Role of spheroidal particles in closure studies for aerosol microphysical–optical properties Sorribas, M. Olmo Reyes, Francisco José Quirantes Sierra, Arturo Lyamani, H. Gil-Ojeda, M. Alados Arboledas, Lucas Horvath, H. Atmospheric aerosol Spheroidal particles Spherical particles Aerosol microphysical properties Aerosol optical properties "This is the peer reviewed version of the following article: Sorribas, M.; et al. Role of spheroidal particles in closure studies for aerosol microphysical-optical properties. Quarterly Journal of the Royal Meteorological Society, 141(692): 2700-2707 (2015), which has been published in final form at http://dx.doi.org/10.1002/qj.2557 . This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving." A study has been carried out to assess the discrepancies between computed and observed aerosol scattering and backscattering properties in the atmosphere. The goals were: (i) to analyse the uncertainty associated with computed optical properties when spherical and spheroidal approximations are used, and (ii) to estimate nephelometry errors due to angular truncation and non-Lambertian illumination of the light source in terms of size range, particle shape and aerosol chemical compounds. Mie and T-matrix theories were used for computing light optical properties for spherical and spheroidal particles, respectively, from observed particle size distributions. The scattering coefficient of the fine mode was not much influenced by the particle shape. However, computed backscattering values underestimated the observed values by ∼15%. For the coarse mode, the spheroidal approximation yielded better results than that for spherical particles, especially for backscattering properties. Even after applying the spheroidal approximation, computed scattering and backscattering values within the coarse mode underestimated the observed values by ∼49% and ∼11%, respectively. The angular correction most widely used to correct the nephelometer data was discussed to explore its uncertainty. In the case of the scattering properties within the coarse mode, the change of the computed optical parameter is ∼+8% and for the scattering and backscattering values within the fine mode it is lower than ∼±4% for spherical and spheroidal particles. Additionally, if the spheroidal particles are used to evaluate the aerosol optical properties, the correction must be reconsidered with the aim of reducing the uncertainty found for scattering within the coarse mode. This is recommended for sites with desert dust influence; then the deviation of the computed scattering can be up to 13%. 2017-12-21T07:38:09Z 2017-12-21T07:38:09Z 2015-05 journal article Sorribas, M.; et al. Role of spheroidal particles in closure studies for aerosol microphysical-optical properties. Quarterly Journal of the Royal Meteorological Society, 141(692): 2700-2707 (2015). [http://hdl.handle.net/10481/48632] 0035-9009 1477-870X http://hdl.handle.net/10481/48632 10.1002/qj.2557 eng info:eu-repo/grantAgreement/EC/H2020/654109 info:eu-repo/grantAgreement/EC/H2020/262254 http://creativecommons.org/licenses/by-nc-nd/3.0/ open access Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License Royal Meteorological Society; Wiley