Aerosol size distribution and aerosol optical depth at a savannah in the south-west of Africa: Results of optical measurements

1986 ◽  
Vol 17 (3) ◽  
pp. 245-248 ◽  
Author(s):  
E. Thomalla ◽  
H. Kremser ◽  
P. Koepke ◽  
H. Quenzel
Keyword(s):  
Size Distribution ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Optical Measurements ◽  
Aerosol Size Distribution ◽  
The South ◽  
South West

scholarly journals Using MODIS and AERONET to Determine GCM Aerosol Size

2006 ◽  
Vol 63 (4) ◽  
pp. 1338-1347 ◽  
Author(s):  
Glen Lesins ◽  
Ulrike Lohmann
Keyword(s):  
Size Distribution ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
General Circulation ◽  
Climate Model ◽  
General Circulation Models ◽  
Aerosol Size Distribution ◽  
Error Source ◽  
Fine Mode ◽  
Fine Mode Aerosol

Abstract Aerosol size is still a poorly constrained quantity in general circulation models (GCMs). By using the modal radii of the coarse and fine mode retrieved from 103 stations in the Aerosol Robotic Network (AERONET) and the fine mode aerosol optical depth fraction derived from both the Moderate Resolute Imaging Spectroradiometer (MODIS) Terra and AERONET, a globally and monthly averaged aerosol size distribution dataset was computed assuming internally mixed aerosols. Different methods were employed in creating the size distribution datasets that were input to the ECHAM4 climate model giving a globally averaged aerosol optical depth (AOD) at 500 nm that ranged from 0.11 to 0.20 depending on the method. This translates into a globally averaged direct aerosol top-of-atmosphere forcing range from −1.6 to −3.9 W m−2. Reducing the uncertainty in the aerosol sizes is important when using AOD to validate models since mass burden errors can then be assumed to be the main AOD error source. This paper explores a procedure that can help achieve this goal.

scholarly journals The European aerosol budget in 2006

2010 ◽  
Vol 10 (9) ◽  
pp. 21391-21437 ◽  
Author(s):  
J. M. J. Aan de Brugh ◽  
M. Schaap ◽  
E. Vignati ◽  
F. Dentener ◽  
M. Kahnert ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Transport Model ◽  
Ground Level ◽  
Sea Salt ◽  
Optical Measurements ◽  
Aerosol Size Distribution ◽  
Anthropogenic Aerosols ◽  
Removal Rates ◽  
Wet Removal

Abstract. This paper presents the aerosol budget over Europe in 2006 calculated with the global transport model TM5 coupled to the size-resolved aerosol module M7. Comparison with ground observations indicates that the model reproduces the observed concentrations quite well with an expected slight underestimation of PM10 due to missing emissions (e.g. resuspension). We observe that a little less than half of the anthropogenic aerosols emitted in Europe are exported and the rest is removed by deposition. The anthropogenic aerosols are removed mostly by rain (95%) and only 5% is removed by dry deposition. For the larger natural aerosols, especially sea salt, a larger fraction is removed by dry processes (sea salt: 70%, mineral dust: 35%). We observe transport of aerosols in the jet stream in the higher atmosphere and an import of Sahara dust from the south at high altitudes. Comparison with optical measurements shows that the model reproduces the Ångström parameter very well, which indicates a correct simulation of the aerosol size distribution. However, we observe an underestimation of the aerosol optical depth. Because the surface concentrations are close to the observations, the shortage of aerosol in the model is probably at higher altitudes. We show that the discrepancies are mainly caused by an overestimation of wet-removal rates. To match the observations, the wet-removal rates have to be scaled down by a factor of about 5. In that case the modelled ground-level concentrations of sulphate and sea salt increase by 50% (which deteriorates the match), while other components stay roughly the same. Finally, it is shown that in particular events, improved fire emission estimates may significantly improve the ability of the model to simulate the aerosol optical depth. We stress that discrepancies in aerosol models can be adequately analysed if all models would provide (regional) aerosol budgets, as presented in the current study.

scholarly journals Columnar aerosol size distribution function obtained by inversion of spectral optical depth measurements for the Zanjan, Iran

2010 ◽  
Vol 3 (3) ◽  
pp. 2367-2387 ◽  
Author(s):  
A. Masoumi ◽  
A. Bayat ◽  
H. R. Khalesifard
Keyword(s):  
Distribution Function ◽  
Size Distribution ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Size Distribution Function ◽  
Aerosol Size Distribution ◽  
Inversion Algorithm ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. We are reporting the calculated values of columnar aerosol size distribution function for atmosphere of Zanjan, a city in Northwest Iran (36.70° N, 48.51° E). Ground-based measurements of the total optical depth of the Zanjan atmosphere at 440 nm, 670 nm, 870 nm, and 1020 nm are recorded using a Cimel CE318-2 sunphotometer in the period of October 2006 to September 2008. The spectral aerosol optical depth has been obtained by subtraction of molecular optical depth from the total optical depth for each wavelength channel. Also the Ångström exponent is determined by a logarithmic fit to the aerosol optical depth when it is plotted versus the logarithm of the wavelength. Daily averages of the measured aerosol optical depth and Ångström exponent values have been implemented in an inversion algorithm for calculation of the columnar aerosol size distribution function. In this algorithm, the aerosols are considered as spheres of different size and refractive index of 1.45. We found that for 82% of the days, aerosols are in the coarse mode. For these days, more than 50% of the aerosol volume concentration has a radius >1 μm. We believe this is related to the geographical location of Zanjan in a mostly dry area and subject to frequent dust winds.

scholarly journals The European aerosol budget in 2006

2011 ◽  
Vol 11 (3) ◽  
pp. 1117-1139 ◽  
Author(s):  
J. M. J. Aan de Brugh ◽  
M. Schaap ◽  
E. Vignati ◽  
F. Dentener ◽  
M. Kahnert ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Transport Model ◽  
Ground Level ◽  
Sea Salt ◽  
Optical Measurements ◽  
Aerosol Size Distribution ◽  
Anthropogenic Aerosols ◽  
Removal Rates ◽  
Wet Removal

Abstract. This paper presents the aerosol budget over Europe in 2006 calculated with the global transport model TM5 coupled to the size-resolved aerosol module M7. Comparison with ground observations indicates that the model reproduces the observed concentrations quite well with an expected slight underestimation of PM10 due to missing emissions (e.g. resuspension). We model that a little less than half of the anthropogenic aerosols emitted in Europe are exported and the rest is removed by deposition. The anthropogenic aerosols are removed mostly by rain (95%) and only 5% is removed by dry deposition. For the larger natural aerosols, especially sea salt, a larger fraction is removed by dry processes (sea salt: 70%, mineral dust: 35%). We model transport of aerosols in the jet stream in the higher atmosphere and an import of Sahara dust from the south at high altitudes. Comparison with optical measurements shows that the model reproduces the Ångström parameter very well, which indicates a correct simulation of the aerosol size distribution. However, we underestimate the aerosol optical depth. Because the surface concentrations are close to the observations, the shortage of aerosol in the model is probably at higher altitudes. We show that the discrepancies are mainly caused by an overestimation of wet-removal rates. To match the observations, the wet-removal rates have to be scaled down by a factor of about 5. In that case the modelled ground-level concentrations of sulphate and sea salt increase by 50% (which deteriorates the match), while other components stay roughly the same. Finally, it is shown that in particular events, improved fire emission estimates may significantly improve the ability of the model to simulate the aerosol optical depth. We stress that discrepancies in aerosol models can be adequately analysed if all models would provide (regional) aerosol budgets, as presented in the current study.

scholarly journals A low-cost monitor for measurement of fine particulate matter and aerosol optical depth – Part 2: Citizen-science pilot campaign in northern Colorado

2019 ◽  
Vol 12 (12) ◽  
pp. 6385-6399 ◽  
Author(s):  
Bonne Ford ◽  
Jeffrey R. Pierce ◽  
Eric Wendt ◽  
Marilee Long ◽  
Shantanu Jathar ◽  
...  
Keyword(s):  
Particulate Matter ◽  
Air Quality ◽  
Aerosol Optical Depth ◽  
Citizen Science ◽  
Optical Depth ◽  
Spatial Scales ◽  
Fine Particulate Matter ◽  
Optical Measurements ◽  
Fine Particulate ◽  
Northern Colorado

Abstract. A pilot field campaign was conducted in the fall and winter of 2017 in northern Colorado to test the deployment of the Aerosol Mass and Optical Depth (AMOD) instrument as part of the Citizen-Enabled Aerosol Measurements for Satellites (CEAMS) network. Citizen scientists were recruited to set up the device to take filter and optical measurements of aerosols in their backyards. The goal of the network is to provide more surface particulate matter and aerosol optical depth (AOD) measurements to increase the spatial and temporal resolution of ratios of fine particulate matter (PM2.5) to AOD and to improve satellite-based estimates of air quality. Participants collected 65 filters and 160 multi-wavelength AOD measurements, from which 109 successful PM2.5 : AOD ratios were calculated. We show that PM2.5, AOD, and their ratio (PM2.5 : AOD) often vary substantially over relatively short spatial scales; this spatial variation is not typically resolved by satellite- and model-based PM2.5 exposure estimates. The success of the pilot campaign suggests that citizen-science networks are a viable means for providing new insight into surface air quality. We also discuss lessons learned and AMOD design modifications, which will be used in future wider deployments of the CEAMS network.

scholarly journals Simultaneous retrieval of aerosol and cloud properties during the MILAGRO field campaign

2011 ◽  
Vol 11 (13) ◽  
pp. 6245-6263 ◽  
Author(s):  
K. Knobelspiesse ◽  
B. Cairns ◽  
J. Redemann ◽  
R. W. Bergstrom ◽  
A. Stohl
Keyword(s):  
Optical Properties ◽  
Size Distribution ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Droplet Size ◽  
Cloud Droplet ◽  
Droplet Size Distribution ◽  
Cloud Droplet Size Distribution ◽  
Distribution Parameters ◽  
Aerosol Properties

Abstract. Estimation of Direct Climate Forcing (DCF) due to aerosols in cloudy areas has historically been a difficult task, mainly because of a lack of appropriate measurements. Recently, passive remote sensing instruments have been developed that have the potential to retrieve both cloud and aerosol properties using polarimetric, multiple view angle, and multi spectral observations, and therefore determine DCF from aerosols above clouds. One such instrument is the Research Scanning Polarimeter (RSP), an airborne prototype of a sensor on the NASA Glory satellite, which unfortunately failed to reach orbit during its launch in March of 2011. In the spring of 2006, the RSP was deployed on an aircraft based in Veracruz, Mexico, as part of the Megacity Initiative: Local and Global Research Observations (MILAGRO) field campaign. On 13 March, the RSP over flew an aerosol layer lofted above a low altitude marine stratocumulus cloud close to shore in the Gulf of Mexico. We investigate the feasibility of retrieving aerosol properties over clouds using these data. Our approach is to first determine cloud droplet size distribution using the angular location of the cloud bow and other features in the polarized reflectance. The selected cloud was then used in a multiple scattering radiative transfer model optimization to determine the aerosol optical properties and fine tune the cloud size distribution. In this scene, we were able to retrieve aerosol optical depth, the fine mode aerosol size distribution parameters and the cloud droplet size distribution parameters to a degree of accuracy required for climate modeling. This required assumptions about the aerosol vertical distribution and the optical properties of the coarse aerosol size mode. A sensitivity study was also performed to place this study in the context of future systematic scanning polarimeter observations, which found that the aerosol complex refractive index can also be observed accurately if the aerosol optical depth is larger than roughly 0.8 at a wavelength of (0.555 μm).

scholarly journals Observations of rapid aerosol optical depth enhancements in the vicinity of polluted cumulus clouds

2014 ◽  
Vol 14 (21) ◽  
pp. 11633-11656 ◽  
Author(s):  
T. F. Eck ◽  
B. N. Holben ◽  
J. S. Reid ◽  
A. Arola ◽  
R. A. Ferrare ◽  
...  
Keyword(s):  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Diurnal Cycle ◽  
Airborne Lidar ◽  
Cloud Formation ◽  
Aerosol Size Distribution ◽  
Cumulus Clouds ◽  
Cloud Processing ◽  
Aerosol Scattering ◽  
Fine Mode

Abstract. During the July 2011 Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) field experiment in Maryland, significant enhancements in Aerosol Robotic Network (AERONET) sun–sky radiometer measured aerosol optical depth (AOD) were observed in the immediate vicinity of non-precipitating cumulus clouds on some days. Both measured Ångström exponents and aerosol size distribution retrievals made before, during and after cumulus development often suggest little change in fine mode particle size; therefore, implying possible new particle formation in addition to cloud processing and humidification of existing particles. In addition to sun–sky radiometer measurements of large enhancements of fine mode AOD, lidar measurements made from both ground-based and aircraft-based instruments during the experiment also measured large increases in aerosol signal at altitudes associated with the presence of fair weather cumulus clouds. These data show modifications of the aerosol vertical profile as a result of the aerosol enhancements at and below cloud altitudes. The airborne lidar data were utilized to estimate the spatial extent of these aerosol enhancements, finding increased AOD, backscatter and extinction out to 2.5 km distance from the cloud edge. Furthermore, in situ measurements made from aircraft vertical profiles over an AERONET site during the experiment also showed large increases in aerosol scattering and aerosol volume after cloud formation as compared to before. The 15-year AERONET database of AOD measurements at the Goddard Space Flight Center (GSFC), Maryland site, was investigated in order to obtain a climatological perspective of this phenomenon of AOD enhancement. Analysis of the diurnal cycle of AOD in summer showed significant increases in AOD from morning to late afternoon, corresponding to the diurnal cycle of cumulus development.

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