Study of the relative humidity dependence of aerosol light-scattering in southern Spain
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AutorTitos Vela, Gloria; Lyamani, H.; Cazorla Cabrera, Alberto; Sorribas, M.; Foyo-Moreno, I.; Wiedensohler, A.; Alados-Arboledas, Lucas
Taylor and Francis
Aerosol particle light scatteringHygroscopic growthScattering enhancementRadiative forcingField measurements
Titos Vela, G.; et al. Study of the relative humidity dependence of aerosol light-scattering in southern Spain. Tellus B: Chemical and Physical Meteorology, 66(1): 24536 (2014). [http://hdl.handle.net/10481/47093]
PatrocinadorThis work was supported by the Andalusia Regional Government through projects P10-RNM-6299 and P12-RNM-2409; by the Spanish Ministry of Economy and Competitiveness through projects CGL2010-18782, CSD2007-00067, CGL2011-13580-E/CLI and CGL2011-16124-E; and by EU through ACTRIS project (EU INFRA-2010-1.1.16-262254).; G. Titos was funded by the program FPI of the Spanish Ministry of Economy and Competitiveness – Secretariat of Science, Innovation and Development under grant BES-2011-043721.
This investigation focuses on the characterisation of the aerosol particle hygroscopicity. Aerosol particle optical properties were measured at Granada, Spain, during winter and spring seasons in 2013. Measured optical properties included particle light-absorption coefficient (sap) and particle light-scattering coefficient (ssp) at dry conditions and at relative humidity (RH) of 85 +/- 10%. The scattering enhancement factor, f(RH=85%), had a mean value of 1.5 +/- 0.2 and 1.6 +/- 0.3 for winter and spring campaigns, respectively. Cases of high scattering enhancement were more frequent during the spring campaign with 27% of the f(RH=85%) values above 1.8, while during the winter campaign only 8% of the data were above 1.8. A Saharan dust event (SDE), which occurred during the spring campaign, was characterised by a predominance of large particles with low hygroscopicity. For the day when the SDE was more intense, a mean daily value of f(RH=85%)=1.3 +/- 0.2 was calculated. f(RH=85%) diurnal cycle showed two minima during the morning and afternoon traffic rush hours due to the increase in non-hygroscopic particles such as black carbon and road dust. This was confirmed by small values of the single-scattering albedo and the scattering Angstrom exponent. A significant correlation between f(RH=85%) and the fraction of particulate organic matter and sulphate was obtained. Finally, the impact of ambient RH in the aerosol radiative forcing was found to be very small due to the low ambient RH. For high RH values, the hygroscopic effect should be taken into account since the aerosol forcing efficiency changed from -13W/m2 at dry conditions to -17W/m2 at RH=85%.