A31C-0062 0800h
Overview of the Light Aircraft Aerosol Research Inlet (LAARI)
Aircraft provide a mobile platform for measuring vertical profile aerosol properties. The efficacy of these measurements, however, is constrained by the aerosol inlet sampling efficiency. Larger particles are often lost to turbulent deposition and impaction inside the inlet and sampling lines, respectively. This precludes the measurement of coarse mode particles, important to visibility and radiative transfer studies. Turbulent deposition of large particles occurs when the sample air stream slows down within the inlet from the aircraft velocity to the recommended sampling velocities of the aerosol instruments (\sim10 m s$^{-1}$). Low-turbulence inlets that reduce turbulent deposition through the use of a porous diffuser cones are necessary for large aircraft with air speeds of 80 to 200 m s$^{-1}$, but these are not feasible for light aircraft because of space and power requirements and may not even be necessary given the low air speeds of small aircraft. We have designed an aerosol inlet for a light aircraft platform with an average air speed of 60 m s$^{-1}$ and a sample flow rate of 28.5 L min$^{-1}$. The hemi-elliptical shaped, stainless steel inlet is 12.7 cm long. The front orifice has a 0.3175 cm diameter and the internal diameter expands to 0.9525 cm over a length of 9.2075 cm at an included angle of 4.3\deg. The linear velocity of the sample stream as it exits the inlet is 6.7 m s$^{-1}$. The calculated Reynolds number (Re) at the opening is 11,430 and decreases to 3,811 at the inlet terminus, with a pressure drop across the inlet opening of only 42 mb at an average flight temperature and pressure. Sampling line impaction is reduced by decreasing the number of bends upstream of the instruments. We have accomplished this by designing a parallel sampling manifold that splits the sample stream into four separate streams, three of which are split from the primary sample stream at an angle of 15\deg. Theoretical investigations of sample flow and particle losses are underway with Computational Fluid Dynamics (CFD) software from FlowLab. Wind tunnel analyses using a Vibrating Orifice Aerosol Generator (VOAG) with optical particle counters upstream and downstream of the inlet and sampling lines will validate the theoretical calculations and provide empirical sampling efficiency values. This new inlet design will facilitate the more efficient collection of ambient particles, especially those in the coarse mode, from light aircraft. Because light aircraft are less expensive to operate than large aircraft and can make measurements in the lower atmosphere on a more routine basis, the Light Aircraft Aerosol Research Inlet (LAARI) will herald a new era of measurement capabilities in satellite validation work, column closure tests, and climate change studies.
A31C-0063 0800h
Chemical Analysis of Aerosols for Characterization of Long-Range Transport at Mt. Lassen, CA
Effective regional air pollution regulation requires an understanding of long-range aerosol transport and natural aerosol chemistry. Sample collection was performed at the Interagency Monitoring of Protected Visual Environments (IMPROVE) sampling site on Mt. Lassen in the Sierra Nevada range at 1755 m elevation. The site is in Northern California at Longitude 121° 34' 40", Latitude 40° 32' 25". Size segregated and time resolved aerosol samples were collected with an 8 DRUM sampler from April 15th to May 24th 2002 as part of the NOAA Intercontinental Transport and Chemical Transformation Experiment (ITCT). The samples were analyzed with Synchrotron X-Ray Fluorescence (S-XRF) and Time of Flight mass spectroscopy (TOFMS). The total aerosol concentration exhibits a clear daily cycling of total mass, due to a nighttime down-slope air circulation from the free troposphere. The sulfate peaked in concentration during the night. Elemental data is suggestive of dust transport from continental Asia. The micron size ranges were dominated by nitrate, while the sub-micron size ranges had high levels of sulfate. Chemical analysis shows oceanic influence through strong correlations between methyl sulfonic acid (MSA), iodine, and oxalate. The appearance of the oceanic biogenic tracers in the sub-micron fraction is most likely a result of vertical mixing over the Pacific Ocean. MSA follows a diurnal pattern similar to sulfate, however the differences suggest both an oceanic and continental source for sulfate. The carbon particulate signal did not show any diurnal pattern during the measurement period.
A31C-0064 0800h
Aerosol Ions and Their Gaseous Precursors over North America and their Sensitivity to Nitrogen Emissions
During the ITCT-2K2 and ICARTT-2k4 experiments, a regional chemical transport model, STEM-2K3, was applied to study developed to study the aerosol ions, their precursors, and photochemistry. The major anions: sulfate and nitrate, show obvious geographic distribution from west to east coasts: nitrate is the dominant anion in west coast, and sulfate is the major anion in east coast. It reflects the distribution of NOx and SO2 sources and the influence of prevailing wind directions. The model also reveals that sulfate is the major component of aerosol extinction coefficients in Eastern and Southeastern USA during the ICARTT experiment. Ammonia emissions play an important role on controlling the ratio of nitrate versus HNO3 over inland states. Sea salt is the one of major influence factors in the coast regions. Our three-dimensional model revealed the procedure of aerosol secondary uptake when airmasses move from west to east. Using modeled regional tracers to identify the airmass sources, the aerosols also show source-related distributions. The SO2 industrial emissions, such as power plants, are the major sources of sulfate. The sulfate formation illustrates the non-local effect associated with transport and diffusion. Simulated carbonaceous concentrations are also discussed with equilibrium assumption. The consideration of aerosol secondary partition is important not only for aerosol prediction, but also for gaseous chemistry. The sensitivity studies with and without nitrate aerosol formation revealed its influence on gaseous HNO3, NOy concentrations and photochemical products.
A31C-0065 0800h
Effect of Coatings on Laser Induced Incandescence (LII) of Soot
Combustion-generated soot is the most significant contributor to positive radiative forcing by atmospheric aerosols. The exact magnitude of this forcing is, however, highly uncertain due to (1) the lack of an accurate global inventory of atmospheric black carbon aerosol distributions and (2) an inadequate understanding of the optical properties of such particles, associated with their complex morphology and composition. Therefore, both development of new techniques for characterizing realistic soot particles and detailed investigations of their optical properties are needed for a reliable assessment of the direct forcing by anthropogenic black carbon. We present laboratory studies exploring applicability of the laser induced incandescence technique to quantitative detection of black carbon aerosols in the atmosphere. In these experiments, sulfuric-acid-coated soot particles were sampled with a scanning mobility particle sizer (SMPS) and detected with LII to yield the following information: (1) the sensitivity of LII to black carbon as a function of SMPS-derived coating thickness and (2) the degree of coating desorption and soot fragmentation as a function of laser fluence. The energy balance equation was solved to model the particle-laser interactions, accounting forparticle heating by light absorption and cooling by radiative emmission, conduction, sublimation, and coating evaporation, and the results were compared with experimental data.
A31C-0066 0800h
Optical, Physical, and Chemical Properties of Soot in Aerosol Samples From the UAE
Soot from the fine-fraction of aerosol samples collected in the lower troposphere (1.2 km) during the summer of 2002 over the Gulf of Oman (UAE) was characterized using high-resolution transmission electron microscopy (HRTEM) and electron energy-loss spectroscopy (EELS). The soot occurs in aggregates of individual spherules up to 40 nm in diameter. Each consists of an amorphous nucleus around 3 nm in diameter, surrounded by a 2- to 15-nm concentric band of graphene segments with 3.5-nm spacings. Two structure types are readily distinguishable. Type one has a single nucleus surrounded by a broad zone of concentric graphene, and type two has multiple amorphous nuclei within the core, surrounded by graphene stacks that become longer and more concentric towards the spherule perimeter. Both types have amorphous coatings 1- to 3-nm thick, but they are typically broader on type two. The soot optical properties were investigated for the UV-VIS region using EELS. The surface low-loss spectra are characterized by well-defined peaks within the visible range at 240, 340, and 553 nm. In contrast, bulk spectra from the cores of the spherules are characterized by a gradual rise in spectral absorbance, with a maxima at 209 nm, corresponding to the $\pi$ to $\pi$* inter-band transitions of graphite. Thus, chemical and structural differences between soot cores and rims may correlate with measurable optical differences. Since the high surface area and amorphous surfaces of the soot potentially affect its behaviour within the atmosphere, we will investigate the relationship between the optical, chemical and structural properties of soot in more detail. Scanning transmission electron microscopy combined with EELS will allow us to probe the nature of the amorphous surface layers as well as measure optical properties of the different graphene nanostructures.
A31C-0067 0800h
Time Resolved Chemical Analysis of Anthropogenic Aerosols in Norway, a Study of Long-Range Transport
Anthropogenic fine particulate matter produced by the burning of carbonaceous fuels is a complex issue that transcends political and geographical boundaries. Anthropogenic fine aerosols are tranported to Norway from the British Isles and continental Europe. Two 3-DRUM impactor samplers were used to collect size-separated PM2.5 aerosol samples (2.5 - 1.15, 1.15-0.34, 0.34-0.1 m Da) at two sites, Birkenes and Kjeller for a six-week period in June and July. The samples were analyzed with three-hour time resolution by Synchrotron X-ray Fluorescence and Time-of-Flight Mass Spectrometry. S-XRF determined three-hour mass averages for elements heavier than Na, while the TOFMS was used for chemical speciation as a function of time and size. Positive ion spectra showed K+, Na+ and organic molecular ions between 200 - 400 m/z. Negative ion spectra detected carbon clusters, Cl-, Br-, I-, NO2-, NO3-, CN-, CNO-, SO3-, HSO4-, methyl sulfonic acid (MSA), and various organic acid salts. The chemical signature of the sources are identified using high time resolution in combination with air mass back trajectories. Chemical modification of the aerosol during transport is examined as a function of particle size.
A31C-0068 0800h
Evolution of the Optical Properties of Smoke Plumes From Biomass Burning in a Three-Dimensional Transport Model and Comparisons to In Situ and Remote Sensing Observations From SAFARI 2000
We model the evolution of biomass burning aerosols and investigate their optical properties. Our model is an offline three-dimensional aerosol and microphysical transport model driven by assimilated meteorology from the NCEP/NCAR reanalyses and constrained with measurements collected during the Southern African Regional Science Initiative campaign (SAFARI 2000). The aerosol source emissions for the model account for differences in emission profiles in woodlands and grasslands and are based on MODIS burned area information. Detailed simulations were conducted to examine the model's sensitivity to aerosol emissions and microphysical processes, and to see how well our model aerosol optical properties compare to measurements near the sources. Here we investigate the model sensitivity to the diurnal cycle and injection altitude of aerosol emissions. In addition, we test the sensitivity of the model aerosol optical properties to our choice of initial aerosol particle size distribution and the effects of particle coagulation. Modeled smoke aerosol optical thickness, aerosol extinction, angstrom exponent and single scattering albedo are compared to satellite, aircraft and ground-based observations made over central and southern Africa. Air mass back-trajectories at various locations are shown and compared to our model results to identify sources. The results from this study will be useful in future applications relating to the evolution of smoke aerosols from biomass burning fires by testing source functions and illuminating microphysical processes that need to be treated in models.
A31C-0069 0800h
Modeling the Vertically Stratified Atmosphere of Southern Africa During the Biomass Burning Season
The University of Washington Convair-580 research aircraft measured in situ aerosol properties during the biomass burning season of southern Africa in August and September, 2000. During the burning season, the atmosphere in southern Africa consists of persistent regional haze reaching as high as 5 km. The regional haze is often stratified into distinct layers with particle concentrations varying by an order of magnitude. Above the regional haze, particle concentrations decrease significantly. The haze consists primarily of aged biomass burning aerosol, the concentration of which depends on local fire intensities and meteorology. Detailed in situ measurements from near the surface to about 5 km were obtained from the Convair-580. The measurements most relevant to this study are the dry particle size distribution (for particle diameters of 0.10-3.0 microns) and the aerosol single-scattering albedo, which is derived from measurements of the aerosol scattering and absorption coefficients. Regional scale models generally use an averaged particle size distribution and a column-averaged single-scattering albedo based on studies made in the region of interest. However, the vertical stratification of polluted layers found in southern Africa is unaccounted for in such models. In this study, we describe the aerosol properties of polluted layers with a vertical resolution of about 10 m for two cases. We use those data as input to a radiative transfer code. The outgoing radiances from the radiative transfer code will be compared with those measured by the MODIS sensor aboard the Terra satellite, which was correlated both spatially and temporally with the cases explored here. Uncertainties and assumptions in the input will be discussed. We will explore the effects on the outgoing radiances of increasing the vertical resolution in the polluted aerosol layers. Finally, we examine the effects of parameter averaging with respect to the dry particle size distribution and the single-scattering albedo.
A31C-0070 0800h
Chemical and Microphysical Properties of Particles in Aged Forest Fire Plumes From Alaska and Western Canada Observed Over the Northeastern U.S.
During the Intercontinental Transport and Chemical Transformation - New England Air Quality Study (ITCT-NEAQS 2004) in July and August 2004 several forest fires plumes were observed over the northeastern U.S. and southeastern Canada. Satellite data and trajectory analyses indicate that the plumes originated from forest fires burning in Alaska and western Canada. In-situ measurements of the aged forest fire smoke were made on board the NOAA WP-3D research aircraft during several flights over a period of 2 weeks. Concentrations of volatile organic compounds (VOCs) and the chemical composition of single aerosol particles in air masses containing forest fire smoke show significant differences compared to background air or to pollution from urban and industrial sources and unambiguously identify the smoke plumes. Particle size distributions from 0.004 to 8 um were measured with one second resolution in the aged forest fire smoke. The smoke was characterized by mass-weighted diameters between 0.6 and 1 um--much larger than secondary particles typical of urban and industrial sources. Particle volume concentrations were among the highest seen within the ITCT-NEAQS 2004 project, and regional visibility and air quality were significantly affected by the transported smoke. Quantitative compositional measurements were made of the non-refractory fraction of submicron particles, as well as of submicron inorganic ionic compounds and water soluble organic mass, within the forest fire plumes. The submicron aerosol particles in the biomass plumes were largely carbonaceous with very little sulfate, ammonium, or nitrate. A fraction of this carbonaceous material was soluble in water and likely contained oxygenated organic species.
A31C-0071 0800h
Influences of Aging on Soot, Dust and Nucleated Aerosol in Asian Aerosol
We studied size resolved aerosol physio-chemistry in Asian outflow over the Pacific during the spring of 2001 as part of the ACE-Asia and TRACE-P experiments. Soot was found to be generally internally mixed with condensable species (eg. sulfate) within less than one day transport from sources. These data also reveal interactions between pollution and dust aerosol in regions of strong pollution that result in the accumulation of condensable species (eg. sulfate) onto the dust. High temperature (stable at 300C) organic aerosol is also inferred to be present on the soot that can change the soot optical properties. As much as one half of the soluble species normally condensed upon the soot can end up on the dust during the highest dust events encountered. These modify the chemical characteristics of the dust mode and can change the relative composition of the pollution mode. These changes have significant effects upon the optical properties of the pollution mode as well as the scattering response to increasing humidity, f(RH). Hence, these dust and pollution must be modeled interactively in these regions in order to correctly describe these properties. Recently nucleated aerosol were often present at high concentrations in elevated regional pollution events over hundreds of kilometers in extent. However, the occurrence and concentrations of these aerosol were reduced by their exposure to fog or cloudy conditions present in the region during their transport. These events can influence both their nucleation and subsequent growth. Coupled with coagulation with larger aerosol associated with primary emissions (eg. soot) their concentrations are usually rapidly depleted after a day or two. As a result, these recently nucleated aerosol were often greatly reduced after aging. These observations indicate that the Asian aerosol advected over the Pacific is dominated by the primary emissions that determine the optically-active aerosol sizes responsible for their direct radiative effects and also most cloud condensation nuclei (CCN), with nominal diameters over 80nm, that are responsible for their indirect effect.
A31C-0072 0800h
CORRELATION BETWEEN AEROSOL OPTICAL DEPTH AND CO IN THE ATMOSPHERE FOR THE FOREST FIRE EVENTS
The Moderate-resolution Imaging Spectroradiometer (MODIS) provides global observation of aerosol onboard the Terra and Aqua satellites. The satellite data on AOD have been used extensively in the detection, aerosol loading estimation and movement tracking of the yellow sand events. Furthermore, the MODIS provides AOD with the fine mode fraction over ocean and darker land surfaces, but still have limitations to distinguish carbonaceous and sulfate aerosol. Measurement Of Pollution In The Troposphere(MOPITT) onboard the Terra satellite provides quantitative information of carbon monoxide(CO). Measurements of CO whose principal sources arise from anthropogenic emissions such as biomass burning and forest fires, is very useful for tracing fire emissions in the atmosphere. In this study, the satellite data from MODIS and MOPITT were used to analyze correlation between AOD and CO density for the intense fires in the southeast part of Russia in May, 2003, which have affected quality of atmospheric environment over Korea significantly. The AOD distribution from the MODIS for May, 2003 show movement of high AOD regions near the Korean Peninsula. The CO column densities from the MOPITT also show enhanced values for May, 2003. Reasonably good pattern correlation between CO and AOD are found over the source region of forest fire in particular. This multi-instrumental approach to monitor the aerosol in the atmosphere is expected to contribute to the classification of the aerosol characteristics in the atmosphere, carbonaceous aerosol in particular. Furthermore, as the lifetime of CO is long compared to that of aerosol in the atmosphere, the ratio of AOD to CO can be used to trace the emission source and sink regions in the atmosphere. This ratio is expected to be larger near the source region and smaller near the sink, because the aerosol is deposited to the ground leaving the CO in the atmosphere. These results are compared with the backward trajectory analysis by the HYSPLITT model of NOAA.
A31C-0073 0800h
Overview of Dust Model Inter-comparison (DMIP) in East Asia
Dust transport modeling plays an important role in understanding the recent increase of Asian Dust episodes and its impact to the regional climate system. Several dust models have been developed in several research institutes and government agencies independently since 1990s. Their numerical results either look very similar or different. Those disagreements are caused by difference in dust modules (concepts and basic mechanisms) and atmospheric models (meteorological and transport models). Therefore common understanding of performance and uncertainty of dust erosion and transport models in the Asian region becomes very important. To have a better understanding of dust model application, we proposed the dust model intercomparison under the international cooperation networks as a part of activity of ADEC (Aeolian Dust Experiment on Climate Impact) project research. Current participants are Kyusyu Univ. (Japan), Meteorological Research Institute (Japan), Hong-Kong City Univ. (China), Korean Meteorological Agency METRI (Korea), US Naval Research Laboratory (USA), Chinese Meteorological Agency (China), Institute of Atmospheric Physics (China), Insular Coastal Dynamics (Malta) and Meteorological Service of Canada (Canada). As a case study episode, we set two huge dust storms occurred in March and April 2002. Results from the dust transport model from all the participants are compiled on the same methods and examined the model characteristics against the ground and airborne measurement data. We will also examine the dust model results from the horizontal distribution at specified levels, vertical profiles, concentration at special check point and emission flux at source region, and show the important parameters for dust modeling. In this paper, we will introduce the general overview of this DMIP activity and several important conclusions from this activity.
A31C-0074 0800h
Optimization of the particle size bin scheme in modeling dry deposition of dust
Mineral dust is a major component of the tropospheric aerosol and Aeolian erosion is responsible for long-range transfer of large amounts of particles which impact the biogeochemical cycles, the radiative budget and atmospheric chemistry. Dry deposition is a major pathway for the removal of dust particles from the atmosphere, and their lifetime is particularly sensitive to dry deposition due to a size distribution covering the large particle size range. Thus, precise dry deposition schemes are required into dust transport models for a correct assessment of the dust dry deposition fluxes and mass transfers from source regions. Because the dust particle size distribution ranges over several decades and because the dry deposition velocity versus particle size is strongly non-linear, such accuracy needs a large number of size bins in the models, not always compatible with reasonable computation times. In this paper, we present a new approach to optimize the number of size bins for the dry deposition scheme into dust transport models. We develop a method in which the size range covered by each size bin is defined according to the gradient in dry deposition velocity relative to the particle size. Using a 1000-bins simulation as a reference case, we compare the dry deposition fluxes in mass and number computed with our gradient method and with the classical method based on iso-logarithmical bins, for various numbers of size bins. The results show that the new approach leads to improvements in terms of accuracy and time computation for an identical number of bins. We further determine the minimal number of bins to get a given accuracy of the dry deposition flux. For the mass size distribution of dust particles we have used, results indicate that an accuracy of 5% in the dust particle dry deposition flux can be obtained by using only 5 bins where the classical method gives accuracy not better than 40%.
A31C-0075 0800h
Direct Observations of Heterogeneous Dust Processing in the Troposphere: Ambient Measurements, Source Compositions and Laboratory Studies
The size and chemical composition of single dust particles in both background marine air and during dust events was determined using Aerosol Time-of-Flight Mass Spectrometry (ATOFMS) throughout the Indian and Pacific Oceans and Pacific coast during three major field campaigns: INDOEX, ACE-Asia and CIFEX. In general the chemical associations within individual particle spectra for the major dust particle types were very similar in all sampling locations. The dust mass spectra were dominated by various combinations of potassium, calcium, iron, and aluminum, with contributions from silicates, sodium, chloride and titanium oxides. The relative ion intensities often differed suggesting that the dust is a complex, externally mixed aggregate of varying mineral origins. Evidence of heterogeneous processing of the dust particles was also observed with ATOFMS using markers for nitrate, sulphate, and organic species. Aging of dust particles can dramatically alter their radiative and cloud-forming properties, changing the effects that dust will have on global climate. The dust spectra were also compared with those measured from collected dust, sand and soil samples in Asia and the United States. In general the mass spectra of the ambient and source dust particles were very similar, except that for the most part the source samples lacked evidence of atmospheric aging. Preliminary lab studies examining heterogeneous processing of dust in a flow tube will be presented. These studies investigate the relative reactivity of the different types of dust observed in the atmosphere and the competitive heterogeneous chemistry of dust and sea salt particles.
A31C-0076 0800h
Explicit Simulations of Convective-Scale Transport of Mineral Dust in Severe Convective Weather
Convective-scale transport of mineral dust in a severe weather setting is investigated with the approach of three-dimensional cloud-resolving simulations coupled with a dust emission-transport modeling. The simulations are intended to explicitly represent convective- and cloud-scale processes (such as updraft/downdraft, surface cold pool, precipitation) in a squall-line-type convective system, and are performed in an idealized setup in order to focus the primary mechanisms for convective-scale dust transport within a squall-line system. Initialized based on an observation in a severe duststorm case over the Gobi Desert in China, the cloud model well simulates an observational feature of the squall line and the associated duststorm in spite of a simplified model setup. Dust is emitted by strong surface winds associated with a well-developed surface cold pool, and is contained and mixed within the cold pool: a high dust concentration of greater than 10 mg m$^{-3}$ is induced. Owing to a high subgrid-turbulence mixing at the leading edge of the cold pool, the contained dust is transferred out of the cold pool and is entrained into the updraft region at the cold pool edge. Dust is then transported upward by the convective updraft which is continuously regenerated at the cold-pool leading edge and spread in the cross-line directions in a layered form at upper levels by system-scale circulation. Rearward dust transport relative to the leading edge of the system is pronounced at upper levels, according to the prevalent front-to-rear flow typically found in the squall-line systems. These convective-scale mechanisms for dust transport should be applicable to the cases in synoptic-scale cold-frontal rainbands containing a high thunderstorm activity.
A31C-0077 0800h
Heterogeneous Chlorine Chemistry with Mineral Dust Particles in the Marine Boundary Layer: Observation, Modeling, and Potential Impacts
Mineral dust particles were analyzed during a major dust storm episode in the course of the Asian Pacific Regional Aerosol Chemical Characterization Experiment (ACE-Asia) using a transportable aerosol time-of-flight mass spectrometer for single particle characterization. From the chemical information for single particles, including spectral signatures and elemental ratios, the association of dust particles with chlorine was inferred. Furthermore, the analysis allowed for differentiation between the presence of chlorine in dust particles due to uptake of chlorine-containing species or coagulation between sea salt and dust particles. Significant influences on the physical and chemical properties of dust particles, radiative effects, and biogeochemical cycles can be brought about by this chlorine chemistry which needs to be considered to improve model calculations and to properly evaluate the results from field campaigns.
A31C-0078 0800h
A study of dust radiative forcing based on detailed transport and radiation models
Computational results for global radiative forcing due to mineral aerosols is presented. The average dust loading for the Winter, Spring, Summer and Fall seasons are computed by the MATCH transport model using currently active source regions. The MATCH model uses wet and dry deposition as loss mechanisms for four different size bins of aerosols transported by the model. MATCH provides vertically resolved profiles of water vapor, temperature, and dust density over the surface grid with 200km resolution. The diurnally-average dust radiative forcing is computed for each season using the SBDART radiative transfer model at a spectral resolution of 20 cm-1. The radiative properties of the dust are computed assuming spherical particles and a globally uniform size distribution. Both the shortwave and longwave calculation include the effects of radiation scattering. Within each column of the computational grid the surface reflection and emissivity spectral properties are computed as mixtures of 7 discrete surface types. The impact of non-Lambertian reflectance from the wind-roughened ocean surface is analyzed. In the thermal infrared, the effective ocean surface emissivity is shown to depend on precipitable water vapor and cloud cover, but does not strongly depend on the dust optical depth.
A31C-0079 0800h
Three Years of Raman Lidar Observations of Saharan Dust Intrusion Over Potenza
The Sahara desert is the most prominent localized source of atmospheric aerosol with a total amount of emitted dust of about 600 Mt per year. Because of the short distance, intrusions of Saharan dust in the Mediterranean basin are very common. Dust occurrences in the Mediterranean region were investigated by means of satellite measurements, but at the present time, there is a serious lack of knowledge of the vertical structure and of the optical properties of dust injected from Sahara over the Mediterranean area. In the framework of EARLINET (European Aerosol Research LIdar NETwork), the first aerosol lidar network on continental scale, since May 2000 until April 2003, we collected more than 100 cases of Saharan dust intrusions in the center of the Mediterranean area, by means of the IMAA Raman-elastic lidar system located in Potenza, Southern Italy. For each case, the observed aerosol layers have been characterized in terms of aerosol extinction and backscatter coefficients at 355 nm, retrieved from combined Raman elastic-backscatter lidar independent measurements, and thus of the lidar ratio. Moreover, aerosol backscatter coefficient at 532 nm is retrieved from elastic lidar signal with an iterative approach. For this 3-years climatological analysis, the 4-days backtrajectories analysis provided by German Weather Service have been used to identify the origin of the observed aerosol layers as the Sahara region. In particular, we find that typically dust observed in Potenza comes from the Central and Western part of the Sahara, while we observed Saharan dust coming from the East part of the Sahara only in 4 cases. Saharan dust layers have been found to typically extend between 2.5 and 6 km above sea level (a.s.l.), reaching a maximum altitude of about 8 km a.s.l. and with frequent intrusions in the Planetary Boundary Layer. The aerosol layer center of mass, calculated starting from the aerosol backscatter coefficient, has a mean altitude of about 3.5 km a.s.l., extending between 2.3 and 6.6 km a.s.l.. The desert dust strongly contributes to the aerosol load within a mean optical depth of about 0.12. An high variability has been observed for the mean aerosol backscatter and extinction coefficient within the layer as well as of the optical parameters integrated over the whole dust layer, reflecting the large natural variability of Saharan dust emission phenomenon. However, there is a strong seasonal behavior for all considered optical properties: a large amount of dust has been observed during spring and summer, when most of Saharan dust intrusions occur and the mean optical depth of the layer reaches its maximum, instead a lower desert aerosol load is observed during autumn. The lidar ratio mean values calculated along the aerosol dust layer range between 6 and 78 sr, with a mean value of 38 sr. No significant difference has been observed between winter and summer values of lidar ratio, but summer values distribution is wider than the winter one and also the variability along the dust layer is higher than during the winter. A detailed analysis of the lidar ratio values collected within the observed Saharan dust layers shows a trimodal gaussian distribution. A mode centered around 22 sr is related to few cases with high aerosol load in a situation of contamination with the Planetary Boundary Layer. A wider mode at 57 sr is correlated to the tails of the aerosol layer. Finally the most populated mode, centered around 37 sr, results from the central part of the aerosol layer. ACKNOWLEDGMENTS The support of this work by the European Commission under grant EVRI-CT1999-40003 is gratefully acknowledged.
A31C-0080 0800h
Chemical characteristics of aerosols involved in Asian dust of March 2002 collected at Rokkasho Village, Aomori, in northern part of Japan
The Asian dust (Kosa), generated when the surface soil in the arid and semi-arid region of the Asian continental landmass is lifted by winds, is the major mineral aerosol transported from East Asia to the Pacific region. The Kosa particles are thought to be an important factor in the earth_fs climate via radiative forcing. The frequency of dust events giving rise to Kosa aerosols has increased rapidly in the East Asian region since 2000. Therefore, it is important to clarify the physico-chemical properties of the Kosa aerosols. The large-scale Kosa event was observed in northern Japan in March 2002. In this study, the chemical characteristics of aerosols in the Asian dust event of March 2002 were investigated. We collected aerosols using middle volume air sampler (flow rate: 100 L/min) of the Andersen type (size-fractionated aerosols) and high volume air sampler (bulk aerosols). The soluble and insoluble major chemical components in size-fractionated aerosols and total concentration of REE, 232Th, 238U and 137Cs in bulk aerosols were quantitatively measured. In this Kosa event, the aerosol size distribution pattern was a peak mainly derived from soil particles sized 1.1-3.3 micron and over11 micron. During this Kosa event, the atmospheric concentrations of nssCa2+ (nssX : non-sea salt component) and insoluble Al of size-fractionated aerosols increased 7 - 9 times and 50 - 100 times in comparison with the non-Kosa period in the particle size range of 1.1 - 3.3 micron, respectively. The concentration of 137Cs in bulk aerosols also increased. The aerosol size distribution patterns of some components during the Kosa and non-Kosa periods were different. The Kosa particles take in polluted materials along their transportation route. In this Kosa period, the atmospheric concentration of nssSO42- increased in comparison with the non-Kosa period, but the NO3- concentration decreased. In general, NO3- does not exist in arid and semi-arid regions. This means that the amounts of anthropogenic SO42- and NO3- adsorbed on the Kosa aerosol surfaces were small during their transportation process in this Kosa event. The REE patterns (chondrite normalized) of Kosa aerosols (bulk) were characterized by being enriched in light REE, and depleted in hige REE. The negative values of the Eu anomaly are 0.80 - 0.85. The REE patterns of Kosa aerosols are similar to the non-Kosa period aerosols. However, there was a difference in the 238U/232Th ratios.
A31C-0081 0800h
The Trace Metals in Atmospheric Aerosols and Their Deposition Over the East China Sea During the Asian Dust Period
The East China Sea is strongly affected by anthropogenic and mineral dust aerosols from Asian continent. Especially, in springtime, dust storms are frequent over Asia and the dust is transported over long distances. Although the deposition of dust from atmosphere to ocean plays an important role in the oceanic biogeochemical cycles, there is a dearth of simultaneous dust particle measurements in the atmosphere and the surface ocean. We continuously measured trace metals in aerosols, rain and the surface seawater over the western North Pacific and the East China Sea from 4 to 20 March 2004. High concentrations of mineral dust and anthropogenic substances were observed in the north of the East China Sea. The mean concentration of Al during the dust period was 4.5 $\mu$g m$^{-3}$, which was about 14 times higher than that in non-dust period. The concentration of Al in the suspended particles in surface seawater during the dust period was 0.88 $\mu$g l$^{-1}$, which was about 2.3 times higher than that in the non-dust period. The concentrations of Al and Fe showed similar variations between aerosols and seawater compared to other trace metals, indicating most of Al and Fe are supplied from atmosphere and these trace metals have lower solubility. During the non-dust and the dust periods, the means of (excess-Zn/Al) $_{suspended particles}$ / (Zn/Al) $_{aerosols}$ were about 0.74 and 1.2, respectively. During non-dust period, the solubility of Zn in the surface seawater is estimated to be 20-40% and is higher than that of Al (0.6-10% ;Duce et al.,1991). The atmospheric deposition of highly soluble trace metals to seawater might affect biogeochemical cycles in this region. During dust period, the deposition rate of giant particles ($>$10$\mu$m) of Al increased compared to that of Zn, therefore the settling velocity of Al in seawater seemed to be higher than that of Zn. The trace metals associated with large size particles play an important role in the underlying sediments though their role in dissolved state in the surface seawater may be limited.
A31C-0082 0800h
Submicron Sea Salt Aerosol Inside and Outside of the Surf Plume: Size Segregated and Total Sea salt Aerosol Distributions by Single Particle Analysis at a Coastal Marine Site
The uncertainties in the shape of the source function for sea salt aerosols as well as in the of the shape of the size distribution of sea salt aerosol in the marine boundary layer (MBL) are considered, after even greater uncertainties for dust aerosol, the biggest open question to assess the impact of aerosols on climate change [1]. In a recent intercomparison of global models, satellite retrievals and ground-based measurements, Kinne et al [2] found large discrepancies between simulated and measured aerosol extinction in the Southern Ocean, and suggested that this might be indicative of an underestimation of the contribution of submicron sea salt aerosol in current models. Although since at least Murphy et al's [3] the importance of submicron sea salt aerosol in the clean MBL for radiative forcing is recognized, high quality data on the size distribution and on the source function of sea salt in this size range is sparse. Field measurements from O'Dowd et al and Clarke et al [4,5], based on the aerosol volatility technique, yielded contrasting results in the two size regions crucial for direct and indirect forcing. We have developed a sea salt specific aerosol particle sizer [6,7], the Aerosol Sodium Detector (ASD), that in its current, improved version is able to quantitatively measure the amount of sea salt in single aerosol particles using sodium as a proxy in the range between 1 fg NaCl equivalent (95 nm NaCl dry diameter) and 7000 fg NaCl equivalent (1800 nm diameter) with a sizing accuracy better than 5% and no losses within the valid detection range. This instrument was deployed at a coastal site at Bellows AFB in Oahu, Hawaii to study the contribution of sea salt to the total aerosol load in both remote marine air and the surf zone at wind speeds up to 10 m/s. Full sea salt number size distributions were acquired continuously in 2 s samples and matched the results of a commercial aerodynamic particle sizer down to 400 nm better than 20% in all cases. The distributions showed a main submicron mode at 520 nm dry diameter as well as a second mode below 300 nm that was strongly enhanced in breaking waves, in agreement with Clarke et al's recent findings [5]. Total sea salt particle count down to the detection limit was about 12-14 part/cc at 9.5 m/s u10. In size-segregated mode, the extent of internal mixing of surf zone aerosol was monitored. The results were consistent with pure sea salt with little processing down to the detection limit of 100 nm. Average size dependent sea salt mixing ratios were calculated, with sea salt being the primary aerosol component down to 200 nm, in good agreement with Murphy et al's reported ratios [3]. The results of this study suggest a much larger contribution to total aerosol scattering by sea salt aerosols in remote marine air than current parameterizations of the sea salt size distribution imply [4,8]. They also hint at a very effective removal process of very small sea salt particles ($<$200 nm) formed in breaking waves in the MBL. References: 1.Penner, J. et al.,in: 3rd IPCC Report, 2001, Cambridge University Press: Cambridge. p.289-348. 2.Kinne, S. et al., J. Geophys. Res.-Atmos., 2003. 108(D20). 3.Murphy, D.M. et al., Nature, 1998, 392(6671): p.62-65. 4.O'Dowd, C.D. et al., Atmos. Environ., 1997, 31(1): p.73-80. 5.Clarke, A.D. et al., J. Atmos. Ocean. Tech., 2003, 20(10): p.1362-1374. 6.Clark, C.D. et al., J. Aerosol Sci., 2001, 32(6):p.765-778. 7.Campuzano-Jost, P. et al., J. Atmos. Ocean. Tech., 2003, 20(10):p.1421-1430. 8.Gong, S.L., Global Biogeochem. Cy., 2003, 17(4).
A31C-0083 0800h
Sub-Micron Sea-Salt Particle Flux From Laboratory Foams
Sea-salt particles are generated, in part, by bursting bubbles entrained in whitecap foams. Remote marine aerosol can include a significant number of sub-micron sea-salt particles (Mason, 2001). For example, O`Dowd and Smith (1993) found that remote marine aerosol number concentrations in the particle size range 0.1--3.0 $\mu$m were dominated by sea-salt particles for moderate-to-high wind speeds. Sub-micron sea-salt particles may be a significant source of cloud condensation nuclei in clean maritime air (Mason, 2001) and may also contribute to air-sea fluxes of latent heat (Andreas, 1992). Estimates of sub-micron sea-salt fluxes vary by an order of magnitude (Reid et al., 2001). Here we present laboratory measurements of the size and flux of sub-micron sea-salt particles from foams like those present on the oceans. These experiments were designed to examine the effect of seawater organic content, the spatial variation of which may account for the disparity between experimental measurements. Seawater samples were collected off the Scripps Institute of Oceanography Pier. Experiments were completed within 24-48 hours of seawater collection. Bubbles were generated using an air diffuser in a clean glass column filled with seawater (diameter = 15 cm, height = 40 cm). In order to study the influence of organics, sea spray was generated from seawater solutions containing a range of organic concentrations: artificial seawater (3.5 % salinity, no organics), filtered seawater, artificial seawater containing 1% filtered seawater, artificial seawater containing 10% filtered seawater, and unfiltered seawater. The sea spray was dried and subsequently sampled using a TSI (St. Paul, MN) Model 3080 Scanning Mobility Particle Sizer in order to measure the size distribution. For each seawater solution, the measured size distributions were monodisperse and the mean dry particle diameter were approximately the same ranging from 109--117 nm. The total number flux of sea spray was also independent of organic content. At a wind speed of 20 m s$^{-1}$, the flux of sub-micron sea-salt particles per ocean surface area according to our experimental data is 6\times10$^5$ m$^{-2}$ s$^{-1}$, or 30 times that predicted by the exponential model proposed by Mason (2001). However, the experimentally measured number flux is several orders of magnitude below earlier estimates made by Blanchard (1969). These experiments suggest that spatial variation in seawater organic content does not account for the large discrepancies in experimental measurements of sub-micron sea-salt flux.
A31C-0084 0800h
Size Distribution of Sea-Salt Emissions as a Function of Relative Humidity
Here we introduced a simple method for correcting sea-salt particle-size distributions as a function of relative humidity. Distinct from previous approaches, our derivation uses particle size at formation as the reference state rather than dry particle size. The correction factors, corresponding to the size at formation and the size at 80% RH, are given as polynomial functions of local relative humidity which are straightforward to implement. Without major compromises, the correction factors are thermodynamically accurate and can be applied between 0.45 and 0.99 RH. Since the thermodynamic properties of sea-salt electrolytes are weakly dependent on ambient temperature, these factors can be regarded as temperature independent. The correction factor w.r.t. to the size at 80% RH is in excellent agreement with those from Fitzgerald's and Gerber's growth equations; while the correction factor w.r.t. the size at formation has the advantage of being independent of dry size and relative humidity at formation. The resultant sea-salt emissions can be used directly in atmospheric model simulations at urban, regional and global scales without further correction. Application of this method to several common open-ocean and surf-zone sea-salt-particle source functions is described.
A31C-0085 0800h
An FTIR Study of Sulfur Dioxide (SO$_{2}) Uptake and Oxidation on Hydroxyl (OH) Radical Processed Sea-salt Components: Implications for Sulfur Accumulation in Sea-salt Aerosol
Both the uptake of sulfur dioxide and the rate of its subsequent aqueous oxidation to sulfate by ozone (O$_{3}) are strongly enhanced at high pH. Recent studies have implied an increase in sea salt particle alkalinity, or a delay of acidification, when reacted with hydroxyl (OH) radicals. Diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) has been applied to examine how the interaction of sulfur dioxide (SO$_{2}) with sea salt aerosol analogs is affected by prior OH radical processing. The role of water films present on partially deliquesced sea salt particles is highlighted. Implications for atmospheric SO$_{2} concentrations and aerosol formation will be discussed.
A31C-0086 0800h
Nitrate and sulfate in the marine boundary layer around Japan: Implications to chloride depletion
Gases and aerosols react with sea salt in the marine boundary layer. Atmospheric nitrate and sulfate are known to result in the chloride depletion by altering the nature of sea salt or mineral dust aerosol and ultimately may influence the marine ecosystem processes. Thus, it is important to understand these process and depositions of nitrate and sulfate to the sea. Significant quantities of anthropogenic gases and aerosol from the Asian Continent are transported over the North Pacific Ocean. A self-cruising observation boat (Self Cruising Ocean Observation Platform; SCOOP) was fabricated to monitor aerosol and gaseous compounds in the marine atmosphere as a part of VMAP project. The atmospheric samples were collected during SCOOP cruises (No. 0102; 26-31 August 2001and No. 0103; 3-8 December 2001) to the south of Honshu, Japan and near Hachijo Island, respectively. Ambient aerosols segregated into two size fractions (d$<$2.5 $\mu$m: fine mode; d$>$2.5 $\mu$m: coarse mode) were colleted at 4 hours intervals on a PTFE fiber filter by a dichotomous virtual impactor. Cl$^{-}$, NO$_{3}$$^{-}$, SO$_{4}$$^{2-}$, Na$^{+}$, K$^{+}$, NH$_{4}$$^{+}$, Mg$^{2+}$, and Ca$^{2+}$ in two size ranges were extracted into ultra pure water and analyzed by IC. During both the cruises air masses originated mainly from the northern and the central China. Mean concentrations of NO$_{3}$$^{-}$, nss-SO$_{4}$$^{2-}$, NH$_{4}$$^{+}$ and chloride depletion and in the fine particles were 4.5 $\pm$ 4.8, 36.7$\pm$30.5, 51.8$\pm$46.6, 12.7$\pm$9.9 nmol m$^{-3}$, respectively, in the SCOOP-0102 cruise and 4.6$\pm$3.6, 29.3$\pm$16.9, 41.7$\pm$27.7, 15.7$\pm$9.6 nmol m$^{-3}$, respectively, in the SCOOP-0103 cruise. Sulfate in fine particles was almost neutralized with ammonium ion and seems to be a predominant reactant causing chloride depletion. Although nitrate role appears to be limited, it was an initiator of the depletion reaction when sulfate was almost neutralized by ammonium ion. Our results suggest that chloride depletion reaction in fine mode can be controlled by the difference in concentrations of sulfate and ammonium ions and that nitrate can denature the mineral dust more than sulfate.