scholarly journals A comparison of lognormal and gamma size distributions for characterizing the stratospheric aerosol phase function from OPC measurements

2019 ◽  
Author(s):  
Ernest Nyaku ◽  
Robert Loughman ◽  
Pawan K. Bhartia ◽  
Terry Deshler ◽  
Zhong Chen ◽  
...  
Keyword(s):  
Gamma Distribution ◽  
Phase Function ◽  
Stratospheric Aerosol ◽  
Aerosol Size Distribution ◽  
Size Distributions ◽  
Distribution Models ◽  
Concentration Data ◽  
Radiation Model ◽  
Better Than

Abstract. A series of in situ measurements made by optical particle counters (OPC) at Laramie, Wyoming provides size-resolved stratospheric aerosol concentration data for the period of 2008–2017. These data are analyzed in this study for the purpose of assessing the sensitivity of the stratospheric aerosol phase function to the aerosol size distribution (ASD) model used to fit the measurements. The two unimodal ASD models investigated are the uni-modal lognormal (UMLN) and gamma distribution models, with the minimum χ2 method employed to assess how well each ASD fits the measurements. The aerosol phase function (APF) for each ASD is calculated using Mie theory, and is compared to the APF derived from the Community Aerosol and Radiation Model for Atmospheres (CARMA) sectional aerosol microphysics module. Comparing the χ2 values for the fits at altitudes 20 km and 25 km shows that the UMLN distribution better represents the OPC measurements. The importance of data at aerosol radius below 0.1 μm is also demonstrated: When these data are not available from OPC measurements, the gamma distribution provides a more stable derived APF. The gamma distribution also fits the CARMA model results better than the UMLN model, when the CARMA model results are binned to mimic the OPC measurement bins (and therefore measurements between 0.05 and 0.1 μm are excluded).

scholarly journals A comparison of lognormal and gamma size distributions for characterizing the stratospheric aerosol phase function from optical particle counter measurements

2020 ◽  
Vol 13 (3) ◽  
pp. 1071-1087 ◽  
Author(s):  
Ernest Nyaku ◽  
Robert Loughman ◽  
Pawan K. Bhartia ◽  
Terry Deshler ◽  
Zhong Chen ◽  
...  
Keyword(s):  
Gamma Distribution ◽  
Phase Function ◽  
Stratospheric Aerosol ◽  
Aerosol Size Distribution ◽  
Distribution Models ◽  
Concentration Data ◽  
Gamma Distributions ◽  
Phase Functions ◽  
Better Than

Abstract. A series of in situ measurements made by optical particle counters (OPCs) at Laramie, Wyoming, provides size-resolved stratospheric aerosol concentration data over the period 1971–2018. A subset of these data covering the period of 2008–2017 is analyzed in this study for the purpose of assessing the sensitivity of the stratospheric aerosol phase function to the aerosol size distribution (ASD) model used to fit the measurements. The two unimodal ASD models investigated are the unimodal lognormal (UMLN) and gamma distribution models, with the minimum χ2 method employed to assess how well each ASD fits the measurements. The aerosol phase function (Pa(Θ)) for each ASD is calculated using Mie theory and is compared to the Pa(Θ) derived from the Community Aerosol and Radiation Model for Atmospheres (CARMA) sectional aerosol microphysics module. Comparing the χ2 values for the fits at altitudes of 20 and 25 km shows that the UMLN distribution better represents the OPC measurements; however, the gamma distribution fits the CARMA model results better than the UMLN model when the CARMA model results are subsetted into the OPC measurement bins. Comparing phase functions derived from the UMLN distribution fit to OPC data with gamma distributions fit to CARMA model results at the location of the OPC measurements shows a satisfying agreement (±5 %) within the scattering angle range of limb sounding satellites. This uncertainty is considerably larger if the CARMA data are fit with a UMLN.

scholarly journals Performance Assessment of Portable Optical Particle Spectrometer (POPS)

Sensors ◽  
2020 ◽  
Vol 20 (21) ◽  
pp. 6294
Author(s):  
Fan Mei ◽  
Gavin McMeeking ◽  
Mikhail Pekour ◽  
Ru-Shan Gao ◽  
Gourihar Kulkarni ◽  
...  
Keyword(s):  
High Sensitivity ◽  
Apparent Size ◽  
Aerosol Size Distribution ◽  
Size Distributions ◽  
Flow Temperature ◽  
Atmospheric Research ◽  
Miniaturized Instrumentation ◽  
Aerial Systems ◽  
Laser Heater

Accurate representation of atmospheric aerosol properties is a long-standing problem in atmospheric research. Modern pilotless aerial systems provide a new platform for atmospheric in situ measurement. However, small airborne platforms require miniaturized instrumentation due to apparent size, power, and weight limitations. A Portable Optical Particle Spectrometer (POPS) is an emerged instrument to measure ambient aerosol size distribution with high time and size resolution, designed for deployment on a small unmanned aerial system (UAS) or tethered balloon system (TBS) platforms. This study evaluates the performance of a POPS with an upgraded laser heater and additional temperature sensors in the aerosol pathway. POPS maintains its performance under different environmental conditions as long as the laser temperature remains above 25 °C and the aerosol flow temperature inside the optical chamber is 15 °C higher than the ambient temperature. The comparison between POPS and an Ultra-High Sensitivity Aerosol Spectrometer (UHSAS) suggests that the coincidence error is less than 25% when the number concentration is less than 4000 cm−3. The size distributions measured by both of them remained unaffected up to 15,000 cm−3. While both instruments’ sizing accuracy is affected by the aerosol chemical composition and morphology, the influence is more profound on the POPS.

scholarly journals On the Quantitative Low-Level Aerosol Measurements Using Ceilometer-Type Lidar

2009 ◽  
Vol 26 (11) ◽  
pp. 2340-2352 ◽  
Author(s):  
Anu-Maija Sundström ◽  
Timo Nousiainen ◽  
Tuukka Petäjä
Keyword(s):  
Size Distribution ◽  
Theoretical Calculations ◽  
Measurement Instrument ◽  
Aerosol Size Distribution ◽  
Lidar Measurement ◽  
Size Distributions ◽  
Absolute Accuracy ◽  
Particle Composition ◽  
Aerosol Measurement

Abstract The objective of this work is to investigate whether a commercial ceilometer-type lidar can be used as a quantitative aerosol measurement instrument. To this end, lidar backscattering measurements are compared with exact theoretical calculations of backscattering, which are based on in situ–measured size distributions and account for uncertainties in particle composition and shape. The results show that the differences between simulated and measured backscattering remain nearly constant and within the uncertainties involved. The differences are most plausibly explained by an error in the overlap function of the lidar and/or errors in the calibration of either the lidar or the in situ instruments used to measure the aerosol size distribution. Occasionally, large differences occur that are obviously connected to the unrepresentativeness of the in situ and lidar measurement volumes because of insufficient atmospheric mixing. The results imply that the absolute accuracy of the instrument investigated might be sufficient for quantitative aerosol measurements in some applications. A fix for the overlap function, however, would be desirable.

scholarly journals SALSA2.0: The sectional aerosol module of the aerosol-chemistry-climate model ECHAM6.3.0-HAM2.3-MOZ1.0

2018 ◽  
Author(s):  
Harri Kokkola ◽  
Thomas Kühn ◽  
Anton Laakso ◽  
Tommi Bergman ◽  
Kari E. J. Lehtinen ◽  
...  
Keyword(s):  
Climate Model ◽  
Stratospheric Aerosol ◽  
Aerosol Size Distribution ◽  
Global Burden ◽  
Size Distributions ◽  
Aerosol Chemistry ◽  
Microphysics Scheme ◽  
Size Dependent ◽  
Aerosol Mass ◽  
Aerosol Module

Abstract. In this paper, we present the implementation and evaluation of the aerosol microphysics module SALSA2.0 in the framework of the aerosol-chemistry-climate model ECHAM-HAMMOZ. It is an alternative microphysics module to the default modal microphysics scheme M7 in ECHAM-HAMMOZ. The SALSA2.0 implementation is evaluated against the observations of aerosol optical properties, aerosol mass, and size distributions. We also compare the skill of SALSA2.0 in reproducing the observed quantities to the skill of the M7 implementation. The largest differences between SALSA2.0 and M7 are evident over regions where the aerosol size distribution is heavily modified by the microphysical processing of aerosol particles. Such regions are, for example, highly polluted regions and regions strongly affected by biomass burning. In addition, in a simulation of the 1991 Mt Pinatubo eruption in which a stratospheric sulfate plume was formed, the global burden and the effective radii of the stratospheric aerosol are very different in SALSA2.0 and M7. While SALSA2.0 was able to reproduce the observed time evolution of the global burden of sulfate and the effective radii of stratospheric aerosol, M7 strongly overestimates the removal of coarse stratospheric particles and thus underestimates the effective radius of stratospheric aerosol. As the mode widths of M7 have been optimized for the troposphere and were not designed to represent stratospheric aerosol the ability of M7 to simulate the volcano plume was improved by modifying the mode widths decreasing the standard deviations of the accumulation and coarse modes from 1.59 and 2.0, respectively, to 1.2. Overall, SALSA2.0 shows promise in improving the aerosol description of ECHAM-HAMMOZ and can be further improved by implementing methods for aerosol processes that are more suitable for the sectional method, e.g size dependent emissions for aerosol species and size resolved wet deposition.

scholarly journals Analysis of number size distributions of tropical free tropospheric aerosol particles observed at Pico Espejo (4765 m a.s.l.), Venezuela

2011 ◽  
Vol 11 (7) ◽  
pp. 3319-3332 ◽  
Author(s):  
T. Schmeissner ◽  
R. Krejci ◽  
J. Ström ◽  
W. Birmili ◽  
A. Wiedensohler ◽  
...  
Keyword(s):  
Particle Number ◽  
Dry Season ◽  
Number Concentration ◽  
Aerosol Size Distribution ◽  
Particle Number Concentration ◽  
Size Distributions ◽  
Wet Season ◽  
Concentration Data ◽  
Diurnal Variability ◽  
Tropospheric Aerosol

Abstract. The first long-term measurements of aerosol number and size distributions in South-American tropical free troposphere (FT) were performed from March 2007 until March 2009. The measurements took place at the high altitude Atmospheric Research Station Alexander von Humboldt. The station is located on top of the Sierra Nevada mountain ridge at 4765 m a.s.l. nearby the city of Mérida, Venezuela. Aerosol size distribution and number concentration data was obtained with a custom-built Differential Mobility Particle Sizer (DMPS) system and a Condensational Particle Counter (CPC). The analysis of the annual and diurnal variability of the tropical FT aerosol focused mainly on possible links to the atmospheric general circulation in the tropics. Considerable annual and diurnal cycles of the particle number concentration were observed. Highest total particle number concentrations were measured during the dry season (January–March, 519 ± 613 cm−3), lowest during the wet season (July–September, 318 ± 194 cm−3). The more humid FT (relative humidity (RH) range 50–95 %) contained generally higher aerosol particle number concentrations (573 ± 768 cm−3 during dry season, 320 ± 195 cm−3 during wet season) than the dry FT (RH < 50 %, 454 ± 332 cm−3 during dry season, 275 ± 172 cm−3 during wet season), indicating the importance of convection for aerosol distributions in the tropical FT. The diurnal cycle in the variability of the particle number concentration was mainly driven by local orography.

A High Angle, Double Tilting Cold Stage for the AEI EM7

1974 ◽  
Vol 32 ◽  
pp. 450-451
Author(s):  
P.R. Swann ◽  
A.E. Lloyd
Keyword(s):  
Habit Plane ◽  
Temperature Control ◽  
Tilt Angle ◽  
Cooling System ◽  
Thermal Drift ◽  
High Angle ◽  
Cold Stage ◽  
High Degree ◽  
Better Than

Figure 1 shows the design of a specimen stage used for the in situ observation of phase transformations in the temperature range between ambient and −160°C. The design has the following features a high degree of specimen stability during tilting linear tilt actuation about two orthogonal axes for accurate control of tilt angle read-out high angle tilt range for stereo work and habit plane determination simple, robust construction temperature control of better than ±0.5°C minimum thermal drift and transmission of vibration from the cooling system.

STUDIES ON THE AROMATISATION OF NEUTRAL STEROIDS IN PREGNANT WOMEN

1964 ◽  
Vol 45 (4) ◽  
pp. 535-559 ◽  
Author(s):  
E. Bolté ◽  
S. Mancuso ◽  
G. Eriksson ◽  
N. Wiqvist ◽  
E. Diczfalusy
Keyword(s):  
Pregnant Women ◽  
Comparative Studies ◽  
Chorionic Gonadotrophin ◽  
Human Chorionic Gonadotrophin ◽  
Radioactive Material ◽  
Placental Barrier ◽  
Therapeutic Abortion ◽  
Limited Ability ◽  
Better Than

ABSTRACT In 15 cases of therapeutic abortion by laparotomy the placenta was disconnected from the foetus and perfused in situ with tracer amounts of radioactive dehydroepiandrosterone (DHA), dehydroepiandrosterone sulphate (DHAS), androst-4-ene-3,17-dione (A), testosterone (T) and 17β-oestradiol (OE2). Analysis of the placentas, perfusates and urine samples revealed an extensive aromatisation of DHA, A and T; more than 70% of the radioactive material recovered was phenolic, and at least 80 % of this phenolic material was identified as oestrone (OE1), 17β-oestradiol (OE2) and oestriol (OE3), the latter being detected only in the urine. Comparative studies indicated that A and T were aromatised somewhat better than DHA and that all three unconjugated steroids were aromatised to a much greater extent than DHAS. Radioactive OE1 and OE2 were isolated and identified in the placentas and perfusates, but no OE3, epimeric oestriols, or ring D ketols could be detected in these sources, not even when human chorionic gonadotrophin (HCG) was added to the blood prior to perfusion. Lack of placental 16-hydroxylation was also apparent when OE2 was perfused. Regardless of the precursor perfused, there was three times more OE2 than OE1 in the placenta and three times more OE1 than OE2 in the perfusate. This was also the case following perfusion with OE2. The results are interpreted as suggesting the existence in the pregnant human of a placental »barrier« limiting the passage of circulating androgen. The barrier consists of a) limited ability to transfer directly DHAS and b) an enzymic mechanism resulting in the rapid and extensive aromatisation of the important androgens DHA, A and T.

TRACERS DERIVED IN SITU REPLICATE AND MIX BETTER THAN FALLOUT TRACERS INCORPORATED INTO GRAIN COATINGS

2017 ◽  
Author(s):  
Amanda H. Schmidt ◽  
◽  
Paul R. Bierman ◽  
Veronica Sosa-Gonzalez ◽  
Thomas B. Neilson ◽  
...  
Keyword(s):  
Better Than
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