A synergetic approach for estimating the local direct aerosol forcing: Application to an urban zone during the Expérience sur Site pour Contraindre les Modèles de Pollution et de Transport d'Emission (ESCOMPTE) experiment

Abstract

[1] A method dedicated to the investigation of direct radiative forcing of the main anthropogenic aerosol species (ammonium sulfate, black carbon, particulate organic matter) is presented. We computed the direct radiative aerosol forcing at the top of atmosphere (TOA), at the bottom of atmosphere (BOA), and into the atmospheric layer (ATM). The methodology is based on chemical, photometric, and satellite measurements. We first determined the optical properties of the main aerosol species and then computed their direct radiative impact at local scale. The method was applied to a periurban zone during the Expérience sur Site pour Contraindre les Modèles de Pollution et de Transport d'Emission experiment. Optical computations indicate that the single scattering albedo, for the total aerosol population in the external mixture, is equal to 0.83 ± 0.04 at 550 nm, indicative of a strong absorption of the solar radiation. At the same time the mean asymmetry parameter is equal to 0.59 ± 0.04, and the mean aerosol optical thickness is equal to 0.30 ± 0.02, at 550 nm. The anthropogenic urban aerosol layer reduces significantly the daily surface illumination (À24 W m À2 > DF BOA > À47.5 W m À2 ) by reflection to space (À6 W m À2 > DF TOA > À9 W m À2 ) and by absorption of the solar radiation into the atmosphere (17 W m À2 < DF ATM < 39 W m À2 ). The available resulting energy in the atmospheric column heats the lowermost part of the atmosphere from 1.1°K d À1 to 2.8°K d À1 . Our study shows that the black carbon particles have a large contribution to the BOA forcing (almost 50% of the total daily forcing), whereas the ammonium sulfate particles contribute only to about 10%. Conversely, the TOA daily forcing is mostly driven by the ammonium sulfate aerosol (around 50%).

Optical, physical and chemical properties of aerosols transported to a coastal site in the western Mediterranean: a focus on primary marine aerosols

“…Intermediate BOA DRE are calculated under polluted and biomass burning influence (from 5-12 July), and range from −13 to −38 W m −2 . Such values are classically derived over the western Mediterranean for polluted particles (Roger et al, 2006).…”

Aerosol complexity in megacities: From size‐resolved chemical composition to optical properties of the Beijing atmospheric particles

“…[8] Aerosol radiative effects primarily rely on their single scattering albedo w o and their asymmetry parameter g. It has been shown recently that using adequate algorithms, these two parameters could be retrieved based on the chemical composition of each aerosol mode [Roger et al, 2006]. Calculations may account for the heterogeneous nature of particles which are also considered as spheroids [Dubovik et al, 2002].…”

“…As detailed hereafter, the model comprises a lognormal distribution showing several modes, each mode being fully defined by its lognormal parameters and its chemical composition. Using adequate algorithms [Roger et al, 2006], these parameters allow retrieval of other properties (aerosol number and optical properties) some of them being compared to direct measurements, thus insuring quality and consistency of data.…”

Aerosol optical properties and radiative forcing in the high Himalaya based on measurements at the Nepal Climate Observatory-Pyramid site (5079 m a.s.l.)

“…To derive the local direct aerosol forcing, we have used the GAME code (Global Atmospheric ModEl code; Dubuisson et al, 1996) set in the configuration described in Roger et al (2006). The absorption is based on the results of a line by line code (Scott, 1974) and includes the gas-phase absorbers in the short-wave region.…”