A11D-0145
Aerosol Absorption and Radiative Forcing Estimations using Sun Photometry and Ground- Based Broadband Radiometry at Kanpur, India During the 2008 TIGERZ Campaign
The TIGERZ campaign was conducted in May and June of 2008 in northern India to investigate the unique combination of aerosols (dust, smoke, industrial pollution) found in the Indo-Gangetic region. Six permanent sunphotometer sites were established in Northern India with four sites positioned along the approximate ground track of the CALIPSO sensor that passed near Kanpur to acquire high frequency aerosol optical depth data and make sky radiance measurements that were processed to determine aerosol properties such as size distribution and absorption at four wavelengths. During days with a CALIPSO overpass by Kanpur (as well as for the closest tracks to the East and West), an additional three Cimel sunphotometers were positioned within 100m of the satellite track. Such collocated measurements allow for joint inversions using both ground based sky radiance measurements from Cimels and radiance measurements from CALIPSO. Preliminary results from the investigation will be shared including calculations of single scattering albedo (SSA) trends determined from Cimel sunphotometer and pyranometer measurements, lidar ratio statistics (calculated from the sunphotometer radiances) compared with the lookup values used by CALIPSO for this region and modeled aerosol forcing for the region. The Cimel sunphotometer routinely provides single scattering albedo as a calculated aerosol product, however these values are typically limited values acquired during almucantars from low sun conditions (solar zenith greater than 45 degrees) when sensitivity to aerosol absorption is maximized. With a fully characterized aerosol and a suitable radiative model, it's possible to estimate the SSA using a well-calibrated radiometer. During TIGERZ, we installed a Kipp and Zonen pyranometers that took flux measurements at 2-minute intervals alongside the Kanpur sunphotometer. In principle, the advantage of using the pyranometer in this scenario is that we are able to evaluate SSA for high sun angles when aerosol absorption information is unavailable from the sunphotometer. One month (May 2008) of single scattering albedos derived from irradiance measurements are presented and compared with the equivalent parameter determined from the standard Cimel almucantar protocol.
A11D-0146
Reusing Information Management Services for Recommended Decadal Study Missions That Facilitate Aerosol and Cloud Studies
NASA Earth Sciences Division (ESD), and its preceding Earth science organizations, has made great
investments in the development and maintenance of data management systems, as well as information
technologies, for the purpose of maximizing the use and usefulness of NASA generated Earth science data.
Earth science information systems, evolving with the maturation and implementation of advancing
technologies, reside at NASA data centers, known as Distributed Active Archive Centers (DAACs). With
information management system infrastructure in place, and system data and user services already
developed and operational, only very small delta costs are required to fully support data archival, processing,
and data support services required by the recommended Decadal Study missions. This presentation
describes the services and capabilities of the Goddard Space Flight Center (GSFC) Earth Sciences Data and
Information Services Center (GES DISC) (one of NASAs DAACs) and their potential reuse for these future
missions. After 14 years working with instrument teams and the broader science community, GES DISC
personnel expertise in atmospheric, water cycle, and atmospheric modeling data and information services, as
well as Earth science missions, information system engineering, operations, and user services have
developed a series of modular, reusable data management components currently is use in several projects.
The knowledge and experience gained at the GES DISC lend themselves to providing science driven
information systems in the areas of aerosols, clouds, and atmospheric chemicals to be measured by
recommended Decadal Survey missions. Available reusable capabilities include data archive and distribution
(Simple, Scalable, Script-based, Science [S4] Product Archive aka S4PA), data processing (S4 Processor for
Measurements aka S4PM), data search (Mirador), data browse, visualization, and analysis (Giovanni), and
data mining services. In addition, recent enhancements, such as Open Geospatial Consortium (OGC), Inc.
interoperability implementations and data fusion prototypes, will be described. As a result of the information
management systems developed by NASAs GES DISC, not only are large cost savings realized through
system reuse, but maintenance costs are also minimized due to the simplicity of their implementations.
http://disc.gsfc.nasa.gov/
A11D-0147
Modeling dust emissions and transport within Europe: the Ukraine March 2007 event
A dust event was observed in Europe on March 23-25, 2007. Surface observations in Central Europe showed huge concentrations of particulate matter. At the same time, dust models diagnosed a Saharan dust outbreak flowing from Sahara to Europe. However, Lidar measurements and surface stations in Eastern Europe diagnosed a dust event originating from Ukraine related to chernozemic erodible lands. Using surface and satellite measurements with modeling results, it is demonstrated that the finally huge surface concentrations recorded in the Netherlands, Belgium and the North of France were mostly due to the extremely rare Ukraine dust event whereas Saharan dust events usually produce only mid- troposphere plumes. To investigate this episode, the chemistry-transport model CHIMERE is modified in order to account for erodibility of chernozemic soil inside Europe. A size distribution for chernozemic dust emission is proposed. Over Western Europe the model reproduces the observed PM concentration peaks up to 200 μg.m-3 with a large contribution of Ukraine dust, up to 170 μg.m-3. This first model study of dust emissions due to European arable land shows that it is possible to fairly retrieve the magnitude of surface concentrations far away from the emission sources.
A11D-0148
Modeling the Thermodynamics of Mixed Organic-Inorganic Aerosols to Predict Water Activities and Phase Equilibria
Tropospheric aerosol particles contain mixtures of inorganic salts, acids, water, and a large variety of organic compounds. Interactions between these substances in liquid mixtures lead to discrepancies from ideal thermodynamic behavior. While the thermodynamics of aqueous inorganic systems at atmospheric temperatures are well established, little is known about the physicochemistry of mixed organic-inorganic particles. Salting-out and salting-in effects result from organic-inorganic interactions and are used to improve industrial separation processes. In the atmosphere, they may influence the aerosol phases. Liquid-liquid phase separations into a mainly polar (aqueous) and a less polar organic phase may considerably influence the gas/particle partitioning of semi-volatile substances compared to a single phase estimation. Moreover, the phases present in the aerosol define the reaction medium for heterogeneous and multiphase chemistry occurring in aerosol particles. A correct description of these phases is needed when gas- or cloud-phase reaction schemes are adapted to aerosols. Non-ideal thermodynamic behavior in mixtures is usually described by an expression for the excess Gibbs energy. We present the group-contribution model AIOMFAC (Aerosol Inorganic-Organic Mixtures Functional groups Activity Coefficients), which explicitly accounts for molecular interactions between solution constituents, both organic and inorganic, to calculate activities, chemical potentials and the total Gibbs energy of mixed systems. This model allows to compute vapor-liquid (VLE), liquid-liquid (LLE) and solid-liquid (SLE) equilibria within one framework. Focusing on atmospheric applications we considered eight different cations, five anions and a wide range of alcohols/polyols as organic compounds. With AIOMFAC, the activities of the components within an aqueous electrolyte solution are very well represented up to high ionic strength. We show that the semiempirical middle-range parametrization of direct organic-inorganic interactions in alcohol-water-salt solutions enables accurate computations of liquid-liquid equilibria -- and phase diagrams in general.
A11D-0149
Evidence of the Aerosol Core/Shell Mixing State Over Europe by Using CHIMERE Simulations and AERONET Inversions.
The aim of this work consists to infer the most probable mixing state of aerosols over the European region during polluted events. The methodology presented here is based on the aerosol single scattering albedo (SSA) sensitivity to the mixing state of particles. Three different mixing cases; external mixing, internal mixing, and core-shell type mixing have been considered. Composite SSA have been computed for one intense pollution event over the European region and are compared with the AErosol RObotic NETwork (AERONET) retrieved SSA values. The most probable mixing state seems to be core-shell mixing, with secondary scattering aerosols coating over primary absorbing soot. This study shows that the internal mixing way should be used in modelling exercises for simulating aerosol direct radiative forcing and climate impact over European region.
A11D-0150
Stabilization of Mass Absorption Cross Section of Elemental Carbon for Filter-Based Absorption Photometer by Heated Inlet
Accurate measurements of elemental carbon (EC) or black carbon on a long-term basis are important for the studies of impacts of EC on climate and human health. In principle, mass concentrations of EC (MEC) can be estimated by the measurement of light absorption coefficient by EC. Filter-based methods, which quantify the absorption coefficient (kabs) from the change in transmission through a filter loaded with particles, have been widely used to measure MEC because of the ease of the operation. However, in practice, reliable determination of MEC has been very difficult because of the large variability in the mass absorption cross sections (Cabs), which is a conversion factor from kabs to MEC. Coating of EC by volatile compounds and co-existence of light-scattering particles greatly contributes to the variability of Cabs. In order to overcome this difficulty, volatile aerosol components were removed before collection of EC particles on filters by heating an inlet section to 400°C. The heated inlet vaporized almost completely sulfate, nitrate, ammonium, and organics without any detectable loss of EC. Simultaneous measurements of kabs by two types photometers (Particle Soot Absorption Photometer (PSAP) and Continuous Soot Monitoring System (COSMOS)) together with MEC by the EC-OC analyzer were made to determine Cabs at 6 different locations in Asia (Japan, Korea, China, and Thailand) in different seasons. The Cabs was stable to be 10.5±0.7 m2 g-1 at the wavelength of 565 nm for EC strongly impacted by emissions from vehicles and biomass burning. The stability of the Cabs for different EC sources and under the different physical and chemical conditions provides a firm basis for its use in estimating MEC in fine mode with an accuracy of about 10%.
A11D-0151
Particulate Emissions from Commercial Shipping. Chemical, Physical and Optical Properties.
Commercial shipping operations contribute combustion emissions across local, regional and global scales, burn low quality fuels and are subject to some of the most relaxed emission regulations. Aerosol emissions from shipping are known to have effects on cloud formation and health yet the uncertainty associated with these emissions is large. In fact, most emission factors for aerosol emissions are calculated from indirect measurements. Here we present a database of emission factors for most of the relevant climate and health related parameters from over 200 unique commercial shipping vessels. Data were collected in the Gulf of Mexico and Houston area during the 2006 GoMACCS field campaign on-board the NOAA research vessel Ronald H Brown. Measurements presented include emission factors for black carbon (BC), organic aerosol (OA), sulfate (SO4), particle number (CN) and total aerosol (as the sum of BC, OA and SO4). The results presented extend the range of directly measured aerosol emission factors for commercial shipping vessels well beyond existing measurements.
A11D-0152
An Experimental Study of Relative Humidity Effect on OH Uptake by Surfaces of Atmospheric Importance
An experimental study of the dependence of the OH uptake coefficient over a relative humidity of 0-48 % was carried out at 100 Torr and room temperature, using a differential bead-filled flow tube coupled to a high-pressure chemical ionization mass spectrometer. Various organic (paraffin wax, pyrene, glutaric acid, and soot) and inorganic (NaCl, KCl, MgCl2, CaCl2, Na2SO4, and sea salt) surfaces served as proxies for tropospheric aerosols. A virtual cylindrical flow tube approximation and a surface coating dilution technique were successfully employed in the study, which included measurements of high radical uptake with an initial probability of near unity. For inorganic salts, the effect of water vapor, enhancement or inhibition of the OH uptake coefficient, was found to be dependent on the blocking of anions and changes in surface pH. Although OH uptake by NaCl, the major component of sea-salt aerosols, is weakly dependent on water vapor, it is enhanced by a factor of 2 for MgCl2 and determines the net relative humidity dependence of the radical uptake on sea salt, which is enhanced by a factor of 4. For the organic surfaces studied, the enhancement effect of a factor 4 was also observed only for a hydrophilic organic surface, namely, glutaric acid. Results of the uptake studies suggest that the effect of relative humidity is important and should be accounted for in atmospheric modeling of tropospheric aerosol chemistry.
A11D-0153
Modeling Studies on Aging of Black Carbon and its Impact on Aerosol Optical and Cloud Condensation Nuclei Properties in Outflow From Anthropogenic Sources
In order to resolve the mixing state of black carbon (BC) aerosols explicitly in model simulations, a two- dimensional aerosol representation, in which aerosols are given for individual particle diameters and BC mass fractions, is introduced in this study. This representation was incorporated into an aerosol module, the Model of Aerosol Dynamics, Reaction, Ionization, and Dissolution (MADRID), and a new box model, MADRID- BC, was developed. MADRID-BC can accurately simulate the time evolution of the entire BC mixing states resulting from condensation/evaporation processes and evaluate the influence of the BC mixing states on aerosol optical and cloud condensation nuclei (CCN) properties. Aircraft observations conducted in March 2004 show that the mass fraction of thickly-coated BC particles increased in air horizontally transported out from an urban area in Japan within the planetary boundary layer over the ocean. MADRID-BC generally reproduces this feature well when observed bulk aerosol concentrations are used as constraints, and presents the changes in the entire BC mixing states during transport. Model simulations show that for particles with BC core diameters of 0.1-0.2 mm, the particle diameters, including both core and coating materials, had already increased by a factor of 1.6 on average when they left the source region and by as large as a factor of 1.9 of the BC core diameters after their transport over the ocean for a half day. Our simulations also show that the coatings on BC particles enhance light absorption at a wavelength of 550 nm by 38% in air leaving the source region and by 59% after the half day transport. The influences of the BC mixing states on CCN properties are also presented.
A11D-0154
Modeling The Optical Depth And Number Concentration Of Sea Salt Aerosol In A Coupled Microphysical And Climate Model
We model the number and optical depth of the sea salt aerosol (SSA) using a coupled microphysical/climate model based on the NCAR community atmospheric model (CAM) and the University of Colorado / NASA Community Aerosol and Radiation Model for Atmospheres (CARMA). Production, transport, vertical diffusion, particle growth and removal processes are represented in the model. Sea salt particle production for a size distribution containing both super- and sub-micron particles is based on a combined sea salt source function of Gong [2003] and Martensson [2003]. Particle dry deposition and wet deposition are calculated on a size- resolved basis. The mass prediction compares well with sea salt mass data from the University of Miami network [Savoie and Prospero, 1977]. The optical depths of size-resolved SSA at different locations are compared with Mulcahy [2008]'s relationship between the optical depth and the wind speed. The number loading is evaluated from size distribution data, and from cloud condensation nuclei (CCN) observations.
A11D-0155
On-line size-resolved chemical speciation of PM1 with a high resolution aerosol mass spectrometer during the 2008 Beijing Olympics
An intensive field measurement campaign, known as CAREBEIJING, was conducted to monitor air quality in Beijing under effects of large emission reduction during the 2008 Beijing Olympics. Various gaseous and particulate pollutants were measured on-line during this campaign. A new Aerodyne high-resolution aerosol mass spectrometer (HR-AMS) of Peking University was deployed to measure continuously the concentrations and size-resolved chemical compositions of PM1 in the city between July 23 and September 25 (August 8 to 23 for the Olympic Games). The 10-min averaged PM1 mass concentrations varied from a few ug m-3 to more than 200 ug m-3 during this study. The composition and size distributions of PM1 also varied dynamically, reflecting influences from local emissions, regional transport, secondary aerosol production, as well as removal processes by precipitation. During the whole sampling period, we observed several episodes of high loading (average PM1 over 100 ug m-3) and relatively low-aerosol loading (average PM1 less than 15 ug m-3). In addition, the size distributions of sulfate, nitrate, ammonium, and organics and their dynamic variations in association with different sources and processes will also be discussed.
A11D-0156
Use Of Cosmogenic 35S To Trace The Uptake Process Of SO2 In Aerosols In The Atmosphere
Environmental issues, such as acid rain and global warming, are linked to increased sulfur emissions and sulfate production in the atmosphere. Sulfate aerosol particles act as cloud condensation nuclei and can reduce the greenhouse effect by the indirect effect. Our understanding of the chemical and photochemical processes that govern the chemical transformations and transport of sulfur compounds in the atmosphere is still incomplete due to the complex, multivalent nature of sulfur and uncertainties in aerosol chemistry and transport (particularly trans-oceanic). We explore the use of cosmogenically produced 35S (half-life~87 days) to trace the uptake of SO2 gas into aerosols, as a function of aerosol size, in two different environments by simultaneously collecting and measuring [35SO42- ]and [35SO2]. These measurements can in turn be used to understand the time scales of SO2 oxidation to SO42-, aerosol 'age' and boundary layer dynamics. Aerosol samples are collected on glass fiber filters twice a week at Scripps Institute of Oceanography Pier in La Jolla, CA and the San Fernando Valley, CA for a 21-day period. SO2 (g) was collected on KOH impregnated filters placed after a 4-stage aerosol filter stack. We present preliminary results for both fine and coarse aerosol sulfate [35SO4] as well as [35SO2]. These measurements were done using low-noise liquid scintillation spectroscopy. By measuring the activity of each sample repeatedly over a period of 100 days, the exponential decay of 35S was observed, confirming the identity of the radioactive signal. The coastal and inland measurements are compared and implications for the atmospheric chemistry of SO2 and SO4 are discussed. Finally, we assess the potential of using [35SO4]/[nss-SO4] as a tracer of primary sulfate and trans-oceanic transport by coupling the measurements of the cation (Na+, Ca2+, K+, Mg2+, NH4+) and anion (Cl, NO3, SO4) concentrations in the aerosols.
A11D-0157
Day and Night Dust Retrievals from MODIS IR Band Measurements using Artificial Neural Network (ANN) model
Artificial Neural Network (ANN) on the East Asia domain (20°N-55°N, 90°E-145°E) during the springs of 2006 and 2007 was investigated for retrieving aerosol optical thickness (AOT) of dust aerosol at both daytime and nighttime. The input data for ANN include brightness temperature, BTD (11 μm - 12 μm), spectral emissivity, surface temperature (Land: Price [1984] Equation, Ocean: The IMAPP MODIS Algorithm), relative airmass of satellite, and topography (SRTM30). The D*-parameter is adopted as dust detection algorithm which was developed by Hansell et al [2007]. The target data of the ANN is corresponding AOT at 550nm obtained from MODIS aerosol product (MYD04). After optimization and training, ANN AOT is retrieved. Among the many dust episodes during the spring of 2006, only the 8 April 2006 case was selected for the detailed analysis. Because it is one of the strongest episodes and shows a well-developed root penetrating the Korean peninsula and reaching the Japanese area. It is shown that ANN AOT coincide well with MODIS AOT having correlation coefficient of 0.8502 when the training and applying periods are the same (spring of 2006). Even a different period with training ANN AOT has a good relationship with MODIS AOT with the correlation coefficient of 0.7766 (spring 2007). This yearly difference is resulted from vegetation change and fixed IGBP land cover map. Also notable is that ANN AOT is underestimated in most IGBP types having low slope and negative mean bias. This study showed that ANN model has a good potential to retrieve AOT. More examinations and trials are needed, however, to improve this ANN algorithm using IR bands. Also this model should be extended to specify the dust aerosol property from other aerosols and clouds to assure that it has a capability during both daytime and nighttime.
A11D-0158
A Study of Seasonal Temperature PDF of SAGE II 1.02 micron Extinction Coefficients Over the Asian Deserts
Dust is an important component of aerosol in the troposphere and it affects air quality and climate. To explore the identification and influence of lofted dust on the measurements from the satellit instrument of the Stratospheric Aerosol and Gas Experiment (SAGE ) II, the probability density functions (PDFs) of the temperature associated with SAGE II 1.02 micron extinction coefficients over desert regions, including the Central Asian Deserts, Taklimakan Desert, and Gobi Desert, are compared with those outside desert regions at similar latitudes on a seasonal basis. This PDF analysis has been applied to the SAGE II cloud as well as aerosol data obtained by using a two-wavelength cloud-aerosol separation method. The results show basically a year round single mode of the PDF associated with cloud as weel as the background aerosol outside the desert regions. Over the desert regions, the analysis shows the seasonally upward spread of desert dust as the occurrence of a higher temperature mode of the PDF, in addition to the PDF for cloud and bckground aerosol, leading to a bimodal PDF distribution. Interestingly, no lofted dust is found over desert region in the upper troposphere in winter. The present results demonstrated the feasibility of detecting the lofted dust from the desert during the non-winter seasons by searching the higher temperature mode in the bimodal PDF. The influence of seasonal large-scale circulation on the background aerosol, cloud and lofted dust is also discussed.
A11D-0159
Future Sulfate-Nitrate-Ammonium Aerosol Levels in the United States
Global simulations of sulfate, nitrate, and ammonium aerosols are performed for the present-day and 2050 using the chemical transport model GEOS-Chem. Changes in climate and emissions projected by the IPCC A1B scenario are imposed separately and together with the primary focus of the work on future inorganic aerosol levels over the United States. Climate change alone is predicted to lead to decreases in levels of sulfate and ammonium in the southeast U.S. but increases in the midwest and northeast U.S. Nitrate concentrations are projected to decrease across the U.S. as a result of climate change alone. Changes in transport, precipitation, oxidant levels, boundary layer depth, and temperature are important factors influencing aerosol levels. In the U.S., climate change alone can cause changes in annually averaged sulfate-nitrate-ammonium of up to 0.61 μg/m3, with seasonal changes often being much larger in magnitude. When changes in anthropogenic emissions are considered (with or without changes in climate), domestic sulfate concentrations are projected to decrease due to sulfur dioxide emission reductions, and nitrate concentrations are predicted to generally increase due to higher ammonia emissions combined with decreases in sulfate. The ammonium burden is projected to increase from 0.24 Tg to 0.36 Tg, and the sulfate burden to increase from 0.28 TgS to 0.40 TgS as a result of globally higher ammonia and sulfate emissions in the future. The global nitrate burden is predicted to remain essentially constant at 0.35 Tg with changes in both emissions and climate as a result of the competing effects of higher precursor emissions and increased temperature.
A11D-0160
Atmospheric aerosol variation in Okinawa Island in Japan by MAX-DOAS using a new cloud screening method
Atmospheric aerosol profile observation using Multi AXis Differential Optical Absorption Spectroscopy (MAX- DOAS) is being conducted at Cape Hedo (26.87N, 128.25E) in the north of Okinawa Island in Japan since 30 March 2007 [Irie et al., AGU 2008 Fall Meeting]. Comparison with ground-based lidar and sky radiometer measurements for cloud free condition covering a period more than one year shows good agreement between the three observations despite different geometries. MAX-DOAS cloud screening method based on physical properties of cloud has been developed using the MAX-DOAS relative humidity and the MAX-DOAS color index, defined by the ratio of the intensities of 500 nm and 380 nm. This method consists of two steps: cloud screening in the troposphere is applied using the color index and cloud at 0-1 km is judged by the relative humidity. The former is consistent with the lidar cloud screening at 0-6 km and the later has a strong negative correlation between the lidar cloud height and the relative humidity. Using this cloud screening method we investigate aerosol variation at 0-1 km. Clear annual minimum is found in August-September with a low variability in relation to ocean source of clean air mass, whereas maximum is found during November- May with a large variability in relation to continental source of polluted air mass.
A11D-0161
Functional Group Analysis of Biomass Burning Particles Using Infrared Spectroscopy
Biomass burning is a significant source of particulate organic carbon in the atmosphere. These particles affect the energy balance of the atmosphere directly by absorbing and scattering solar radiation, and indirectly through their ability to act as cloud condensation nuclei (CCN). The chemical composition of biomass burning particles influences their ability to act as CCN, thus understanding the chemistry of these particles is required for understanding their effects on climate and air quality. As climate change influences the frequency and severity of boreal forest fires, the influence of biomass burning aerosols on the atmosphere may become significantly greater. Only a small portion of the organic carbon (OC) fraction of these particles has been identified at the molecular level, although several studies have explored the general chemical classes found in biomass burning smoke. To complement those studies and provide additional information about the reactive functional groups present, we are developing a method for polarity-based separation of compound classes found in the OC fraction, followed by infrared (IR) spectroscopic analysis of each polarity fraction. It is our goal to find a simple, relatively low-tech method which will provide a moderate chemical understanding of the entire suite of compounds present in the OC fraction of biomass burning particles. Here we present preliminary results from pine and oak samples representative of Midwestern United States forests burned at several different temperatures. Wood type and combustion temperature are both seen to affect the composition of the particles. The latter seems to affect relative contributions of certain functional groups, while oak demonstrates at least one additional chemical class of compounds, particularly at lower burning temperatures, where gradual solid-gas phase reactions can produce relatively large amounts of incompletely oxidized products.
A11D-0162
Inter-comparison of Microphysical Cloud Properties for MODIS and PATMOS-x Climatologies
One year of liquid cloud physical and microphysical properties are evaluated using coincident retrievals from the most current processed versions of NOAA's Advanced Very High Resolution Radiometer (AVHRR) Pathfinder Atmospheres Extended (PATMOS-x) and MODIS (MODerate Resolution Imaging Spectroradiometer) climatologies. Differences in liquid droplet effective radius, liquid water path, liquid cloud fraction and optical depth are found between the two climatologies. Some of these differences are consistent over time and space, such as MODIS mean retrievals of liquid cloud droplet effective radius being almost universally higher than those of PATMOS-x, while the magnitude and sign of others are dependent on geographic location and whether the retrieval is over ocean or land. It is found that at least some of these differences are related to the methods used to determine the viability of partially cloudy pixels, while others are related to the spectral properties of the satellite instrument or the algorithms used to process the raw measurements. An attempt is made to categorize these differences by source and magnitude. Potential effects of these results are discussed.
A11D-0163
Extraction of Optical Constants from Mid-IR Spectra of Small Aerosol Particles
Aerosol particles directly influence the Earth's radiation budget by absorbing and scattering incident short-
wave (solar) radiation and long-wave terrestrial radiation. Broadband infrared measurements can provide
valuable information on aerosol's composition and size distribution. However, quantitative analysis of mid-
infrared aerosol extinction spectra in terms of their characteristics relies on complex refractive indices for the
various aerosol constituents. Derivation of such optical constants is complicated, especially in the mid-
infrared region, mainly due to the great variability of the imaginary part (k) of the complex refractive index
N, and its influence on the real part (n). Most of previously reported methods for determining these
constants (Wagner et al., 2005; Dohm et al., 2004; Earle et al, 2006) use aerosols with size
distributions for which scattering occurs in the spectral range of the measurement, and so the explicit Mie
theory calculations for the scattering and absorption efficiencies are required. These calculations necessitate
some assumptions on the particles size distribution and an initial guess of the k spectrum in order to
extract the optical properties from the acquired spectra. Also, the solution uniqueness relies on the fact that
the particles are large enough. In the present work, we seek to simplify the above procedure and use small
particles' spectra of known size distributions to deduce the optical constants.
For particles (such as poly-disperse aerosols) having geometric mean of less than 0.15 μm, absorbance
spectra in the mid-infrared range do not show any scattering features. Therefore, Rayleigh theory can be
used to extract the imaginary part of the complex function f, where f=[(N2-1)/(N2+2)]. The
real part of the f function is then extracted using the Kramers-Kronig transformation and the n and k can be derived using the relation between f, ε (complex dielectric function). k and n
(Bohren and Huffman, 1983).
The method was tested on crystalline ammonium sulfate aerosols, enabling comparison with existing data.
Solutions were used to create aerosol flows with various size distributions and total number of particles.
Particle size distribution and mid-IR spectra were recorded simultaneously using a Scanning Mobility Particle
Sizing (SMPS) system placed in series with a long-path IR cell. The optical constants estimated
experimentally using the proposed method matched closely those previously reported by Earle et al.,
2006.
References
Wagner R., Benz S., Mohler O., Saathoff H., Schnaiter M.,Schurath U., 2005, JPC A, 109, 7099-7112
Dohm, M.T., Potscavage, A. M., and Niedziela, R. F., 2004, JPC A, 108, 5365-5376
Earle M.E., R. G. Pancescu, B. Cosic, A. Y. Zasetsky, and J. J. Sloan, 2006, JPC A, 110, 13022-13028
Ohta,K. and Ishid, H., 1988, Applied Spec., 42(6), 952-957
Bohren and Huffman, 1983, Absorption and scattering of light by small particles, Wiley-VCH publication.
class="ab'>
A11D-0164
Measurements of Optical Properties of Aerosols by Cavity Ring-Down Spectroscopy in Mega-City Tokyo, Japan
Aerosol particles have an important role in radiation balance in the atmosphere by scattering and absorbing incident light. Therefore, accurate determination of the optical properties of atmospheric aerosols is essential. There are two components to aerosol optical extinction: scattering and absorption. Extinction coefficients of atmospheric aerosol have commonly been determined by measuring scattering coefficients using nephelometer (Neph) and absorption coefficients using an aethalometer or particle/soot absorption photometer (PSAP). Both the aethalometer and PSAP rely on collection of the aerosol particles onto a filter substrate followed by a measurement of light reflectance and/or transmittance. Because of the temporal variations of the conversion parameter, these techniques may have relatively large uncertainties. Extinction coefficients can also be measured using cavity ring-down spectroscopy (CRDS). In this work, simultaneous measurements of extinction, scattering, and absorption coefficients of the ambient aerosols were performed in central Tokyo from 14 August to 2 September 2007 using a newly developed CRDS instrument, Neph and PSAP, respectively. Gas phase ozone concentrations were also measured using a commercial instrument. Extinction coefficients measured using CRDS were compared with those determined from the sum of scattering and absorption coefficients measured by nephelometer and PSAP. By comparing the single scattering albedo (SSA) calculated by three different combinations from extinction, scattering, and absorption, it is suggested that the PSAP overestimates absorption coefficients by a factor of 2. By taking the overestimation of the PSAP into account, the extinction coefficients measured by CRDS were in excellent agreement with those for Neph+PSAP with the ratio of (Neph+PSAP)/CRDS = 1.02, except for the data on days when high concentrations of ozone (more than 130 ppbv) were observed. For the data when high concentrations of ozone were observed, extinction coefficients for Neph+PSAP were 15-30 % larger than those for CRDS. Using the corrected data, SSA values during summertime in central Tokyo are estimated.
A11D-0165
Shortwave Forcing by Shallow Cumuli over the Southern Great Plains
Shallow cumuli are ubiquitous over large areas of the globe, including both the interior of continents and the trade wind regions over the oceans. Measurements made at the Atmospheric Radiation Measurement (ARM) Climate Research Facility (ACRF) Southern Great Plains site provide a unique long-term data set that can be used to investigate the influence that these clouds have on the shortwave energy budget at a continental location. Using data collected for the summers of 2000 through 2007, inclusive, over 900 hours with fair- weather cumuli were identified using data from a cloud radar, lidar, ceilometer and Total Sky Imager. The ARM Shortwave Flux Analysis data product was used to determine the shortwave forcing on a range of time scales. This work shows that the hourly-average shortwave forcing is on the order of -60 W m-2. When the data is adjusted to account for times without shallow clouds, the shortwave forcing over the entire summer (defined as May through August) is still significant, -2 W m-2. Additional analysis provides insight into the annual variability of the forcing, as well as examining the frequency of positive shortwave forcing.
A11D-0166
Measurements of Individual Black Carbon Particle Mixing State in Diverse Biomass Burning Plumes
Individual black carbon-containing particles in biomass burning (BB) emissions of various ages have been measured and compared. Fresh BB emissions measured at low altitude during the 2006 TexAQS campaign contrast with older plumes transported over long distances that have different chemical signatures. Although the mass distributions of BC associated with the emissions do not differ strongly from one plume to another, the amount of non-refractory materials associated with them is roughly correlated to the time since emission. Here we estimate a condensation rate onto BC cores and discuss the relative importance of BC emission state and aging on determining mixing state of BC particles.
A11D-0167
Sub-cloud Evaporation in Marine Stratocumulus and Implications for Water and Energy Budgets
We report in situ aircraft measurements of the cloud drop size distribution (DSD) and derive sub-cloud evaporation rates below marine stratocumulus. Measurements come from the Artium Flight Phase Doppler Interferometer (F/PDI) during the Marine Stratus Experiment in July 2005. Drizzle in the sub-cloud layer is important to the water and energy budgets of the stratocumulus-topped marine boundary layer (MBL). The rate of drop evaporation after drizzle falls below cloud base into the sub-cloud layer is dependent on the DSD at cloud base, as well as the sub-cloud relative humidity and temperature. In turn, such evaporation can be an important for the dynamics within the boundary layer and, via feedbacks, impact the cloud layer itself. For example, sub-cloud evaporative cooling can lead to large scale changes in boundary layer turbulence and buoyancy production. These evaporative effects change the overall stability of the MBL and may promote the decoupling of the mixed layer. Understanding how the evaporation of drizzle quantitatively affects the MBL system is important in predicting the subsequent evolution and lifetime of the cloud.
A11D-0168
Comparison of CloudSat 2B-CLDCLASS observations to trained student surface observations from the CloudSat Education Network.
Individual surface observations of cloud type taken by trained student observers participating in the CloudSat Education Network (CEN) are compared with observations from the CloudSat 2B-CLDCLASS cloud classification product. The CloudSat Education Network consists of over eighty schools trained in cloud observations, and are located across five continents. Surface observations of clouds from the CEN are taken coincident with CloudSat overpasses of the CEN school location, facilitating direct comparison between the satellite-derived cloud type product and the surface observations. Agreement between the two sets of observations are comparable to studies using WMO observations made by trained meteorologists, making the near-global CEN network a potentially useful source for ground verification of satellite-observed cloud properties.
A11D-0169
Aerosol Extinction and Single Scattering Albedo Downwind of the Summer 2008 California Wildfires Measured With Photoacoustic Spectrometers and Sunphotometers From 355 nm to 1047 nm.
Hundreds of wildfires in Northern California were sparked by lightning during the summer of 2008, resulting in downwind smoke for much of June and July associated with the flaming and smoldering stages of the fires. These fires are consistent with a growing trend towards increasing biomass burning worldwide. Climate impacts from the smoke depend critically on the smoke amount and aerosol optical properties. We report comparison of aerosol optics measurements in Reno Nevada made during the very smoky summer month of July with the relatively clean, average month of August. Photoacoustic instruments equipped with integrating nephelometers were used to measure aerosol light scattering and absorption at wavelengths of 355 nm, 405 nm, 532 nm, 870 nm, and 1047 nm. Total aerosol optical depth was measured with a sun photometer operating at 430nm, 470nm, 530nm, 660nm, 870nm and 950nm. A spectrometer based sun photometer with an operating range from 390nm to 880 nm was also used for a few days as well. These measurements document the intensity of the smoke optical impacts downwind. They are processed further to reveal a strong variation of the aerosol light absorption on wavelength, indicating the presence of light absorbing organic material and perhaps wavelength dependent absorption caused by black carbon particles coated with organic and inorganic particulate matter. On the day with most smoke in Reno (July 10, 2008) Angstrom coefficients for absorption as high as 3.6 were found for wavelengths of 405 nm and 870 nm, with the corresponding single scattering albedo near 0.92 at 405 nm. Aerosol optical depths of 3.5 were found for 430 nm on July 10th from the sun photometer measurements. A roughly fourfold increase in aerosol optical quantities was observed between the months of July and August 2008, attesting to the large average effects of biomass aerosols from the California wildfires.
A11D-0170
Regional Urban Aerosol Retrieval With MODIS: High-Resolution Algorithm Application and Extension of Look-up Tables
Aerosols play an important role for the global climate by modulating the Earth's energy budget. Air quality and related health issues for humans are also tightly linked with concentration, composition, and size of aerosol particles. Satellite remote sensing with the MODIS sensor on NASA's Aqua and Terra platforms is one means to investigate aerosols globally. However, due to the global scope of the operational mission only globally based aerosol models can be employed in the look-up table approach of the retrieval algorithm. The relatively coarse resolution of 10x10km also largely prevents the detection of small scale structures in the aerosol optical depth (AOD) on a regional level. Consequently, the operational MODIS aerosol algorithm over land has been specifically adapted to the New York City area. First, the operational look-up table was extended based on local aerosol climatology obtained using five years of AERONET measurements at the City College of New York site. These models were then used to create appropriate LUT using the 6S radiative transfer model. Second, regional surface reflectance ratio parameterizations which better characterize the urban surface properties were implemented in the algorithm. These two modifications ultimately allow the retrieval algorithm to be applied at the actual sensor resolution of 500x500m. This presentation focuses on estimating the errors that are inherent in the operational processing compared to a regionally refined processing scheme. In particular, we remove artificial hot spots in the aerosol retrieval and are able to extract realistic high resolution aerosol structure.
A11D-0171
Seasonal variation of water-soluble chemical components in the bulk atmospheric aerosols collected at Okinawa Island, Japan
The economic development and population growth in recent Asia spread air pollution. Emission rate of air pollutants from Asia, in particular oxides of nitrogen, surpassed those from North America and Europe and should continue to exceed them for decades. The study of the air pollution transported from Asian continent has gained a special attention in Japan. Okinawa Island is situated approximately 1500 km south of Tokyo, Japan, 2000 km southeast of Beijing, China, and 1000 km south of South Korea. Its location is ideal in observing East Asian atmospheric aerosols because maritime air mass prevails during summer, while continental air mass dominates during fall, winter, and spring. The maritime air mass data can be seen as background and can be compared with continental air masses which have been affected by anthropogenic activities. In 2005, Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS) was established by the National Institute for Environmental Studies (NIES) at the northern tip of Okinawa Island, Japan to monitor the air quality of Asia. Bulk aerosol samples were collected on quartz filters by using a high volume air sampler. Sampling duration was one week for each sample. We determined the concentrations of water-soluble anions, cations and dissolved organic carbon in the bulk aerosols collected at the CHAAMS, using ion chromatography, atomic absorption spectrometry, and total organic carbon analyzer, respectively. Seasonal variation of water-soluble chemical components showed that the concentrations were relatively low in summer, higher in fall and winter, and the highest in spring. When air mass came from Asian Continent, the concentrations of water-soluble chemical components were much higher compared to the other directions.
A11D-0172
The Heterogeneous Oxidation of Organic Droplets -Temperature and Physical Phase Effects
The heterogeneous reactions of oleic acid droplets with ozone are studied at different temperatures to imitating the atmospheric condition. The reactions are monitored concomitantly by using attenuated total reflectance Fourier Transform infrared spectroscopy (ATR-FT-IR) for the organic species and UV-VIS spectrometry for the ozone concentration, in order to investigate reaction rate discrepancies reported in literature as well as the oxidation mechanism, temperature and physical phase effects. The less and semi- volatile products are identified and resolved by a liquid chromatography and a gas chromatography mass spectrometer, respectively. The identified products are predominantly composed by nananoic acid and azelaic acid and might be due to propagation reactions possibly initiated by a secondary reaction such as the stabilized Criegee intermediates reacting with oleic acid. For temperature effect, the oxidation rate decreases with temperature when the oleic acid droplets are in the same physical phases. As oleic acid turns into the solid phase, the oxidation mechanism is observed to be different from the liquid phase. Furthermore, the concentration of ozone was monitored to examine the kinetics of the oxidation reaction. The integrated ozone profile recorded by UV-VIS spectrometry shows that the consumed ozone represents only approximately 12% of total oleic acid for the solid cases at 4°C in contrast to 30% for the liquid cases at 25°C, and hence confirmed the existence of secondary reactions.
A11D-0173
Photo-initiated Reactions of Methylglyoxal and Other Organics in the Condensed Phase: Impact on UV-vis Absorbance of Aerosols
Solar ultraviolet-visible (UV-vis) radiation can initiate photochemical reactions of organic compounds in aerosols that may be important sinks for the particle-phase reactants as well as sources for new organic products in both the particle and gas phases. Furthermore, the optical characteristics of organic aerosols may be altered by the photochemical destruction (or production) of organics that absorb solar UV-vis radiation. Here we present laboratory results that demonstrate that solar irradiation (simulated with a xenon lamp) of solutions of organic compounds can either increase or decrease the UV-vis absorbance of the solution depending on conditions--namely acidity. For example, UV-vis irradiation of aqueous solutions of methylglyoxal resulted in solutions that absorbed less UV radiation than the original, while irradiation of methylglyoxal in concentrated (~50wt%) sulfuric acid solutions resulted in solutions that absorbed more UV radiation. In order to identify the molecules and/or reactions responsible for these changes in optical properties, we used High Performance Liquid Chromatography (HPLC) and Attenuated Total Reflectance- Fourier Transform Infrared (ATR-FTIR) spectroscopy to monitor loss of organic reactant and the appearance of photo-products. These results are used to evaluate the potential impacts of particle-phase organic photochemistry on the optical properties of atmospheric organic aerosols.
A11D-0174
Characterization of Polyfunctional Oligomers From Pyruvic Acid Photolysis in Water
Humic substances (HUMICS) are widespread in natural surface waters, where they ultimately undergo solar photolysis into small alpha-dicarbonylic species, such as glyoxal, glyoxylic and pyruvic acids. Humic-like substances (HULIS) are also found in the atmospheric aerosol. We report a laboratory study of the photolysis of aqueous pyruvic acid (PA), solutions at concentrations representative of the atmospheric aerosol using UV-absorption, high resolution electrospray mass (EMS), and nuclear magnetic resonance (NMR) spectrometries. PA yields polyfunctional oligomers reaching molecular masses of up to 900 Da, some of which absorb into the visible. Exact mass determinations (to the fourth decimal place) yielded unique molecular formulae in most cases, which were confirmed by collisionally induced dissociation (CID) patterns and the analysis of the products of photolysis of [2-13C] and [3-13C] PA isotopologues. The lowest energy CID channels corresponded to neutral fragment losses of masses: 18 (H2O), 44 (CO2), 46 (HCOOH) and 62 (CO3H2. 13C- and 1H- NMR of [2-13C] and [3-13C] PA photolysis mixtures revealed the presence of various carbonyl functionalities (190 to 230 ppm) displaying 2J(CC) and 3J(CC) couplings among themselves and with anomeric carbons (~ 96 ppm). Based on this evidence, we propose molecular structures and a mechanism of formation for these oligomers.