Cover Sheets:
Naval Research Laboratory (NRL)
Calspan-University of Buffalo Research Center (CUBRC)
University of Washington
Response to concern expressed by NOPP Panel

1. Abstract
2. Table of Partnerships
3. NOPP Objectives

4. Tasks to be Performed

5. Offerors' Capabilities and Related Experience

6. The Qualifications and Experience of the Principal Investigators

Principal Investigator: Dr. William Hoppel

Co-Principal Investigator: Mr. Thomas Albrechcinski

Co-Principal Investigator: Professor Dean A. Hegg

1. The Panel evaluating the pre-proposal expressed concern about "fluid dynamical scale issues and other related effects" and that the "chamber may introduce too many limitations to generalize the results to field conditions". In response we would like to make the following comments:
i.) The processes this proposal addresses are, for the most part, microscopic phenomena; such as, the absorption of trace gases at the surface of cloud droplets and the rate constants for chemistry occurring in the droplets, the gas-phase oxidation pathways for DMS and the related rate constants, and heterogeneous chemistry of sea-salt particles. These processes care little about the macroscopic state of the atmosphere. In analogy to fluid mechanics these processes are like viscosity, thermal conductivity, or density, which can be determined in the laboratory and appear as coefficients in the macroscopic equations. The extension of our results to the real atmosphere is via the aerosol general dynamic equation, which is the basic equation used in the associated macroscopic aerosol modeling effort and couples to the fluid mechanical equations via transport and mixing terms. For aerosol modeling it is just as important to get the microphysical part right before extending the model to the atmosphere as it is for the fluid dynamist to get the viscosity, thermal conductivity, and density right before modeling the environment.
ii.) We see no way that the "chamber will introduce too many limitations to generalize the results to field conditions". Quite to the contrary we are proposing to do studies of microphysical processes which have not been tractable during field measurements. The complexity of the natural atmosphere and the spatial variability make it nearly impossible to arrive at definitive results with regards to the phenomena to be studied. The beauty of the proposed measurements is that they can be performed on a system with fixed volume (lagrangian reference frame), with controlled (but realistic) composition; the volume is large enough so that it will support a number of investigators and yet small enough to have negligible spatial variability, so that each investigator is essentially looking at the same sample.
iii.) We have briefly addressed this issue in the full proposal.

2. A second question which the Panel is likely to raise is with regard to the probability that all participants by letter of intent-to-participate will obtain the required funding. Full participation of these seven institutions are not required to make the experiment successful. However it is very likely that we will have full participation. In this regard we would like to point out the following:
i.) Three of the participants by letter-of-intent are from national facilities and already have labor and instrumentation costs covered. They only have to raise a small amount of funds for deployment. Their participation is nearly certain.
ii.) The universities participating are well established and have proven track records at winning grants. Furthermore these experiments have been endorsed by IGAC (see proposal). This endorsement will be helpful when these investigators approach the U.S. sponsors of IGAC (NSF and NOAA).
iii.) Additional institutions have expressed an interest in participating, but have not been encouraged to do so because of space limitations and measurement redundancy. If some proposed participants cannot participate, replacements will be sought.

This proposal supports the broad goal of developing a marine and coastal aerosol model which can be included in meteorological models to predict radiative transfer within the (atmospheric) marine boundary layer (MBL). An accurate model of the MBL aerosol is necessary to properly address radiative transfer in marine forecast models as well as to predict the extinction of electro-optical (E-O) signals and hence effectiveness of DOD E-O systems operating in marine and coastal regions. It is proposed to use the Calspan 600 m³ environmental chamber to study (1) the effect of cloud processing on the MBL aerosol size distribution, (2) gas-phase growth of aerosols which results from oxidation of Dimethyl Sulfide (DMS), given off by phytoplankton, to nonvolatile sulfate, (3) nucleation of MBL aerosol directly from involatile products produced by photolysis of DMS and SO₂, and (4) and heterogeneous oxidation of SO₂ by ozone in sea-salt aerosol. The Calspan 600 m³ chamber offers a unique capability in that it can function not only as a photolysis chamber but also as a cloud chamber, and is large enough to support the number of investigators required to obtain closure. The proposed study will bring together ten partners already doing research on marine aerosols and provide a catalyst to do an extremely meaningful experiment requiring expertise which does not reside at a single institution. Most partners will participate using their own resources and the bulk of the NOPP funding will go to support the facility.

This proposal is designed to bring together a number of institutions already doing research on marine aerosols and provide a catalyst to do an extremely meaningful experiment requiring expertise which does not reside at a single institution. Because of the existing resources provided by the individual institutes, much, if not most, of the overall cost will be borne by existing programs. Participating institutions are:

As stated in Section 3.a., the long-term goals to which the proposed study contributes is the modeling of marine and coastal aerosols and their effect on radiative transfer. These goals are important in calculating radiative transfer in meteorological models, climate models, and for predicting the effectiveness of DOD, electro-optical systems in the marine and coastal environment.

NRL has a strong ongoing marine aerosol and cloud physics research program to understand and model the effects of the marine environment on naval systems and to transition advances made in aerosol research to meteorological models of various scales. Of particular importance to this proposal is a new five year Accelerated Research Initiative on Coastal Aerosol Processes started in FY97.

The University of Washington has a long history of research on marine aerosols, marine cloud physics, and the dynamics of the marine atmosphere. In the past ten years, projects involving the assessment of anthropogenic emissions on the climatology of the marine atmosphere have also come to the fore. Support for this research has been derived from a variety of sources including NSF, NASA, NOAA and ONR. The relevant faculty at the University are currently engaged in a number of projects involving these areas of interest which are scheduled to persist for several more years. For example, Prof. Hegg is participating in the MAST project (sponsored by ONR), ACE-1 and ACE-2 (sponsored by NSF and NOAA), and TARFOX (sponsored by NSF, NOAA, NASA, and ONR).

A primary objective of the CUBRC organization is the development of sustained research initiatives in environmental sciences addressing technology needs of the U.S. Government and its agencies. Through one of its parent organizations (Calspan SRL Corp.), the world class 600 cubic meter Environmental Chamber, supporting facilities, and staff will be made available to serve the research interests of this program.

The organizations participating by letter-of-intent all have significant experience and on-going programs relating to marine aerosols. NCAR, Lawrence Berkeley National Laboratory and Atmospheric Environmental Service of Canada have been assigned national roles in examining the effect of aerosols on radiative transfer, especially the aerosol contribution to radiative transfer in global models and climate change models.

The study of atmospheric aerosols is multi-disciplinary, and requires expertise in both physical and chemical processes, in gas-phase and condensed-phase reactions, and in the modeling of these processes. Particle sizes span the difficult region between kinetic theory and continuum mechanics. Further progress can only be made as we pool resources of a number of experts in joint experiments. The approach here has been to identify the interacting physical and chemical processes and assemble the required facility and expertise to obtain closure in studying the net effect the processes have on the aerosol size distribution and chemical composition. CUBRC is furnishing the chamber, chamber operations, and substantial supporting measurements. NRL is providing high resolution size distribution measurements of the evolution of the aerosol size distribution. During cloud processing experiments, NRL will measure the cloud droplet spectrum and other cloud microphysical properties.

In addition to some of the more common trace gas measurements, such as SO₂, O₃, NO_x and methane, which can be measured with commercially available instruments, some very difficult and unique measurements are required. These include measurements of OH, gaseous H₂SO₄ and MSA, H₂O₂, NH₃, DMS, speciated HCs, and intermediates of DMS oxidation. There is no single institution which can provide all these measurements. We have put together a team which can provide the required resources. A list of measurements, the most important element of the shared resources and the institution providing the measurement is provided in the Table 2 (page 16).

Two levels of cost sharing can be identified. The first has to do with the immediate costs to carry out the proposed experiments, including data analyses, associated modeling, and reporting the results. This cost sharing is shown by institution in the Table of Partners in Section 2. Only $624K of $1679K is being requested of NOPP by the partners. These funds are primarily for the chamber and provides the catalyst to bring the partners together.
The second level of cost leveraging relates to the funding which the partners are committing to the long term goals to which this work is contributing. More than ten million dollars per year are being spent by the partners to address the effect which marine aerosols have on electro-optical propagation, climate change, and radiative transfer. The results of the proposed experiments can be transitioned immediately to these on-going programs.

There have been a number of large field programs designed to study aerosols in the marine environment (for example ASTEX/MAGE, ACE-1, MAST, ACE-2). While these experiments have been indispensable in increasing our understanding of the large-scale features of marine aerosols, they give only the integrated effect of many individual processes operating in concert. From this data it is difficult, if not impossible, to extract detailed quantitative information and rate constants for the individual physical and chemical processes. The approach proposed here would use the large CALSPAN 600 m³ environmental chamber to carry out a series of experiments to isolate and study a number of mechanisms known to be important in the oceanic environment focusing particularly on the mechanism of cloud processing. The importance of doing the experiment in the dispersed phase and in a large environmental chamber cannot be over-emphasized. Reaction of trace gases in equilibrium with bulk solutions can be studied in the laboratory but the applicability of these studies have been questioned [Hansen et al. (1991), Jayne et al. (1990), Hoppel et al. (1994)] because of the huge difference in the surface-to-volume ratio of bulk and disperse systems. The time scales of vapor diffusion, liquid-phase diffusion and the effect of the accommodation coefficient are much different in disperse and bulk systems. Expansion cloud chambers offer a controlled environment where the method of cloud formation simulates nature, and where the trace gas concentrations can be strictly monitored. The problem with small laboratory cloud chambers is that the fall-out time is too short to study most reactions (at least at concentrations which are applicable to the atmosphere), For example, a cloud composed of 10 mm radius droplets falls at a rate of 0.8 m min^-1, and the cloud would be completely depleted in about a minute in a 1 m high chamber.

Because the processes addressed in this proposal are microscopic phenomena, problems of scaling to the real atmosphere are minimal and the results obtained in the chamber are immediately available as inputs into the aerosol models. In this respect the processes to be studied are analogous to the parameters like viscosity, thermal conductivity, and density which are determined by molecular processes and appear as parameters in the macroscopic equations of fluid dynamics. The extension of our results to the real atmosphere will be via the aerosol general dynamic equation, which is the basic equation used in the associated aerosol modeling efforts. For aerosol modeling it is just as important to get the microphysical part right before extending the model to the atmosphere as it is for the fluid dynamist to get the viscosity, thermal conductivity, and density right before extending the fluid dynamical equations to environmental calculations.

A detailed process-oriented model for aerosols in the marine and coastal environment is under development at NRL (Naval Research Laboratory), as is the integration of the aerosol model with a 3-D coastal and marine mesoscale model. This model contains all major source, sink, and transformation processes which are presently known to be important in predicting the evolution of the aerosol size distribution in the MBL including exchange between the MBL and the free troposphere. However, there is considerable uncertainty in the exact mechanisms, rate constants, etc., which need to be resolved before the model can be used with confidence. This proposal would bring together the expertise and facilities from several institutions to address the following aerosol processes important in the marine environment:

(1) Cloud processing of MBL aerosol. Recently it has been shown that the most powerful mechanism for adding inorganic mass to the submicron aerosol is the constant cycling of MBL air through MBL clouds. During cloud processing, a portion of the aerosol population (CCN) is activated to form cloud droplets. These cloud droplets act as little chemical factories converting trace gases (SO₂, NO_x, etc.) to involatile material (sulfate, nitrates, etc.) which remains as increased aerosol material upon evaporation of the cloud droplet. The cloud-residue mode becomes the dominant feature of the MBL aerosol size distribution. However the chemical mechanisms and rate constants of the various reactions are not well characterized for the dispersed system (clouds) where the surface to volume ratio is very large. Furthermore, the formation mechanisms and sources of organic species (such as carboxylic acids) are not known with certainty, although these are known to be associated with MBL aerosols. This proposal would address the cloud processing issues using the unique 600 m³ facility as detailed in Section 4.d.

(2) Gas-phase growth of MBL aerosols. It has been observed that submicron aerosols are composed largely of non-sea-salt sulfate. The origin of this sulfate in more remote oceanic regions is predominantly DMS given off by phytoplankton. This source of sulfur, when averaged globally, is less, but the same order of magnitude as anthropogenically produced SO₂. The gas-phase oxidation products, branching ratios, and mechanisms which form particulate sulfate are not established and would be investigated in the Calspan 600 m³ facility as detailed in Section 4.d.

(3) Nucleation of MBL aerosol. While MBL aerosols are thought to grow to a size sufficiently large to activate in clouds via processes to be investigated in (2), a distinct but related issue is the source of the particles upon which such processes may act. One proposed source is the spontaneous formation of particles from gas phase reaction products by heteromolecular nucleation, abetted by the high relative humidity near clouds. While theoretical models of the nucleation process abound, few laboratory studies have addressed binary nucleation and none ternary nucleation. The chamber experiments proposed here provide a unique opportunity to elucidate this important question.

(4) Heterogeneous reactions of SO₂ with sea-salt aerosol has recently been postulated as a major sink for S0₂ in the marine environment. The high pH and buffering capacity of sea-salt encourages oxidation of dissolved SO₂ and dissolved O₃. The Calspan 600 m³ facility offers a unique facility to study this process at high humidity as exists in the MBL.

(5) The NRL process-oriented model will he used interactively as a diagnostic tool to interpret the results obtained in (1)-(4) above and to improve the model, as will the U. of Washington liquid-phase and gas phase chemistry models. Science studies using the models and existing aerosol data bases (for example, ACE1, ACE2, NRL airship data) will commence and extend beyond the two year proposed life of this program.

The studies described above will be carried out using the 600 m³ (10 m high) environmental chamber which also functions as a cloud chamber. It is unique in that it is designed to withstand the forces created during the compression/expansion cycle required in an expansion cloud chamber. For example, the force caused by a 20 mb expansion in this large chamber is about 60 tons. (A 20 mb expansion corresponds to about a 150 m change in altitude and a liquid water content of about 0.5 g m^-3, starting from saturation.) The chamber is Teflon coated, has an extensive air handling system, and irradiation lamps that simulate the solar spectrum at an intensity of half the noontime solar energy at 40 deg latitude. The chamber is large enough to support a number of investigators without significantly affecting the contents. (For example, 20 instruments sampling at the rate of 100 cm³ sec^-1 will remove only 0.2% of the air in 10 minutes.) A cloud can easily be maintained for 3 to 5 minutes in the lower quarter of the chamber where the measurements are made; in the upper part of the chamber depletion occurs due to gravitational settling. The expansion rate can be varied to control total liquid water content, cloud droplet number, supersaturation achieved, and cloud droplet radii. The expansion is adiabatic and the microphysics of cloud formation can be accurately modeled (see Hoppel et al., 1994). Preliminary experiments in the chamber have shown that measuring the aerosol size distribution before and after a cloud cycle with a differential mobility size spectrometer achieves a measurement sensitivity for liquid-phase oxidation of trace gases in the disperse state never before obtained.

The project can be broken out into the following Tasks:

4.d.1. Planning. If this proposal is funded a planning/steering committee consisting of the P.I.s and other participants will immediately be established. (1) The first task will be to review the science issues in light of the resources and identify any further resources which would enhance the project, and if identified, to marshal additional resources. (2) Plans for executing the chamber characterization experiments will be finalized. (3) Detailed plans for the main experiments will be formulated including space allocation, and establishing operating procedures. (4) Data handling procedures for (i) real-time operational decision aids, for (ii) daily data exchange and daily reevaluations of procedures, and (iii) post-experiment data exchange and analyses will be established. (5) Joint studies using collective data sets will be initiated, and the protocol for exchanging data, using collective data sets, and publishing results will be established.

4.d.2. Chamber Characterization Experiment . These experiments are proposed to be carried out in the Sept - Dec. 1997 time frame and will be executed primarily by CUBRC and NRL. Issues to be addressed include wall losses for certain trace reactants to be used in the main experiments, concentrations and species of residual hydrocarbon in the chamber, characterization of the photolysis lamps, testing of new supporting equipment, development of alternative methods to control expansion during cloud formation, and testing and characterizing methods of generating test aerosol populations in the chamber. Many of these issues have been addressed during past experiments in the chamber, but we feel these issues must be revisited in light of the special nature of the proposed experiments; special procedures must be tested and potential problems eliminated prior to assembly of the entire team for the main experiments.

4.d.3. Main Chamber Experiments. The primary deployment to the chamber is proposed to be for a six week period in the April-June 1998 time frame. The experiments can be classified as:

(1) Cloud processing of aerosol. The purpose of these experiments is to measure the size resolved increase in aerosol mass which results from liquid-phase oxidation of SO₂ to sulfate by ozone and H₂O₂ during cloud processing. These experiments will determine the chemical mechanisms and rate constants for the oxidation of SO₂. A typical experiment will consist of the following: (1) A test aerosol will be produced in the chamber either by nucleation of new (H₂SO₄) particles with subsequent growth to the desired size, by direct injection of aerosol of known composition, or by flushing of chamber with outside air to obtain natural aerosol. (2) After an aerosol of desired size and composition is obtained, the chamber is humidified by evaporation of pure water until the dew point depression is less than 0.3 C and pressurized by 10 to 30 mb), (3) the desired reactant concentrations (SO₂, O₃, H₂O₂, NH₃) are added to the chamber. 4) The stirring fan is turned off and cloud formed by expansion (adiabatic cooling caused by exhausting air). The cloud is held from 3 to 5 minutes allowing reactions of soluble reactant gases to take place in the cloud droplets. (5) The chamber is then re-pressurized causing evaporation of all cloud droplets. The change in the aerosol size distribution measured just before and after the cloud cycle gives the size resolved mass conversion. This methodology has been tested and found to yield extremely sensitive measure of size resolved mass conversion (Hoppel et al., 1994). The number and size of the cloud droplets can be controlled by the parameters of the expansion. The magnitude of the expansion determines the total liquid water and the rate of expansion, together with the precursor aerosol size distribution determines the number of cloud droplets. While the primary studies will be SO₂ oxidation by O₃ or H₂O₂, the effect of NH₃ (via pH) on O₃ oxidation of SO₂ the effect of alkaline aerosol (sea-salt), and the effect of organic aerosol will also be investigated.

(2) Photolysis of DMS (Dimethylsulfide). DMS is produced by phyloplankton. It is insoluble and therefore expelled from the ocean and has a relative short lifetime in the atmosphere before it is oxidized. While the initial oxidation step is generally believed to be initiated by OH, the intermediate steps and end products are still a matter of much controversy. Known end products are SO₂, MSA, DMSO, DMSO₂ but the branching ratios and the conditions (like temperature, trace amounts of NO_x, etc.) which determines the branching ratios are not known. Furthermore little is understood about the mechanisms by which the above-mentioned end products are converted to particulate matter and show up as non-seasalt sulfate aerosol in the marine environment. The experiments proposed here will observe these kinetics with instrumentation never before available. Of particular importance here is the unique measurements of OH and gas-phase H₂SO₄ and MSA which will be provided by Dr.Fred Eisele of NCAR. The ability to turn the photolysis lamps on and off while watching the decay of OH, H₂SO₄ and MSA will add a unique diagnostic capability, not found in nature, to the photolysis experiments.

We envision a typical DMS photolysis experiment to consist of: (1) starting with a clean chamber (overnight filtering), any residual trace gases in the chamber will be characterized. (2) DMS will be added to the chamber (with and without O₃) and photolysis will begin. DMS, OH, SO₂, H₂SO_4, MSA, DMSO, DMSO₂, and O₃ will all be monitored, as will the size distribution of any particles formed in the chamber. From the observed data much can be deduced about the DMS oxidation scheme which is taking place and the results will be compared to prior speculation on oxidation pathways for DMS. (3) Subsequent experiments will depend on the results found in this type experiment. Other experiments which will elucidate the role NO_x, and temperature have on the oxidation pathway will be carried out.

(3) Homogeneous nucleation of aerosols from gas-phase H₂SO₄ and water, with and without NH₃. Nucleation of aerosol particles from the gas phase is a strong function of the partial pressures of both H₂SO₄ and H₂O in the case of binary nucleation and additionally of NH₃ in the case of ternary nucleation. Furthermore both temperature and the surface area of preexisting aerosol play critical roles. In the MBL, where numerous instances of such nucleation have been reported, it is difficult if not impossible to de-convolute the relative impact of these variables to arrive at a functional form for the nucleation mechanism. However, the chamber experiments proposed here will indeed permit such an assessment. A sensitivity matrix for all of the key parameters will be constructed from theoretical considerations and each parameter varied in isolation through an extensive series of chamber runs, many of which can be run in conjunction with other chamber experiments. Particularly valuable will be runs in which NH₃ is varied, since little if any such data have yet been generated. Similarly, investigations of nucleation in the course of cloud evaporation (or formation) in the chamber will constitute an important but, as yet, little explored laboratory analogue for both field observations and theoretical models.

(4) Heterogeneous chemistry involving SO₂ oxidation by O₃ in sea-salt aerosol under humid but subsaturated conditions. It has been known for some time that oxidation of SO₂ by O₃ proceeds very rapidly in cloud droplets if the pH is high but the rate drops precipitously as the droplet pH goes below about 5. Only recently has the importance of this process been appreciated for sea-salt aerosol in the moist but subsaturated MBL. The potential of sea-salt to act as a sink for SO₂ lies in the buffering action of sea salt solutions. Ozone oxidation of SO₂ in sea salt produces non-sea-salt sulfate which may be accompanied by emission of HCl or chlorine gas. Here we propose to introduce sea-salt aerosol by nebulizing real and synthetic) solutions of sea water, add SO₂ and O₃ into a moist, but subsaturated chamber and then measure the rate of removal of SO₂, the change in the mass of the aerosol (from measured size distribution) and the change in composition of the aerosol at the beginning and end of the experiment. From these measurements the mechanism of SO₂ oxidation and resultant products will be identified.

4.e. Anticipated Results.

Numbers correspond to issues as stated in 4.b. and tasks in 4.d.3 above.

(1.) Cloud Processing of MBL aerosol. Results of oxidation of SO₂ by various oxidants, with and without NH₃ present during cloud cycling experiments in the Calspan environmental chamber will (a) give information on the chemical reactions taking place, (b) yield mass conversion rates (rate constants) for the various oxidation pathways, and (c) resolve issues at to whether or not bulk-phase reactions rates can be used for the dispersed phase (cloud).

(2) Gas-phase growth of MBL aerosols. (a) Detailed information on the oxidation pathway for DMS all the way to production of particulate matter will be obtained. Prior experiments indicated oxidation of DMS by OH did not produce particulate sulfate without the presence of NO_x. The oxidation of DMS involves a host of possibilities, too numerous to reiterate here, but the Calspan facility offers the possibility to investigate the gas-phase chemistry of DMS oxidation in a controlled atmosphere simulating oceanic conditions. (b) In all gas-phase models, oxidation of SO₂ is by OH. However, significant oxidation of SO₂ has been observed in the dark, and chamber simulations using naturally occurring hydrocarbons with O₃ yielded oxidation rates comparable (and larger) than in the illuminated chamber. This later oxidation is probably the result of SO₂ oxidation by Criegee intermediates and/or OH formed by reactions of O₃ with hydrocarbons. Experiments will be carried out to determine if it is legitimate to consider only SO₂ oxidation by OH in the marine environment

(3) Nucleation of MBL aerosols. Results from the nucleation experiments will permit the assessment of the validity of various nucleation models. Additionally, it will provide, at the very least, the basis for a purely empirical nucleation parameterization which could be used in more elaborate aerosol models of the MBL. Such models, in turn, would permit the evaluation of potential cloud-aerosol feedbacks which could have profound implications for both radiative transfer in the MBL and global climate change.

(4) Heterogeneous reactions of SO₂ with (wet) sea-salt aerosol. Measurements of the observed oxidation rate of dissolved SO₂ by O₃ in wet sea-salt aerosol will result in the rate constant for this reaction, while chemical diagnostics will determine the salt components participating in the reactions.

(5) The quantitative results from (1)-(3) will not only improve our understanding of physical and chemical mechanisms taking place but will yield quantitative rate constants which can be used in the aerosol model. The model can then be used to study the relative importance of the various processes under different MBL conditions.

This research will make a necessary and substantial contribution to the long term goal of developing a reliable MBL aerosol model integrated into a coastal and marine mesoscale meteorological model. Items (1), (4) and (5) must be considered low risk, high payoff research. Items (1) and (4) are low risk because NRL, jointly with CUBRC, demonstrated (Hoppel et al. 1994) the extreme sensitivity which this methodology brings to measuring mass increase during cloud cycling experiments and in high relative humidity environments.

5.1. Naval Research laboratory. P.I.: Dr. William Hoppel. NRL has had an ongoing measurement and modeling program addressing aerosols in the marine environment. This program has been closely coordinated with the ONR contract program and included major involvement in two ONR ARIs (Accelerated Research Initiatives): Transformation Dynamics of Aerosols and the MAST (Monterey Area Ship Track) Experiment. The prior experiments in Calspan's environmental chamber (Hoppel et al., 1994) were sponsored by ONR. More recently (1997), NRL management approved an NRL ARI expanding NRL's aerosol research to include elements in the Chemistry and Optics Divisions ($1.4M/year for 4 years). Because of NRL's prior experience in Calspan's chamber and understanding of the overall science and management issues, NRL scientists will play the lead role in the proposed research. However, the funding requested by NRL will be to cover only expenses incidental to their participation in the experiment. Existing instrumentation, modeling effort and data analyses will be provided out of the existing programs. NRL's prior experience in Calspan's chamber can be leveraged; the following are of particular importance: (1) a microphysical cloud formation model which simulates the aerosol activation and droplet formation in the Calspan chamber, (2) measurement methodology to measure the change in the aerosol size distribution before and after a cloud cycle to obtain mass conversion in cloud droplets, (3) methodology to produce initial size distributions of sulfate or sea-salt aerosol of prescribed size. Under the expanded NRL in-house program, we anticipate the Chemistry Division will provide us with chemical diagnostic tools which were lacking during the prior experiments and supplement those being provided by other partners.

(Here we include only the three P.I.s who are receiving funding from NOPP - for special capabilities of those participating by letter-of-intent see Section 5 above.)

6.1. Dr. William Hoppel, P.I. and project coordinator, is head of the Aerosol and Cloud Physics Section of the Remote Sensing Division, at the Naval Research Laboratory. The research he directs includes both measurement and modeling aspects of aerosol and cloud physics. He also serves as the P.I. for an NRL Accelerated Research Initiative on Coastal Aerosol Processes which includes elements of aerosol research being carried out in five different NRL divisions. The most recent research accomplishment has been to pioneer the use of the airship to make high resolution measurements of marine boundary layer aerosol and clouds. These measurements have been used to study the effect of cloud processing on the subcloud aerosol, observe nucleation events under a number of MBL conditions and to study the phenomena of cloud tracts visible in satellite imagery. The 1991 ONR Calspan Chamber experiments demonstrated the utility of the chamber to study cloud processing was the result of a proposal Dr. Hoppel submitted to ONR. (For further information see attached vitae.)

6.2. Mr. Thomas Albrechcinski. Co-P.I. is a senior staff engineer and head of the Hypersonics and Propulsion Branch at Calspan SRL Corporation. In relation to the 600 m³ facility, he directed a multi-year research program investigating the effects of atmospheric residence time and exposure on diesel emissions employing the 600 m³ Atmospheric Simulation Facility. These studies demonstrated that atmospheric contaminants can alter the composition of the adsorbed organic fraction of diesel aerosol and resulted in significant increase in the observed mutagenic activity of organic extracts. (For further information see attached Vitae)

6.3. Professor Dean Hegg is an expert in cloud chemistry and has developed models of liquid-phase oxidation of trace gases, as well as gas-phase air chemistry models, including binary and ternary nucleation of aerosol particles. His chemical modeling expertise will be used to design quantitative experiments, interpret/analyze data, and compare results with current models. Research interests are gas-to-particle conversion in the atmosphere, chemistry of clouds and rain, and the atmospheric sulfur and nitrogen cycles. He has authored 70 papers published in refereed scientific journals. Currently he is a member of the Cloud Physics Committee of the American Meteorology Society, the National Academy of Sciences Panel on Aerosol Radiative Forcing and Climate, and the co-chair of the International Global Atmospheric Chemistry (IGAC) Committee on Aerosol-Cloud Interactions. (For further information see attached Vitea)

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