Effect of hygroscopic growth on the aerosol light-scattering coefficient: A review of measurements, techniques and error sources
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AutorTitos Vela, Gloria; Cazorla Cabrera, Alberto; Zieger, Paul; Andrews, E.; Lyamani, H.; Granados-Muñoz, María José; Olmo Reyes, Francisco José; Alados-Arboledas, Lucas
Scattering enhancementHygroscopicityWater uptakeAerosol light scattering
Titos Vela, G.; et al. Effect of hygroscopic growth on the aerosol light-scattering coefficient: A review of measurements, techniques and error sources. Atmospheric Environment 141: 494-507 (2016). [http://hdl.handle.net/10481/42355]
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 and FEDER through project CGL2013_45410-R; and by European Union’s Horizon 2020 research and innovation programme under grant agreement No 654109, ACTRIS-2. G. Titos was partially funded by Programa del Plan Propio de Investigación “Contrato Puente” of the University of Granada. We thank the Stockholm International Meteorological Institute (IMI) for travel support of G. Titos.
Knowledge of the scattering enhancement factor, f(RH), is important for an accurate description of direct aerosol radiative forcing. This factor is defined as the ratio between the scattering coefficient at enhanced relative humidity, RH, to a reference (dry) scattering coefficient. Here, we review the different experimental designs used to measure the scattering coefficient at dry and humidified conditions as well as the procedures followed to analyze the measurements. Several empirical parameterizations for the relationship between f(RH) and RH have been proposed in the literature. These parameterizations have been reviewed and tested using experimental data representative of different hygroscopic growth behavior and a new parameterization is presented. The potential sources of error in f(RH) are discussed. A Monte Carlo method is used to investigate the overall measurement uncertainty, which is found to be around 20 e40% for moderately hygroscopic aerosols. The main factors contributing to this uncertainty are the uncertainty in RH measurement, the dry reference state and the nephelometer uncertainty. A literature survey of nephelometry-based f(RH) measurements is presented as a function of aerosol type. In general, the highest f(RH) values were measured in clean marine environments, with pollution having a major influence on f(RH). Dust aerosol tended to have the lowest reported hygroscopicity of any of the aerosol types studied. Major open questions and suggestions for future research priorities are outlined.