The optical constants of several atmospheric aerosol species: Ammonium sulfate, aluminum oxide, and sodium chloride

Abstract

The optical constants of substances composing atmospheric aerosols are required to evaluate properly the effects of aerosols on the earth's radiation balance. We briefly review techniques for determining optical constants and also discuss pitfalls in using measured optical constants to simulate the optical constants of the real particles found in the atmosphere. We then compile the optical constants of (NH4hSO4, Al:Os, and NaCI. The optical constants of Al:Os and NaCI are derived from values quoted in the literature. The optical constants of (NH4):SO• are derived partly from values quoted in the literature and partly from our own measurements. Spitzer, W. G., and D. A. Kleinman, Infrared lattice bands of quartz, Phys. Rev., 121, 1324, 1961•." Strukov, Bi A., The temperature dependence of birefringence in crystals of ammonium sulfate and ammonium fluoroberYllate, Sot). Phys. Crystallogr., 6, 511, 1961. Toon, O. B., and J. B. Pollack, A global average model of atmospheric aerosols for radiative transfer calculations, J. Appl. Meteorol., 15, 225, 1976. Toon, O. B., J. B. Pollack, and C. Sagan, Properties of suspended aerosols from their infrared spectra: Application to Martian dust storms of 1971, Icarus, in press, 1976. Verleur, H. W., Determination of optical constants from reflectance or transmittance measurements on bulk crystals or thin films, d. Opt. Soc. Amer., 58, 1356, 1968. Volz, F. E., Infrared refractive index of atmospheric aerosol substances, Appl. Opt., 11, 755, 1972. Volz, F. E., Infrared optical constants of ammonium sulfate, Sahara dust, volcanic pumice, and flyash, Appl. Opt., 12, 564, 1973.

Effects of mixing on extinction by carbonaceous particles

“…The imaginary part of the refractive index of pure (NH4)2SO 4 is •< 10 -7 in the visible [Toon et al, 1976], and the soluble fraction of the atmospheric aerosol is often dominated It is also likely that some, if not all, of the absorption reported above for soluble aerosol is spurious, an artifact of absorption measurements on scattering media, and some of the work cited above has been criticized for such an oversight [Bergstrom, 1973;Egan and Hilgeman, 1979]. Accordingly, we will treat the soluble material in the composite particles as nonabsorbing sulfate compounds.…”

An update on polar aerosol optical properties using POLAR-AOD and other measurements performed during the International Polar Year

“…The spectral patterns of the real part n r and imaginary part n i of the particulate refractive index were then calculated as weighted averages of the two optical parameters found for sulphates (Toon and Pollack, 1976), nitrates (Tang and Munkelwitz, 1996), sea salt (Shettle and Fenn, 1979), mineral dust (Dust-Like component of Vermote et al (1997)), BC (Soot component of Vermote et al (1997)), and WSOM (Water-Soluble component of Vermote et al (1997)), using as weights the composition mass percentages given in Fig. 10 for the overall particle size-distributions sampled during the JuneeSeptember (summer) and OctobereMay (winterespring) periods.…”

Raman lidar and aircraft measurements of tropospheric aerosol particles during the Asian dust event over central Japan: Case study on 23 April 1996

“…To obtain the appropriate size distributions of the aerosols for this aircraft measurement, we used the size bins recalculated for the aerosol refractive indices (Figure 1) that were determined from the chemical analysis; we assumed a refractive index (n) of 1.46 + 0i (96 wt% ammonium bisulfate solution [Tang and Munkelwitz, 1994]) at q = 307 K and 301 K, n = 1.53 + 10 À7 i (ammonium sulfate [Toon et al, 1976]) at q = 293 K for particles of radius less than 0.5 mm, and n = 1.55 + 0.005i (typical value of mineral dust Tanaka et al, 1989]) for radii larger than 0.5 mm, over the height range of the measurement.…”

“…The refractive indices of the fine particle mode (radius 0.5 mm) were determined based on the chemical analyses (described in section 3.2): n = 1.53 + 10 À7 i (dry ammonium sulfate ((NH 4 ) 2 SO 4 ) [Toon et al, 1976]) or n = 1.46 + 0i (96 weight percent (wt%) of ammonium bisulfate (NH 4 HSO 4 ) solution [Tang and Munkelwitz, 1994]), depending on the height. The refractive index of the coarse particles mode (radius > 0.5 mm) was assumed, based on the SEM microanalysis (section 3.2), to be n = 1.55 + 0.005i (or 1.55 + 0.01i), obtained from previous studies of yellow sand (Asian mineral dust) measured in Japan Tanaka et al, 1989].…”