A global study of hygroscopicity-driven light-scattering enhancement in the context of other in situ aerosol optical properties

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dc.contributor.author Titos, Gloria
dc.contributor.author Burgos, Maria A.
dc.contributor.author Zieger, Paul
dc.contributor.author Alados-Arboledas, Lucas
dc.contributor.author Baltensperger, Urs
dc.contributor.author Jefferson, Anne
dc.contributor.author Sherman, James
dc.contributor.author Weingartner, Ernest
dc.contributor.author Henzing, Bas
dc.contributor.author Luoma, Krista
dc.contributor.author O'Dowd, Colin
dc.contributor.author Wiedensohler, Alfred
dc.contributor.author Andrews, Elisabeth
dc.date.accessioned 2021-11-03T09:26:02Z
dc.date.available 2021-11-03T09:26:02Z
dc.date.issued 2021-09-02
dc.identifier.citation Titos , G , Burgos , M A , Zieger , P , Alados-Arboledas , L , Baltensperger , U , Jefferson , A , Sherman , J , Weingartner , E , Henzing , B , Luoma , K , O'Dowd , C , Wiedensohler , A & Andrews , E 2021 , ' A global study of hygroscopicity-driven light-scattering enhancement in the context of other in situ aerosol optical properties ' , Atmospheric Chemistry and Physics , vol. 21 , no. 17 , pp. 13031-13050 . https://doi.org/10.5194/acp-21-13031-2021
dc.identifier.other PURE: 170018913
dc.identifier.other PURE UUID: a464778c-bbb6-4da1-9164-3d5518801f35
dc.identifier.other WOS: 000692941900004
dc.identifier.other Scopus: 85114346310
dc.identifier.other ORCID: /0000-0001-8841-3050/work/102573301
dc.identifier.uri http://hdl.handle.net/10138/335980
dc.description.abstract The scattering and backscattering enhancement factors (f (RH) and f(b)(RH)) describe how aerosol particle light scattering and backscattering, respectively, change with relative humidity (RH). They are important parameters in estimating direct aerosol radiative forcing (DARF). In this study we use the dataset presented in Burgos et al. (2019) that compiles f(RH) and f(b)(RH) measurements at three wavelengths (i.e., 450, 550 and 700 nm) performed with tandem nephelometer systems at multiple sites around the world. We present an overview of f (RH) and f(b)(RH) based on both long-term and campaign observations from 23 sites representing a range of aerosol types. The scattering enhancement shows a strong variability from site to site, with no clear pattern with respect to the total scattering coefficient. In general, higher f(RH) is observed at Arctic and marine sites, while lower values are found at urban and desert sites, although a consistent pattern as a function of site type is not observed. The backscattering enhancement f(b)(RH) is consistently lower than f(RH) at all sites, with the difference between f(RH) and f(b)(RH) increasing for aerosol with higher f(RH). This is consistent with Mie theory, which predicts higher enhancement of the light scattering in the forward than in the backward direction as the particle takes up water. Our results show that the scattering enhancement is higher for PM1 than PM10 at most sites, which is also supported by theory due to the change in scattering efficiency with the size parameter that relates particle size and the wavelength of incident light. At marine-influenced sites this difference is enhanced when coarse particles (likely sea salt) predominate. For most sites, f (RH) is observed to increase with increasing wavelength, except at sites with a known dust influence where the spectral dependence of f (RH) is found to be low or even exhibit the opposite pattern. The impact of RH on aerosol properties used to calculate radiative forcing (e.g., single-scattering albedo, omega(0), and backscattered fraction, b) is evaluated. The single-scattering albedo generally increases with RH, while b decreases. The net effect of aerosol hygroscopicity on radiative forcing efficiency (RFE) is an increase in the absolute forcing effect (negative sign) by a factor of up to 4 at RH = 90% compared to dry conditions (RH < 40 %). Because of the scarcity of scattering enhancement measurements, an attempt was made to use other more commonly available aerosol parameters (i.e., omega(0) and scattering Angstrom exponent, ffsp) to parameterize f (RH). The majority of sites (75 %) showed a consistent trend with omega(0) (higher f (RH D 85 %) for higher omega(0)), while no clear pattern was observed between f (RH = 85 %) and ffsp. This suggests that aerosol omega(0) is more promising than ffsp as a surrogate for the scattering enhancement factor, although neither parameter is ideal. Nonetheless, the qualitative relationship observed between omega(0) and f (RH) could serve as a constraint on global model simulations. en
dc.format.extent 20
dc.language.iso eng
dc.relation.ispartof Atmospheric Chemistry and Physics
dc.rights cc_by
dc.rights.uri info:eu-repo/semantics/openAccess
dc.subject 114 Physical sciences
dc.title A global study of hygroscopicity-driven light-scattering enhancement in the context of other in situ aerosol optical properties en
dc.type Article
dc.contributor.organization Institute for Atmospheric and Earth System Research (INAR)
dc.description.reviewstatus Peer reviewed
dc.relation.doi https://doi.org/10.5194/acp-21-13031-2021
dc.relation.issn 1680-7316
dc.rights.accesslevel openAccess
dc.type.version publishedVersion

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