Intense dust and extremely fresh biomass burning outbreak in Barcelona, Spain: Characterization of their optical properties and estimation of their direct radiative forcing
Résumé
An extremely fresh smoke plume (<5 h) was transported over Barcelona on 23 July 2009, just 5 h after an intense Saharan dust event finalized. Both events were observed by sun-photometer, lidar and satellite systems. Results indicate surprisingly large absorption of mixed dust particles (SSA ~ 0.83 ± 0.04) with lower SSA than that observed for smoke (0.86 ± 0.04) particles at 440 nm. Our investigation shows that dust particles may have mixed during their transport with anthropogenic and smoke particles. Dust and smoke layers are observed between 1-6 and 1-4 km, with associated lidar ratios at 532 nm of 51 and 36 sr, respectively. Due to low SSAs and moderate surface albedos, shortwave (SW) radiative forcing calculations reveal that a large part of the solar energy losses at the surface is gained by the atmosphere for each aerosol. Here, dust particles produced a positive instantaneous forcing at TOA ( + 8 W m−2 at 12 UT), while the smoke produced a negative forcing of − 13 W m−2 at 17 UT. The associated SW heating rate is calculated to be around 2-3 K day−1 for both dust and smoke aerosols.
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