Comparison of aerosol extinction coefficients, surface area density, and volume density from SAGE II and in situ aircraft measurements

2008 ◽  
Vol 113 (D10) ◽  
Author(s):  
J. M. Reeves ◽  
J. C. Wilson ◽  
C. A. Brock ◽  
T. P. Bui
Keyword(s):  
Surface Area ◽  
Volume Density ◽  
Aerosol Extinction ◽  
Aircraft Measurements ◽  
Area Density ◽  
Extinction Coefficients

scholarly journals Optimal estimation retrieval of aerosol microphysical properties from SAGE~II satellite observations in the volcanically unperturbed lower stratosphere

2010 ◽  
Vol 10 (9) ◽  
pp. 4295-4317 ◽  
Author(s):  
D. Wurl ◽  
R. G. Grainger ◽  
A. J. McDonald ◽  
T. Deshler
Keyword(s):  
Surface Area ◽  
Lower Stratosphere ◽  
Optimal Estimation ◽  
Retrieval Algorithm ◽  
Aerosol Extinction ◽  
Size Distributions ◽  
Extinction Data ◽  
Aerosol Properties ◽  
Area And Volume

Abstract. Stratospheric aerosol particles under non-volcanic conditions are typically smaller than 0.1 μm. Due to fundamental limitations of the scattering theory in the Rayleigh limit, these tiny particles are hard to measure by satellite instruments. As a consequence, current estimates of global aerosol properties retrieved from spectral aerosol extinction measurements tend to be strongly biased. Aerosol surface area densities, for instance, are observed to be about 40% smaller than those derived from correlative in situ measurements (Deshler et al., 2003). An accurate knowledge of the global distribution of aerosol properties is, however, essential to better understand and quantify the role they play in atmospheric chemistry, dynamics, radiation and climate. To address this need a new retrieval algorithm was developed, which employs a nonlinear Optimal Estimation (OE) method to iteratively solve for the monomodal size distribution parameters which are statistically most consistent with both the satellite-measured multi-wavelength aerosol extinction data and a priori information. By thus combining spectral extinction measurements (at visible to near infrared wavelengths) with prior knowledge of aerosol properties at background level, even the smallest particles are taken into account which are practically invisible to optical remote sensing instruments. The performance of the OE retrieval algorithm was assessed based on synthetic spectral extinction data generated from both monomodal and small-mode-dominant bimodal sulphuric acid aerosol size distributions. For monomodal background aerosol, the new algorithm was shown to fairly accurately retrieve the particle sizes and associated integrated properties (surface area and volume densities), even in the presence of large extinction uncertainty. The associated retrieved uncertainties are a good estimate of the true errors. In the case of bimodal background aerosol, where the retrieved (monomodal) size distributions naturally differ from the correct bimodal values, the associated surface area (A) and volume densities (V) are, nevertheless, fairly accurately retrieved, except at values larger than 1.0 μm2 cm−3 (A) and 0.05 μm3 cm−3 (V), where they tend to underestimate the true bimodal values. Due to the limited information content in the SAGE II spectral extinction measurements this kind of forward model error cannot be avoided here. Nevertheless, the retrieved uncertainties are a good estimate of the true errors in the retrieved integrated properties, except where the surface area density exceeds the 1.0 μm2 cm−3 threshold. When applied to near-global SAGE II satellite extinction measured in 1999 the retrieved OE surface area and volume densities are observed to be larger by, respectively, 20–50% and 10–40% compared to those estimates obtained by the SAGE~II operational retrieval algorithm. An examination of the OE algorithm biases with in situ data indicates that the new OE aerosol property estimates tend to be more realistic than previous estimates obtained from remotely sensed data through other retrieval techniques. Based on the results of this study we therefore suggest that the new Optimal Estimation retrieval algorithm is able to contribute to an advancement in aerosol research by considerably improving current estimates of aerosol properties in the lower stratosphere under low aerosol loading conditions.

scholarly journals Studying the vertical aerosol extinction coefficient by comparing in situ airborne data and elastic backscatter lidar

2016 ◽  
Vol 16 (7) ◽  
pp. 4539-4554 ◽  
Author(s):  
Bernadette Rosati ◽  
Erik Herrmann ◽  
Silvia Bucci ◽  
Federico Fierli ◽  
Francesco Cairo ◽  
...  
Keyword(s):  
Absorption Coefficient ◽  
Aerosol Particle ◽  
Index Of Refraction ◽  
Aerosol Extinction ◽  
Hygroscopic Growth ◽  
Dynamic Features ◽  
Extinction Coefficients ◽  
Po Valley ◽  
Ground Station

Abstract. Vertical profiles of aerosol particle optical properties were explored in a case study near the San Pietro Capofiume (SPC) ground station during the PEGASOS Po Valley campaign in the summer of 2012. A Zeppelin NT airship was employed to investigate the effect of the dynamics of the planetary boundary layer at altitudes between ∼  50 and 800 m above ground. Determined properties included the aerosol particle size distribution, the hygroscopic growth factor, the effective index of refraction and the light absorption coefficient. The first three parameters were used to retrieve the light scattering coefficient. Simultaneously, direct measurements of both the scattering and absorption coefficient were carried out at the SPC ground station. Additionally, a single wavelength polarization diversity elastic lidar system provided estimates of aerosol extinction coefficients using the Klett method to accomplish the inversion of the signal, for a vertically resolved comparison between in situ and remote-sensing results. Note, however, that the comparison was for the most part done in the altitude range where the overlap function is incomplete and accordingly uncertainties are larger. First, the airborne results at low altitudes were validated with the ground measurements. Agreement within approximately ±25 and ±20 % was found for the dry scattering and absorption coefficient, respectively. The single scattering albedo, ranged between 0.83 and 0.95, indicating the importance of the absorbing particles in the Po Valley region. A clear layering of the atmosphere was observed during the beginning of the flight (until ∼  10:00 LT – local time) before the mixing layer (ML) was fully developed. Highest extinction coefficients were found at low altitudes, in the new ML, while values in the residual layer, which could be probed at the beginning of the flight at elevated altitudes, were lower. At the end of the flight (after ∼  12:00 LT) the ML was fully developed, resulting in constant extinction coefficients at all altitudes measured on the Zeppelin NT. Lidar estimates captured these dynamic features well and good agreement was found for the extinction coefficients compared to the in situ results, using fixed lidar ratios (LR) between 30 and 70 sr for the altitudes probed with the Zeppelin. These LR are consistent with values for continental aerosol particles that can be expected in this region.

scholarly journals The CU Airborne MAX-DOAS instrument: vertical profiling of aerosol extinction and trace gases

2013 ◽  
Vol 6 (3) ◽  
pp. 719-739 ◽  
Author(s):  
S. Baidar ◽  
H. Oetjen ◽  
S. Coburn ◽  
B. Dix ◽  
I. Ortega ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Air Quality ◽  
Spatial Scales ◽  
Trace Gases ◽  
Stray Light ◽  
Aerosol Extinction ◽  
Vertical Profiles ◽  
Maximum Information ◽  
Extinction Coefficients

Abstract. The University of Colorado Airborne Multi-Axis Differential Optical Absorption Spectroscopy (CU AMAX-DOAS) instrument uses solar stray light to detect and quantify multiple trace gases, including nitrogen dioxide (NO2), glyoxal (CHOCHO), formaldehyde (HCHO), water vapor (H2O), nitrous acid (HONO), iodine monoxide (IO), bromine monoxide (BrO), and oxygen dimers (O4) at multiple wavelengths (absorption bands at 360, 477, 577, 632 nm) simultaneously in the open atmosphere. The instrument is unique as it (1) features a motion compensation system that decouples the telescope field of view from aircraft movements in real time (<0.35° accuracy), and (2) includes measurements of solar stray light photons from nadir, zenith, and multiple elevation angles forward and below the plane by the same spectrometer/detector system. Sets of solar stray light spectra collected from nadir to zenith scans provide some vertical profile information within 2 km above and below the aircraft altitude, and the vertical column density (VCD) below the aircraft is measured in nadir view. Maximum information about vertical profiles is derived simultaneously for trace gas concentrations and aerosol extinction coefficients over similar spatial scales and with a vertical resolution of typically 250 m during aircraft ascent/descent. The instrument is described, and data from flights over California during the CalNex (California Research at the Nexus of Air Quality and Climate Change) and CARES (Carbonaceous Aerosols and Radiative Effects Study) air quality field campaigns is presented. Horizontal distributions of NO2 VCD (below the aircraft) maps are sampled with typically 1 km resolution, and show good agreement with two ground-based MAX-DOAS instruments (slope = 0.95 ± 0.09, R2 = 0.86). As a case study vertical profiles of NO2, CHOCHO, HCHO, and H2O concentrations and aerosol extinction coefficients, ε, at 477 nm calculated from O4 measurements from a low approach at Brackett airfield inside the South Coast Air Basin (SCAB) are presented. These profiles contain ~12 degrees of freedom (DOF) over a 3.5 km altitude range, an independent information approximately every 250 m. The boundary layer NO2 concentration, and the integral aerosol extinction over height (aerosol optical depth, AOD) agrees well with nearby ground-based in situ NO2 measurement, and AERONET station. The detection limits of NO2, CHOCHO, HCHO, H2O442, &amp;varepsilon;360, &amp;varepsilon;477 for 30 s integration time spectra recorded forward of the plane are 5 ppt, 3 ppt, 100 ppt, 42 ppm, 0.004 km−1, 0.002 km−1 in the free troposphere (FT), and 30 ppt, 16 ppt, 540 ppt, 252 ppm, 0.012 km−1, 0.006 km−1 inside the boundary layer (BL), respectively. Mobile column observations of trace gases and aerosols are complimentary to in situ observations, and help bridge the spatial scales that are probed by satellites and ground-based observations, and predicted by atmospheric models.

scholarly journals The Spectral Aerosol Extinction Monitoring System (SǼMS): setup, observational products, and comparisons

2014 ◽  
Vol 7 (3) ◽  
pp. 701-712 ◽  
Author(s):  
A. Skupin ◽  
A. Ansmann ◽  
R. Engelmann ◽  
H. Baars ◽  
T. Müller
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Monitoring System ◽  
Aerosol Extinction ◽  
Extinction Coefficients ◽  
Spectrally Resolved ◽  
Automated Instrument ◽  
Statistical Results

Abstract. The Spectral Aerosol Extinction Monitoring System (SǼMS) is presented that allows us to continuously measure the spectral extinction coefficient of atmospheric aerosol particles along an approximately 2.7 km long optical path at 30–50 m height above ground in Leipzig (51.3° N, 12.4° E), Germany. The fully automated instrument measures the ambient aerosol extinction coefficients from 300 to 1000 nm. The main goal of SǼMS observations are long-term studies of the relationship between particle extinction and relative humidity from below 40% to almost 100%. The setup is presented and observations (a case study and statistical results for 2009) are discussed in terms of time series of 550 nm particle optical depth, Ångström exponent, and particle size distribution retrieved from the spectrally resolved extinction. The SǼMS measurements are compared with simultaneously performed EARLINET (European Aerosol Research Lidar Network) lidar, AERONET (Aerosol Robotic Network) sun photometer, and in situ aerosol observations of particle size distribution and related extinction coefficients on the roof of our institute. Consistency between the different measurements is found, which corroborates the quality of the SǼMS observations. Statistical results of a period of 1 yr (2009) show mode extinction values of 0.09 km−1 (SǼMS), 0.075 km−1 (AERONET), and 0.03 km−1 (in situ). Ångström exponents for this period are 0.19 (390–880 nm, SǼMS) and 1.55 (440–870 nm, AERONET).

scholarly journals Comparison of vertical aerosol extinction coefficients from in-situ and LIDAR measurements

2015 ◽  
Vol 15 (13) ◽  
pp. 18609-18651
Author(s):  
B. Rosati ◽  
E. Herrmann ◽  
S. Bucci ◽  
F. Fierli ◽  
F. Cairo ◽  
...  
Keyword(s):  
Absorption Coefficient ◽  
Local Time ◽  
Index Of Refraction ◽  
Aerosol Size Distribution ◽  
Aerosol Extinction ◽  
Dynamic Features ◽  
Extinction Coefficients ◽  
Po Valley ◽  
Ground Station

Abstract. Vertical profiles of aerosol optical properties were explored in a case study near the San Pietro Capofiume (SPC) ground station during the PEGASOS Po Valley campaign in the summer of 2012. A Zeppelin NT airship was employed to investigate the effect of the dynamics of the planetary boundary layer at altitudes between ~ 50–800 m above ground. Determined properties included the aerosol size distribution, the hygroscopic growth factor, the effective index of refraction and the light absorption coefficient. The first three parameters were used to retrieve the light scattering coefficient. Simultaneously, direct measurements of both the scattering and absorption coefficient were carried out at the SPC ground station. Additionally, a LIDAR system provided aerosol extinction coefficients for a vertically resolved comparison between in-situ and remote sensing results. First, the airborne results at low altitudes were validated with the ground measurements. Agreement within approximately ±25 and ±20% was found for the dry scattering and absorption coefficient, respectively. The single scattering albedo, ranged between 0.83 to 0.95, indicating the importance of the absorbing particles in the Po Valley region. A clear layering of the atmosphere was observed during the beginning of the flight (until ~ 10 local time) before the mixed layer (ML) was fully developed. Highest extinction coefficients were found at low altitudes, in the new ML, while values in the residual layer, which could be probed at the beginning of the flight at elevated altitudes, were lower. At the end of the flight (after ~ 12 local time) the ML was fully developed, resulting in constant extinction coefficients at all altitudes measured on the Zeppelin NT. LIDAR results captured these dynamic features well and good agreement was found for the extinction coefficients compared to the in-situ results, using fixed LIDAR ratios (LR) between 30 and 70 sr for the altitudes probed with the Zeppelin. These LR are consistent with values for continental aerosol particles that can be expected in this region.

scholarly journals SAGE II measurements of stratospheric aerosol properties at non-volcanic levels

2008 ◽  
Vol 8 (4) ◽  
pp. 983-995 ◽  
Author(s):  
L. W. Thomason ◽  
S. P. Burton ◽  
B.-P. Luo ◽  
T. Peter
Keyword(s):  
Surface Area ◽  
Historical Record ◽  
Stratospheric Aerosol ◽  
The Other ◽  
Processing Algorithm ◽  
Aerosol Extinction ◽  
Retrieval Process ◽  
Satellite Measurements ◽  
Area Density ◽  
Aerosol Properties

Abstract. Since 2000, stratospheric aerosol levels have been relatively stable and at the lowest levels observed in the historical record. Given the challenges of making satellite measurements of aerosol properties at these levels, we have performed a study of the sensitivity of the product to the major components of the processing algorithm used in the production of SAGE II aerosol extinction measurements and the retrieval process that produces the operational surface area density (SAD) product. We find that the aerosol extinction measurements, particularly at 1020 nm, remain robust and reliable at the observed aerosol levels. On the other hand, during background periods, the SAD operational product has an uncertainty of at least a factor of 2 due to the lack of sensitivity to particles with radii less than 100 nm.

scholarly journals SAGE II measurements of stratospheric aerosol properties at non-volcanic levels

2007 ◽  
Vol 7 (3) ◽  
pp. 6959-6997 ◽  
Author(s):  
L. W. Thomason ◽  
S. P. Burton ◽  
B.-P. Luo ◽  
T. Peter
Keyword(s):  
Surface Area ◽  
Historical Record ◽  
Stratospheric Aerosol ◽  
The Other ◽  
Processing Algorithm ◽  
Aerosol Extinction ◽  
Retrieval Process ◽  
Satellite Measurements ◽  
Area Density ◽  
Aerosol Properties

Abstract. Since 2000, stratospheric aerosol levels have been relatively stable and at the lowest levels observed in the historical record. Given the challenges of making satellite measurements of aerosol properties at these levels, we have performed a study of the sensitivity of the product to the major components of the processing algorithm used in the production of SAGE II aerosol extinction measurements and the retrieval process that produces the operational surface area density (SAD) product. We find that the aerosol extinction measurements, particularly at 1020 nm, remain robust and reliable at the observed aerosol levels. On the other hand, background periods, the SAD operational product has an uncertainty of at least a factor of 2 due to the lack of sensitivity to particles with radii less than 100 nm.

scholarly journals Diurnal Behavior of Aerosol Optical Properties Studied with Lidar and Ground-Based Instruments

2020 ◽  
Vol 237 ◽  
pp. 02011
Author(s):  
Prane Mariel Ong ◽  
Nofel Lagrosas ◽  
Tatsuo Shiina ◽  
Hiroaki Kuze
Keyword(s):  
Single Scattering ◽  
In Situ Monitoring ◽  
Aerosol Extinction ◽  
Size Change ◽  
Near Surface ◽  
Extinction Coefficients ◽  
Number Distribution ◽  
Combined Use ◽  
Diurnal Behavior

The combined use of remote sensing and in-situ monitoring instruments could help improve the assessment of near-surface aerosol properties. In this paper, we analyze the diurnal behavior of aerosol extinction coefficients, αExt(λ), at λ=349 and 550 nm using a lidar and a present weather detector, respectively. We utilize the aerosol optical thickness (AOT), single scattering albedo (SSA), and Ångström exponent (AE) from SKYNET sky radiometer, and AE from aethalometer, and the number distribution from optical particle counter to evaluate the effect of relative humidity (RH) on aerosol extinction coefficients. It is found that although αExt(λ) often exhibits a positive correlation with the ambient RH, this relation is obscured when both the number distribution and particle size change simultaneously. Moreover, αExt at 349 nm is more sensitive to this change than at 550 nm.

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