scholarly journals Influence of semi-volatile aerosols on physical and optical properties of aerosols in the Kathmandu Valley

2017 ◽  
Author(s):  
Sujan Shrestha ◽  
Siva Praveen Puppala ◽  
Bhupesh Adhikary ◽  
Kundan Lal Shrestha ◽  
Arnico K. Panday
Keyword(s):  
Optical Properties ◽  
Size Distribution ◽  
Room Temperature ◽  
Ambient Air ◽  
Aerosol Size Distribution ◽  
Volatile Fraction ◽  
Kathmandu Valley ◽  
Effective Diameter ◽  
Distribution Analysis ◽  
Aerosol Fraction

Abstract. A field study was conducted in the urban atmosphere of the Kathmandu Valley to study influence of the semi-volatile aerosol fraction on physical and optical properties of aerosols. The study was carried out during the pre-monsoon season of 2015. Our experimental setup consisted of a single ambient air inlet from which the flow was split into two sets of identical sampling instruments; the first set was connected directly with an ambient sample while the second set received the air sample through a thermodenuder (TDD). Four sets of experiments were conducted for our study to understand aerosol number, size distribution, absorption, and scattering properties using Condensation Particle Counter (CPC), Scanning Mobility Particle Sizer (SMPS), Aethalometer (AE33) and Nephelometer respectively. The influence of semi-volatile aerosols were calculated based on the difference of aerosol properties at room temperature, 50 °C, 100 °C, 150 °C, 200 °C, 250 °C and 300 °C through set TDD temperatures to ambient sample. Our results show that with increasing TDD temperature, the evaporated fraction of semi-volatile aerosols also increased. At room temperature the semi-volatile fraction of aerosol number was 12 %, while at 300 °C it was as high as 49 % of ambient aerosol. Aerosol size distribution analysis from SMPS shows that with an increase in temperature from 50 °C to 300 °C, the peak mobility diameter of particles shifted from around 60 nm to 40 nm. However, no distinct change in the effective diameter of the aerosol size distribution was observed with increase in set TDD temperature. The change in size of aerosols due to loss of semi-volatile component had a stronger influence (~ 70 %) at larger size bins when compared to (~ 20 %) at smaller bins of SMPS. At 300 °C, the semi-volatile aerosols amplified BC absorption by approximately 28 % while scattering by the semi-volatile aerosols contributed up to 71 % of total scattering. The Scattering Angstrom Exponent (SAE) of the semi-volatile aerosol fraction was found to be more sensitive at lower temperatures (

scholarly journals Evaluating model parameterizations of submicron aerosol scattering and absorption with in situ data from ARCTAS 2008

2016 ◽  
Vol 16 (14) ◽  
pp. 9435-9455 ◽  
Author(s):  
Matthew J. Alvarado ◽  
Chantelle R. Lonsdale ◽  
Helen L. Macintyre ◽  
Huisheng Bian ◽  
Mian Chin ◽  
...  
Keyword(s):  
Optical Properties ◽  
Size Distribution ◽  
Aerosol Size Distribution ◽  
Visible Radiation ◽  
Submicron Aerosol ◽  
In Situ Data ◽  
Aerosol Absorption ◽  
Aerosol Scattering ◽  
The Impact

Abstract. Accurate modeling of the scattering and absorption of ultraviolet and visible radiation by aerosols is essential for accurate simulations of atmospheric chemistry and climate. Closure studies using in situ measurements of aerosol scattering and absorption can be used to evaluate and improve models of aerosol optical properties without interference from model errors in aerosol emissions, transport, chemistry, or deposition rates. Here we evaluate the ability of four externally mixed, fixed size distribution parameterizations used in global models to simulate submicron aerosol scattering and absorption at three wavelengths using in situ data gathered during the 2008 Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) campaign. The four models are the NASA Global Modeling Initiative (GMI) Combo model, GEOS-Chem v9-02, the baseline configuration of a version of GEOS-Chem with online radiative transfer calculations (called GC-RT), and the Optical Properties of Aerosol and Clouds (OPAC v3.1) package. We also use the ARCTAS data to perform the first evaluation of the ability of the Aerosol Simulation Program (ASP v2.1) to simulate submicron aerosol scattering and absorption when in situ data on the aerosol size distribution are used, and examine the impact of different mixing rules for black carbon (BC) on the results. We find that the GMI model tends to overestimate submicron scattering and absorption at shorter wavelengths by 10–23 %, and that GMI has smaller absolute mean biases for submicron absorption than OPAC v3.1, GEOS-Chem v9-02, or GC-RT. However, the changes to the density and refractive index of BC in GC-RT improve the simulation of submicron aerosol absorption at all wavelengths relative to GEOS-Chem v9-02. Adding a variable size distribution, as in ASP v2.1, improves model performance for scattering but not for absorption, likely due to the assumption in ASP v2.1 that BC is present at a constant mass fraction throughout the aerosol size distribution. Using a core-shell mixing rule in ASP overestimates aerosol absorption, especially for the fresh biomass burning aerosol measured in ARCTAS-B, suggesting the need for modeling the time-varying mixing states of aerosols in future versions of ASP.

scholarly journals Quantitative evaluation of seven optical sensors for cloud microphysical measurements at the Puy-de-Dôme Observatory, France

2015 ◽  
Vol 8 (10) ◽  
pp. 4347-4367 ◽  
Author(s):  
G. Guyot ◽  
C. Gourbeyre ◽  
G. Febvre ◽  
V. Shcherbakov ◽  
F. Burnet ◽  
...  
Keyword(s):  
Optical Properties ◽  
Wind Tunnel ◽  
Optical Sensors ◽  
Wind Direction ◽  
Total Concentration ◽  
Measurement Techniques ◽  
Ambient Air ◽  
Number Concentration ◽  
Effective Diameter ◽  
Particle Volume

Abstract. Clouds have an important role in Earth's radiative budget. Since the late 1970s, considerable instrumental developments have been made in order to quantify cloud microphysical and optical properties, for both airborne and ground-based applications. Intercomparison studies have been carried out in the past to assess the reliability of cloud microphysical properties inferred from various measurement techniques. However, observational uncertainties still exist, especially for droplet size distribution measurements and need to be reduced. In this work, we discuss results from an intercomparison campaign, performed at the Puy de Dôme in May 2013. During this campaign, a unique set of cloud instruments was operating simultaneously in ambient air conditions and in a wind tunnel. A Particle Volume Monitor (PVM-100), a Forward Scattering Spectrometer Probe (FSSP), a Fog Monitor (FM-100), and a Present Weather Detector (PWD) were sampling on the roof of the station. Within a wind tunnel located underneath the roof, two Cloud Droplet Probes (CDPs) and a modified FSSP (SPP-100) were operating. The main objectives of this paper are (1) to study the effects of wind direction and speed on ground-based cloud observations, (2) to quantify the cloud parameters discrepancies observed by the different instruments, and (3) to develop methods to improve the quantification of the measurements. The results revealed that all instruments showed a good agreement in their sizing abilities, both in terms of amplitude and variability. However, some of them, especially the FM-100, the FSSP and the SPP, displayed large discrepancies in their capability to assess the magnitude of the total number concentration of the cloud droplets. As a result, the total liquid water content can differ by up to a factor of 5 between the probes. The use of a standardization procedure, based on data of integrating probes (PVM-100 or visibilimeter) and extinction coefficient comparison substantially enhanced the instrumental agreement. During this experiment, the total concentration agreed in variations with the visibilimeter, except for the FSSP, so a corrective factor can be applied and it ranges from 0.44 to 2.2. This intercomparison study highlights the necessity to have an instrument which provides a bulk measurement of cloud microphysical or optical properties during cloud ground-based campaigns. Moreover, the FM and FSSP orientation was modified with an angle ranging from 30 to 90° angle with wind speeds from 3 to 7 m s−1. The results show that the induced number concentration loss is between 29 and 98 % for the FSSP and between 15 and 68 % for the FM-100. In particular, FSSP experiments showed strong discrepancies when the wind speed was lower than 3 m s−1 and/or when the angle between the wind direction and the orientation of the instruments is greater than 30°. An inadequate orientation of the FSSP towards the wind direction leads to an underestimation of the measured effective diameter.

scholarly journals Evaluating Model Parameterizations of Submicron Aerosol Scattering and Absorption with In Situ Data from ARCTAS 2008

2016 ◽  
Author(s):  
M. J. Alvarado ◽  
C. R. Lonsdale ◽  
H. L. Macintyre ◽  
H. Bian ◽  
M. Chin ◽  
...  
Keyword(s):  
Optical Properties ◽  
Size Distribution ◽  
Aerosol Size Distribution ◽  
Visible Radiation ◽  
Submicron Aerosol ◽  
In Situ Data ◽  
Aerosol Absorption ◽  
Aerosol Scattering ◽  
The Impact

Abstract. Accurate modeling of the scattering and absorption of ultraviolet and visible radiation by aerosols is essential for accurate simulations of atmospheric chemistry and climate. Closure studies using in situ measurements of aerosol scattering and absorption can be used to evaluate and improve models of aerosol optical properties without interference from model errors in aerosol emissions, transport, chemistry, or deposition rates. Here we evaluate the ability of four externally mixed, fixed size distribution parameterizations used in global models to simulate submicron aerosol scattering and absorption at three wavelengths using in situ data gathered during the 2008 Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) campaign. The four models are the NASA Global Modeling Initiative (GMI) Combo model, GEOS-Chem v9-02, the baseline configuration of a version of GEOS-Chem with online radiative transfer calculations (called GC-RT), and the Optical Properties of Aerosol and Clouds (OPAC v3.1) package. We also use the ARCTAS data to perform the first evaluation of the ability of the Aerosol Simulation Program (ASP v2.1) to simulate submicron aerosol scattering and absorption when in situ data on the aerosol size distribution is used, and examine the impact of different mixing rules for black carbon (BC) on the results. We find that the GMI model tends to overestimate submicron scattering and absorption at shorter wavelengths by 10–23 %, and that GMI has smaller absolute mean biases for submicron absorption than OPAC v3.1, GEOS-Chem v9-02, or GC-RT. However, the changes to the density and refractive index of BC in GC-RT improve the simulation of submicron aerosol absorption at all wavelengths relative to GEOS-Chem v9-02. Adding in situ size distribution information, as in ASP v2.1, improves model performance for scattering but not for absorption, likely due to the assumption in ASP v2.1 that BC is present at a constant mass fraction through out the aerosol size distribution. Using a core-shell mixing state in ASP overestimates aerosol absorption, especially for the fresh biomass burning aerosol measured in ARCTAS-B, suggesting the need for time-varying mixing states in future versions of ASP.

scholarly journals Quantifying the aerosol effect on droplet size distribution at cloud top

2019 ◽  
Vol 19 (11) ◽  
pp. 7839-7857
Author(s):  
Lianet Hernández Pardo ◽  
Luiz Augusto Toledo Machado ◽  
Micael Amore Cecchini ◽  
Madeleine Sánchez Gácita
Keyword(s):  
Size Distribution ◽  
Droplet Size ◽  
Initial Conditions ◽  
Cloud Condensation Nuclei ◽  
Droplet Size Distribution ◽  
Number Concentration ◽  
Population Characteristics ◽  
Aerosol Size Distribution ◽  
Effective Diameter ◽  
Distribution Sensitivity

Abstract. This work uses the number concentration-effective diameter phase-space to test cloud sensitivity to variations in the aerosol population characteristics, such as the aerosol size distribution, number concentration and hygroscopicity. It is based on the information from the top of a cloud simulated by a bin-microphysics single-column model, for initial conditions typical of the Amazon, using different assumptions regarding the entrainment and the aerosol size distribution. It is shown that the cloud-top evolution can be very sensitive to aerosol properties, but the relative importance of each parameter is variable. The sensitivity to each aerosol characteristic varies as a function of the parameter tested and is conditioned by the base values of the other parameters, showing a specific dependence for each configuration of the model. When both the entrainment and the bin treatment of the aerosol are allowed, the largest influence on the droplet size distribution sensitivity was obtained for the median radius of the aerosols and not for the total number concentration of aerosols. Our results reinforce that the cloud condensation nuclei activity can not be predicted solely on the basis of the w∕Na supersaturation-based regimes.

Spatial and temporal variability of aerosol: size distribution and optical properties

2003 ◽  
Vol 66 (1-2) ◽  
pp. 1-19 ◽  
Author(s):  
M Masmoudi ◽  
M Chaabane ◽  
D Tanré ◽  
P Gouloup ◽  
L Blarel ◽  
...  
Keyword(s):  
Optical Properties ◽  
Size Distribution ◽  
Temporal Variability ◽  
Aerosol Size Distribution ◽  
Spatial And Temporal Variability

scholarly journals Optical Properties of the Urban Aerosol Particles Obtained from Ground Based Measurements and Satellite-Based Modelling Studies

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Genrik Mordas ◽  
Nina Prokopciuk ◽  
Steigvilė Byčenkienė ◽  
Jelena Andriejauskienė ◽  
Vidmantas Ulevicius
Keyword(s):  
Optical Properties ◽  
Light Scattering ◽  
Urban Environment ◽  
Size Distribution ◽  
Number Concentration ◽  
Scattering Coefficient ◽  
Dust Particles ◽  
Aerosol Size Distribution ◽  
Air Masses ◽  
The Impact

Applications of satellite remote sensing data combined with ground measurements and model simulation were applied to study aerosol optical properties as well as aerosol long-range transport under the impact of large scale circulation in the urban environment in Lithuania (Vilnius). Measurements included the light scattering coefficients at 3 wavelengths (450, 550, and 700 nm) measured with an integrating nephelometer and aerosol particle size distribution (0.5–12 μm) and number concentration (Dpa> 0.5 μm) registered by aerodynamic particle sizer. Particle number concentration and mean light scattering coefficient varied from relatively low values of 6.0 cm−3and 12.8 Mm−1associated with air masses passed over Atlantic Ocean to relatively high value of 119 cm−3and 276 Mm−1associated with South-Western air masses. Analysis shows such increase in the aerosol light scattering coefficient (276 Mm−1) during the 3rd of July 2012 was attributed to a major Sahara dust storm. Aerosol size distribution with pronounced coarse particles dominance was attributed to the presence of dust particles, while resuspended dust within the urban environment was not observed.

scholarly journals Quantifying the aerosol effect on droplet size distribution at cloud-top

2018 ◽  
Author(s):  
Lianet Hernández Pardo ◽  
Luiz Augusto Toledo Machado ◽  
Micael Amore Cecchini ◽  
Madeleine Sánchez Gácita
Keyword(s):  
Size Distribution ◽  
Initial Conditions ◽  
Droplet Size Distribution ◽  
Cloud Microphysics ◽  
Number Concentration ◽  
Population Characteristics ◽  
Aerosol Size Distribution ◽  
Effective Diameter ◽  
Bin Microphysics ◽  
Aerosol Properties

Abstract. This work uses the number concentration-effective diameter phase-space to test cloud sensitivity to variations in the aerosol population characteristics, such as the aerosol size distribution, number concentration and hygroscopicity. It is based on the information from the top of a cloud simulated by a bin-microphysics single-column model, for initial conditions typical of the Amazon. It is shown that the cloud-top evolution can be very sensitive to aerosol properties, but the relative importance of each parameter is variable. The sensitivity to each aerosol characteristic varies as a function of the tested parameter and is conditioned by the base values of the other parameters. The median radius of the aerosols showed the largest influence on this sensitivity. We show that all aerosol properties can have significant impacts on cloud microphysics, especially if the median radius of the aerosol size distribution is smaller than 0.05 μm.

scholarly journals Coarse-mode mineral dust size distributions, composition and optical properties from AER-D aircraft measurements over the tropical eastern Atlantic

2018 ◽  
Vol 18 (23) ◽  
pp. 17225-17257 ◽  
Author(s):  
Claire L. Ryder ◽  
Franco Marenco ◽  
Jennifer K. Brooke ◽  
Victor Estelles ◽  
Richard Cotton ◽  
...  
Keyword(s):  
Optical Properties ◽  
Size Distribution ◽  
Climate Models ◽  
Mineral Dust ◽  
Radiation Balance ◽  
Effective Diameter ◽  
Size Distributions ◽  
Transport Pathway ◽  
Coarse Mode ◽  
Dust Composition

Abstract. Mineral dust is an important component of the climate system, affecting the radiation balance, cloud properties, biogeochemical cycles, regional circulation and precipitation, as well as having negative effects on aviation, solar energy generation and human health. Dust size and composition has an impact on all these processes. However, changes in dust size distribution and composition during transport, particularly for coarse particles, are poorly understood and poorly represented in climate models. Here we present new in situ airborne observations of dust in the Saharan Air Layer (SAL) and the marine boundary layer (MBL) at the beginning of its transatlantic transport pathway, from the AERosol Properties – Dust (AER-D) fieldwork in August 2015, within the peak season of North African dust export. This study focuses on coarse-mode dust properties, including size distribution, mass loading, shape, composition, refractive indices and optical properties. Size distributions from 0.1 to 100 µm diameter (d) are presented, fully incorporating the coarse and giant modes of dust. Within the MBL, mean effective diameter (deff) and volume median diameter (VMD) were 4.6 and 6.0 µm respectively, giant particles with a mode at 20–30 µm were observed, and composition was dominated by quartz and alumino-silicates at d > 1 µm. Within the SAL, particles larger than 20 µm diameter were always present up to 5 km altitude, in concentrations over 10−5 cm−3, constituting up to 40 % of total dust mass. Mean deff and VMD were 4.0 and 5.5 µm respectively. Larger particles were detected in the SAL than can be explained by sedimentation theory alone. Coarse-mode composition was dominated by quartz and alumino-silicates; the accumulation mode showed a strong contribution from sulfate-rich and sea salt particles. In the SAL, measured single scattering albedos (SSAs) at 550 nm representing d < 2.5 µm were 0.93 to 0.98 (mean 0.97). Optical properties calculated for the full size distribution (0.1 < d < 100 µm) resulted in lower SSAs of 0.91–0.98 (mean 0.95) and mass extinction coefficients of 0.27–0.35 m2 g−1 (mean 0.32 m2 g−1). Variability in SSA was mainly controlled by variability in dust composition (principally iron) rather than by variations in the size distribution, in contrast with previous observations over the Sahara where size is the dominant influence. It is important that models are able to capture the variability and evolution of both dust composition and size distribution with transport in order to accurately represent the impacts of dust on climate. These results provide a new SAL dust dataset, fully representing coarse and giant particles, to aid model validation and development.

Near-Field and Far-Field Sampling of Aerosol Plumes to Evaluate Particulate Emission Rates From a Falling Particle Receiver During On-Sun Testing

2021 ◽  
Author(s):  
Andrew Glen ◽  
Darielle Dexheimer ◽  
Andres L. Sanchez ◽  
Clifford K. Ho ◽  
Swarup China ◽  
...  
Keyword(s):  
Size Distribution ◽  
Near Field ◽  
Measurement Techniques ◽  
Ambient Air ◽  
Industrial Applications ◽  
Aerosol Size Distribution ◽  
Far Field ◽  
Emission Rates ◽  
Particulate Emission ◽  
Field Instrumentation

Abstract High-temperature falling particle receivers are being investigated for next-generation concentrating solar power applications. Small sand-like particles are released into an open-cavity receiver and are irradiated by concentrated sunlight from a field of heliostats. The particles are heated to temperatures over 700 °C and can be stored to produce heat for electricity generation or industrial applications when needed. As the particles fall through the receiver, particles and particulate fragments in the form of aerosolized dust can be emitted from the aperture, which can lower thermal efficiency, increase costs of particle replacement, and pose a particulate matter (PM) inhalation risk. This paper describes sampling methods that were deployed during on-sun tests to record near-field (several meters) and far-field (tens to hundreds of meters) concentrations of aerosol particles within emitted plumes. The objective was to quantify the particulate emission rates and loss from the falling particle receiver in relation to OSHA and EPA National Ambient Air Quality Standards (NAAQS). Near-field instrumentation placed on the platform in proximity to the receiver aperture included several real-time aerosol size distribution and concentration measurement techniques, including a TSI Aerodynamic Particle Sizers (APS), TSI DustTraks, Handix Portable Optical Particle Spectrometers (POPS), Alphasense Optical Particle Counters (OPC), TSI Condensation Particle Counters (CPC), Cascade Particle Impactors, 3D-printed prototype tipping buckets, and meteorological instrumentation. Far-field particle sampling techniques utilized multiple tethered balloons located upwind and downwind of the particle receiver to measure the advected plume concentrations using a suite of airborne aerosol and meteorological instruments including POPS, CPCs, OPCs and cascade impactors. The combined aerosol size distribution for all these instruments spanned particle sizes from 0.02 μm – 500 μm. Results showed a strong influence of wind direction on particle emissions and concentration, with preliminary results showing representative concentrations below both the OSHA and NAAQS standards.

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