Optical extinction of size-controlled aerosols generated from squid chromatophore pigments

An iterative correction approach used to retrieve the refractive index of squid pigment aerosols

“…Both Mie traces fit within the error bars of the corrected data, showing that the mixing rule provides a good estimate of the effective RI that was measured by the CRD. Despite correlating to a value on the lower end of our originally reported real RI, our data never exceeded a 20% difference with our retrieved value obtained via optical extinction measurements (figure 4(b)), resulting in a better fit than our uncorrected data compared to calculated Mie values [26].…”

“…In an effort to move away from solution-based experiments, we also manufactured squid pigment aerosols. This process enabled us to directly measure the size-dependent optical extinction of pigment particles suspended in nitrogen gas using a cavity ring-down (CRD) spectrometer, a technique common in atmospheric chemistry [26]. Our data suggested good agreement between extinction data measured at 532 nm and the calculated Mie values; however, we still observed a 5%-30% error between the experimental and calculated methods.…”

“…In our previous report, we concluded that it was possible that the aerosols had solvent inclusions or that solvent was mixed in with the pigment while they were being measured by the CRD but had evaporated while under the high vacuum of the SEM. This was evident in the difference between the DMA selected size of the particles and what was measured by the SEM [26]. Thus, to account for solvent effects within the generated pigment aerosols, we employed the Maxwell-Garnett mixing rule.…”

“…All analysis is done using the experimental data set reported by Dinneen and coworkers in a previous report [25,26], where we determined extinction cross-sections of atomized squid pigment aerosol from 1% by weight solutions in 0.2 M hydrochloric acid in water. Seven aerosol mobility diameters from 216 to 545 nm were selected using a differential mobility analyzer (DMA, TSI model 3080L), and interrogated with a custom CRD spectrometer (<9% relative humidity) to measure extinction; separately a SEM was used to validate the aerosol diameters.…”

“…Prior to making measurements, the accuracy of the CRD was examined using squalene with a flow of 0.30 l min −1 at the condensation particle counter; the same flow is used for these experiments [19]. Abbe refractometer experiments were performed at 25 °C and CRD experiments were performed between 20 °C and 22 °C [25,26]. Here, we describe methods used for the Mie correction, refractive index retrievals, and solvent mixing calculations of the data.…”