Abstract
Abstract. Characterizing chemical and physical aerosol properties is important to understand their sources, effects, and feedback mechanisms in the atmosphere. This study proposes a scheme to classify aerosol populations based on their spectral optical properties (absorption and scattering). The scheme is obtained thanks to the outstanding set of information on particle size and composition these properties contain. The spectral variability of the aerosol single scattering albedo (dSSA), and the extinction, scattering and absorption Angstrom exponents (EAE, SAE and AAE, respectively) were observed on the basis of two-year measurements of aerosol optical properties (scattering and absorption coefficients at blue, green and red wavelengths) performed in the suburbs of Rome (Italy). Optical measurements of various aerosol types were coupled to measurements of particle number size distributions and relevant optical properties simulations (Mie theory). These latter allowed the investigation of the role of the particle size and composition in the bulk aerosol properties observed. The combination of simulations and measurements suggested a general "paradigm" built on dSSA, SAE and AAE to optically classify aerosols. The paradigm proved suitable to identify the presence of key aerosol populations, including soot, biomass burning, organics, dust and marine particles. The work highlights that (i) aerosol populations show distinctive combinations of SAE and dSSA times AAE, these variables being linked by a linear inverse relation varying with varying SSA; (ii) fine particles show EAE > 1.5, whilst EAE < 2 is found for both coarse particles and ultrafine soot-rich aerosols; (iii) fine and coarse particles both show SSA > 0.8, whilst ultrafine urban Aitken mode and soot particles show SSA < 0.8. The proposed paradigm agrees with aerosol observations performed during past major field campaigns, this indicating that relations concerning the paradigm have a general validity.
Highlights
Variations of their opticaIlnpsrtorpuemrtieesnantadtcioapnability to act as cloud condensation nuclei (CMCeNt)haoreddsetearmndinant for the climaticticemamrpbaoscnt.aceous material, sulfate, nitrate, ammonium, trace metals, sea salts, and crustal elements – their sizes spanning over more than four the suburbs of region at a suburban Mediterranean site (Rome) (Italy)
The advantage of using extinction Angstrom exponent (EAE) is that it takes contemporarily into account SAE and absorption Angstrom exponent (AAE); this is a disadvantage as EAE fails in separating particle size effects from particle composition effects
small OM condensation mode” (SOM), large OM accumulation mode” (LOM), and coarse dust mode” (CDM) are clearly separated by their SAE467–660, SAE decreasing with www.atmos-chem-phys.net/13/2455/2013/
Summary
Variations of their opticaIlnpsrtorpuemrtieesnantadtcioapnability to act as cloud condensation nuclei (CMCeNt)haoreddsetearmndinant for the climatic (direct and indirect, Tropospheric aerosols mDreasaypteaccotiSnvteayliysn)ticemamrpbaoscnt.aceous material, sulfate, nitrate, ammonium, trace metals, sea salts, and crustal elements – their sizes spanning over more than four the suburbs of Rome (Italy). Optical measurements of various aerosol types were coupled to measurements of particle number size distributions and relevant optical properties simulations (Mie theory). These latter allowed the investigation of the role of the particle size and composition in the orders of magnitude, fromGaefeowsncaineomnetitfeircs to several micarnodmceotmerpso(sei.tgio.M,n StooegidnefteehleldrDawneidthvPtehaneloidripsm,mi2x0ien0g6n)st.taPtaertaincdlesshiazpees identify aerosol populations – each of them having specific chemical, optical and physical properties, as well as sources. The size-resolved understanding of the particle numbers, and in particular of and dSSA times AAE, these variables being linked by a linear inverse relation varying with varying SSA; (ii) fine parthe carbonaceous gaps to assess the aiemropOsaoclcts,oefiasanairmpSoonlcgluiettihonencmoenajocrlimknaotewl(eKdugleticles show EAE > 1.5, whilst EAE < 2 is found for both coarse particles and ultrafine soot-rich aerosols; (iii) fine and coarse particles both show SSA > 0.8, whilst ultrafine urban Aitken mode and soot particles show SSA < 0.8. A complete knowledge of the nature of brown carbon remains indefinite
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