INVESTIGATING THE ROLES OF AEROSOLS, STRATOSPHERIC TRANSPORT, AND NATURAL AND ANTHROPOGENIC EMISSIONS ON TROPOSPHERIC OZONE USING A TROPOSPHERIC/STRATOSPHERIC MODEL

Cynthia Atherton
Lawrence Livermore National Laboratory
7000 East Avenue
Livermore, CA 94551-9900
510-422-1825
510-422-7675fax
cyndi@tropos.llnl.gov

A global, three-dimensional atmospheric model, named IMPACT, is being developed that contains both a prognostic stratosphere and troposphere. Previously the model was applied to stratospheric and limited tropospheric tracer calculations. It is currently being expanded to include the physics and chemistry necessary to simulate the troposphere. The chemistry, transport, and deposition are "driven" by meteorology supplied either from a general circulation model or data assimilated fields. Using assimilated meteorological data for time periods of measurement campaigns allows model results to be directly compared to observations and aid in their interpretation. IMPACT contains a more highly defined boundary layer than earlier tropospheric models and its domain allows investigation of regional to global issues in the boundary layer, free troposphere, upper troposphere, tropopause and stratosphere on a seasonal basis. IMPACT runs on a variety of platforms, including massively parallel computers.

IMPACT is used in this project to study tropospheric ozone that is transported from the stratosphere and formed in situ. This project (1) conducts sensitivity studies to understand how aerosols chemically affect ozone (O₃) and other species on regional to global scales. Emission sensitivity studies are then carried out to (2) determine the importance of natural versus anthropogenic processes in tropospheric O₃ production, (3) predict if regions are HC or NO_x limited in O₃ production, and (4) begin analysis of possible emission control strategies for O₃ and other species on a regional to global scale and seasonal basis. Throughout this work, IMPACT results are compared to ground and aircraft observations to illustrate areas for model improvement. IMPACT may then (5) be used predictively for future measurement campaigns.

Richard Barchet
Pacific Northwest National laboratory
P.O. Box 999
Richland, WA 99352
509-372-6158
509-372-6168fax
wr_barchet@pnl.gov

A Gulfstream 1 twin turboprop aircraft is operated as a research facility in support of the Atmospheric Chemistry Program and other DOE Programs. It is equipped for atmospheric chemistry, aerosol, turbulence, and radiative transfer research by investigators. Up to 250 hours of research flying is provided by the facility in support of research programs. Support includes assistance with the installation of investigator-provided equipment, instrument calibration and maintenance, off-site logistics, air and ground crews, and all aircraft maintenance and air-crew certification. Comprehensive data files of all variables measured during a flight are generated. Data tapes are sent to or computer files are made available to investigators within a month after the end of a field study. Further information can be found at http://www.pnl.gov/atmos_sciences/as_g1_2.html.

Carmen Benkovitz
Brookhaven National Laboratory
Bldg. 815E, ECD
Upton, NY 11973-5000
516-344-4135
516-344-2887
cmb@bnl.gov

Accurate information on the spatial and temporal distribution of emissions that contribute to atmospheric aerosol loading is a crucial input to the modeling and field studies of DOE's Atmospheric Chemistry Program, and more broadly in support of national and international activities to evaluate climate variations and changes. This project develops quantitative estimates, and the uncertainty associated with these estimates, of the emissions of sulfur compounds and primary particles, the two most important sources of atmospheric aerosols. The approach of this research is to assemble, evaluate, develop, and convert to appropriate format the most accurate information on emissions from major source categories. This work is being carried out within the framework of the Global Emissions Inventory Activity (GEIA) of the International Global Atmospheric Chemistry (IGAC) Programme. Resulting inventories will be made available through appropriate Data Centers.

This project develops gridded estimates with a resolution of one degree latitude by one degree longitude of emissions of the following trace species: (a) anthropogenic SO₂ and primary sulfate, (b) marine dimethyl sulfide (DMS), (c) terrestrial biogenic sulfur compounds, (d) volcanic sulfur compounds and primary particles, and e) primary particles from major anthropogenic and biogenic sources. Primary particle inventories include mass, size distribution and chemical composition. These results will provide participants in DOE's Atmospheric Chemistry Program and the broader scientific community with accurate global emissions estimates compiled using unified methodologies of some of the key species pertinent to atmospheric chemistry, especially atmospheric chemistry of aerosols, air quality, and climatic conditions of the present and future.

Carl Berkowitz
Pacific Northwest National laboratory
P.O. Box 999
Richland, WA 99352
509-372-6183
509-372-6168fax
cm_berkowitz@pnl.gov

Chester Spicer
Battelle Columbus Laboratory

James Cowin
Pacific Northwest National Laboratory

The concentration and distribution of hydrocarbons and nitrogen oxides govern the net production of tropospheric ozone. Discrepancies between the field data and modeling results have revealed significant uncertainties in our ability to simulate the oxidized nitrogen species. These uncertainties reduce the utility of models as tools for the design of ozone control strategies. This project focuses on two important sources of modeling uncertainty implicated in these discrepancies: nitrogen reactions on the surfaces of aerosols and atmospheric mixing.

This project is a closely integrated laboratory, field, and modeling study to asses and reduce these uncertainties. The laboratory component elucidates nitrogen reaction kinetics on the surfaces of carbonaceous aerosols. The modeling component incorporates the resulting kinetic mechanisms into a three-dimensional box-model study of multi-phase chemical systems. The field component of the study provides observations of nocturnal ozone NO_y and related gas and aerosol information, to assess model performance. The importance of the aerosol surface reactions and atmospheric mixing is then evaluated for conditions observed during the field campaign by using the modeling system to calculate sensitivity coefficients for ozone and related compounds in relation to aerosol kinetics, mixing, and other chemical and physical processes in the models. The final product will be a quantitative assessment and reduction in uncertainty for model simulations of heterogeneous chemistry and mixing on NO_y in the nighttime atmospheric boundary layer.

Guy P. Brasseur
National Center for Atmospheric Research
P. O Box 3000
Boulder, CO 80303
303-497-1401
303-497-1401
brasseur@ncar.ucar.edu

XueXi Tie and Stacy Walters
National Center for Atmospheric Research

The purpose of this project is to assess the impact of human activities on the global budget of tropospheric ozone. Specifically, changes resulting from fossil fuel combustion, and other anthropogenic activities such as aircraft operations are considered. The impact of processes that affect tropospheric ozone and its precursors are investigated and quantified. The influence of heterogeneous chemistry associated with the presence of aerosols in the troposphere is considered. The study is performed using global chemical transport models (MOZART and IMAGES) in connection with available observational data. Simulations also assess changes in the ozone budget from the pre-industrial era to the present, and to the future.

Gregory Carmichael
University of Iowa
Department of Chemical & Biochemical Engineering
Center for Global & Regional Environmental Research (CGRER)
Iowa City, Iowa 52240
319-335-1399
319-3351415fax
gcarmich@icaen.uiowa.edu

Vicki Grassian
Department of Chemistry, University of Iowa

Florian A. Potra
Departments of Mathematics and Computer Science, University of Iowa

The need to analyze ozone and aerosols together, and the lack of fundamental information on potentially important chemical processes, provide the motivation for this project. The importance of heterogeneous reactions in tropospheric ozone and aerosol formation, and their impact on O₃-precursor relationships are studied through a multidisciplinary approach that combines modeling and laboratory components. The primary objectives of this study are to:

• Evaluate the extent to which heterogeneous chemistry affects the photochemical oxidant cycle, particularly, tropospheric ozone formation;
• Conduct laboratory studies on heterogeneous reactions involving VOCs on aerosol surfaces; and
• Explore the sensitivity of ozone and aerosol composition to changes in precursor emissions on regional scales.

The importance of heterogeneous reactions in tropospheric ozone formation and its impact on O₃- aerosol precursor relationships are studied using both box and three-dimensional models. Heterogeneous chemistry effects are evaluated initially with a time-dependent multi-phase chemistry box model. A combined aerosol and gas-phase chemistry model has been developed for this purpose, in which the detailed multicomponent aerosol dynamics and heterogeneous chemistry on the aerosol surface are explicitly included. The important heterogeneous processes are identified through sensitivity studies. Regional simulations for both the eastern and western United States using the heterogeneous chemistry based on laboratory and box model studies are also performed, to evaluate these processes under different aerosol, emissions and ambient conditions. Simulations with and without aerosol reactions, and for various levels of NO_x and VOC emissions are conducted to evaluate how the heterogeneous reactions perturb the ozone and secondary aerosol precursor relationships. The modeling activity provides both a means to rapidly evaluate the significance of the new laboratory findings and helps guide the laboratory studies. Laboratory studies are directed to those areas that have high sensitivity and high uncertainty. The experimental methods to be used in the laboratory studies include Fourier-transform infrared spectroscopy and Knudsen cell measurements. A molecular level understanding of the mechanism of adsorption and reaction of atmospheric gases on aerosol surfaces will be obtained from the infrared data and more quantitative reaction probability data will be obtained from the Knudsen cell measurements.

The research is directed towards efforts to significantly enhance our understanding of one of the most uncertain areas of atmospheric chemistry, i.e., heterogeneous processes. The combined laboratory and modeling studies will improve our basic understanding of the chemistry on aerosol surfaces, will demonstrate and elucidate the interactions and interrelationships between ozone and aerosol processes will assess whether these processes can alter the O₃-precursor relationships upon which present emission reduction strategies are based, and will provide needed scientific information regarding linkages between tropospheric ozone and secondary aerosol abatement. The new laboratory data and the modeling efforts to predict the aerosol composition of both the inorganic and organic fractions will also be of direct value to aerosol radiative forcing and climate change studies. Furthermore, the study links laboratory and modeling activities, as well as modeling efforts at different scales (through a collaborative effort with other ACP modeling activities).

Lawrence Kleinman and Leonard Newman
Brookhaven National Laboratory

Field campaigns and analysis activities are carried out to obtain a mechanistic understanding of the processes responsible for formation of ozone and related pollutants. Campaigns utilizing the DOE G-1 as the measurement platform are planned for the Southwestern and Northeastern US. Measurements include primary species such as ozone, oxides of nitrogen, and light hydrocarbons, as well as product species such as aldehydes, peroxides, and nitrates. The relationship between the concentrations of these species, in the context of their spatial and temporal distribution, is used to identify and quantify the importance of potential pathways for the chemical production of ozone in the atmosphere. This information is used to test and refine the numerical models needed to understand the formation of ozone and other photochemical oxidants, and to evaluate alternate strategies for the management of these pollutants. This work is conducted independently, and in conjunction with, the Southern Oxidants Study (SOS) and the North American Research Strategy for Tropospheric Ozone (NARSTO) programs. SOS and NARSTO are national programs directed towards understanding why large regions of the United States, including rural areas, exceed the national air quality standard for ozone.

Paul Davidovits
Boston College
Department of Chemistry
Chestnut Hill, MA 02167
617-552-3617
617-552-2705
paul.davidovits@bc.edu

Douglas Worsnop, John Jayne and, Charles Kolb
Aerodyne Research, Inc.

A series of experiments is carried out to study heterogeneous processes related to the chemistry of tropospheric oxidants and aerosols. Studies focus on the heterogeneous chemistry of NO_x, O₃, HO₂, HONO, and volatile organic compounds (VOCs). Experiments are specially focused on understanding the nature of interactions at the gas-liquid interface. These studies fall into four categories:

• Continuation of uptake studies with O₃, HO₂, NO_x, HONO, and a series of VOCs by liquids as a function of acid and various ionic concentrations. The effect of photochemistry on these processes is examined.
• Co-deposition of O₃, HO₂, NO_x, HONO, and VOCs to determine the effect of surface reactions and surface complexes on the uptake of gas phase species. The studies with atmospherically relevant gas phase organic molecules focuses on the question of whether the condensation of the organic species alters the surface and affects the uptake of other gas phase species. The effect of photochemistry and ionic additives on these processes will be examined.
• Studies of processes that interconvert NO_y and NO_x.
• Photochemical free radical detection production and chemistry in media simulating liquid aerosols.

J. Christopher Doran
Pacific Northwest National laboratory
P.O. Box 999
Richland, WA 99352
509-372-6149
509-372-6168fax
jc_doran@pnl.gov

Carl Berkowitz and Jerome Fast
Pacific Northwest National Laboratory

Thomas Kelly
Battelle Columbus Laboratory

This project responds to a critical concern summarized in the 1998 NARSTO assessment, viz., to "understand, further identify, isolate, and explain the fundamental physical, chemical, and meteorological processes responsible for ozone accumulation on urban and regional scales." Two principal questions are addressed: (1) how do near-surface concentrations of ozone depend on the vertical distribution of ozone and its precursors, the evolving boundary layer structure of the atmosphere, and the vertical transport and mixing of material between surface and elevated layers; and (2) what are the relative contributions from local sources and from advection of material from upwind regional sources to the vertical distributions of ozone, VOCs, and NO_x. To answer these questions, this project carries out a coordinated chemistry and boundary layer meteorology field experiment in the northeastern United States to obtain data from chemical sensors on board DOE's G-1 aircraft, surface chemistry monitoring networks, ozone sondes, surface meteorology networks, and a supplementary array of radar wind profilers and radiosondes. Analyses are carried out using both conceptual and numerical modeling approaches; the latter will make use of the Global Chemistry Model photochemical model, the Regional Atmospheric Modeling System mesoscale model, a coupled version of the two, and a Lagrangian Particle Dispersion Model. The proposed work represents a major advance in the way that the ACP has traditionally carried out its work because it considers both air chemistry and meteorological processes as closely coupled, with an understanding of the latter elements essential for a full understanding of the former.

Paul Doskey
Environmental Research Division, Bldg. 203
Argonne National Laboratory
9700 S. Cass Ave.
Argonne, IL 60439
630-252-7662
630-252-5498fax
paul_doskey@qmgate.anl.gov

This project (1) conducts research on the effect of energy-related trace chemicals on the photochemistry of the atmosphere, (2) investigates the long-range transport of these substances and their transformation products to receptor areas, and (3) provides capabilities to measure nonmethane organic compounds (NMOCs) to other ACP researchers studying photochemistry on regional and local scales. The overall objective is to investigate the role of locally emitted NMOCs on regional atmospheric chemistry. The NMOCs have biogenic and anthropogenic sources and are important reactants in a complex mechanism that allows ozone to accumulate in the atmospheric boundary layer (ABL). The net transport of the NMOCs and their oxidation products from the ABL to the free atmosphere is affected by physical and chemical processes. To investigate the relative importance of these processes on the net transport, it is necessary to make direct measurements of the vertical concentration profiles of the NMOCs and their oxidation products and compare the measured profiles with profiles generated by coupled chemistry-transport models. The approach of this study involves a combination of (1) field measurements of diurnal vertical concentration profiles of biogenic NMOCs and their oxidation products above deciduous and coniferous forests by using an aircraft and (2) modeling efforts. Collaborative work with Pacific Northwest National Laboratory and Brookhaven National Laboratory is carried out by using research aircraft.

Jerome Fast
Pacific Northwest National laboratory
P.O. Box 999
Richland, WA 99352
509-372-6116
509-372-6168fax
jd_fast@pnl.gov

Xindi Bian and Carl Berkowitz
Pacific Northwest National laboratory

This project conducts a series of photochemical modeling studies to evaluate the contribution of stratospheric ozone to high surface ozone concentrations and carries out an extensive analysis of air chemistry and meteorological data collected over the past 10 year. The hypothesis that forms the basis of this research is that variations in the mid-tropospheric ozone resulting from stratospheric intrusions frequently contribute to high ozone concentrations at the surface that exceed the National Ambient Air Quality Standard for ozone. The approach combines data analysis and numerical modeling that will enable description of the meteorological processes by which ozone is brought from the lower stratosphere to the surface and evaluation of the contributions of stratospheric and tropospheric sources of ozone to the observed surface ozone concentrations during individual episodes. The data analysis consists of potential vorticity calculations, satellite measurements of total column ozone, ozone profiles, near-surface ozone measurements, and other supplemental meteorological measurements over North America to find evidence of stratospheric intrusions of ozone. A series of modeling studies will be performed using a coupled photochemical-mesoscale modeling system to elucidate the interactions of synoptic, mesoscale, and boundary layer processes responsible for the downward transport of ozone within the troposphere and to evaluate the relative contribution of naturally occurring ozone of stratospheric origin and tropospheric sources (natural and anthropogenic) to high surface ozone concentrations over the eastern Unites States. This issue is also among the high priority concerns of the North American Research Strategy for Tropospheric Ozone program.

A quantitative understanding of the formation and fate of ozone on scales from global through regional to local is critical due to its central role in the chemistry and radiation balance of the atmosphere, as well as its well documented effects on human health. O₃ is formed from reactions involving volatile organic compounds (VOC) and NO_x associated with energy production. While the chemistry is well recognized to be largely driven by OH during the day and NO₃ at night, recent laboratory and field measurements suggest that there are also photolyzable sources of chlorine atoms in the troposphere. Given the high reactivity of chlorine atoms, they too may play a significant role in the formation and fate of tropospheric O₃.

Sea salt particles are the likely chlorine atom source. However, the reactions converting chloride ion in these particles to photochemically active gaseous species are not well established. At the present time, there are large discrepancies in the reported values of the reaction probabilities for one series of candidate reactions, those of oxides of nitrogen with NaCl. This is undoubtedly due to a lack of understanding of the mechanism of the surface reactions and the factors which control it on a molecular level. Another uncertainty arises from recent studies which suggest that NaCl may not be the sole, or perhaps even the major, component contributing to the reactivity of whole sea salt.

For this project, laboratory studies are conducted using diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) and a Knudsen cell to elucidate the kinetics and mechanisms of the reactions of synthetic sea salt and its components with various oxides of nitrogen, O₃ , HOCl and HOBr. The initial studies of the chlorine atom-isoprene reaction as a source of unique products that might serve as markers of chlorine atom chemistry is being extended to include varying concentrations of NO_x using a combination of long path (40-50 m) FTIR, GC, GC-MS and atmospheric pressure ionization mass spectrometry. The mechanism of the recently observed production of Cl₂ from the photochemical reaction of ozone with aqueous salt aerosols is being investigated with a new 500-L aerosol chamber equipped with long-path FTIR and uv-visible spectroscopic systems as well as atmospheric pressure ionization mass spectrometry. Finally, our experimental results are incorporated into a new airshed model that treats gas-aerosol interactions and aqueous phase chemistry in a dynamic fashion, in a new collaboration with Professor Donald Dabdub at UC Irvine. The results of these studies will be a quantitative assessment of the role of chlorine atom chemistry on the formation and fate of O₃, and the contribution of energy-related pollutants to this chemistry. The results will be applicable to both remote regions as well as polluted coastal urban areas of interest to the NARSTO program.

Jeffrey Gaffney
Environmental Research Division, Bldg. 203
Argonne National Laboratory
9700 S. Cass Ave.
Argonne, IL 60439
630-252-5178
630-252-5498fax
jeff_gaffney@qmgate.anl.gov

Nancy Marley
Argonne National Laboratory

Organic oxidants, particularly peroxyacyl nitrates, organic peracids, and organic peroxides, are produced from the oxidation of numerous reactive precursor hydrocarbons. These tropospheric pollutants are important as toxins, transport agents for nitrogen oxides, reactive species (aerosol and gas phases), and as indicators of the chemical processes involving peroxy radicals occurring in the troposphere. This project is a continuation of research examining the tropospheric chemistry of organic oxidants and their precursors in laboratory and field studies. The objectives of this project are 1) to develop a better fundamental understanding of the chemical and physical properties of organic oxidants, 2) to study their chemical reactions and formation from precursors, and 3) to develop novel instrumentation for the determination of the tropospheric concentrations of organic oxidant and their precursors under different conditions. This research is exploring the relationships of organic oxidants with ozone involving laboratory and field studies to accomplish these objectives. Novel instrumentation based upon chemiluminescent detection principles is being developed, tested, and applied to the rapid measurement of peroxyacyl nitrates (PANs) and reactive hydrocarbon precursors (specifically olefins and oxygenates). In addition, chemiluminescent detection is proposed as a potential method for analysis of peracids and peroxides. Laboratory studies are conducted examining the gas-phase and liquid-phase chemistries of PANs, peracids, and aldehydes under low NO conditions representative of regional scale tropospheric situations using Fourier transform infrared spectroscopy and cylindrical internal reflectance and long-path gas cell techniques. Automated gas chromatographic analyzers equipped with electron capture detection have been used to measure peroxyacetyl nitrate (PAN) and the higher analog PANs in Mexico City as part of DOE supported field studies examining oxidant and aerosol chemistries in a megacity environment. Proposed here are continuation studies based upon earlier work focused on maintaining core-level competencies in organic oxidant chemistries and in further development of instrumentation and establishment of a better fundamental understanding of organic oxidants and their precursors.

Bruce Garrett
Pacific Northwest National laboratory
P.O. Box 999
Richland, WA 99352
509-375-2587
509-375-6631fax
bc_garrett@pnl.gov

Nels Laulainen
Pacific Northwest National Laboratory

This project supports the goal of developing a comprehensive understanding of atmospheric processes controlling the transport, transformation, and fate of energy-related pollutants (e.g., sulfur and nitrogen oxides, volatile organic compounds, and ozone), including gas-to-particle conversion. Because of the impact of aerosols on oxidant levels, visibility, climate, and health effects, the need has been identified to evaluate the causes of variations of tropospheric aerosol chemical composition and concentrations, including determination of the sources of aerosol particles and the fraction that are primary and secondary in origin. This project is focused on mechanistic theoretical and laboratory studies leading to improved understanding of gas-to-particle conversion processes for forming new aerosol particles.

This project carries out combined molecular-level theory and laboratory studies to develop a detailed understanding of the mechanisms of aerosol formation in mixed chemical (multicomponent) systems that are important in the troposphere. The goal of this work is to provide the capability of predicting the aerosol formation potential in complex atmospheric environments. The major objectives are:

• Development of a molecular-level theoretical formulation of aerosol nucleation that demonstrates an understanding of the factors controlling aerosol formation in binary and ternary systems
• Evaluation of the theoretical formulation through laboratory studies using a laminar flow tube reactor (LTRF) with particle composition analysis by ion cyclotron resonance and mass spectrometric techniques
• Specific multicomponent systems include water-sulfuric acid, water -sulfuric acid-ammonia, and selected organic compounds in combination with water and sulfuric acid.

Jeremy Hales
Envair
60 Eagle Reach Court
Pasco, WA 99301
509-546-9541
509-546-9522fax
jake@odysseus.owt.com

The primary objective of this project is to support the activities of the Management Coordinator for North American Research Strategy for Tropospheric Ozone (NARSTO). NARSTO is a effort in Canada, Mexico, and the United States dedicated to providing the scientific and engineering basis for dealing with tropospheric ozone pollution on the North American continent. Basic elements of the NARSTO program are described in the November 1994 EPA document titled "NARSTO Research Strategy and Charter." The members of NARSTO are from several government agencies, industrial and private organizations, and universities. The U.S. DOE is a charter member of NARSTO. Further information on NARSTO organization and activities can be found on the world-wide web at http://narsto.owt.com/Narsto/.

Among other activities, the Management Coordinator, provides substantial technical networking for NARSTO with the extended world community, especially WMO and EUROTRAC. The Management Coordinator continues to serve on WMO, NAS, and Eurotrac committees in this networking capacity. In addition, some research activities for ACP are carried out on the modeling of long-range transport, chemical transformation, and fate of trace atmospheric chemicals.

Bruce Hicks
NOAA Air Resources Laboratory
1315 East West Highway
Silver Spring, MD 20910
301-713-0684
301-713-0119
Bruce.Hicks@noaa.gov

The objective of this work is to provide, through agency collaboration, a center of excellence in the United States that would impose quality-assurance (QA) techniques on data collected by national air- and precipitation-chemistry monitoring networks operating in the Americas (North, Central, and South). The WMO has adopted a scheme in which three QA centers will deal with data-intercomparability problems in three major regions of the world: the Americas, Europe and Africa, and Asia and Oceania. The QA Center for the Americas has special focus on surface ozone, airborne radioactivity, aerosol optical depth, and precipitation chemistry. The QA Center for the Americas is funded jointly by DOE, EPA, and NOAA. The final products of this activity are regional and global data sets created by combining observations made in different nations with a variety of sampling methods that previously did not share common data-quality guidelines or calibration procedures or benefit from periodic intercomparisons and other confidence-building steps.

Ignatius Tang
Brookhaven National Laboratory

This project continues previous research on single particles, to provide the atmospheric science community with essential optical and thermodynamic properties of most common atmospheric aerosols. Two parallel paths are followed: 1. A study of mixed aerosols of atmospheric importance, which are composed of organic and inorganic compounds. Recent field studies have shown that observed light scattering characteristics cannot be accounted for on the basis of inorganic salt particles alone. Many such particles were in fact shown to consist of a mixture of organic and inorganic components. Presently, very little is known about the formation and properties of mixed particles. This project uses field data, in order to construct model aerosol particles and investigate their properties, using single-particle levitation techniques. 2. A study of upper troposphere and lower stratosphere particles, utilizing new low-temperature apparatus. A new cryogenic single particle levitation system has been constructed and deployed. The utility of this system has been demonstrated in a study of the freezing behavior of sulfuric acid aerosols, and the system has recently derived the first phase diagram for the ammonium bisulfate water system. The processes are investigated that trigger cirrus and polar stratospheric cloud formation and determine the exact composition and phase of these clouds using Raman Spectroscopy.

Yin-Nan Lee
Brookhaven National Laboratory
Bldg. 815E, ECD
Upton, NY 11973-5000
516-344-3294
516-344-2887
ynlee@bnl.gov

Multi-phase chemistry of atmospheric trace species involving condensed water such as hydrometeors (clouds and fog) and surface water (oceans, lakes, and the tissue fluid of living organisms) plays an important role in transformation, transport, and removal of these trace gases. This project evaluates the fundamental chemical information (such as kinetics and equilibrium data, and field measurement data) needed to quantitatively evaluate the contribution of gas-liquid processes to the formation, destruction, distribution, and environmental impact of tropospheric ozone. The key processes include radical sources and sinks, uptake of O₃ and its precursors by atmospheric water and subsequent environmental effects, oxidation of reduced sulfur compounds, cycling of reactive nitrogen species, and degradation of organic compounds and chemistry of secondary products. This project focuses on (1) evaluating the aqueous phase reaction kinetics of O₃, NO₂ and peroxyacetyl nitrate (PAN) with pertinent environmental substrates found in natural water (e.g., humic materials) and leaf tissue (e.g., glutathione); (2) evaluating the aqueous-phase properties of hydroxycarbonyl compounds, as well as HNO₄ and HOCH₂C(O)O₂NO₂; (3) developing instrumentation for gaseous HNO₃ and hydroxyacetone; (4) performing field measurement of these compounds, including formaldehyde, to better understand the role secondary products play in O₃ production. The data will be incorporated into numerical models for an accurate description of photochemistry of O₃ and a reliable assessment of environmental impact of man-made emissions.

Judith Lloyd
State University of New York-Old Westbury
Department of Chemistry and Physics
P.O Box 210
Old Westbury, NY 11568
516-876-2728
516-876-2746
jlloyd@bnl.gov

The principal objective of this work is to contribute to the understanding of the production and fate of atmospheric peroxides and peroxy radicals. Along with other atmospheric oxidants, these species have an important role in the production of tropospheric ozone, sulfate aerosol haze and acid precipitation. Successful remediation strategies for these environmental problems require a knowledge base of the abundance, transport properties and reaction kinetics of the entire suite of species that participate in their formation.

While measurement techniques for many trace gas constituents of the atmosphere have reached maturity, such is not the case for peroxides and peroxy radicals. A major objective of this project is the continued development and assessment of methods for the analysis of these unstable species, for both aircraft and ground deployment. Peroxide measurements will be made aboard the DOE G-1 aircraft in 1998 in Phoenix, AZ, and a year-round series of intensives at BNL's NARSTO NE PAMS site will continue. Observed peroxide concentrations are interpreted with the following specific objectives:

to evaluate the geographical, temporal and vertical trends in peroxides, especially regarding their speciation;
to confirm our understanding of peroxide sources and sinks;
to evaluate, along with observed trends in concentration of other species, the extent to which ozone is locally or regionally produced; and;
to provide peroxide data to the modeling community for the verification of model performance and assessment of regulatory efforts.

In addition, method development on a chemiluminescence-based peroxy radical analyzer will continue during the project period.

Sasha Madronich,
National Center for Atmospheric Research
P. O. Box 3000
Boulder, Colorado 80303
303-497-1430
303-497-1400fax
sasha@ucar.edu

Knut Stamnes
University of Alaska, Fairbanks

Air pollution is widely recognized as an effective partial shield against the solar ultraviolet (UV) radiation reaching the Earth's surface, and as a modifier of photolysis rates in the troposphere. These important effects are still poorly understood due to the complexity of modeling radiative transfer in such highly heterogeneous scattering/absorbing environments. A three-year program is underway using our Tropospheric Ultraviolet and Visible (TUV) model to (1) categorize and quantify these effects in the presence of various realistic levels of air pollution, (2) evaluate the model with, and provide a theoretical framework for the interpretation of, UV measurements obtained under highly polluted conditions, (3) assess the UV consequences of long-term changes in air quality, and (4) develop simple parameterizations of pollution effects on UV radiation, for use in three-dimensional chemistry-transport models.

Michael McElroy
Harvard University
Department of Earth and Planetary Sciences
29 Oxford Street
Cambridge, MA 02138
617-495-2351
617-495-8839
mbm@io.harvard.edu

Hans Schneider
Harvard University

This project investigates the role of tropospheric planetary waves in modulating transport processes affecting the abundance and distribution of ozone in the stratosphere and to improve our understanding of processes regulating transport of ozone from the stratosphere to the upper troposphere where ozone is known to play an important role in the radiative energy balance of the earth. An interactive two-dimensional (2-D) model of the chemistry and dynamics of the stratosphere as well as a three-dimensional dynamics model are used to facilitate this research.

New evidence (Fusco and Salby, 1997) suggests that planetary wave activity is subject to variations not only on annual but also on decadel time scales. It is shown that trends observed over the past 15 years both in column ozone and lower stratospheric temperature can be reproduced in an interactive 2-D model if we account for plausible variations in wave driving of the stratospheric circulation. We propose a detailed analysis of the relative importance of chemical and dynamic influences in determining past trends in ozone. Insights gained in this study will be used to estimate possible changes in ozone that might arise over the next several decades.

Ozone sonde data (Logan, 1997) provide the most reliable information on the abundance and distribution of ozone in the critical region near the tropopause. The data show a characteristic double maximum that appears to be consistent with a shallow layer of reduced quasi-horizontal mixing above the tropopause. We propose to use ozone sonde data in combination with our model to deduce the structure of vertical and horizontal diffusive transport in the lower stratosphere.

Peter McMurry
University of Minnesota
Department of Mechanical Engineering
111 Church St., SE
Minneapolis, MN 55455
612-625-3345
612-625-6069
mcmurry@me.umn.edu

Fred Eisele
National Center for Atmospheric Research

Paul Ziemann
University of California, Riverside

This research showed previously that atmospheric nucleation sulfuric acid almost certainly participates in the production of new particles by homogeneous nucleation in the atmosphere, but that particle production likely involves species in addition to H₂SO₄ and H₂O. Most models currently assume binary nucleation of H₂SO₄ and H₂O. The current project investigates the extent to which NH₃ plays an important role and secondary organics contributes to the growth of freshly nucleated particles, especially in areas that are impacted by biogenic emissions such as terpenes. The composition of freshly nucleated particles is measured in the ~3 nm size range to gain new insights into the nucleation and growth processes. Due to the minute quantity of mass associated with such particles, this measurement represents a difficult challenge. To maximize chances of success, two approaches to this problem are being explored. In the first, the freshly nucleated particles are separated from the remainder of the aerosol by electrostatic classification and then collected with a specially-designed electrostatic precipitator. After collection for periods of a few minutes the particles are volatilized and their composition determined using chemical ionization mass spectrometry. In the second approach, an impactor is used to separate the freshly nucleated particles from the remainder of the aerosol and then aerodynamically focus the ultrafine particles into a high-vacuum chamber for collection. After collecting for a few minutes the particles will be volatilized and their composition determined using electron impact ionization mass spectrometry.

Tihomir Novakov
Lawrence Berkeley National Laboratory
Environmental Technologies Division, MS-73
One Cyclotron Road
Berkeley, CA 94720
510-486-5319
510-486-4733
tnovakov@lbl.gov

This project has a laboratory and a field component. Laboratory studies are designed to determine critical diameter and critical supersaturation of (i) single component organic compounds with different solubilities, (ii) multicomponent soluble and insoluble organic particles, (iii) mixed inorganic and organic aerosols, and (iv) effects of organic surfactants. Field measurements are aimed at (i) assessing the significance and magnitude of sampling artifacts commonly encountered with collection and analyses of the organic aerosol material and (ii) quantifying the contributions of organic and inorganic species to aerosol and cloud condensation nuclei (CCN) concentrations. Activities are performed at two marine sites: Cape San Juan, Puerto Rico, and Point Reyes, California. These field measurements are supplemented by participating in larger field experiments conducted by others. The field efforts are aimed primarily at analyzing shipboard, aircraft, and ground samples for organic carbon and will add to our knowledge of the distributions and concentrations of carbonaceous aerosols at a number of locations.

Joyce Penner
Department of Atmospheric, Oceanic and Space Physics
2455 Hayward
Ann Arbor, MI 48109-2143
734-936-0519
734-764-5137fax
penner@umich.edu

The DOE Atmospheric Chemistry Program is designed to provide DOE with information pertaining to the role of energy-related pollutants in altering the atmospheric environment. One important area of alteration is caused by the emissions of carbon monoxide, methane, nitrogen oxides and volatile organic carbon species (VOCs) from the burning of fossil fuels. These emissions combine in the presence of sunlight to form ozone in the troposphere. It has been effectively argued that these emissions are causing large increases in tropospheric ozone over vast regions. The emissions of these species also cause changes to the concentration of hydroxyl radical and other oxidizing species. Changes to these oxidants may cause changes in other greenhouse gases, such as methane, which are removed through chemical oxidation processes in the troposphere.

This research has developed a global tropospheric chemical model that is capable of treating the chemistry of CO, CH₄, NO_x, and a full suite of VOCs. The model is computationally fast, while providing much better chemical resolution than is presently available in other tropospheric chemistry models, and the model is configured so that it may also be run interactively with a climate model. This project develops emissions inventories and examines numerical formulations that are appropriate to the suite of VOCs which are included in the model. This model is used to examine the role of organic species in the chemical climatology of the global troposphere. Model results are carefully compared with atmospheric measurements and separate tracer transport tests to help build confidence in the quality of the simulations, allowing an evaluation the impact of energy-related emissions on the global troposphere.

Stephen Schwartz
Brookhaven National Laboratory
Bldg. 815E, ECD
Upton, NY 11973-5000
516-344-3100
516-344-2887
ses@bnl.gov

Carmen Benkovitz and Robert McGraw
Brookhaven National Laboratory

This project develops, applies, and evaluates a hemispheric scale aerosol model driven by observation-derived synoptic meteorological data. Use of observation-derived meteorological data to drive the model is essential to permit comparison of modeled aerosol loading, composition, and microphysical properties with in-situ and remote-sensing observations as a function of location and time. Staged model development incorporates explicit treatment of aerosol microphysics (nucleation, growth, cloud activation) and inclusion of additional species beyond sulfate, now included in the model (windblown dust, sea salt, carbonaceous material). Successive stages of the model are run for periods of field measurement campaigns by ACP and others, specifically including ACE-2 (North Atlantic Regional Aerosol Characterization Experiment, summer 1997) aiding both model evaluation and interpretation of controlling processes.

Stephen R. Springston
Brookhaven National Laboratory
Bldg. 815E, ECD
Upton, NY 11973-5000
516-344-4477
516-344-2887
srs@bnl.gov

Leonard Newman
Brookhaven National Laboratory

This project provides instruments for ACP activities in which Brookhaven National Laboratory participates scientifically. The same instruments will also be provided on a deployment cost basis for other ACP activities in which BNL does not participate scientifically. Research-grade analyzers are available for ozone, nitrogen oxides (NO, NO₂ and NO_y), carbon monoxide, sulfur dioxide and other species. The need for specialized measurement capabilities is driven by the scientific objectives of measurement programs planned by the ACP. The low concentrations of trace species and the unique requirements of aircraft-based sampling necessitate the equipment to be provided. Modifications are proposed for increasing the specificity of the existing 3-channel, oxides of nitrogen instrument and to improve the sensitivity of the present carbon monoxide analyzer by 3 to 10 fold. Investigations into the mass balance of nitrogen species and aircraft inlet losses are planned.

Wei-Chyung Wang
Atmospheric Science Research Center
State University of New York
251 Fuller Road
Albany, NY 12203
518-437-8708
518-437-8713fax
wang@climate.cestm.albany.edu

The goal of the present project is to develop a coupled climate-chemistry model for the purpose of: (1) understanding the physical, chemical and dynamic processes that control mid-latitude O₃ in the lower stratosphere and free troposphere; and (2) developing improved predictions of future O₃ changes in these regions and their influence on (and response to) future climate changes due to increasing greenhouse gases CO₂, N₂O, CH₄ and the CFCs, and changes of O₃ precursor gases.

To accomplish this goal, a two-stage strategy is planned:

(1) to conduct "uncoupled" chemical transport model (CTM) and global and regional climate model experiments to study the physical, chemical, and dynamic processes affecting O₃, to evaluate the importance of O₃ changes on regional climate, and to study how climate change affects O₃ distribution; and

(2) to improve the consistency of the treatment of physical, chemical and dynamic processes in CTM, and global and regional climate models.

The first stage studies has been completed by using radiation and atmospheric models (2- and 3-D CTMs and global climate models) to conduct sensitivity experiments of O₃ changes to changes in its precursor gases as well as to global warming, and to study the radiative forcing and climate response due to observed and CTM simulated O₃ changes. These "uncoupled" studies provide insight into the climate-chemistry interaction. This project conducts research in the second stage focusing on the climatic and chemical processes, in particular the processes involving clouds and transport, which affect O₃ in the lower stratosphere and upper troposphere. Both gas-phase and heterogeneous chemistry are considered. In addition, changes of UV radiation reaching the surface due to changes in O₃ and climate (through clouds) are studied.

Rodney Weber
Brookhaven National Laboratory
Bldg. 815E, ECD
Upton, NY 11973-5000
516-344-6198
516-344-2887
rweber@bnl.gov

Peter M. McMurry
University of Minnesota

This project addresses the development of instrumentation for in situ measurement of aerosols to improve understanding of the mechanisms of tropospheric new particle formation and growth. An advanced technique is being developed for rapid in situ measurement of tropospheric nanoparticle spectra (2.7 to 10 nm). This is achieved by performing laboratory experiments aimed at improving our understanding of factors which influence Ultrafine Condensation Nucleus Counter (UCNC) photo-detector pulse height distributions. These findings are incorporated into a new UCNC optimized for aircraft-based measurements of nanoparticle size distributions by pulse height analysis (PHA). Kernel functions are refined to improve inversion of ambient pulse heights distributions. The research is a continuation of our efforts to develop superior techniques for measuring ambient nanoparticles. Combined with existing aerosol measurement capabilities, these instruments will support the Atmospheric Chemistry Program and its future research efforts aimed at understanding the interactions between tropospheric trace gas species and aerosol particles.

Marvin Wesely
Environmental Research Division, Bldg. 203
Argonne National Laboratory
9700 South Cass Avenue
Argonne, IL 60439
630-252-5827
630-252-5498
mlwesely@anl.gov

Paul Doskey
Argonne National Laboratory

This project investigates the dry air-surface exchange of energy-related trace chemicals over North America and the surrounding oceanic areas through field measurements, theoretical studies, parameterization of exchange rates, and numerical modeling. Emphasis is on estimating the air-surface exchange rates of energy-related sulfur and nitrogen compounds, atmospheric oxidants, and selected reactive hydrocarbons with Argonne's air-surface exchange model. Field studies use micrometeorological techniques to measure air-surface exchange rates. Effective application of the resulting parameterizations requires highly detailed information on such surface conditions, which is inferred by use of remote sensing observations from satellites. Research on improved parameterization of processes is conducted in the following areas: (1) temporal and spatial variations in soil moisture conditions and their effects on air-surface exchange; (2) rapid conversion of NO emitted from soils to NO₂ deposited on the surface from the atmospheric surface layer; (3) dry deposition of peroxyacetyl nitrate; (4) natural emissions of NO and reactive hydrocarbons; and (5) deposition of submicron particles as a function of both chemical species and size. The focus of much of this work is improvements in an existing dry air-surface exchange model for application in regional- and large-scale atmospheric chemistry numerical models. Modeling efforts and selected field experiments will be conducted in conjunction with ACP field campaigns on the behavior of oxidants and fine particles over regional scales.

Douglas Worsnop
Aerodyne Research, Inc.
45 Manning Road
Billerica, MA 08121-3976
508-663-9500
508-663-4918fax
worsnop@aerodyne.com

Paul Davidovits
Boston College

John Jayne and Charles Kolb
Aerodyne Research, Inc.

Recent advances in the development of laboratory tools available to study the kinetic processes leading to atmospheric aerosol formation and growth promise to greatly extend our understanding of aerosol formation mechanisms and their rates. This project focuses on the coupling of a novel, atmospheric pressure flow reactor, capable of fully simulating the temperature and pressure variations found in the troposphere, with two advanced and highly sensitive detection technologies. The first detection method, atmospheric pressure chemical ionization mass spectrometry is designed to accurately and sensitively detect the gaseous aerosol precursors and small molecular clusters which participate in the nucleation of new aerosol particles and the growth of pre-existing aerosol particles by condensation of gaseous vapor species. The second detection method is an innovative aerosol mass spectrometer that can simultaneously enumerate and size aerosol particles with diameters between 0.05 and 10 micrometers as well as chemically characterize individual aerosol particles as a function of their size. The combination of these advanced laboratory techniques allows the direct study of aerosol nucleation and growth processes under much better chemical control and with much better temporal resolution than can be achieved under conditions encountered in more traditional aerosol reaction chambers utilizing traditional light scattering and/or gas and aerosol sampling diagnostics.

This project uses this combination of laboratory tools to investigate the kinetics of both the nucleation processes that can lead to new particle formation in the troposphere and the vapor/particle condensation and particle-particle agglomeration processes that can lead to particle growth and chemical evolution in tropospheric aerosols. A laboratory program exploring these issues will help elucidate the factors controlling both the formation of new tropospheric particles and those that lead to growth and chemical differentiation of existing particles. A sophisticated understanding of the mechanisms and kinetics of these processes can be incorporated into atmospheric models to help understand key issues including the identification of PM-2.5 sources, the determination of the fraction of PM-2.5 that form in the atmosphere (secondary aerosol formation), and the degree to which the distribution between primary and secondary aerosol changes with particle size.