Abstract
Abstract. Knowledge on the microphysical properties of atmospheric aerosols is essential to better evaluate their radiative forcing. This paper presents an estimate of the real part of the refractive indices (n) and effective densities (ρeff) of chemically segregated atmospheric aerosols in Guangzhou, China. Vacuum aerodynamic diameter, chemical compositions, and light-scattering intensities of individual particles were simultaneously measured by a single-particle aerosol mass spectrometer (SPAMS) during the fall of 2012. On the basis of Mie theory, n at a wavelength of 532 nm and ρeff were estimated for 17 particle types in four categories: organics (OC), elemental carbon (EC), internally mixed EC and OC (ECOC), and Metal-rich. The results indicate the presence of spherical or nearly spherical shapes for the majority of particle types, whose partial scattering cross-section versus sizes were well fitted to Mie theoretical modeling results. While sharing n in a narrow range (1.47–1.53), majority of particle types exhibited a wide range of ρeff (0.87–1.51 g cm−3). The OC group is associated with the lowest ρeff (0.87–1.07 g cm−3), and the Metal-rich group with the highest ones (1.29–1.51 g cm−3). It is noteworthy that a specific EC type exhibits a complex scattering curve versus size due to the presence of both compact and irregularly shaped particles. Overall, the results on the detailed relationship between physical and chemical properties benefits future research on the impact of aerosols on visibility and climate.
Highlights
Aerosols represent the largest uncertainty in estimating radiative forcing, through strongly affecting the energy balance of the Earth by scattering and/or absorbing solar radiation (IPCC, 2007; Jacobson, 2001; Ramanathan and Carmichael, 2008), and cloud formation (Jacobson, 2006; Rosenfeld et al, 2008)
It is pointed that assuming negligible absorption for the internally mixed elemental carbon (EC) particle types might introduce uncertainties for the estimation of n
Using Mie theory core-shell modeling, the scattering of the internally mixed EC particle types can be reasonably well described with the coating (< 100 nm) refractive index as an input (Moffet and Prather, 2009)
Summary
Aerosols represent the largest uncertainty in estimating radiative forcing, through strongly affecting the energy balance of the Earth by scattering and/or absorbing solar radiation (IPCC, 2007; Jacobson, 2001; Ramanathan and Carmichael, 2008), and cloud formation (Jacobson, 2006; Rosenfeld et al, 2008). They strongly affect visibility, causing severe haze problems in polluted regions (Wu et al, 2005; Zhang et al, 2010). The chemical composition, size, optical property, shape, and density of aerosols are generally measured by independent analytical techniques, which may inevitably introduce uncertainties when establishing their relationships
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