Relationships between extinction, absorption, backscattering, and mass content of sulfuric acid aerosols

Linear relationships between aerosol extinction, absorption, backscatter, and mass content are derived for polydispersions of sulfuric acid aerosols. These relationships are independent of the form of the size distribution and are a consequence of approximating the corresponding Mie efficiency factors (the extinction efficiency Q(e), the absorption efficiency Q(a), and the backscatter gain G) by linear functions of the particle size parameter x. The relationships are valid only at particular wavelengths that depend on the range of particle sizes present in particular polydispersion. For example, at a wavelength λ = 0.694 μm the relation between aerosol backscatter coefficient σ(bs) (m^-1 sr^-1) and mass content M (g m^-3) is σ(bs) = 0.048 M for 75% sulfuric acid (25% water) aerosol, under the restriction that particles in the polydispersion have sizes not exceeding about 1.5 μm in radius. Possible applications of the relationships are (1) inference of path-integrated mass content of sulfuric acid aerosol (for example, the clouds of Venus) from an infrared laser transmission measurement through the aerosol cloud, (2) determination of sulfuric acid aerosol mass content at a particular point in an aerosol cloud from aerosol absorption measurements at that point with a CO₂ (λ = 10.6 μm) laser spectrophone, (3) inference of path-integrated stratospheric aerosol mass from aerosol extinction measurerements made by solar occultation for wavelengths λ = 0.55 and 1 μm, and (4) inference of vertical profiles of stratospheric aerosol mass from ruby lidar (λ = 0.694 μm) backscatter measurements.