On the interpretation of the loading correction of the aethalometer

[摘要] Aerosol optical properties were measured with a seven-wavelengthaethalometer and a three-wavelength nephelometer at the suburban site SORPESin Nanjing, China, in September 2013–January 2015. The aethalometercompensation parameter k, calculated with the Virkkula et al. (2007) methoddepended on the backscatter fraction, measured with an independent method,the integrating nephelometer. At λ = 660 nm the daily averagedcompensation parameter k ≈ 0.0017 ± 0.0002 and0.0042 ± 0.0013 when backscatter fraction at λ = 635 nm wasin the ranges of 0.100 ± 0.005 and 0.160 ± 0.005, respectively.Also, the wavelength dependency of the compensation parameter depended on thebackscatter fraction: when b(λ = 525 nm) was less thanapproximately 0.13 the compensation parameter decreased with wavelength andat larger b it increased with wavelength. This dependency has not beenconsidered in any of the algorithms that are currently used for processingaethalometer data. The compensation parameter also depended on thesingle-scattering albedo ω₀ so that k decreased with increasingω₀. For the green light (λ = 520 nm) in the ω₀range 0.870 ± 0.005, the average (± standard deviation) k ≈ 0.0047 ± 0.006 and in the ω₀ range 0.960 ± 0.005, k≈ 0.0028 ± 0.0007. This difference was larger for thenear-infrared light (λ = 880 nm): in the ω₀ range0.860 ± 0.005, k ≈ 0.0055 ± 0.0023 and in theω₀ range 0.960 ± 0.005, k ≈ 0.0019 ± 0.0011.The negative dependence of k on ω₀ was also shown with a simpletheoretical analysis.

[学科分类] 几何与拓扑