Simultaneous measurements of the relative-humidity-dependent aerosol light extinction, scattering, absorption, and single-scattering albedo with a humidified cavity-enhanced albedometer
Abstract. Hygroscopic aerosols take up water and grow with
increasing relative humidity (RH), giving rise to large changes in light
extinction ( bext ), scattering ( bscat ), absorption ( babs ), and
single scattering albedo (SSA, ω ). The optical hygroscopic growth
factors for each parameter ( f (RH) ext , scat , abs , ω ) are thus
important for assessing aerosol effects on regional air quality, atmospheric
visibility, and radiative forcing. The RH dependence of aerosol scattering
and extinction has been studied in many laboratory and field studies.
However, owing partly to the absence of suitable instrumentation, there are
few reports of the RH dependence of aerosol absorption and ω . In
this work, we report the development of a humidified cavity-enhanced
albedometer (H-CEA) for simultaneous measurements of
 f (RH) ext , scat , abs , ω at λ=532  nm from 10 % to 88 %
RH. The instrument's performance was evaluated with laboratory-generated
ammonium sulfate, sodium chloride, and nigrosin aerosols. Measured
hygroscopic growth factors for different parameters were in good agreement
with model calculations and literature-reported values, demonstrating the
accuracy of the H-CEA for measuring RH-dependent optical properties.