Intense dust and extremely fresh biomass burning outbreak in Barcelona, Spain: Characterization of their optical properties and estimation of their direct radiative forcing

Abstract

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.