ data of our ASP colleagues to identify specific field samples (by collection time) for extensive laboratory analyses at EMSL. Field sampling is carried out using commercial and home built aerosol samplers that allow laboratory analysis of samples to provide quantitative mass loading measurements and single particle characterization respectively.
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Characterization of Aerosol Organic Matter: Detection, Formation and Optical and Radiative Effects
PI: Yin-Nan Lee, BNL
A better understanding of organic aerosol regarding sources, formation, and properties is needed to improve the ability to predict atmospheric distributions of aerosol particles and to assess their radiative effects. A rapid on-line technique coupling a particle-into-liquid sampler (PILS) and a total organic carbon (TOC) detector for measuring the TOC and water-soluble organic carbon (WSOC) in aerosol particles at a time resolution of better than three minutes suitable for aircraft measurement will be developed. Using the fast data obtained, the rates of secondary organic
aerosol formation in environments of different emission characteristics will be determined and compared with photochemical model predictions for mechanistic insights. The contributions of TOC and WSOC to the simultaneously determined aerosol properties, including hygroscopicity, light scattering, and cloud condensation nuclei (CCN) formation will also be investigated. In addition, the so-called humic-like substances (HULIS), which account for an appreciable fraction of WSOC, will be characterized to gain an understanding of their sources and effects.
Keywords: chemical composition, secondary organic aerosol, total organic carbon, water soluble organic carbon, radiative effects
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Studies of Cloud Microphysical and Optical Properties
PI: Yangang Liu, BNL
This project focuses on the specification of the microphysical properties of clouds and on the relationship between cloud microphysics and cloud radiative properties. The overall objective is to improve the treatment of cloud microphysics of liquid-water clouds in global circulation models (GCMs). A primary focus of this work is the specification of the cloud-droplet-effective radius, a key variable used to calculate cloud-radiative properties in GCMs, in terms of the major environmental variables (e.g., cloud updraft velocity, turbulence and anthropogenic aerosols).
Another focus is the scale dependency of droplet-size distributions and key quantities (e.g., droplet concentrations, liquid water content, spectral dispersion, and effective radius) and the relationship between scale dependency and cloud variability. Both analysis of observational data (e.g., in situ and cloud radar) and theoretical studies will be carried out to achieve the objectives, with an emphasis on the former. Theoretical studies will focus on developing a physical understanding of the effects of updraft, turbulence and anthropogenic aerosols on the properties of the droplet-size distributions, and to scale issues. The theoretical work will be driven/evaluated by analysis and examination of observational data.
Keywords: cloud radiative properties, cloud parameterization, cloud microphysics, cloud dynamics, aerosol loading
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Aerosol Precursors and Aerosol Instrumentation: Field Measurements and Method Development
PI: Nancy Marley, ANL
Determining the overall impact of atmospheric aerosols on radiative balance requires measurement of the relative amounts of scattering aerosols (e.g., ammonium nitrate, ammonium sulfate) and absorbing aerosols (e.g., carbon), their distributions, and their chemical properties. A suite of state-of-the-art instrumentation is essential for characterizing aerosol formation, loadings, and life cycles in Atmospheric Science Program (ASP) field studies. We are developing and deploying such a suite of instrumentation for measurements including (1) aerosol absorption as a function of wavelength, measured continuously with a seven-channel aethalometer, with simultaneous determination of fine-aerosol particle scattering with a three-wavelength ephelometer; (2) collection of size-fractionated aerosol samples, followed by water extraction to evaluate contributions of highly colored “humic-like” substances; (3) laboratory characterization of submicron aerosol samples with multiple spectroscopy methods in the ultraviolet-visible and infrared regions; (4) determination of the relative contributions of absorbing and scattering aerosols as a function of wavelength with a continuous-wavelength nephelometer developed for direct comparison with the aethalometer measurements; and (5) field measurements of ammonia with a near-infrared tunable diode laser instrument tested in Mexico City in 2003. All of these data are made available to the ASP community.
Key Words: aerosol optical characterization, aerosol radiative effects, atmospheric aerosols, humic-like substances, particulate matter, precursor gases.
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New Particle Formation: Mechanisms and Influence on Atmospheric Aerosol Properties
PI: Robert McGraw, BNL
The proposed research focuses on the nucleation mechanisms governing new particle formation in the atmosphere. Its objectives are to provide an interpretation for field measurements of new particle formation and to assess the importance of nucleation-mode particles as a contributor to both cloud- and climate-influencing properties of the atmospheric aerosol. While too small initially to have direct atmospheric significance, nucleation-mode particles may grow in size and, ultimately, become part of the larger particle population. The proposed research will examine the
pathways and growth rates through which new particles grow and contribute as cloud condensation nuclei (CCN) and to the accumulation-mode particle population. The proposed research will examine the effect of atmospheric composition, especially atmospheric trace species (organic as well as inorganic precursors) and develop correlations between field measurements of atmospheric composition and observations of new particle formation. The so-called "nucleation theorem" will be used to correlate trace species measurements with nuclei size and chemical composition and rates of new particle formation. The parameterizations for coupled nucleation and growth processes developed under the proposed research will be in a form suitable for incorporation into regional-to-global scale atmospheric models currently under development in other programs.
Keywords: Nucleation, new particle formation, gas-to-particle conversion, aerosol dynamics, aerosol growth
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Aerosol Processing by Clouds: Model Evaluation and Parameterization Development
PI: Mikhail Ovtchinnikov, PNNL
The effect of clouds on aerosol distribution is important but quantitatively poorly understood and crudely represented in regional and global models. Our objectives are to improve understanding of aerosol processing by clouds and to transfer this knowledge into parameterizations suitable for large-scale models. Aerosol transformations will be studied using the Cloud and Aerosol Interactive Model (CLAIM), which combines a three-dimensional large eddy simulation framework with a new comprehensive representation of aerosol and cloud processes based on a two-dimensional (dry and total volumes) particle size distribution function. This approach, while computationally intensive, provides a benchmark that consistently tracks evolution of aerosol subjected to micro and macrophysical processes including particle transport, sedimentation, activation/resuspension, condensation/evaporation, collision/coalescence, aqueous chemistry, and in- and below-cloud scavenging. The dependency of cloud processing on aerosol composition will be further studied in a Lagrangian parcel model, where multiple distributions of inorganic and organic aerosols will be simulated along the trajectories generated by the CLAIM. Both models will be thoroughly evaluated in case studies based on Atmospheric Science Program field campaigns. In addition to testing the fidelity of the model predictions, our simulations will contribute to designing sampling strategies and improving.
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Chief Scientist for the Atmospheric Science Program
PI: Stephen Schwartz, BNL
In recognition of the importance of aerosol radiative forcing of climate change, the Department of Energy (DOE) is focusing research efforts in the Atmospheric Science Program (ASP) to improve understanding and model-based representation of the processes controlling aerosol loading, distribution, and pertinent properties, relevant to the influence of aerosols on climate. This project consists of the activities of the Chief Scientist for the ASP. The Chief Scientist provides scientific leadership and vision to this program and enhances, facilitates, and promotes application of the research conducted in this program; provides leadership and guidance to program participants regarding the direction and course of the science conducted in the program; draws generalizations and conclusions from the work as reflected in the measurements and model calculations of the several investigators; represents this program in the broader national and international arena of climate change research; arranges and leads meetings of the ASP Science
Team and others, and of smaller groups as required; establishes and maintains the project-data archive and data visualization tools; and, develops and maintains the program website.
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Modeling Aerosol Processes in the DOE Atmospheric Science Program
PI: Stephen Schwartz, BNL
Representing the processes responsible for aerosol loading, geographical distribution, and microphysical properties in chemical transport models is essential to demonstrating understanding of these processes, to quantifying that understanding, to attributing aerosols to responsible source types, locations, and processes and, ultimately, to determining the influence of aerosols on climate and climate change. This project develops, applies, and evaluates
aerosol microphysical modules based upon a variety of designs and modeling approaches. Host gridded models of varying dimensionality (1-, 2-, and 3-dimensional) are used, where appropriate, specifically, including the Community Multiscale Air Quality Modeling System for urban-to-regional scale modeling, which is well-suited for interchanging alternative modules for various processes, and the Brookhaven National Laboratory (BNL) Global Chemistry Model driven by Observation-derived meteorology (GChM-O). Novel methods are utilized to incorporate field measurements in host models. A key deliverable will be a new aerosol module for simulation of generally mixed aerosols based on the quadrature method of moments. Model application and evaluation will focus on the locations and time periods of field projects to be conducted within the United States (US) Department of Energy (DOE) Atmospheric Science Program (ASP) and rely heavily on measurements conducted in those field projects. This project supports the ASP
functional category "fundamental theoretical and process modeling" and addresses, primarily, the science category "transformation of particles and gaseous precursors".
Keywords: climate, aerosol, microphysics, model, forcing
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Measurement of Aerosol Absorption Using Photothermal Interferometry
PI: Arthur Sedlacek III, BNL
One of the central goals in the community is to better quantify the individual roles that aerosol absorption and scattering have on radiative balance. However, despite focused work on this issue, significant discrepancies on aerosol absorption still exist between measurements inferred from remote sensing and those obtained by in situ techniques. This is due, in large part, to the simple fact that the scattering channel dominates aerosol extinction and, thereby, makes measurement of the absorption difficult. An alternative method to measuring aerosol absorption is proposed herein: Measurement of the thermal dissipation of the spectrally absorbed energy through interferometry. The use of this coherent optical detection technique is particularly well suited to measuring the refractive index change that accompanies this energy transfer
process. The primary goal of this project is to conduct in situ measurements of aerosol absorption during Atmospheric Sciences Program (ASP) field campaigns. To meet this goal, construction of a prototype system will be undertaken to gain experience with the technique, characterize the sensitivity, and develop calibration. In addition to these activities, comparisons will be made with the filter-based technique [e.g., Particle Soot Absorption Photometer (PSAP)] and with other in situ instruments [Cavity Ringdown (CRD) and photoacoustic spectroscopy] both in the laboratory and in the field. It is envisioned that this instrument will find utility in a laboratory setting for measuring fundamental optical properties of prepared (well-characterized) aerosols, as a potential calibration tool for the widely-used PSAP method and as a fieldable instrument in ASP field studies.
Keywords: photothermal; interferometry; aerosol absorption; single scattering albedo
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Meteorological and Aerosol Measurements for DOE’s Atmospheric Science Program
PI: William Shaw, PNNL
The deployment of the instruments and the acquisition of the data described in this proposal address critical needs for DOE’s Atmospheric Science Program (ASP). Measurements of meteorological processes, aerosol size distributions, and aerosol scattering and absorption are of fundamental importance in field programs designed to measure the fate of aerosols in the atmosphere and their effects on atmospheric radiation. We propose to maintain and deploy a suite of ground-based instruments for ASP field campaigns that will provide researchers with essential data on atmospheric boundary layer structure and aerosol characteristics. Instruments to be provided include one or two 915-Mhz radar wind profilers, a Doppler sodar, a rawinsonde system, several surface weather stations for measuring temperature, wind velocity, and humidity, two 3-λ nephelometers, an optical particle counter (PCASP-100x), and two particle soot absorption photometers (PSAPs). Members of the ASP science team who require these data to help interpret results from anticipated field campaigns will be able to request the use of these instruments.
Key Words: instruments, meteorology, aerosols
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Chemistry and Microphysics of the Troposphere: Core Measurements for Field Programs
PI: Stephen Springston, BNL
This proposal is to provide a core set of field measurements essential to the study of aerosol radiative forcing and its effects on climate. Existing research-grade instruments will be operated on behalf of the program for aerosol precursors, atmospheric oxidants, aerosol microphysical properties, aerosol composition and ancillary trace gases.This equipment has been field proven and meets the unique requirements of aircraft-based sampling. Multiple associated infrastructure activities are an important component of this proposal and include providing quality assurance, aircraft installation, trained operators, ‘first-look’ data in the field, final-data reduction and archival
distribution of final-form results. To meet the needs of Atmospheric Science Program (ASP) goals, the instrument systems supported through this proposal will be expanded to encompass anticipated measurement capabilities as required by climate-related aerosol studies.
Keywords: instrumentation, aerosol characterization, trace gases, data archive, aircraft platform
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Fast Measurements of Aerosol Size Distribution, Hygroscopicity, and Volatility for Aircraft Deployment
PI: Jian Wang, BNL
Brookhaven National Laboratory (BNL) proposes to develop two novel instruments for aircraft-based measurements of aerosol size distribution, hygroscopicity, and chemical composition. The proposed developments support field studies using aircraft as a primary measurement platform. The first instrument, referred to as an Aerosol Mobility Size Spectrometer (AMSS), separates charged aerosol particles into different flow streams according to their sizes. The separated particles are grown into supermicron droplets in a supersaturated environment and are, subsequently, detected by an imaging system. The imaging system records mobility-dependent particle positions and their numbers, which are then used to derive particle size distribution spectra. By eliminating the necessity to scan over a range of particle sizes, AMSS significantly improves measurement speed and counting statistics. The second proposed instrument, referred to as an Aerosol Hygroscopicity and Volatility Spectrometer (AHVS), first selects monodisperse dry aerosol through a differential mobility analyzer. The monodispersed aerosol is then directed to either a humidifier (hygroscopicity measurements) or a thermal denuder (volatility measurements). The size distributions of processed aerosols, which are measured by an AMSS downstream, are used to derive aerosol hygroscopicity and volatility. The hygroscopicity and volatility measurements will also be combined to derive size-resolved aerosol chemical
compositions and mixing states.
Keywords: Aerosol size distribution, hygroscopicity, volatility, chemical composition, aircraft-based measurements
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