Physical and optical properties of aerosols over an urban location in western India: Implications for shortwave radiative forcing

Abstract Simultaneous and collocated measurements of total and hemispherical backscattering coefficients (σ and β, respectively) at three wavelengths, mass size distributions, and columnar spectral aerosol optical depth (AOD) were made onboard an extensive cruise experiment covering, for the first time, the entire Bay of Bengal (BoB) and northern Indian Ocean. The results are synthesized to understand the optical properties of aerosols in the marine atmospheric boundary layer and their dependence on the size distribution. The observations revealed distinct spatial and spectral variations of all the aerosol parameters over the BoB and the presence of strong latitudinal gradients. The size distributions varied spatially, with the majority of accumulation modes decreasing from north to south. The scattering coefficient decreased from very high values (resembling those reported for continental/urban locations) in the northern BoB to very low values seen over near-pristine environments in the southeastern BoB. The average mass scattering efficiency of BoB aerosols was found to be 2.66 ± 0.1 m2 g−1 at 550 nm. The spectral dependence of columnar AOD deviated significantly from that of the scattering coefficients in the northern BoB, implying vertical heterogeneity in the aerosol type in that region. However, a more homogeneous scenario was observed in the southern BoB. Simultaneous lidar and in situ measurements onboard an aircraft over the ocean revealed the presence of elevated aerosol layers of enhanced extinction at altitudes of 1 to 3 km with an offshore extent of a few hundred kilometers. Back-trajectory analyses showed these layers to be associated with advection from west Asia and western India. The large spatial variations and vertical heterogeneity in aerosol properties, revealed by the present study, need to be included in the regional radiative forcing over the Bay of Bengal.

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Radiative forcing of the desert aerosol at Ouarzazate (Morocco)

E3S Web of Conferences ◽

10.1051/e3sconf/20183703004 ◽

2018 ◽

Vol 37 ◽

pp. 03004

Author(s):

Abdelouahid Tahiri ◽

Mohamed Diouri

Keyword(s):

Optical Properties ◽

Atmospheric Aerosol ◽

Radiative Forcing ◽

Cloud Formation ◽

Optical Parameters ◽

Aerosol Radiative Forcing ◽

Daily Average ◽

Definition Of ◽

Aerosol Radiative

The atmospheric aerosol contributes to the definition of the climate with direct effect, the diffusion and absorption of solar and terrestrial radiations, and indirect, the cloud formation process where aerosols behave as condensation nuclei and alter the optical properties. Satellites and ground-based networks (solar photometers) allow the terrestrial aerosol observation and the determination of impact. Desert aerosol considered among the main types of tropospheric aerosols whose optical property uncertainties are still quite important. The analysis concerns the optical parameters recorded in 2015 at Ouarzazate solar photometric station (AERONET/PHOTONS network, http://aeronet.gsfc.nasa.gov/) close to Saharan zone. The daily average aerosol optical depthτaer at 0.5μm, are relatively high in summer and less degree in spring (from 0.01 to 1.82). Daily average of the Angstrom coefficients α vary between 0.01 and 1.55. The daily average of aerosol radiative forcing at the surface range between -150W/m2 and -10 W/m2 with peaks recorded in summer, characterized locally by large loads of desert aerosol in agreement with the advections of the Southeast of Morocco. Those recorded at the Top of the atmosphere show a variation from -74 W/m2 to +24 W/m2

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A new approach for retrieving the UV–vis optical properties of ambient aerosols

Atmospheric Measurement Techniques ◽

10.5194/amt-9-3477-2016 ◽

2016 ◽

Vol 9 (8) ◽

pp. 3477-3490 ◽

Cited By ~ 17

Author(s):

Nir Bluvshtein ◽

J. Michel Flores ◽

Lior Segev ◽

Yinon Rudich

Keyword(s):

Optical Properties ◽

Atmospheric Aerosols ◽

Radiative Forcing ◽

Complex Refractive Index ◽

Single Scattering ◽

Aerosol Size Distribution ◽

Distribution Data ◽

Ambient Aerosols ◽

New Approach ◽

Effective Radiative Forcing

Abstract. Atmospheric aerosols play an important part in the Earth's energy budget by scattering and absorbing incoming solar and outgoing terrestrial radiation. To quantify the effective radiative forcing due to aerosol–radiation interactions, researchers must obtain a detailed understanding of the spectrally dependent intensive and extensive optical properties of different aerosol types. Our new approach retrieves the optical coefficients and the single-scattering albedo of the total aerosol population over 300 to 650 nm wavelength, using extinction measurements from a broadband cavity-enhanced spectrometer at 315 to 345 nm and 390 to 420 nm, extinction and absorption measurements at 404 nm from a photoacoustic cell coupled to a cavity ring-down spectrometer, and scattering measurements from a three-wavelength integrating nephelometer. By combining these measurements with aerosol size distribution data, we retrieved the time- and wavelength-dependent effective complex refractive index of the aerosols. Retrieval simulations and laboratory measurements of brown carbon proxies showed low absolute errors and good agreement with expected and reported values. Finally, we implemented this new broadband method to achieve continuous spectral- and time-dependent monitoring of ambient aerosol population, including, for the first time, extinction measurements using cavity-enhanced spectrometry in the 315 to 345 nm UV range, in which significant light absorption may occur.

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Sensitivity of aerosol radiative effects to different mixing assumptions in the AEROPT 1.0 submodel of the EMAC atmospheric-chemistry–climate model

Geoscientific Model Development ◽

10.5194/gmd-7-2503-2014 ◽

2014 ◽

Vol 7 (5) ◽

pp. 2503-2516 ◽

Cited By ~ 23

Author(s):

K. Klingmüller ◽

B. Steil ◽

C. Brühl ◽

H. Tost ◽

J. Lelieveld

Keyword(s):

Optical Properties ◽

Radiative Transfer ◽

Black Carbon ◽

Atmospheric Chemistry ◽

Radiative Forcing ◽

Climate Model ◽

Mixing Rule ◽

Aerosol Optical Properties ◽

Internal Mixing ◽

Aerosol Radiative

Abstract. The modelling of aerosol radiative forcing is a major cause of uncertainty in the assessment of global and regional atmospheric energy budgets and climate change. One reason is the strong dependence of the aerosol optical properties on the mixing state of aerosol components, such as absorbing black carbon and, predominantly scattering sulfates. Using a new column version of the aerosol optical properties and radiative-transfer code of the ECHAM/MESSy atmospheric-chemistry–climate model (EMAC), we study the radiative transfer applying various mixing states. The aerosol optics code builds on the AEROPT (AERosol OPTical properties) submodel, which assumes homogeneous internal mixing utilising the volume average refractive index mixing rule. We have extended the submodel to additionally account for external mixing, partial external mixing and multilayered particles. Furthermore, we have implemented the volume average dielectric constant and Maxwell Garnett mixing rule. We performed regional case studies considering columns over China, India and Africa, corroborating much stronger absorption by internal than external mixtures. Well-mixed aerosol is a good approximation for particles with a black-carbon core, whereas particles with black carbon at the surface absorb significantly less. Based on a model simulation for the year 2005, we calculate that the global aerosol direct radiative forcing for homogeneous internal mixing differs from that for external mixing by about 0.5 W m−2.

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A new radiation infrastructure for the Modular Earth Submodel System (MESSy, based on version 2.51)

10.5194/gmd-2015-277 ◽

2016 ◽

Cited By ~ 1

Author(s):

Simone Dietmüller ◽

Patrick Jöckel ◽

Holger Tost ◽

Markus Kunze ◽

Cathrin Gellhorn ◽

...

Keyword(s):

Optical Properties ◽

Atmospheric Chemistry ◽

Radiative Forcing ◽

General Circulation ◽

Circulation Model ◽

Shortwave Radiation ◽

Aerosol Optical Properties ◽

On Line ◽

User Friendly ◽

Radiation Scheme

Abstract. The Modular Earth Submodel System (MESSy) provides an interface to couple submodels to a basemodel via a highly flexible data management facility (Jöckel et al., 2010). In the present paper we present the four new radiation related submodels RAD, AEROPT, CLOUDOPT and ORBIT. The submodel RAD (with shortwave radiation scheme RAD_FUBRAD) simulates the radiative transfer, the submodel AEROPT calculates the aerosol optical properties, the submodel CLOUDOPT calculates the cloud optical properties, and the submodel ORBIT is responsible for Earth orbit calculations. These submodels are coupled via the standard MESSy infrastructure and are largely based on the original radiation scheme of the general circulation model ECHAM5, however, expanded with additional features. These features comprise, among others, user-friendly and flexibly controllable (by namelists) on-line radiative forcing calculations by multiple diagnostic calls of the radiation routines. With this, it is now possible to calculate radiative forcing (instantaneous as well as stratosphere adjusted) of various greenhouse gases simultaneously in only one simulation, as well as the radiative forcing of cloud perturbations. Examples of on-line radiative forcing calculations in the ECHAM/MESSy Atmospheric Chemistry (EMAC) model are presented.

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Supplementary material to "Chemical composition, optical properties and radiative forcing efficiency of nascent particulate matter emitted by an aircraft turbofan burning conventional and alternative fuels"

10.5194/acp-2018-1171-supplement ◽

2018 ◽

Author(s):

Miriam Elser ◽

Benjamin T. Brem ◽

Lukas Durdina ◽

David Schönenberger ◽

Frithjof Siegerist ◽

...

Keyword(s):

Optical Properties ◽

Particulate Matter ◽

Chemical Composition ◽

Radiative Forcing ◽

Alternative Fuels ◽

Supplementary Material

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Tropospheric aerosol scattering and absorption over Central Europe: a closure study for the dry particle state

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-13-27811-2013 ◽

2013 ◽

Vol 13 (10) ◽

pp. 27811-27854 ◽

Cited By ~ 1

Author(s):

N. Ma ◽

W. Birmili ◽

T. Müller ◽

T. Tuch ◽

Y. F. Cheng ◽

...

Keyword(s):

Optical Properties ◽

Direct Measurement ◽

Radiative Forcing ◽

Control Measure ◽

Atmospheric Stability ◽

Scattering Coefficient ◽

Particle State ◽

Air Mass ◽

Aerosol Scattering ◽

Tropospheric Aerosol

Abstract. This work analyses optical properties of the dry tropospheric aerosol measured at the regional GAW observation site Melpitz in East Germany. For a continuous observation period between 2007 and 2010, we provide representative values of the dry-state scattering coefficient, the hemispheric backscattering coefficient, the absorption coefficient, single scattering albedo, and the Ångström exponent. Besides the direct measurement, the aerosol scattering coefficient was alternatively computed from experimental particle number size distributions using a Mie code. Within pre-defined limits, a closure could be achieved with the direct measurement. The achievement of closure implies that such calculations can be used as a high-level quality control measure for data sets involving multiple instrumentation. All dry optical properties showed significant annual variations, which were attributed to corresponding variations in the regional emission fluxes, the intensity of secondary particle formation, and the mixed layer height. Air mass classification showed that atmospheric stability is a major factor influencing the dry aerosol properties at the GAW station. In the cold season, temperature inversions limit the volume available for atmospheric mixing, so that the aerosol optical properties near the ground proved quite sensitive to the geographical origin of the air mass. In the warm season, when the atmosphere is usually well-mixed during day-time, considerably less variability was observed for the optical properties between different air masses. This work provides, on the basis of quality-checked in-situ measurements, a first step towards a climatological assessment of direct aerosol radiative forcing in the region under study.

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