A quantitative test of infrared optical constants for supercooled sulphuric and nitric acid droplet aerosols

Abstract

Abstract. In situ Fourier transform infrared (FTIR) extinction spectra of supercooled H 2 SO 4 /H 2 O and HNO 3 /H 2 O solution droplets were recorded in the large coolable aerosol chamber AIDA (Aerosol Interactions and Dynamics in the Atmosphere) of Forschungszentrum Karlsruhe for a range of aerosol compositions and at temperatures extending down to 192 K. The measured spectra were quantitatively analysed in terms of aerosol composition and mass concentration by using Mie theory in combination with published refractive index data as input parameters. Simultaneously, total sulphuric acid and nitric acid mass concentrations from filter analysis and total water concentrations measured with the Lyman-α hygrometer of Forschungszentrum Jülich were used to calculate the aerosol composition at thermodynamic equilibrium inside the aerosol chamber. By comparing these measured aerosol parameters with those retrieved from the analysis of the FTIR spectra, the accuracy of the literature data sets of refractive indices could be assessed. In summary, four data sets were tested in the H 2 SO 4 /H 2 O system as well as two data sets in the HNO 3 /H 2 O system, partly revealing significant discrepancies in the retrieved aerosol properties. Potential explanations for these differences are discussed in this paper.

Effect of sulfuric acid coating on heterogeneous ice nucleation by soot aerosol particles

“…In situ FTIR extinction measurements are sensitive to ice mass concentrations above 5 μg m −3 . A White‐type multiple reflection cell with a maximum path length of 254.3 m [ Wagner et al , 2003] is used to measure FTIR extinction spectra of ice crystals in time steps of ∼20 s. The spectra are recorded with a Bruker IFS 66v FTIR spectrometer between 800 and 6000 cm −1 with a resolution of 4 cm −1 . Ice particle number concentrations are retrieved from the FTIR spectra using a method described by Mangold et al [2005].…”

MIPAS observations of volcanic sulfate aerosol and sulfur dioxide in the stratosphere

“…Over this time period, three different primary instrument types were used. The most recent type (laser particle counters, LPCs) of the three instrument types was used first in 2006, became the standard Laramie instrument in 2008, and was, as an example, also flown on quasi-Lagrangian balloons in Antarctica in 2010 (Ward et al, 2014). While the transition from the first instrument to the second was documented in , a similar study comparing the third Wyoming instrument with the second instrument is a work in progress.…”

“…1b). This particular data set has been chosen because in an evaluation of optical constants for sulfuric acid, Wagner et al (2003) found these data sets to be best consistent with observations in the aerosol chamber AIDA (Aerosol Interactions and Dynamics in the Atmosphere). The spectral range selected for the retrieval (1216.5-1219.5 cm −1 ) is situated at the long wavelength end of MI-PAS band B as indicated by the two vertical lines in Fig.…”

Aerosol Chamber Study of Optical Constants and N2O5 Uptake on Supercooled H2SO4/H2O/HNO3 Solution Droplets at Polar Stratospheric Cloud Temperatures

“…26 Total aerosol sulfate and nitrate mass concentrations of the binary H 2 SO 4 /H 2 O and ternary H 2 SO 4 /H 2 O/HNO 3 solution droplets were determined by ion chromatographic analysis of nylon filter samples, type Nylabsorb (Gelman Sciences), which minimize evaporation losses in particular of nitric acid, as described in detail in our recent publication. 8 To minimize adsorptive losses of HNO 3 in the sampling tube, a heated Teflon tube (T ) 293 K) was used in the sampling line. As the filter holders are located outside the cold housing of the AIDA chamber, nitric acid vapor from particles evaporating in the sampling tube as well as the interstitial HNO 3 vapor in equilibrium with the STS droplets will contribute to the Nylon filter loading.…”