A Temperature- and Composition-Dependent Study of H₂SO₄ Aerosol Optical Constants Using Fourier Transform and Tunable Diode Laser Infrared Spectroscopy

Abstract

Frequency-dependent optical constants have been determined from the Fourier transform infrared spectra of laboratory-generated liquid sulfuric acid/water aerosols over a range of temperatures and compositions that are relevant to the upper troposphere and lower stratosphere of Earth. The compositions of the particles were determined in situ using a tunable diode laser to monitor equilibrium water vapor pressures. The infrared complex refractive indices of sulfuric acid are shown to be strongly dependent on temperature and composition, because of changes in the equilibrium between sulfate and bisulfate ions. Results from this study also have implications in understanding the temperature dependence of intermolecular interactions within ionic solutions. The database presented here is the most extensive yet available for the liquid solutions of sulfuric acid.

Spectroscopic evidence for NAT, STS, and ice in MIPAS infrared limb emission measurements of polar stratospheric clouds

“…This was also suggested by Wagner et al (2003). Using their own data for HNO 3 /H 2 O and H 2 SO 4 /H 2 O (Niedziela et al, 1999), combined with the mixing rule by Biermann et al (2000), the agreement between calculation and measurement of ternary solutions improved considerably (Norman et al, 2002). Remaining differences were attributed to the mixing rule itself.…”

“…To simulate STS PSCs within MIPAS spectra, we calculated refractive indices using the mixing rule by combining different sets of binary optical constants: (1) those provided by Biermann et al (2000), and (2) HNO 3 /H 2 O by combined with H 2 SO 4 /H 2 O by Niedziela et al (1999).…”

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

“…1. Here the optical constants used in our study, which are based on Niedziela et al (1999) for 75 wt % and 230 K (bold red line), are compared to data at other concentrations and temperatures, based on optical constants given by Niedziela et al (1999) (Fig. 1a) and Lund Myhre et al (2003) (Fig.…”

“…Solid lines indicate the uncertainties used to calculate the "total" error. Indicated errors are "noi" -single scan spectral noise; "T" -temperature uncertainty 2 K; "vmr" -10 % uncertainty in volume mixing ratios of interfering gases; "htang" -300 m tangent altitude uncertainty; "Niedziela_240K_60wts" -use of optical constants by Niedziela et al (1999) for 240 K and 69 wt % instead of Niedziela et al (1999) mental errors that have been investigated but are not listed in Fig. 2 are uncertainties due to the knowledge of the instrumental line shape and radiometric gain and offset calibration error.…”

“…Increased interest in stratospheric sulfate aerosol is also connected to its potential use in climate engineering schemes (e.g. Niemeier and Timmreck, 2015;Rasch et al, 2008). The negative radiative effect of stratospheric aerosol (Andersson et al, 2015;Brühl et al, 2015;Ridley et al, 2014;Santer et al, 2014;Solomon et al, 2011;Vernier et al, 2011) is discussed as being one of the causes of the global warming "hiatus" experienced during the first decade of this century (Haywood et al, 2014;Santer et al, 2014;Fyfe et al, 2013).…”