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Sachio Ohta – One of the best experts on this subject based on the ideXlab platform.

  • Influence of submicron absorptive Aerosol on Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS)‐derived marine reflectance during Aerosol Characterization Experiment (ACE)‐Asia
    Journal of Geophysical Research, 2003
    Co-Authors: Hajime Fukushima, Robert Frouin, B. Greg Mitchell, Itsushi Uno, Tamio Takamura, Sachio Ohta
    Abstract:

    [1] Sea-viewing Wide Field-of-view Sensor observation of the east Asian seas during the March–April 2001 Aerosol Characterization Experiment-Asia shows large areas of underestimated or even negative water-leaving radiance in the blue. To investigate the cause of the problem, three cloud-free matchup stations around Japan were analyzed, where in situ measurements were made onboard R/V Ronald H. Brown at the time of satellite overpass. Using an optimization method, information on the possible composition of Aerosols was obtained from sky radiance data collected onboard the ship. An iterative radiative transfer simulation was carried out in an attempt to reproduce the satellite-measured top-of-atmosphere reflectance. The resulting water reflectance and Aerosol optical thickness (AOT) agreed well with in situ measurements when the effect of submicron absorbing particles was considered in the radiative transfer simulation. The error in the retrieved water reflectance was much decreased, with average values of about 6% at 412 and 443 nm for the three stations. The effect of the Asian dust was also simulated in comparison with that of small absorptive Aerosols. The underestimation could not be solely attributed to Asian dust. It was also found that at one of the stations, where the presence of dust Aerosols was anticipated, an Aerosol model mixed with both dust and soot improved the accuracy of the estimated AOT compared with the case of soot as the only absorptive Aerosol (error of 13% at 865 nm instead of 44%). Submicron absorbing particles, in addition of the Asian dust, should be considered in the optical remote sensing of east Asian waters.

  • Wide Field-of-view Sensor (SeaWiFS)-derived marine reflectance during Aerosol Characterization Experiment (ACE)-Asia
    , 2003
    Co-Authors: Hajime Fukushima, Robert Frouin, B. Greg Mitchell, Itsushi Uno, Tamio Takamura, Sachio Ohta
    Abstract:

    [1] Sea-viewing Wide Field-of-view Sensor observation of the east Asian seas during the March–April 2001 Aerosol Characterization Experiment-Asia shows large areas of underestimated or even negative water-leaving radiance in the blue. To investigate the cause of the problem, three cloud-free matchup stations around Japan were analyzed, where in situ measurements were made onboard R/V Ronald H. Brown at the time of satellite overpass. Using an optimization method, information on the possible composition of Aerosols was obtained from sky radiance data collected onboard the ship. An iterative radiative transfer simulation was carried out in an attempt to reproduce the satellitemeasured top-of-atmosphere reflectance. The resulting water reflectance and Aerosol optical thickness (AOT) agreed well with in situ measurements when the effect of submicron absorbing particles was considered in the radiative transfer simulation. The error in the retrieved water reflectance was much decreased, with average values of about 6% at 412 and 443 nm for the three stations. The effect of the Asian dust was also simulated in comparison with that of small absorptive Aerosols. The underestimation could not be solely attributed to Asian dust. It was also found that at one of the stations, where the presence of dust Aerosols was anticipated, an Aerosol model mixed with both dust and soot improved the accuracy of the estimated AOTcompared with the case of soot as the only absorptive Aerosol (error of 13% at 865 nm instead of 44%). Submicron absorbing particles, in addition of the Asian dust, should be considered in the optical remote sensing of east Asian waters. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0345 Atmospheric Composition and Structure: Pollution— urban and regional (0305); 4275 Oceanography: General: Remote sensing and electromagnetic processes (0689); KEYWORDS: radiative transfer simulation, soot Aerosol, Asian dust, atmospheric correction, remote sensing, ocean color Citation: Li, L., H. Fukushima, R. Frouin, B. G. Mitchell, M.-X. He, I. Uno, T. Takamura, and S. Ohta, Influence of submicron absorptive Aerosol on Sea-viewing Wide Field-of-view Sensor (SeaWiFS)-derived marine reflectance during Aerosol Characterization Experiment (ACE)-Asia, J. Geophys. Res., 108(D15), 4472, doi:10.1029/2002JD002776, 2003.

William C. Malm – One of the best experts on this subject based on the ideXlab platform.

  • Composition of the fine organic Aerosol in Yosemite National Park during the 2002 Yosemite Aerosol Characterization Study
    Atmospheric Environment, 2006
    Co-Authors: Guenter Engling, Sonia M. Kreidenweis, Pierre Herckes, William C. Malm, Jeffrey L. Collett
    Abstract:

    Abstract The Yosemite Aerosol Characterization Study (YACS) was conducted during the summer of 2002 to investigate regional haze in Yosemite National Park by characterizing the chemical, physical and optical properties of the ambient Aerosol. Previous analyses reveal that the composition of PM2.5 during YACS was dominated by carbonaceous material derived primarily from contemporary carbon sources rather than fossil fuelfuel combcombustion. In addition to several local wildfires and prescribed burns, two regional haze episodes during YACS were strongly influenced by smoke from biomass burning that was subject to long-range transport. Several classes of biomass burning smoke tracers, including anhydrosugars, methoxyphenols, and resin acids, were used to determine contributions of primary biomass burning smoke to PM2.5. Levoglucosan was measured with peak concentrations of 234 ng/m3 during periods with smoke influence from local fires, and primary biomass burning smoke contributions to fine particle organic carbon were estimated to be as high as 100% on individual days during that period. Relatively high concentrations of monoterpene oxidation products and other organic compounds of secondary origin, such as dicarboxylic acids, indicated secondary organic Aerosol (SOA) to be an important contributor to contemporary carbon. Biomass combustion plumes impacting the measurement site are likely a significant contributor to the observed SOA. Low concentrations of organic compounds of anthropogenic origin, such as hopanes and steranes, indicated contributions from automobile exhaust to organic carbon of approximately 10% on average. Overall, the fine Aerosol in Yosemite National Park during the summer of 2002 was dominated by natural sources, in particular by smoke from wildfires and by secondary organic Aerosol of biogenic origin.

  • Intercomparison and closure calculations using measurements of Aerosol species and optical properties during the Yosemite Aerosol Characterization Study
    Journal of Geophysical Research: Atmospheres, 2005
    Co-Authors: William C. Malm, Sonia M. Kreidenweis, Jeffrey L. Collett, Derek E. Day, Gavin R. Mcmeeking, Christian M. Carrico, Taehyoung Lee, Jacqueline Carrillo, Bret A. Schichtel
    Abstract:

    [1] Physical and optical properties of inorganic Aerosols have been extensively studied, but less is known about carbonaceous Aerosols, especially as they relate to the non-urban settings such as our nation’s national parks and wilderness areas. Therefore an Aerosol Characterization study was conceived and implemented at one national park that is highly impacted by carbonaceous Aerosols, Yosemite. The primary objective of the study was to characterize the physical, chemical, and optical properties of a carbon-dominated Aerosol, including the ratio of total organic matter weight to organic carbon, organic mass scattering efficiencies, and the hygroscopic characteristics of a carbon-laden ambient Aerosol, while a secondary objective was to evaluate a variety of semi-continuous monitoring systems. Inorganic ions were characterized using 24-hour samples that were collected using the URG and Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring systems, the micro-orifice uniform deposit impactor (MOUDI) cascade impaimpactor, as well as the semi-continuous particle-into-liquid sampler (PILS) technology. Likewise, carbonaceous material was collected over 24-hour periods using IMPROVE technology along with the thermal optical reflectance (TOR) analysis, while semi-continuous total carbon concentrations were measured using the Rupprecht and Patashnick (R&P) instrument. Dry Aerosol number size distributions were measured using a differential mobility analyzer (DMA) and optical particle counter, scattering coefficients at near-ambient conditions were measured with nephelometers fitted with PM10 and PM2.5 inlets, and “dry” PM2.5 scattering was measured after passing ambient air through Perma Pure Nafion® dryers. In general, the 24-hour “bulk” measurements of various Aerosol species compared more favorably with each other than with the semi-continuous data. Semi-continuous sulfate measurements correlated well with the 24-hour measurements, but were biased low by about 0.15 μg/m3. Semi-continuous carbon concentrations did not compare favorably with 24-hour measurements. Fine mass closure calculations suggested that the factor for estimating organic mass from measurements of carbon was approximately 1.8. Furthermore, fine scattering closure calculations showed that the use of 4.0 m2/g for the fine organic mass scattering coefficient was an underestimate by at least 30% for periods with high organic mass concentrations.

  • Observations of smoke‐influenced Aerosol during the Yosemite Aerosol Characterization Study: Size distributions and chemical composition
    Journal of Geophysical Research, 2005
    Co-Authors: Gavin R. Mcmeeking, Sonia M. Kreidenweis, Jeffrey L. Collett, Christian M. Carrico, Taehyoung Lee, William C. Malm
    Abstract:

    [1] The Yosemite Aerosol Characterization Study (YACS) took place in Yosemite National Park from 15 July to 5 September 2002, during which time air masses arriving at the site were believed to have been influenced by smoke from numerous wildfires active in the western United States. Physical, optical, and chemical Aerosol measurements were made to characterize visibility and to help define Aerosol sources contributing to haze in the park, with a particular emphasis on the role of prescribed and wild fires. Measurements of dry Aerosol size distributions were made with a differential mobility analyzer (DMA) and an optical particle counter (OPC). An iterative alignment method assuming a range of refractive indices was applied to OPC size distributions to match them to DMA size distributions, returning the real refractive index that yielded the best fit and generating a complete size distribution for 0.04 < Dp < 2 μm. Retrieved dry Aerosol real refractive indices generally ranged from 1.56 to 1.59 and were comparable to values estimated from composition measurements. Organic carbon was the dominant Aerosol species during the study, particularly during periods identified as smoke impacted. Mie theory was used to determine mass scattering efficiencies (λ = 530 nm) from measured dry size distributions using retrieved refractive indices. These ranged from 3 to 6 m2 g−1, with the highest values occurring during smoke-impacted episodes.

Sonia M. Kreidenweis – One of the best experts on this subject based on the ideXlab platform.

  • Particle size distributions of organic Aerosol constituents during the 2002 Yosemite Aerosol Characterization Study.
    Environmental Science & Technology, 2006
    Co-Authors: Pierre Herckes, Sonia M. Kreidenweis, Guenter Engling, Jeffrey L. Collett
    Abstract:

    The Yosemite Aerosol Characterization Study (YACS) was conducted in the summer of 2002 to investigate sources of regional haze in Yosemite National Park. Organic carbon and molecular source marker species size distributions were investigated during hazy and clear periods. More than 75% of the organic carbon mass was associated with submicron Aerosol particles. Most molecular marker species for wood smoke, an important source of particulate matter during the study, were contained in submicron particles, although on some fire influenced days, levoglucosan shifted toward larger sizes. Various wood smoke marker species exhibited slightly different size distributions in the samples, suggesting different, size dependent emission or atmospheric processing rates of these species. Secondary biogenic compounds including pinic and pinonic acids were associated with smaller particles. Pinonaldehyde, however, exhibited a broader distribution, likely due to its higher volatility. Dicarboxylic acids were associated mainly with submicron particles. Hopanes, molecular markers for vehicle emissions, were mostly contained in smaller particles but exhibited some tailing into larger size classes.

  • Composition of the fine organic Aerosol in Yosemite National Park during the 2002 Yosemite Aerosol Characterization Study
    Atmospheric Environment, 2006
    Co-Authors: Guenter Engling, Sonia M. Kreidenweis, Pierre Herckes, William C. Malm, Jeffrey L. Collett
    Abstract:

    Abstract The Yosemite Aerosol Characterization Study (YACS) was conducted during the summer of 2002 to investigate regional haze in Yosemite National Park by characterizing the chemical, physical and optical properties of the ambient Aerosol. Previous analyses reveal that the composition of PM2.5 during YACS was dominated by carbonaceous material derived primarily from contemporary carbon sources rather than fossil fuel combustion. In addition to several local wildfires and prescribed burns, two regional haze episodes during YACS were strongly influenced by smoke from biomass burning that was subject to long-range transport. Several classes of biomass burning smoke tracers, including anhydrosugars, methoxyphenols, and resin acids, were used to determine contributions of primary biomass burning smoke to PM2.5. Levoglucosan was measured with peak concentrations of 234 ng/m3 during periods with smoke influence from local fires, and primary biomass burning smoke contributions to fine particle organic carbon were estimated to be as high as 100% on individual days during that period. Relatively high concentrations of monoterpene oxidation products and other organic compounds of secondary origin, such as dicarboxylic acids, indicated secondary organic Aerosol (SOA) to be an important contributor to contemporary carbon. Biomass combustion plumes impacting the measurement site are likely a significant contributor to the observed SOA. Low concentrations of organic compounds of anthropogenic origin, such as hopanes and steranes, indicated contributions from automobile exhaust to organic carbon of approximately 10% on average. Overall, the fine Aerosol in Yosemite National Park during the summer of 2002 was dominated by natural sources, in particular by smoke from wildfires and by secondary organic Aerosol of biogenic origin.

  • Intercomparison and closure calculations using measurements of Aerosol species and optical properties during the Yosemite Aerosol Characterization Study
    Journal of Geophysical Research: Atmospheres, 2005
    Co-Authors: William C. Malm, Sonia M. Kreidenweis, Jeffrey L. Collett, Derek E. Day, Gavin R. Mcmeeking, Christian M. Carrico, Taehyoung Lee, Jacqueline Carrillo, Bret A. Schichtel
    Abstract:

    [1] Physical and optical properties of inorganic Aerosols have been extensively studied, but less is known about carbonaceous Aerosols, especially as they relate to the non-urban settings such as our nation’s national parks and wilderness areas. Therefore an Aerosol Characterization study was conceived and implemented at one national park that is highly impacted by carbonaceous Aerosols, Yosemite. The primary objective of the study was to characterize the physical, chemical, and optical properties of a carbon-dominated Aerosol, including the ratio of total organic matter weight to organic carbon, organic mass scattering efficiencies, and the hygroscopic characteristics of a carbon-laden ambient Aerosol, while a secondary objective was to evaluate a variety of semi-continuous monitoring systems. Inorganic ions were characterized using 24-hour samples that were collected using the URG and Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring systems, the micro-orifice uniform deposit impactor (MOUDI) cascade impactor, as well as the semi-continuous particle-into-liquid sampler (PILS) technology. Likewise, carbonaceous material was collected over 24-hour periods using IMPROVE technology along with the thermal optical reflectance (TOR) analysis, while semi-continuous total carbon concentrations were measured using the Rupprecht and Patashnick (R&P) instrument. Dry Aerosol number size distributions were measured using a differential mobility analyzer (DMA) and optical particle counter, scattering coefficients at near-ambient conditions were measured with nephelometers fitted with PM10 and PM2.5 inlets, and “dry” PM2.5 scattering was measured after passing ambient air through Perma Pure Nafion® dryers. In general, the 24-hour “bulk” measurements of various Aerosol species compared more favorably with each other than with the semi-continuous data. Semi-continuous sulfate measurements correlated well with the 24-hour measurements, but were biased low by about 0.15 μg/m3. Semi-continuous carbon concentrations did not compare favorably with 24-hour measurements. Fine mass closure calculations suggested that the factor for estimating organic mass from measurements of carbon was approximately 1.8. Furthermore, fine scattering closure calculations showed that the use of 4.0 m2/g for the fine organic mass scattering coefficient was an underestimate by at least 30% for periods with high organic mass concentrations.

Timothy S. Bates – One of the best experts on this subject based on the ideXlab platform.

  • A continental outbreak of air during the Second Aerosol Characterization Experiment (ACE 2): A Lagrangian experiment
    Journal of Geophysical Research: Atmospheres, 2000
    Co-Authors: Karsten Suhre, D. W. Johnson, Céline Mari, R. Rosset, Simon R. Osborne, Robert Wood, Timothy S. Bates, Frank Raes
    Abstract:

    A mesoscale meteorological model is used to simulate the continental outbreak of air that occured over North Atlantic Ocean during the Second Aerosol Characterization Experiment (ACE 2). Comparison with Meteosat 6 visible images shows that the model is able to reproduce most of the observed cloud features in the entire modeling domain, including a frontal system, orographic clouds over the Pyrenees and the Iberian Peninsula, boundary layer clouds in the ACE 2 region, and cloud-free areas in the dry air outflow off the Portuguese coast. The model reproduces correctly the temperature, humidity, wind speed and direction, cloud water content, and light precipitation events observed by the aircraft during the Lagrangian experiment, while following a tagged boundary layer air parcel over a 28-hour long period. A passive tracer, introduced in the model at the time corresponding to the balloon launch, followed the balloon track with an error in position that is smaller than 1° after 24-hours with about 20% higher speed. An estimate of the boundary layer entrainment velocity is obtained, based on observed boundary layer growth rates and modeled vertical wind speed. The average entrainment velocity of 1.28 cm/s for the 28-hour Lagrangian period agrees with experimentally derived entrainment velocities.

  • The 2nd Aerosol Characterization Experiment (ACE‐2): general overview and main results
    Tellus B: Chemical and Physical Meteorology, 2000
    Co-Authors: Frank Raes, Timothy S. Bates, Frank Mcgovern, Marc Van Liedekerke
    Abstract:

    This overview summarizes the objectives of the Aerosol Characterization Experiments (ACEs) of the International Global Atmospheric Chemistry (IGAC) project and the research strategy implemented in the second of this series of experiments (ACE-2). ACE-2 took place from 16 June to 24 July 1997, over the sub-tropical North-East Atlantic. It provided an opportunity to study the properties, processes and effects of contrasting Aerosol types in this region, including background marine and anthropogenic pollution Aerosol in the marine boundary layer (MBL), and background Aerosol and mineral dust in the overlaying free troposphere (FT). The major achievements of ACE-2 include:(a) identification of entrainment, in-cloud scavenging and coagulation as the major processes transforming a pollution Aerosol transported within the MBL; (b) the first documentation of the indirect radiative effect of Aerosols at the scale of a cloud ensemble in continental pollution outflow; (c) observation of a wide range in the contribution of organic material to the sub-micron Aerosol mass, with possibly the highest contribution in the free tropospheric; (d) improved understanding of the role of condensing HCl, HNO 3 and NH 3 as a growth mechanism of sub-micron Aerosols in polluted air<air masses advecting over the ocean. A close connection was observed between meteorological factors (such as horizontal and vertical wind speed, boundary layer development, entrainment, humidity fields) and Aerosol and cloud characteristics. In the ACE-2 region, these meteorological factors, rather than Aerosol microphysics and chemistry, often dominated the shaping of the Aerosol size distribution and/or their effect on radiation and clouds. The ACE-2 data presently analyzed provide a qualitative, and in many cases a quantitative understanding of the complex gas/Aerosol/cloud system in the sub-tropical marine environment. This will guide future model development. Some major data sets are still to be analyzed. DOI: 10.1034/j.1600-0889.2000.00124.x

  • One‐dimensional modeling of sulfur species during the First Aerosol Characterization Experiment (ACE 1) Lagrangian B
    Journal of Geophysical Research: Atmospheres, 1999
    Co-Authors: Céline Mari, Karsten Suhre, R. Rosset, Timothy S. Bates, Barry J. Huebert, Donald C. Thornton, Alan R. Bandy, Steve Businger
    Abstract:

    A one-dimensional Lagrangian model is used to simulate vertical profiles and temporal evolution of dimethylsulfide (DMS), sulfur dioxdioxide (SO2), Aerosol methane sulfonate, and non-sea-salt sulfate (nss sulfate) that were measured during the three flights of the second First Aerosol Characterization Experiment (ACE 1) Lagrangian (Lagrangian B) experiment. Entrainment rate, mixing heights, and cloud occurrence are calculated prognostically in this type of model. The model is forced by geostrophic winds and large scale subsidence from European Centre for Medium-Range Weather Forecasts (ECMWF) analysis and sea surface temperature measured on board Research Vessel Discoverer. Gas phase oxidation and heterogeneous oxidation of SO2 to nss sulfate in clouds and sea-salt particles are considered. The evolution of dynamical variables in the column is found to be well reproduced by the model. The model captures 82% of the variance of observed DMS assuming OH is the only oxidant and a DMS flux term calculated from Liss and Merlivat [1986] parameterization and seawater DMS concentrations measured aboard R/V Discoverer. However, uncertainties in DMS oxidation rates and regional seawater concentrations are too great to identify a best fit wind speed-transfer velocity relationship. SO2 mixing ratios are correctly represented in the model (least squares correlation coefficient r2 = 75%) using a DMS to SO2 conversion efficiency of about 70%. Oxidation of SO2 in sea-salt particle appears to be a dominant process and controls SO2 lifetime during the Lagrangian B at least in the well mixed lower layer. Removing heterogeneous loss of SO2 in sea salt significantly deteriorates the simulation (r2 = 50%). Under cloudy conditions, heterogeneous loss in cloud droplets and in sea-salt particles are competitive (relative rates are 35% and 41%, respectively, during flight 26). Model-generated Aerosol methane sulfonate mixing ratios agree with the observations (r2 = 62.5%) when high branching ratio for an addition oxidation pathway is used. The model estimates nss sulfate mixing ratios with little bias (median simulated-to-observed concentration ratio 1.03 and slope of the regression line 0.7) but captures only one third of the observed variance of nss sulfate. Part of the discrepancy could be due to the assumption of a decrease of nss sulfate mixing ratios with altitude in the model, whereas observations revealed high concentrations at 4500 m during the last two flights suggesting that horizontal transport could be more important than vertical mixing in this region. Nss sulfate is found to be produced photochemically under non cloudy, low wind speed conditions encountered during the first flight. During the last two flights, nss sulfate is produced mainly by oxidation in cloud droplets (48% during flight 25 and 69% during flight 26) and sea-salt particles (50% during flight 25 and 22% during flight 26).

Jeffrey L. Collett – One of the best experts on this subject based on the ideXlab platform.

  • Particle size distributions of organic Aerosol constituents during the 2002 Yosemite Aerosol Characterization Study.
    Environmental Science & Technology, 2006
    Co-Authors: Pierre Herckes, Sonia M. Kreidenweis, Guenter Engling, Jeffrey L. Collett
    Abstract:

    The Yosemite Aerosol Characterization Study (YACS) was conducted in the summer of 2002 to investigate sources of regional haze in Yosemite National Park. Organic carbon and molecular source marker species size distributions were investigated during hazy and clear periods. More than 75% of the organic carbon mass was associated with submicron Aerosol particles. Most molecular marker species for wood smoke, an important source of particulate matter during the study, were contained in submicron particles, although on some fire influenced days, levoglucosan shifted toward larger sizes. Various wood smoke marker species exhibited slightly different size distributions in the samples, suggesting different, size dependent emission or atmospheric processing rates of these species. Secondary biogenic compounds including pinic and pinonic acids were associated with smaller particles. Pinonaldehyde, however, exhibited a broader distribution, likely due to its higher volatility. Dicarboxylic acids were associated mainly with submicron particles. Hopanes, molecular markers for vehicle emissions, were mostly contained in smaller particles but exhibited some tailing into larger size classes.

  • Composition of the fine organic Aerosol in Yosemite National Park during the 2002 Yosemite Aerosol Characterization Study
    Atmospheric Environment, 2006
    Co-Authors: Guenter Engling, Sonia M. Kreidenweis, Pierre Herckes, William C. Malm, Jeffrey L. Collett
    Abstract:

    Abstract The Yosemite Aerosol Characterization Study (YACS) was conducted during the summer of 2002 to investigate regional haze in Yosemite National Park by characterizing the chemical, physical and optical properties of the ambient Aerosol. Previous analyses reveal that the composition of PM2.5 during YACS was dominated by carbonaceous material derived primarily from contemporary carbon sources rather than fossil fuel combustion. In addition to several local wildfires and prescribed burns, two regional haze episodes during YACS were strongly influenced by smoke from biomass burning that was subject to long-range transport. Several classes of biomass burning smoke tracers, including anhydrosugars, methoxyphenols, and resin acids, were used to determine contributions of primary biomass burning smoke to PM2.5. Levoglucosan was measured with peak concentrations of 234 ng/m3 during periods with smoke influence from local fires, and primary biomass burning smoke contributions to fine particle organic carbon were estimated to be as high as 100% on individual days during that period. Relatively high concentrations of monoterpene oxidation products and other organic compounds of secondary origin, such as dicarboxylic acids, indicated secondary organic Aerosol (SOA) to be an important contributor to contemporary carbon. Biomass combustion plumes impacting the measurement site are likely a significant contributor to the observed SOA. Low concentrations of organic compounds of anthropogenic origin, such as hopanes and steranes, indicated contributions from automobile exhaust to organic carbon of approximately 10% on average. Overall, the fine Aerosol in Yosemite National Park during the summer of 2002 was dominated by natural sources, in particular by smoke from wildfires and by secondary organic Aerosol of biogenic origin.

  • Intercomparison and closure calculations using measurements of Aerosol species and optical properties during the Yosemite Aerosol Characterization Study
    Journal of Geophysical Research: Atmospheres, 2005
    Co-Authors: William C. Malm, Sonia M. Kreidenweis, Jeffrey L. Collett, Derek E. Day, Gavin R. Mcmeeking, Christian M. Carrico, Taehyoung Lee, Jacqueline Carrillo, Bret A. Schichtel
    Abstract:

    [1] Physical and optical properties of inorganic Aerosols have been extensively studied, but less is known about carbonaceous Aerosols, especially as they relate to the non-urban settings such as our nation’s national parks and wilderness areas. Therefore an Aerosol Characterization study was conceived and implemented at one national park that is highly impacted by carbonaceous Aerosols, Yosemite. The primary objective of the study was to characterize the physical, chemical, and optical properties of a carbon-dominated Aerosol, including the ratio of total organic matter weight to organic carbon, organic mass scattering efficiencies, and the hygroscopic characteristics of a carbon-laden ambient Aerosol, while a secondary objective was to evaluate a variety of semi-continuous monitoring systems. Inorganic ions were characterized using 24-hour samples that were collected using the URG and Interagency Monitoring of Protected Visual Environments (IMPROVE) monitoring systems, the micro-orifice uniform deposit impactor (MOUDI) cascade impactor, as well as the semi-continuous particle-into-liquid sampler (PILS) technology. Likewise, carbonaceous material was collected over 24-hour periods using IMPROVE technology along with the thermal optical reflectance (TOR) analysis, while semi-continuous total carbon concentrations were measured using the Rupprecht and Patashnick (R&P) instrument. Dry Aerosol number size distributions were measured using a differential mobility analyzer (DMA) and optical particle counter, scattering coefficients at near-ambient conditions were measured with nephelometers fitted with PM10 and PM2.5 inlets, and “dry” PM2.5 scattering was measured after passing ambient air through Perma Pure Nafion® dryers. In general, the 24-hour “bulk” measurements of various Aerosol species compared more favorably with each other than with the semi-continuous data. Semi-continuous sulfate measurements correlated well with the 24-hour measurements, but were biased low by about 0.15 μg/m3. Semi-continuous carbon concentrations did not compare favorably with 24-hour measurements. Fine mass closure calculations suggested that the factor for estimating organic mass from measurements of carbon was approximately 1.8. Furthermore, fine scattering closure calculations showed that the use of 4.0 m2/g for the fine organic mass scattering coefficient was an underestimate by at least 30% for periods with high organic mass concentrations.