A41A-0001 0800h
Continuous Estimates of Secondary Organic Aerosol From the Southeastern Aerosol Research and Characterization Study (SEARCH)
Carbonaceous matter (organic matter + elemental carbon) comprises 30-45% of PM 2.5 mass in the southeastern U. S. Elemental carbon is formed during the incomplete combustion of organic compounds, primarily from fossil-fuel-powered vehicles. The organic material in PM 2.5 is a mixture of a myriad of organic compounds, a portion of which is emitted directly into the atmosphere (primary organic aerosol), and a portion of which that is formed from chemical reactions of reactive organic compounds in the atmosphere (secondary organic aerosol). In order to formulate effective control strategies for atmospheric particulate matter, it is important to gain a better understanding of the relative contributions and sources of primary and secondary organic aerosol. Continuous measurements of PM 2.5 mass and chemical composition have been performed since 1998 as part of the Southeastern Aerosol Research and Characterization study (SEARCH). The SEARCH measurement network consists of eight monitoring sites, organized as three urban-rural pairs in Georgia, Alabama, and Mississippi, and one urban-suburban pair in Florida. At each of these sites a variety of gaseous, particulate, and meteorological measurements are obtained on a routine basis, including continuous particulate elemental carbon via aethalometry and total particulate carbon via a Rupprecht & Patashnick Model 5400 carbon analyzer. In this work, we analyze hourly measurements of particulate elemental carbon and total carbon from the SEARCH network over 1999-2003 to estimate the contribution of secondary organic aerosol in the southeastern U.S. By using elemental carbon as a tracer of primary combustion-generated carbon emissions in conjunction with other continuously-measured gaseous species, we derive estimates of secondary organic aerosol mass as a fraction of total measured organic particulate mass. Urban-rural, seasonal, and weekday-weekend differences in secondary organic aerosol formation are examined.
A41A-0002 0800h
Chamber studies of aerosol growth by glyoxal polymerization
Recent experiments indicate that heterogeneous reactions may contribute to the growth of secondary organic aerosol (SOA). Such reactions increase the partitioning of gas-phase organics into the particle phase, so that even relatively volatile organics may contribute to the organic fraction of atmospheric aerosols. With the aim of obtaining a framework for the inclusion of such reactions into tropospheric models, we measure particle growth by reactive uptake of simple organics, using the same approach taken previously in our laboratory for the measurement of SOA yields from the oxidation of VOC's. Seed aerosol (ammonium sulfate or ammonium sulfate/sulfuric acid) is added to 28 m$^{3}$ Teflon chambers, and after equilibration a single reactive organic is added. For these studies we focus on glyoxal (CHOCHO), a volatile but reactive compound formed in a number of atmospheric oxidation processes and believed to contribute to aerosol growth via heterogeneous reactions. Particle size is monitored using differential mobility analyzers; significant growth is always observed following glyoxal addition. Mass spectrometric measurements of sampled aerosol show an abundance of polymeric products, indicating heterogeneous reactions as the cause of aerosol growth. The influences of seed particle acidity and glyoxal concentration on particle growth and composition are examined, and compared to results from our earlier studies of SOA formation from $\alpha$-pinene ozonolysis.
A41A-0003 0800h
Secondary Organic Aerosol Yield Parameterizations for Regional Air Quality Modelling
A new secondary organic aerosol parameterization based on the Jiang (2004) instantaneous organic aerosol yield (IAY) approach was implemented into the AES Unified Regional Air Quality Modelling System (AURAMS). Results will be presented comparing the new parameterization with the Odum et al. (1997) overall organic aerosol yield (OAY) approach traditionally implemented into regional air quality models. A comparison on a western North American domain suggests a significant increase in modelled organic aerosol concentrations with the new IAY approach in better agreement with measurements collected during the PACIFIC 2001 field program. A model assessment of the primary versus secondary contribution to organic aerosol for the western North American domain will also be presented illustrating the importance of secondary anthropogenic production in the Lower Fraser Valley and secondary biogenic production over the Canadian alpine and boreal forests.
A41A-0004 0800h
Density Changes of Aerosol Particles as a Result of Chemical Reaction
This paper introduces the capability to study simultaneously changes in the density, the chemical composition, the mobility diameter, the aerodynamic diameter, and the layer thickness of multi-layered aerosol particles as they are being altered by heterogeneous chemical reactions. A vaporization-condensation method is used to generate aerosol particles composed of oleic acid outer layers of 2 to 30 nm on 101-nm polystyrene latex cores. The layer density is modified by reaction of oleic acid with ozone for variable exposure times. For increasing ozone exposure, the mobility diameter decreases while the vacuum aerodynamic diameter increases, which for spherical particles, implies that particle density increases. The aerosol particles are confirmed as spherical based upon the small divergence of the particle beam in the aerosol mass spectrometer. The particle and layer densities are calculated by two independent methods, namely one based on the measured aerodynamic and mobility diameters and the other based on the measured mobility diameter and particle mass. The uncertainty estimates for density calculated by the second method are two to three times greater than those of the first method. Both methods indicate that the layer density increases from 0.89 to 1.12 g cm-3 with increasing ozone exposure. Aerosol mass spectrometry shows that, concomitant with the increase in the layer density, the oxygen content of the reacted layer increases. Even after all of the oleic acid has reacted, the layer density and the oxygen content continue to increase slowly with prolonged ozone exposure, a finding which indicates continued chemical reactions of the organic products either with ozone or with themselves. The results of this paper provide new insights into the complex changes occurring for atmospheric particles during the aging processes caused by gas-phase oxidants.
http://www.deas.harvard.edu/environmental-chemistry/pubs.php
A41A-0005 0800h
Reactive Uptake of O$_3$ on Oleic Acid - Alkanoic Acid Mixtures
In the atmosphere gas-phase species react on or in organic particles and potentially modify the particle composition and morphology. These reactions, often referred to as heterogeneous reactions, may change the hygroscopic and the optical properties of the aerosol particles and have a direct influence on air quality and health issues.\The heterogeneous reaction of O$_3$ with pure liquid oleic acid has been studied extensively. In the atmosphere, however, oleic acid is most likely found in mixtures with other species, and these other species may influence the reaction rates, reaction mechanisms, and lifetimes of oleic acid. One major source of oleic acid containing particles is from meat cooking operations. These aerosol particles may comprise up to 20 % of the primary fine organic carbon particle emissions in the Los Angeles area. The identified particulate organic compounds account for 20 wt% of the particle mass. The identified composition of the particles is estimated to be 45 % n-alkanoic acid, 30 % n-alkenoic acids (which is mainly oleic acid), 3 % lactones, 2 % n-alkanes, and 3 % amides. Field measurements suggest that these aerosol particles have lifetimes of several days. In contrast, the laboratory studies on pure oleic acid suggest the lifetime is a few minutes for typical O$_3$ concentrations and particle diameters. Here, we present a comprehensive study of O$_3$ uptake on binary oleic acid mixtures, i.\ e.\ oleic acid/lauric acid and oleic acid/myrisitc acid. Additionally, studies on more realistic multicomponent mixtures will be presented corresponding to compositions of meat cooking aerosols. A chemical ionization mass spectrometer coupled to a rotating flow tube system is used for the investigation.\The heterogeneous uptake coefficient of O$_3$ for the binary mixtures is measured at room temperature as a function of the concentration of the saturated acid. The uptake coefficient decreases with increasing amounts of saturated fatty acids as expected. The addition of small amounts of saturated fatty acids decreases the uptake coefficient more than expected. This may be because the addition of small amounts of saturated fatty acids decreases significantly the amount of oleic acid at the air-liquid interface. The uptake coefficient of O$_3$ is an order of magnitude lower for solid-liquid mixtures. The experiments show that the uptake reaction is affected by the morphology of the mixture. The morphology in turn depends on the method of preparation of the film. The corresponding lifetimes based on the uptake measurements can be up to 11 hours for solid-liquid particles. This may, in part, explain the long lifetimes of oleic acid in the atmosphere.
A41A-0006 0800h
Real-time monitoring of ozonolysis of unsaturated SAMs using ATR-FTIR: kinetics, mechanisms and atmospheric implications
The ozonolysis of organics adsorbed on surfaces is of fundamental chemical interest and potentially important in the lower atmosphere. Most previous studies of such systems have monitored in real time the gas phase moiety, while the condensed phase has been analyzed only before and after oxidation. In the present study, the ozonolysis of three carbon and eight carbon vinyl-terminated self-assembled monolayers (SAMs), directly deposited on a silicon ATR (attenuated total reflectance) crystal, was monitored in real-time at 296 K and atmospheric pressure using ATR-FTIR. For comparison, some studies of saturated C8 SAM were also carried out. The films were also characterized by atomic force microscopy and water contact angle measurements. The kinetics of the loss of the vinyl groups and the formation of carbonyl groups were measured as a function of ozone concentrations over the range of 10$^{11}$ to 10$^{16}$ molecules cm$^{-3}$. The measured reaction probabilities are strongly dependent on ozone concentrations and are shown to be consistent with a Langmuir-Hinshelwood mechanism in which ozone is rapidly adsorbed on the surface and then reacts more slowly with the alkene moiety. Molecular dynamics (MD) simulations support this conclusion, showing that ozone does not simply undergo elastic collisions with the surface, but has a significant residence time on it. However, the kinetics measurements indicate a much longer residence time than the MD calculations, suggesting a chemisorption of ozone. Formaldehyde was observed as a gas phase product by infrared cavity ring down spectroscopy. Possible mechanisms of the ozonolysis and its atmospheric implications are discussed.
A41A-0007 0800h
Temperature and Composition Dependence of Secondary Organic Aerosol Formation From Terpenes
Secondary Organic Aerosols (SOA) are formed in the atmosphere after oxidation of a volatile precursor. SOA comprise approximately 1/3 of the organic aerosol mass, and organic aerosol in turn is often the single most important fraction of total aerosol mass. SOA are also often semi volatile, with substantial mass fractions in both the condensed and vapor phases. The most important source of SOA appears to be ozonolysis of terpenes, including monoterpenes (C$_{10}$H$_{16}$) and sesquiterpenes (C$_{15}$H$_{24}$). Our knowledge of SOA mass yields from terpene ozonolysis is limited in two major ways. First, there are few data constraining the temperature dependence of SOA yields, and second, ozonolysis yields are typically only well constrained under low NO$_x$ conditions. We shall address both of these limitations here. First, to constrain the temperature dependence of SOA production we must separate the effect of temperature on the chemistry itself from the effect of temperature on the vapor pressure. Our solution is to carry out ozonolysis in a temperature-controlled smog chamber at a fixed temperature ranging from 15 to 40 $^o$C and then to vary the chamber temperature through its full range after the chemistry has run to completion. Bulk SOA mass yields are determined through SMPS measurement, while composition is determined via periodic filter sampling followed by solvent extraction derivatization GC/MS. In this way we are able to observe partitioning (vapor pressure) effects in the ozonolysis of d-limonene, culminating in large yields of SOA near 20 $^o$C, followed by a shift in chemistry at lower temperature causing lower SOA yields. Second, to constrain the VOC/NO$_x$ dependence of SOA production, we also carry out experiments in the presence of NO$_x$, under near UV illumination to maintain a stable NO/NO$_2$ ratio. Basic functional group levels (e.g.\ carbonyls vs nitrates) are monitored via FTIR analysis of teflon filter samples. Consistent with expectations, SOA yields decrease with increasing NO$_x$, as progressively more nitrates are observed on collected aerosols.
A41A-0008 0800h
Aerosol Growth Observed in a Sierra Nevada Pine Forest and its Relationship to Biogenic Volatile Organic Compounds and Anthropogenic Pollutants
Forested ecosystems emit significant amounts of volatile organic compounds (VOCs), which impact atmospheric photochemistry through ozone and aerosol production. To study biosphere-atmosphere exchange of ozone and VOCs and their effects on aerosol formation and processing, we have conducted a study at the Blodgett Forest Research Station in the Sierra Nevada Mountains of California. The research site includes automated instrumentation for the in-situ measurement of concentration and biosphere-atmosphere flux of VOCs, ozone, aerosol integrated and size resolved instrumentation, and meteorological variables. The meteorology at the site is fairly consistent with daytime upslope flows carrying pollutants from the Sacramento Valley and evening drainage flows bringing cleaner air from the Sierra Nevada Mountains. Preliminary results have shown that particle concentrations are correlated with both biogenic (alpha-pinene and isoprene) and anthropogenic (toluene) VOC concentrations. In addition, the growth of small, nuclei model particles (<20nm) has been observed just after noon on many days. This presentation will focus on the diurnal aerosol patterns observed at the site, the relative importance of anthropogenic and biogenic sources for aerosol concentrations, and the relationships between VOC measurements, meteorology, and particle formation events. Experimental yield data will be used with measured fine mode aerosol data and measured VOC concentration gradients and fluxes to investigate whether oxidation of various organic precursors can account for the observed aerosol growth.
A41A-0009 0800h
An Electrostatic Sampler to Collect Ultrafine Particles: Design, Calibration and Application.
Ultrafine particles ($<$100 nm) are of increasing importance due to their adverse health effects and their impact on the global climate. However, there is still a lack of knowledge of the characteristics of ultrafine particles in ambient air. Single particle analysis using TEM (Transmission electron microscopy) allows to gather the most comprehensive data - such as morphology, chemistry and crystallinity - of ultrafine particles. Most measurement devices are designed to collect particles for bulk analytical methods, such as gravimetric or bulk chemical analysis. Thus, these devices are not well suited for collection of particles for single particle analysis. Due to their low mass ultrafine particles cannot be collected using inertial impaction at ambient conditions. It is possible to sample ultrafine particles using low pressure impactors, however, sampling with an impactor results in a heterogeneous grain size distribution on the substrate and thus a quantification of particle abundances based on single particle analysis is difficult. A possibility to overcome this problem is to use an electrostatic sampler, as presented in this study. Particles are positively charged using a corona charger and deposited in an electric field directly onto a TEM grid. Calibration runs using either monodisperse Au, W or NaCl particles (30 - 300 nm in diameter) have been performed. For that purpose, the aerosol was split into two parts, one part being directed to the electrostatic sampler, the other to a CPC (condensation particle counter). Particles deposited on the TEM grid were counted using an ESEM (environmental scanning electron microscope). The total amount of particles deposited on the TEM grid was estimated based on the ESEM measurements and compared to the results from the CPC. The calculated sampling efficiency was roughly 3%. Due the radialsymmetric electric field, the amount of deposited particles was highest in the center and lower towards the rim of the TEM grid. The sampler was additionally tested using oil combustion particles. In these experiments, 10 nm size particles were successfully sampled on TEM grids. Thus, the presented electrostatic sampler is well suited for the collection of ultrafine particles from ambient air as well as from test facilities. It will, thus, be of great benefit for applications related to single particle analysis of ultrafine particles.
A41A-0010 0800h
Measurements of Free Tropospheric Aerosol and Ice Nuclei at Storm Peak Laboratory with an Aerodyne Aerosol Mass Spectrometer (AMS)
As part of the INSPECT II field campaign, a multi-institution research team spent six weeks in the spring of 2004 at a mountaintop laboratory with an extensive suite of aerosol measurement equipment including an Aerodyne Aerosol Mass Spectrometer (AMS). The Storm Peak Laboratory is located on the top of Mt. Werner on the grounds of Steamboat Springs ski resort at 10,530 feet above sea level. In the typical diurnal cycle westerly flow transports air up from the populated valley below during the day and free tropospheric air subsides over the site at night. We will present a characterization of the size dependent chemical composition of the background aerosol over the six week campaign from the AMS data. Our observations of the free tropospheric aerosol include the dominance of organics in its chemical composition and some nucleation and growth events. Comparisons will also be made of aerosol composition data provided by two different mass spectrometric techniques (AMS and Particle Analysis by Laser Mass Spectrometry (PALMS)). In addition, several distinct events were observed including the outflow from a wild fire in the Poudre Canyon near Fort Collins in Colorado's Front Range. Lastly, the AMS was used to help characterize the chemical composition of ice nuclei, selected by a Continuous Flow Diffusion Chamber - Counter flow Virtual Impactor (CFDC - CVI).
A41A-0011 0800h
Measurements of Submicron Aerosols in Tokyo using the Aerodyne Aerosol Mass Spectrometer (AMS)
We have conducted ground-based measurements of submicron aerosols in Tokyo using the Aerodyne Aerosol Mass Spectrometer (AMS) since February 2003. Size-resolved chemical composition of non-refractory aerosol (vaporized at 600C under high vacuum) was measured with a time resolution of 10 minutes. The mass concentrations of inorganic species (nitrate, sulfate, chloride, and ammonium) measured by the AMS showed good agreement with those measured by a Particle-Into-Liquid Sampler combined with an Ion Chromatography analyzer (PILS-IC). The mass concentrations of organic compounds measured by the AMS correlated well with organic carbon (OC) mass measured by a Sunset Lab semi-continuous thermal-optical carbon analyzer. The ratio of AMS organics to OC was consistent with the organic matter (OM) to OC ratios that were previously reported by other studies. The correlation of AMS organics with carbon monoxide (CO) and the intensity of a marker peak (m/z 44) were used to estimate the mass concentrations of secondary organic aerosols (SOA). The estimated SOA concentrations showed distinct diurnal variation and correlated with ozone in daytime.
A41A-0012 0800h
Initial Results of Airborne Measurements of PM1.0 Inorganic Ions and Water Soluble Organic Carbon During the New England Air Quality Study, Summer 2004
The Particle-Into-Liquid Sampler (PILS) was deployed on NOAA's WP-3D aircraft during the summer of 2004 in support of the Intercontinental Transport and Chemical Transformation - New England Air Quality Study. Concurrently, the PILS was also deployed on NASA's DC-8 in as part of the Intercontinental Chemical Transport Experiment North America (INTEX-NA). Throughout the duration of the study, semi-continuous measurements of fine (PM1.0) inorganic ion components (sodium, ammonium, potassium, calcium, magnesium, chloride, nitrate, and sulfate) were made on both aircraft and water-soluble organic carbon on the NOAA WP-3D. The measurement domain was extensive, with spatial distribution encompassing Northern Quebec, the Azore Islands, the Gulf of Mexico, and the upper Midwest of the United States. Intensive sampling of the urbanized metropolitan areas of the Northeast (e.g. Boston-New York-Washington corridor), as well as biomass plume studies, were also conducted. Within this measurement domain, a range of aerosol sources were sampled, including fresh power plant plumes, relatively fresh and aged urban plumes, and aged biomass plumes. In this paper, we will present an overview of the measurements, compare the bulk chemical data to fine particle volumes, investigate spatial distributions, compare measurements to surface sites, and identify unique plumes encountered during the mission.
A41A-0013 0800h
Multiwavelength In-situ Aerosol Extinction, Scattering and Absorption During the NEAQS-ITCT 2004 Field Campaign
{\it In-situ}, three wavelength-measurements of aerosol extinction, scattering and absorption of the New York/Boston urban pollution outflow were carried out aboard the NOAA research vessel {\it Ronald H. Brown} during the NEAQS-ITCT 2004 (New England Air Quality Study-Intercontinental Transport and Chemical Transformation Study) field campaign. Aerosol extinction, scattering and absorption-coefficients were measured using an Optical Extinction Cell (OEC) coupled with an integrating nephelometer and multiwavelength, filter-based absorption photometers (PSAP), respectively, operating on a common inlet at low relative humidity ($<$ 30% RH). The samples were limited to particles $<$ 1$\mu$m to focus on the largely pollution related accumulation mode and to minimize the uncertainty due to highly variable near-surface seasalt aerosol. Additionally, two nephelometers and a second PSAP measured the total and sub-micron scattering and backscattering and total absorption, respectively, at $\sim$ 60% RH. Combining the aerosol scattering and extinction coefficients $\sigma_{sp}$ and $\sigma_{ep}$ yields the single-scattering albedo, $\omega=\sigma_{sp}$/$\sigma_{ep}$, and the absorption coefficient, $\sigma_{ap}=\sigma_{ep}-\sigma_{sp}$. Both are key parameters in estimating aerosol direct radiative forcing and were measured in-situ by the coupled OEC/nephelometer-system. Determining $\sigma_{ap}$ by difference using the OEC and nephelometer data and comparing it with the filter based $\sigma_{ap}$ moreover provides a test of the methods and their uncertainties. Additional parameters to be derived from the OEC and nephelometer measurements are the $\AA$ngstrom exponents for $\sigma_{ep}$, $\sigma_{sp}$, and $\sigma_{ap}$, and the hemispheric backscattering ratio. These are important for relating in-situ optical properties to those sensed remotely, eg., ground optical depth from sun photometry or satellite measured radiance and extinction profiles from lidar. The suite of parameters and wavelength dependence provide constraints on model building and closure studies with physical and chemical aerosol properties. The measured and derived data will be discussed in relation to other measurements and the prevailing meteorology and the upwind sources.
http://saga.pmel.noaa.gov/NEAQS-ITCT/
A41A-0014 0800h
In-Situ Measurements of Aerosol Optical Properties using new Cavity Ring-Down and Photoacoustic Instruments and Comparison with more Traditional Techniques
Carbonaceous species (BC and OC) are responsible for most of the absorption associated with aerosol particles. The amount of radiant energy an aerosol absorbs has profound effects on climate and air quality. It is ironic that aerosol absorption coefficient is one of the most difficult aerosol properties to measure. A new cavity ring-down (CRD) instrument, called Cadenza (NASA-ARC), measures the aerosol extinction coefficient for 675 nm and 1550 nm light, and simultaneously measures the scattering coefficient at 675 nm. Absorption coefficient is obtained from the difference of measured extinction and scattering within the instrument. Aerosol absorption coefficient is also measured by a photoacoustic (PA) instrument (DRI) that was operated on an aircraft for the first time during the DOE Aerosol Intensive Operating Period (IOP). This paper will report on measurements made with this new instrument and other in-situ instruments during two field recent field studies. The field study was an airborne campaign, the DOE Aerosol Intensive Operating Period (IOP) flown in May, 2003 over northern Oklahoma. One of the main purposes of the IOP was to assess our ability to measure extinction and absorption coefficient in situ. This paper compares measurements of these aerosol optical properties made by the CRD, PA, nephelometer, and Particle Soot Absorption Photometer (PSAP) aboard the CIRPAS Twin-Otter. During the IOP, several significant aerosol layers were sampled aloft. These layers are identified in the remote (AATS-14) as well as in situ measurements. Extinction profiles measured by Cadenza are compared to those derived from the Ames Airborne Tracking Sunphotometer (AATS-14, NASA-ARC). The regional radiative impact of these layers is assessed by using the measured aerosol optical properties in a radiative transfer model.
A41A-0015 0800h
Retrieving Aerosol Properties by Inverse Methods With Data From Several Instruments
Despite long standing effort, there is still a considerable uncertainty associated with the direct climate forcing of atmospheric aerosol. This is partly due to microphysical aerosol properties which influence the aerosol radiative forcing but cannot be measured directly. Among these properties are the state of mixture of particulate black carbon (BC) and the aerosol asymmetry parameter. The BC state of mixture significantly influences the absorption efficiency of BC and as a result the heating rate of the airmass that contains the BC aerosol. It will be investigated how the approach of combining the information of several instruments using inverse methods can serve to retrieve these microphysical parameters. Many methods for measuring one aerosol property suffer from inter-dependencies to other aerosol properties. For example, when measuring the particle size distribution with an optical particle counter (OPC), assumptions on the shape, morphology, and chemical composition of the aerosol have to be made which determine the optical model and the aerosol refractive index used during data interpretation. The interpretation of nephelometer data in turn needs to make assumptions on the particle size distribution if the truncation of the nephelometer is to be corrected precisely. Using these instruments in parallel on the same aerosol and combining their data into a single retrieval can not only eliminate the named inter-dependencies but additionally yield information on the refractive index and indication on the chemical composition. In this presentation, the method is used to design a more complex combination of mostly optical measurements using existing or modified existing instruments that yields information about the state of mixture of BC. The combination involves measuring the particle size distribution, the bulk chemical composition, the spectral scattering and backscattering coefficients, and the spectral absorption coefficient in a spectral range between 0.3~$\mu$m and 1~$\mu$m wavelength. The optical aerosol properties in the near UV are of particular importance for this application, meaning that existing instruments would need to be modified to implement the measurement strategy. As an example, the method is capable of retrieving the BC state of mixture for continental aerosol with an absorption coefficient of 4~(Mm)$^{-1}$. Deploying this combination of instruments in the field would yield the information on aging of BC which is needed by climate models to improve the assessment of the BC climate effect. Also, it will be shown how the method can be used to retrieve the aerosol asymmetry parameter from a limited set of standard instruments as used by the aerosol monitoring network of the National Oceanic and Atmospheric Administration's Climate Monitoring and Diagnostics Laboratory. This set consists of a three wavelength scattering and backscattering nephelometer and a single wavelength absorption photometer which are alternately operated with 1~$\mu$m and 10~$\mu$m cut-diameter impactors . Together with the extinction coefficient and single scattering albedo readily calculated from this data-set, the retrieved asymmetry parameter yields a complete set of optical properties for calculating the aerosol direct effect on radiative transfer. With the available instruments becoming more and more accurate, retrieval by inverse methods is a means that promises to help reducing the uncertainty of the direct aerosol climate effect.
A41A-0016 0800h
Optical, physical and chemical properties of aerosols at an elevated site (Kleiner Feldberg) in central Europe during the FACE-2004 campaign
As part of the Feldberg Aerosol Characterization Experiment (FACE-2004) optical, physical and chemical measurements of fine aerosols ($<$1.0 $\micron$) were performed at a mountaintop in central Europe. A 1-month long observational campaign was conducted at Kleiner Feldberg in Germany (8.4413 E, 50.2249 N, 810 m asl) from 17 July to 18 August in summer of 2004 with the intensive phase lasting from 19 July to 4 August. Measurements of light scattering by aerosols at dry (at 545 nm), ambient (450, 550 and 700 nm) and humid (545 nm) conditions were conducted during the campaign. In addition, the light absorption coefficient (532 nm) was measured at ambient conditions. The chemical analysis of the aerosols is made using the aerosols mass spectrometer. The extensive aerosols optical parameters (scattering and absorption coefficients) are used to calculate the intensive optical parameters (single scattering albedo and Angstrom exponent). Measurements of aerosol mass concentration (PM 1.0), size distribution, number concentrations and chemical composition are used to retrieve mass scattering and absorption efficiencies as well as to facilitate interpretation of the optical measurements. In addition, observations of carbon monoxide (CO), carbon dioxide (CO$_2$) and meteorological parameters are being investigated to trace the nature and source of the air parcels. These observations suggest that this site shows a signature of mixed weather condition in July-August. In addition to the locally-polluted and regional-background air masses types, there were some events of clean periods when the aerosol mass and scattering coefficient went down to very low levels. The observed size distributions indicate that the most of the particles were below 400 nm in diameter with a number peak at about 80 nm. The observed range (with the averages in parenthesis) of ambient scattering coefficient (550 nm), mass concentration, CO and CN during the campaign were 1-150 (32) Mm$^-$$^1$, 1-80 (16) 10$^-$$^6$g m$^-$$^3$, 120-350 (200) ppb and 1050-40000 (4437) cm$^-$$^3$ respectively. The average mass scattering efficiency at 550 nm is about 2 m$^2$ g$^-$$^1$. Large hygroscopic growth in scattering coefficient is consistent with the presence of significant amount of water soluble inorganic (sulphate, nitrate, ammonium) mass. The optical, physical and chemical properties of aerosols for different meteorological conditions will be presented.
A41A-0017 0800h
Altitude-Dependent Aerosol Optical Depths and Number Densities at El Teide, Tenerife in Canary Islands
Two intensive observing periods were performed during March 23, 2003 and March 18, 2004 at El Pico de Teide, Tenerife in Canary Islands. Measurements of aerosol optical thickness (AOT) and number density (ND) were obtained. The Microtops II ozone-monitor sunphotometer was used to measure aerosol optical thickness. A laser particle counter was used to measure number density. The data presented in this paper provides a picture of the relative changes in the vertical aerosol distribution along the ascent to the summit El Teide. We discuss the relationship between optical depth, vertical distribution of aerosols, air mass source region, and vertically-resolved size distribution for the two cases in spring during March 2003 and 2004.
A41A-0018 0800h
Ionic Composition of Atmospheric Aerosols in Chicago
Ions in atmospheric aerosols were investigated in Chicago under various meteorological conditions. Special emphasis was placed on the lake breeze, an event regularly occurring in Chicago, but most pronounced during the summer months. Aerosol samples were collected by filtration at Loyola University Chicago Air Station (LUCAS) during 2002 and 2004. The station is located in close proximity to Lake Michigan and therefore excellently suited to study the influence of the lake breeze on local air pollution. The samples were analyzed for anions and cations, including low molecular weight organic acids, using ion chromatography after validation of collection and analysis method. In addition, reactive trace gases were monitored to determine the oxidation power of the local atmosphere during aerosol collection. Results showed that sulfate, nitrate and ammonium were the most abundant ions in Chicago air. In general, highest ion concentrations were associated with Southwest wind transporting pollution from the city to the station. Ammonium to sulfate ratios were highest during lake breeze events indicating a processed air mass. This was supported by elevated ozone levels. Finally, we could distinguish between three cases where sulfate, nitrate and oxalate concentrations were found dependent of temperature as well as ozone and nitrogen oxide mixing ratios.
A41A-0019 0800h
Characterization of Airborne Particulate Matter During Lake Breeze Events in Chicago
Particulate air pollution is a constantly growing problem in urban areas. The particulate matter present in pollution events contains often toxic or health impacting species and is responsible for low visibility, might be triggering respiratory diseases like asthma, and can play an important role in formation or duration of smog events. It is not unlikely that local meteorological events such as lake breezes might exacerbate a pollution situation by transporting processed air masses containing secondary pollutants back to shore. To characterize pollution patterns associated with lake breeze events in Chicago, aerosol filter samples were collected for determination of elemental and ionic aerosol composition before and during a lake breeze. Sampling took place at Loyola University Chicago Air Station (LUCAS) during the summer months of 2002 to 2004. The station is located in close proximity to Lake Michigan and therefore ideally suited to observe this event. In addition to atmospheric aerosol sampling, reactive trace gases were monitored and an automated weather station recorded major meteorological parameter. The particulate samples were analyzed by total reflection X-ray fluorescence after digestion of the filter matrix to quantify the elemental concentration in the aerosol and by ion chromatography for determination of ionic species. The results showed that concentrations of some elements, most notably sulfur, increased during a lake breeze significantly as opposed to reference days without a lake breeze. The sulfate concentrations determined by ion chromatography confirmed these findings. High sulfate concentrations are indicative for a processed air mass transported by the lake breeze to the measurement station. As the same air mass was residing above Lake Michigan before onset of the lake breeze, we think that photochemical reactions, initiated by intense sunlight in summer, converted primary species into secondary ones, which were brought back by the lake breeze. This was supported by an increase in nitrate concentrations and elevated ozone mixing ratios shortly after the lake breeze did set in. The results obtained suggest that a lake breeze pattern like occurring in Chicago could have major implications for coastal environments with respect to local climate and human health.
A41A-0020 0800h
A Particulate Matter Air Quality Forecast Modeling System for the Northeast U.S. -Comparisons with July 2001 and January-February 2004 EPA Supersite Field Intensive Data
An air quality forecast modeling system (AQFMS), which has run reliable 24-hr oxidant air quality forecasts for the Northeast United States for over two years, has been further developed to consider the prediction of PM air quality in the region. The AQFMS was designed to operate with forecasted meteorological fields from either of two mesoscale meteorological models, the Penn State/NCAR Mesoscale Model MM5 or the University of Athens' ETA-SKIRON meteorological model. The meteorological fields are used to drive the Comprehensive Air Quality Model with Extensions (CAMx), a photochemical air quality simulation model. This prototype system has been upgraded to incorporated primary particulate emissions and rudimentary secondary formation mechanism for sulfate, nitrate and organic particulate matter since the beginning of year 2004. Archived meteorological forecasts from ETA-SKIRON, generated as part of the PMTACS-NY Supersite Summer 2001 Field Intensive, have been used to re-run the forecasts with the modified chemical mechanical mechanism within the CAMx4 model and the updated emissions generated by the SMOKE emission model based on EPA's National Emission Inventory 1999(NEI99) and Biogenic Emissions Inventory System (BEIS version2). Preliminary assessment of the PM air quality forecast from summer 2001 rerun and the forecast from January-February 2004 are presented. The forecasted PM2.5 total mass and the speciation for the northeast and New York metropolitan areas for the two seasons are compared with measurements performed during the EPA Summer 2001 and January-February 2004 Supersite intensive field campaigns to assess the performance of this modeling system in predicting particulate matter for different seasons and the uncertainties therein.
A41A-0021 0800h
Characterizing Particle Morphology and Density by Combining Aerosol Measurements with Application to Modeling Ambient Aerosol Data from Pittsburgh Air Quality Study (2002) and ICARTT-2004
Different on-line particle sizing techniques report different "equivalent diameters." For example differential mobility analyzers (DMAs) report particle mobility diameter (d$_{m}$), while a number of recently developed instruments (such as the Aerodyne Aerosol Mass Spectrometer, or AMS) can measure vacuum aerodynamic diameter (d$_{va}$). Particle density and morphology have important effects on diameter measurements, leading to differences in the measurements of different instruments that can be exploited to extract information on these particle properties. This Poster presents a framework for combining the information content of different diameter measurements into a single coherent mathematical description of the particles. We show that combining d$_{m}$ and d$_{va}$ measurements for the same particle population allows the placing of constraints on particle density, dynamic shape factor ($\chi$), and fraction of internal void space. Additional information from other measurements, and/or adding some assumptions allows the determination of all parameters. In particular, particle volume and mass can be determined from d$_{m}$ and d$_{va}$ measurements if the particle density is known, and with the assumption $\chi$ does not depend on the flow regime. The amount of information that can be deduced from the combination of d$_{m}$ and d$_{va}$ measurements for various model particle types is shown. A computer model to integrate ambient aerosol measurements from a scanning mobility particle sizer (SMPS) and an AMS is also developed based on the framework developed. Test cases from the Pittsburgh EPA Supersite (2002) are presented. The model fits the ambient data with 3 internally mixed lognormal modes of independent composition utilizing a Levenberg-Marquardt algorithm. This analysis provides information on shape and density of each of the three fitted modes of the ambient aerosol. The model will also be applied to recent results from Chebogue Point, Nova Scotia (ICARTT-2004) with the resulting model output used as an input to a CCN formation model. The modeled aerosol CCN activation will be compared to the measured CCN activation data from the same time period.
A41A-0022 0800h
Scanning Electron Microscope Evaluation of Aerosol Speciation in New York City: Metal Content in Sulfate Aerosols Relative to Total Suspended Particulates
Total suspended PM2.5 particulates measured in northern New York City using a METONE beta-attenuation mass monitor exhibit a local maximum in April 2004 of 29 micrograms per cubic meter. This increase accompanies an April-to-July decrease in trace metals, Ti, Fe, Cu, Zn, Ba, measured for the total suspended particulates by x-ray fluorescence and atomic absorption (AA) spectroscopy (representative May values: 10 mg/m3 Ba, 8.9 mg/m3 Zn, and 0.7 mg/m3 Cu). Scanning electron microscopy and energy dispersive microanalyses (SEM/EDS) of trace-metal-enriched filters reveals that metals are present as both major element and trace element components of aerosols. The dominant major element species include metals, metal sulfides and metal oxides, whereas the trace metals occur principally in sulfates, carbonates and organo-sulfates. Mass balance calculations for the principle species, sulfate-rich aerosols (ca. 50-80% of the population), indicate that the approximately 5% total trace metals in sulfate crystals by SEM/EDS agrees closely with the measured total suspended particulate values obtained by AA for the same samples. Sulfate aerosols comprise a complex class that varies chemically from a nitrogen (ammonium)-based to calcic composition (approximately CaSO4-2.5H2O by SEM/EDS). Compositions include minor classes of alkali-enriched sulfates and iron sulfates. Sulfate accumulation also occurs during impaction resulting occasionally in 20 micron aggregates that vary systematically from a 10 micron calcic sulfate core to an ammonium-carbonate rim. A thermo-gravimetric study of the sulfate aerosols shows that approximately 50 to 80 percent of the sulfate is decomposed by igniting the quartz filters to 500°C; degassing points at 250°C and 320°C are indicative of the destruction of relatively amorphous alkali-nitrogen and related sulfates whereas temperatures in excess of 600°C are required to decompose the crystalline metal sulfates. Residual metals accumulate oxygen during post-320°C firing resulting in a weight recovery of approximately 30%. Preliminary analysis of the back-trajectories of metal-sulfate-enriched air masses is consistent with enrichment from industrial sources.
A41A-0023 0800h
Simultaneous Scanning LIDAR and DOAS Measurements Obtained from High-Sulfur Smelter Emissions During SUDS2004
A mobile scanning LIDAR facility known as RASCAL (Rapid Acquisition SCanning Aerosol Lidar), owned and operated by the Meteorological Service of Canada was deployed for a two week study in June 2004 known as SUDS2004 (Sudbury Study 2004). Two miniaturized spectrometers with a combined range of 295 to 850 nm, under development by Resonance Ltd., were incorporated into RASCAL by sharing the same optical path. The UV absorbances for sulfur dioxide between 300 and 320 nm, as recorded by the spectrometers, were converted to column densities using gas calibration cells and the DOAS technique. This provided simultaneous LIDAR and UV/VIS spectral scanning profiles of emissions from the INCO superstack plume, the second tallest (381 m) industrial stack in the world. The superstack discharges gases and particulates from metal smelting operations with an annual sulfur discharge rate of approximately 2000 kilotons, making this an ideal analog to volcanic gas emissions. To qualify the behavior of gas transport in aerosol plumes, the sulfur dioxide spectral results were combined with the RASCAL three-dimensional real-time images which show the complex mixing behavior of the plume and the boundary layer dynamics. Initially, the ground site was approximately 3.4 km northeast of the superstack on an adjacent hill to provide an unobstructed view of the stack plume for several wind directions. This location allowed for evaluation of both spatial and temporal variations in both parameters. Additionally, the combined system was operated in a zenith-pointing mode, being located directly under the smelter plume. Preliminary results show a strong correlation between sulfur dioxide column concentrations and aerosol concentration.
A41A-0024 0800h
Global Aerosol Measurements from the Geoscience Laser Altimeter System
The Geoscience Laser Altimeter System (GLAS) on board the Ice, Cloud and Land Elevation Satellite provides space-borne laser observations of distribution of atmospheric aerosol layers. Full global observations began in October 2003 and have continued in three four-to-six week operation periods since. Aerosol profile measurement are made at two wavelengths, 532 and 1064 nm, and data products are produced for the height distribution of aerosol scattering, the boundaries of layers including multiple and elevated layers, the optical depth of layers and calculated aerosol extinction. The data products are now in release through the NASA EOS data distribution system. Global summaries of the aerosol distribution observed by GLAS have been produced and are compared to other satellite retrievals such as MODIS. The GLAS aerosol data products will be described and new results on the nature of the global aerosol distribution will be presented.
http://nsidc.org/daac/icesat/
A41A-0025 0800h
The Vertical Dimension In Air Quality Measurements
At present, air quality measurements in general and PM2.5 measurements in particular lack the three-dimensional spatial and temporal resolution that could lead to better understanding and prediction of air quality. The use of satellite products such as the GOES Aerosol and Smoke Product (GASP) and the MODIS optical depth product (MOD04L2) as surrogates for fine particle mass is appealing because of the broad spatial coverage and their rapid updating of these satellite-based measurements. However, measurements made with the UMBC Elastic Lidar Facility (ELF) have shown that poor correlation between the satellite products, which are column measurements, and the PM2.5 measurements on the ground often occurs whenever an aerosol layer is aloft rather than near the ground. These results show that an understanding of the vertical structure of aerosol plumes that can be provided by a lidar system is essential for the understanding and modeling of pollution events and the relationship between the ground-based and satellite-based instruments. This summer, UMBC has been evaluating and comparing several ground- and satellite-based measurements of aerosol optical depth (AOD) with an eye towards the use of these products as a surrogate for PM2.5 measurements. We have investigated the ground-based lidar measurements of AOD with ELF, the GOES product GASP, done in cooperation with NOAA/NESDIS, and the MODIS optical depth product from both the Terra and Aqua satellites. While the results are preliminary, we have noted that overall the GASP and MODIS optical depths are generally not well correlated but MODIS is often in agreement with the ELF lidar results. We have shown previously, for the U.S. Midwest and east, there is reasonable correlation (r2.gt.0.8) between MODIS AOD column measurements and PM2.5 measurements. Unfortunately elsewhere, the correlation between the satellite measurements and the air quality measurement is poor and there are times when the AOD and PM2.5 are not well correlated even in the East. In this talk we will present both a summary of our comparisons and a discussion of specific occurrences of agreement and disagreement including a smoke plume in Baltimore from the Alaska forest fires earlier this summer.
http://alg.umbc.edu
A41A-0026 0800h
Aerosol Optical Thickness Measurements Of The Sky At San Marcos And Seguin, Texas, During 2003
Climatologists, environmental chemists, meteorologists and geographers have investigated the effects of aerosols on the global climate for more than two decades. One of the key parameters in these studies is the optical thickness property of various kinds of aerosols. Since the density, composition and optical properties of aerosols in a column through the atmosphere can change rapidly and unpredictably, careful measurements should be taken over a long period to recognize patterns that might be associated with urban, regional, and continental climatic changes. In this poster, we discuss preliminary results of Aerosol Optical Thickness measurements by two sun photometers at or near solar noon over a period of six months at San Marcos, Texas. We also compare our data with observations from researchers in neighboring cities. We will conclude by discussing the effects on our measurements of regional air pollution events.
A41A-0027 0800h
Uncertainties of clear sky pixels in constructing surface reflectance for aerosol retrieval
The retrieval algorithms for the aerosol optical depth(AOD) from geostationary satellites usually assume clear sky pixel from the background composite which is constructed from the minimum visible reflectance during the previous 21 days to one month. The observed minimum reflectance are regarded as the aerosol free conditions for the pixel and are compared with the top-of-the-atmospehre reflectance from radiative transfer models with zero aerosol optical depth to retrieve surface reflectance. These surface reflectance affects the accuracy of AODs retrieved. Thus, in this study, using the ground-based measurements such as Rotating Shadowband Radiometer at Yonsei University, Seoul are analyzed to assess the uncertainties of the minimum reflectance composite in detail. From the time series of the ground-based dataset, minimum total optical depths(TOD) for the previous one months are obtained and compared with Rayleigh plus ozone optical depths. The result shows significant deviation from clear sky conditions especially in polluted areas from the minimum composite even during the previous 60 days.
A41A-0028 0800h
Aerosol Retrieval in the Troposphere and Stratosphere with OSIRIS Limb Scattered Sunlight Measurements
The currently operational Canadian-built OSIRIS (Optical Spectrograph and InfraRed Imaging System) instrument on the Odin spacecraft includes a single line-of-sight spectrograph that measures limb scattered UV and visible sunlight with 1 nm resolution. Height profiles of the limb radiance from the upper troposphere and stratosphere are obtained at these wavelengths by scanning the optic axis of the instrument. These measurements are used to derive aerosol extinction and number density profiles in the upper troposphere and the stratosphere by using currently accepted climatological values for aerosol particle size and distribution and a radiative transfer model. The limb observation technique in combination with the sun-synchronous Odin orbit allows for a global retrieval of aerosol extinction over a relatively short time period on the order of a few days. This work presents the aerosol retrieval technique from the OSIRIS limb scattered sunlight measurements and provides global distributions of aerosol extinction that show evidence of upper troposphere-lower stratosphere exchange and seasonal trends.
A41A-0029 0800h
Effects Of Aerosol Size Distribution And Vertical Profile On The Polarization Spectra In The Oxygen A-Band
A successive order of scattering vector radiative transfer code was used to simulate the high-resolution polarization spectra in the oxygen A-band. The effects of aerosol size distribution and vertical profile on the radiance and polarization at the top and bottom of the atmosphere were analyzed. Polarized radiances are dominated (>95%) by the first and second orders of scattering. The polarization due to higher orders of scattering can be simply parameterized. These insights provide a methodology for developing a fast forward model of vector radiative transfer and for retrieval algorithms to derive information of aerosol size distribution and vertical profile from high-resolution oxygen A-band measurements
A41A-0030 0800h
Aerosol Anion Analysis Using PDMS Based Microchip Capillary Electrophoresis
We developed a lab-on-a-chip capillary electrophoresis (LOC-CE) system to analyze important inorganic ions such as nitrate and sulfate, found in ambient aerosols. Capillary electrophoresis (CE) is a simple technique for separation and measurement of analytes in solution. Ions are separated, depending on their size and charge, in an electrolyte filled capillary under an electric gradient field. Miniaturized CE systems offer enhanced separation speed while maintaining high separation efficiency and permit multi-channel analysis, presenting great potential for building sensitive, portable, and economical instruments for environmental analysis. The microchip CE system created in our laboratory is simple and effective. The chip is made of PDMS (polydimethylsiloxane). The separation channel is approximately 4.0 cm long and coated with polybrene to modify electroosmotic flow. The electrolyte is composed of 10 mM formic acid adjusted to pH 3. Conductivity detection is used to quantify concentrations of target ions. Sample analysis times are approximately 2 minutes. System calibration was established using standard solutions and detection limits of sulfate and nitrate were determined. Day-to-day and chip-to-chip reproducibility was also evaluated. We applied the microchip CE system to analyze several winter aerosol samples collected in Bondville, IL. Aqueous extracts of these aerosol samples were also analyzed by conventional ion chromatography. Quantifications of sulfate by the CE and IC show good agreement. Additional testing revealed the capability of the microchip CE system to successfully analyze aerosol microdeposits made by impaction of the droplet stream emerging from a water condensation particle collector (WCPC). This is a key step in creating an integrated, on-line particle collection and analysis system.