Assessment of the COVID-19 Lockdown Effects on Spectral Aerosol Scattering and Absorption Properties in Athens, Greece

COVID-19 is evolving into one of the worst pandemics in recent history, claiming a death toll of over 1.5 million as of December 2020. In an attempt to limit the expansion of the pandemic in its initial phase, nearly all countries imposed restriction measures, which resulted in an unprecedented reduction of air pollution. This study aims to assess the impact of the lockdown effects due to COVID-19 on in situ measured aerosol properties, namely spectral-scattering (bsca) and absorption (babs) coefficients, black carbon (BC) concentrations, single-scattering albedo (SSA), scattering and absorption Ångström exponents (SAE, AAE) in Athens, Greece. Moreover, a comparison is performed with the regional background site of Finokalia, Crete, for a better assessment of the urban impact on observed differences. The study examines pre-lockdown (1–22 March 2020), lockdown (23 March–3 May 2020) and post-lockdown (4–31 May 2020) periods, while the aerosol properties are also compared with a 3–4 year preceding period (2016/2017–2019). Comparison of meteorological parameters in Athens, between the lockdown period and respective days in previous years, showed only marginal variation, which is not deemed sufficient in order to justify the notable changes in aerosol concentrations and optical properties. The largest reduction during the lockdown period was observed for babs compared to the pre-lockdown (−39%) and to the same period in previous years (−36%). This was intensified during the morning traffic hours (−60%), reflecting the large decrease in vehicular emissions. Furthermore, AAE increased during the lockdown period due to reduced emissions from fossil-fuel combustion, while a smaller (−21%) decrease was observed for bsca along with slight increases (6%) in SAE and SSA values, indicating that scattering aerosol properties were less affected by the decrease in vehicular emissions, as they are more dependent on regional sources and atmospheric processing. Nighttime BC emissions related to residential wood-burning were slightly increased during the lockdown period, with respect to previous-year means. On the contrary, aerosol and pollution changes during the lockdown period at Finokalia were low and highly sensitive to natural sources and processes.

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

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-9435-2016 ◽

2016 ◽

Vol 16 (14) ◽

pp. 9435-9455 ◽

Cited By ~ 8

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.

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Quantifying the impact of aerosol scattering on the retrieval of methane from airborne remote sensing measurements

Atmospheric Measurement Techniques ◽

10.5194/amt-13-6755-2020 ◽

2020 ◽

Vol 13 (12) ◽

pp. 6755-6769

Author(s):

Yunxia Huang ◽

Vijay Natraj ◽

Zhao-Cheng Zeng ◽

Pushkar Kopparla ◽

Yuk L. Yung

Keyword(s):

Remote Sensing ◽

Surface Albedo ◽

Single Scattering ◽

Water Soluble ◽

Transfer Model ◽

Background Values ◽

Ch4 Emissions ◽

Aerosol Scattering ◽

The Impact ◽

Retrieval Bias

Abstract. As a greenhouse gas with strong global warming potential, atmospheric methane (CH4) emissions have attracted a great deal of attention. Although remote sensing measurements can provide information about CH4 sources and emissions, accurate retrieval is challenging due to the influence of atmospheric aerosol scattering. In this study, imaging spectroscopic measurements from the Airborne Visible/Infrared Imaging Spectrometer – Next Generation (AVIRIS-NG) in the shortwave infrared are used to compare two retrieval techniques – the traditional matched filter (MF) method and the optimal estimation (OE) method, which is a popular approach for trace gas retrievals. Using a numerically efficient radiative transfer model with an exact single-scattering component and a two-stream multiple-scattering component, we also simulate AVIRIS-NG measurements for different scenarios and quantify the impact of aerosol scattering in the two retrieval schemes by including aerosols in the simulations but not in the retrievals. The presence of aerosols causes an underestimation of CH4 in both the MF and OE retrievals; the biases increase with increasing surface albedo and aerosol optical depth (AOD). Aerosol types with high single-scattering albedo and low asymmetry parameter (such as water-soluble aerosols) induce large biases in the retrieval. When scattering effects are neglected, the MF method exhibits lower fractional retrieval bias compared to the OE method at high CH4 concentrations (2–5 times typical background values) and is suitable for detecting strong CH4 emissions. For an AOD value of 0.3, the fractional biases of the MF retrievals are between 1.3 % and 4.5 %, while the corresponding values for OE retrievals are in the 2.8 %–5.6 % range. On the other hand, the OE method is an optimal technique for diffuse sources (<1.5 times typical background values), showing up to 5 times smaller fractional retrieval bias (8.6 %) than the MF method (42.6 %) for the same AOD scenario. However, when aerosol scattering is significant, the OE method is superior since it provides a means to reduce biases by simultaneously retrieving AOD, surface albedo, and CH4. The results indicate that, while the MF method is good for plume detection, the OE method should be employed to quantify CH4 concentrations, especially in the presence of aerosol scattering.

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Vertical profiles of sub-micron aerosol single scattering albedo over Indian region immediately before monsoon onset and during its development: Research from the SWAAMI field campaign

10.5194/acp-2019-657 ◽

2019 ◽

Author(s):

Mohanan R. Manoj ◽

Sreedharan K. Satheesh ◽

Krishnaswamy K. Moorthy ◽

Hugh Coe

Keyword(s):

Active Phase ◽

Single Scattering ◽

Single Scattering Albedo ◽

Development Research ◽

Aerosol Absorption ◽

South West ◽

Aerosol Scattering ◽

First Time ◽

Geographical Locations

Abstract. Vertical structures of aerosol single scattering albedo (SSA), from near the surface through the free troposphere, have been estimated for the first time at distinct geographical locations over the Indian mainland and adjoining oceans, using in-situ measurements of aerosol scattering and absorption coefficients aboard the FAAM BAe-146 aircraft during the South West Asian Aerosol Monsoon Interactions (SWAAMI) campaign from June to July 2016. These are used to examine the spatial variation of SSA profiles and also to characterize its transformation from just prior to the onset of Indian Summer Monsoon (June 2016) to its active phase (July 2016). Very strong aerosol absorption, with SSA values as low as 0.7, persisted in the lower altitudes (

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

10.5194/acp-2015-935 ◽

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.

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Seasonal differences in the vertical profiles of aerosol optical properties over rural Oklahoma

Atmospheric Chemistry and Physics ◽

10.5194/acp-11-10661-2011 ◽

2011 ◽

Vol 11 (20) ◽

pp. 10661-10676 ◽

Cited By ~ 34

Author(s):

E. Andrews ◽

P. J. Sheridan ◽

J. A. Ogren

Keyword(s):

Seasonal Variability ◽

Gulf Coast ◽

Single Scattering ◽

Single Scattering Albedo ◽

Ambient Conditions ◽

Seasonal Differences ◽

Aerosol Loading ◽

Aerosol Absorption ◽

Aerosol Scattering

Abstract. A small airplane made 597 aerosol optical property (light absorption and light scattering) vertical profile measurements over a rural Oklahoma site between March 2000 and December 2007. The aerosol profiles obtained during these 8 yr of measurements suggest significant seasonal differences in aerosol loading (scattering and absorption). The highest amounts of scattering and absorbing aerosol are observed during the summer and the lowest loading occurs during the winter. The relative contribution of aerosol absorption is highest in the winter (i.e., single scattering albedo is lowest in winter), particularly aloft. Aerosol absorption generally decreased with altitude below ~1.5 km and then was relatively constant or decreased more gradually above that. Aerosol scattering decreased sharply with altitude below ~1.5 km but, unlike absorption, also decreased at higher altitudes, albeit less sharply. Scattering Ångström exponents suggest that the aerosol was dominated by sub-micron aerosol during the summer at all altitudes, but that larger particles were present, especially in the spring and winter above 1 km. The seasonal variability observed for aerosol loading is consistent with AERONET aerosol optical depth (AOD) although the AOD values calculated from in situ adjusted to ambient conditions and matching wavelengths are up to a factor of two lower than AERONET AOD values depending on season. The column averaged single scattering albedo derived from in situ airplane measurements are similar in value to the AERONET single scattering albedo inversion product but the seasonal patterns are different – possibly a consequence of the strict constraints on obtaining single scattering albedo from AERONET data. A comparison of extinction Ångström exponent and asymmetry parameter from the airplane and AERONET platforms suggests similar seasonal variability with smaller particles observed in the summer and fall and larger particles observed in spring and winter. The observed seasonal cycle of aerosol loading corresponds with changes in air mass back trajectories: the aerosol scattering was higher when transport was from polluted areas (e.g., the Gulf Coast) and lower when the air came from cleaner regions and/or the upper atmosphere.

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Global variability of aerosol optical properties retrieved from the network of GAW near-surface observatories

10.5194/egusphere-egu2020-3568 ◽

2020 ◽

Author(s):

Alessandro Bigi ◽

Martine Collaud Coen ◽

Elisabeth J. Andrews ◽

Clémence Rose ◽

Cathrine Lund Myhre ◽

...

Keyword(s):

Optical Properties ◽

Single Scattering ◽

Single Scattering Albedo ◽

Scattering Coefficient ◽

Near Surface ◽

World Data ◽

Data Centre ◽

The Impact ◽

Urban Sites ◽

Aerosol Properties

Atmospheric aerosols are known to play a key role in Earth&#8217;s radiative budget, although the quantification of their climate forcing is still highly uncertain. In order to improve the scientific understanding of their climatic effect, in-situ ground-based aerosol properties observations are needed by the research community. Such data would also allow the global assessment of the effect of environmental policies over both the short and the long term.To develop a robust and consistent view over time of the worldwide variability of aerosol properties, data resulting from a fully-characterized value chain, including uncertainty estimation, is needed.The present work is part of a wider project, having among its goals the investigation of the variability of climate-relevant aerosol properties observed at all sites connected to the Global Atmospheric Watch network, whose data are publicly available from the World Data Centre for Aerosols and follow the aforementioned specifications.This work focuses on aerosol optical proprieties, i.e. the aerosol light scattering coefficient (&#963;sp), the aerosol light absorption coefficient (&#963;ap), single scattering albedo (&#969;o) and both scattering and absorption &#197;ngstr&#246;m exponents (&#229;sp and &#229;ap).The analysis includes 108 yearly datasets collected either during 2016 or 2017 at different sites: 53 for absorption and 55 for scattering coefficient datasets, respectively. For 29 of these sites it was also possible to compute single scattering albedo.The spatial variability in extensive and intensive optical properties was analysed in terms of each site&#8217;s geographical location (either polar, continental, coastal or mountain) and its footprint (from pristine to urban, representing increasing levels of anthropogenic influence).The results highlight the impact of anthropogenic emissions and biomass burning on absolute levels and annual variability. The effect of sea spray or long range transport of dust is also evident for several sites, along with the influence of regional emissions. The largest seasonality in aerosol loading was observed at mountain sites under mixed footprint conditions, while the lowest seasonality occurred at urban sites. Urban sites also exhibited the highest &#963;sp and &#963;ap values. The lowest levels in &#963;sp and &#963;ap were observed at some polar sites, along with few coastal and mountain sites, despite their typically mixed footprint.AcknowledgementsThe authors acknowledge WMO-GAW World Data Centre on Aerosol for providing data available at http://ebas.nilu.no

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Long term trends in aerosol optical characteristics in the Po Valley (IT)

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-14-9041-2014 ◽

2014 ◽

Vol 14 (7) ◽

pp. 9041-9065

Author(s):

J. P. Putaud ◽

F. Cavalli ◽

S. Martins dos Santos ◽

A. Dell'Acqua

Keyword(s):

Radiative Forcing ◽

Mass Concentration ◽

Measurement Data ◽

Single Scattering ◽

Single Scattering Albedo ◽

Po Valley ◽

Aerosol Absorption ◽

Aerosol Scattering ◽

The One

Abstract. Aerosols properties have been monitored by ground-based in situ and remote sensing measurements at the station for atmospheric research located in Ispra on the edge of the Po Valley for almost one decade. In-situ measurements are performed according to Global Atmosphere Watch recommendations, and quality is assured through the participation in regular inter-laboratory comparisons. Sunphotometer data are produced by AERONET. Data show significant decreasing trends over 2004–2010 for a number of variables including particulate matter (PM) mass concentration, aerosol scattering, backscattering and absorption coefficients, and aerosol optical thickness (AOT). In-situ measurement data show no significant trend in the aerosol backscatter ratio, but a significant decreasing trend of about −0.7 ± 0.3% in the aerosol single scattering albedo in the visible light range. Similar trends are observed in the aerosol single scattering albedo retrieved from sunphotometer measurements. Correlations appear between in situ PM mass concentration and aerosol scattering coefficient on the one hand, and elemental carbon (EC) and aerosol absorption coefficient on the other hand, however, no increase in the EC / PM ratio was observed, which could have explained the decrease in SSA. The application of a simple approximation to calculate the direct radiative forcing by aerosols suggests a significant diminution in their cooling effect, mainly due to the decrease in AOT. Applying the methodology we present to those sites where the necessary suite of measurements is available would provide important information to inform future policies for air quality enhancement and fast climate change mitigation.

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Vertical profiles of aerosol optical properties over central Illinois and comparison with surface and satellite measurements

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-11695-2012 ◽

2012 ◽

Vol 12 (23) ◽

pp. 11695-11721 ◽

Cited By ~ 35

Author(s):

P. J. Sheridan ◽

E. Andrews ◽

J. A. Ogren ◽

J. L. Tackett ◽

D. M. Winker

Keyword(s):

Relative Humidity ◽

Single Scattering ◽

Single Scattering Albedo ◽

Light Extinction ◽

Vertical Profiles ◽

Satellite Measurements ◽

Central Illinois ◽

532 Nm ◽

Aerosol Properties

Abstract. Between June 2006 and September 2009, an instrumented light aircraft measured over 400 vertical profiles of aerosol and trace gas properties over eastern and central Illinois. The primary objectives of this program were to (1) measure the in situ aerosol properties and determine their vertical and temporal variability and (2) relate these aircraft measurements to concurrent surface and satellite measurements. The primary profile location was within 15 km of the NOAA/ESRL surface aerosol monitoring station near Bondville, Illinois. Identical instruments at the surface and on the aircraft ensured that the data from both platforms would be directly comparable and permitted a determination of how representative surface aerosol properties were of the lower column. Aircraft profiles were also conducted occasionally at two other nearby locations to increase the frequency of A-Train satellite underflights for the purpose of comparing in situ and satellite-retrieved aerosol data. Measurements of aerosol properties conducted at low relative humidity over the Bondville site compare well with the analogous surface aerosol data and do not indicate any major sampling issues or that the aerosol is radically different at the surface compared with the lowest flyby altitude of ~ 240 m above ground level. Statistical analyses of the in situ vertical profile data indicate that aerosol light scattering and absorption (related to aerosol amount) decreases substantially with increasing altitude. Parameters related to the nature of the aerosol (e.g., single-scattering albedo, Ångström exponent, etc.), however, are relatively constant throughout the mixed layer, and do not vary as much as the aerosol amount throughout the profile. While individual profiles often showed more variability, the median in situ single-scattering albedo was 0.93–0.95 for all sampled altitudes. Several parameters (e.g., submicrometer scattering fraction, hemispheric backscattering fraction, and scattering Ångström exponent) suggest that the fraction of smaller particles in the aerosol is larger near the surface than at high altitudes. The observed dependence of scattering on size, wavelength, angular integration range, and relative humidity, together with the spectral dependence of absorption, show that the aerosol at higher altitudes is larger, less hygroscopic, and more strongly absorbing at shorter wavelengths, suggesting an increased contribution from dust or organic aerosols. The aerosol profiles show significant differences among seasons. The largest amounts of aerosol (as determined by median light extinction profile measurements) throughout most of the sampled column were observed during summer, with the lowest amounts in the winter and intermediate values in the spring and fall. The highest three profile levels (3.1, 3.7, 4.6 km), however, showed larger median extinction values in the spring, which could reflect long-range transport of dust or smoke aerosols. The aerosols in the mixed layer were darkest (i.e., lowest single-scattering albedo) in the fall, in agreement with surface measurements at Bondville and other continental sites in the US. In situ profiles of aerosol radiative forcing efficiency showed little seasonal or vertical variability. Underflights of the CALIPSO satellite show reasonable agreement in a majority of retrieved profiles between aircraft-measured extinction at 532 nm (adjusted to ambient relative humidity) and CALIPSO-retrieved extinction, and suggest that routine aircraft profiling programs can be used to better understand and validate satellite retrieval algorithms. CALIPSO tended to overestimate the aerosol extinction at this location in some boundary layer flight segments when scattered or broken clouds were present, which could be related to problems with CALIPSO cloud screening methods. The in situ aircraft-collected aerosol data suggest extinction thresholds for the likelihood of aerosol layers being detected by the CALIOP lidar. In this study, aerosol layers with light extinction (532 nm) values > 50 Mm−1 were detected by CALIPSO ~ 95% of the time, while aerosol layers with extinction values lower than 10 Mm−1 had a detection efficiency of < 2%. For all collocated comparison cases, a 50% probability of detection falls at an in situ extinction level of 20–25 Mm−1. These statistical data offer guidance as to the likelihood of CALIPSO's ability to retrieve aerosol extinction at various locations around the globe.

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Long-term trends in aerosol optical characteristics in the Po Valley, Italy

Atmospheric Chemistry and Physics ◽

10.5194/acp-14-9129-2014 ◽

2014 ◽

Vol 14 (17) ◽

pp. 9129-9136 ◽

Cited By ~ 22

Author(s):

J. P. Putaud ◽

F. Cavalli ◽

S. Martins dos Santos ◽

A. Dell'Acqua

Keyword(s):

Radiative Forcing ◽

Mass Concentration ◽

Measurement Data ◽

Single Scattering ◽

Po Valley ◽

Aerosol Absorption ◽

Aerosol Scattering ◽

Sun Photometer ◽

The One

Abstract. Aerosol properties have been monitored by ground-based in situ and remote sensing measurements at the station for atmospheric research located in Ispra, on the edge of the Po Valley, for almost one decade. In situ measurements are performed according to Global Atmosphere Watch recommendations, and quality is assured through the participation in regular inter-laboratory comparisons. Sun-photometer data are produced by the Aerosol Robotic Network (AERONET). Data show significant decreasing trends over the 2004–2010 period for a number of variables, including particulate matter (PM) mass concentration, aerosol scattering, backscattering and absorption coefficients, and aerosol optical thickness (AOT). In situ measurement data show no significant trends in the aerosol backscatter ratio, but they do show a significant decreasing trend of about −0.7 ± 0.3% yr−1 in the aerosol single scattering albedo (SSA) in the visible light range. Similar trends are observed in the SSA retrieved from sun-photometer measurements. Correlations appear between in situ PM mass concentration and aerosol scattering coefficient, on the one hand, and elemental carbon (EC) concentration and aerosol absorption coefficient, on the other hand. However, no increase in the EC / PM ratio was observed, which could have explained the decrease in SSA. The application of a simple approximation to calculate the direct radiative forcing by aerosols suggests a significant diminution in their cooling effect, mainly due to the decrease in AOT. Applying the methodology we present to those sites, where the necessary suite of measurements is available, would provide important information to inform future policies for air-quality enhancement and fast climate change mitigation.

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Sources of discrepancy between aerosol optical depth obtained from AERONET and in-situ aircraft profiles

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-2987-2012 ◽

2012 ◽

Vol 12 (6) ◽

pp. 2987-3003 ◽

Cited By ~ 27

Author(s):

A. R. Esteve ◽

J. A. Ogren ◽

P. J. Sheridan ◽

E. Andrews ◽

B. N. Holben ◽

...

Keyword(s):

Optical Properties ◽

Aerosol Optical Depth ◽

Optical Depth ◽

Single Scattering ◽

Retrieval Algorithm ◽

Aircraft Measurements ◽

Aerosol Optical Properties ◽

The One ◽

Aerosol Properties

Abstract. Aerosol optical properties were measured by NOAA's Airborne Aerosol Observatory over Bondville, Illinois, during more than two years using a light aircraft. Measured properties included total light scattering, backscattering, and absorption, while calculated parameters included aerosol optical depth (AOD), Ångström exponent, single-scattering albedo, hemispheric backscatter fraction, asymmetry parameter, and submicrometer mode fraction of scattering. The in-situ aircraft measurements are compared here with AERONET measurements and retrievals of the aerosol optical properties at the same location, although it is difficult to verify the AERONET retrieval algorithm at a site that is not highly polluted. The comparison reveals discrepancies between the aerosol properties retrieved from AERONET and from in-situ aircraft measurements. These discrepancies are smaller for the AOD, while the biggest discrepancies are for the other derived aerosol properties. Possible sources of discrepancy between the AOD measured by AERONET and the one calculated from the in-situ aircraft measurements are investigated. The largest portion of the AOD discrepancy is likely due to an incorrect adjustment to ambient RH of the scattering coefficient. Another significant part (along with uncertain nephelometer truncation corrections) may come from the possibility that there might be less aerosol below the lowest flight altitude or that the aircraft inlet excludes aerosol particles larger than 5–7 μm diameter.

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