![]() This wavelength dependence of theĪerosol extinction is thought to be driven primarily by the particle size distribution with only a minor contribution from the compositionallyĭependent aerosol absorption (Eck et al., 2001b Schuster et al., 2006). However, there is long-standing evidence that extinction and aerosol optical depth spectra in the ambient atmosphere exhibit curvature that ![]() Placed important constraints on these relationships, measurements have been typically limited to only one or a few wavelengths of light, which areĮxtrapolated across the ultraviolet (UV)–visible–infrared (IR) spectrum by assuming a power law relationship (e.g., the well-known ÅngströmĮxponent). While numerous airborne and surface-based observations over past decades have Properties and radiative impacts in models and satellite retrievals. Significant natural variability in the size and composition of atmospheric aerosols introduces uncertainty into the representation of their optical Aerosol size distributions were not measuredĭuring KORUS-OC, and the data reported here were limited to the fine fraction, but the ( a 1, a 2) maps obtained from the SpEx data set areĬonsistent with the expectation that ( a 1, a 2) may contain more information than α – a result that will be explored further withįuture SpEx and size distribution data sets. Implies that ( a 1, a 2) contain more information about size distributions than α alone. Previously published work has shown that differentīimodal size distributions of aerosols can exhibit the same α yet have differing spectral curvature with different ( a 1, a 2). Values from spectra obtained from measurement techniques with different λ ch. Since the curvature coefficient values depend on λ ch, it must be taken into account when comparing Λ ch is defined as the single wavelength that characterizes the wavelength range of the measured spectrum (i.e., the Studies that used total column aerosol optical depth observations to examine the information content of spectral curvature, the relationship between α and the second-order polynomial fit coefficients ( a 1 and a 2) was found to depend on the wavelength range of the spectral measurement such that any given α maps into a line in ( a 1, a 2) coefficient space with a slope of −2LN( λ ch), where The logarithmically transformed data provided a much better fit to the measured spectra than the linear fits of power laws. Visible wavelengths and then extrapolated to the UV, highlighting the need for measurements in this wavelength range. This problem was particularly acute for α values calculated over only Power law fits could lead to large errors compared to measured values. The extensive hyperspectral extinctionĭata set acquired revealed that nearly all measured spectra exhibited curvature in logarithmic space, such that Ångström exponent ( α) Particles such that the in situ aerosol sampling suite deployed aboard ship measured fine-mode aerosols only. The sampling inlet had a 50 % size cut of 1.3 µm diameter Sizes and composition at concentrations spanning 2 orders of magnitude. The meteorological conditions encountered during the cruise fostered diverse ambient aerosol populations with varying GoodĪgreement was found between these two sets of extinction coefficients with slopes near unity for all three wavelengths within the SpEx measurement error Here, the performance of SpEx under realistic operating conditions in the field was assessed by comparison to extinction coefficientsĭerived from commercial instruments that measured scattering and filter-based absorption coefficients at three discrete visible wavelengths. Measurements were made with the custom-built SpectralĪerosol Extinction (SpEx) instrument that previously has been characterized only using laboratory-generated aerosols of known size andĬomposition. May–June 2016 Korea–United States Ocean Color (KORUS-OC) oceanographic field campaign are reported. In situ observations of spectrally resolved aerosol extinction coefficients (300–700 nm at ∼ 0.8 nm resolution) from the
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