Parameterization of the optical properties of sulfate aerosols

Abstract

Parameterizations of the shortwave optical properties of ammonium sulfate [(NH 4) 2 SO 4 ], ammonium bisulfate (NH 4 HSO 4), and sulfuric acid (H 2 SO 4) are provided as functions of relative humidity for high and low spectral resolution band models. The optical property parameterization is simple in form and in its dependence on relative humidity. The growth of the aerosol particles is based on equilibrium saturation theory, and the optical properties are computed from Mie theory. The optical properties necessary for the most commonly used radiative transfer methods are provided. Results show that when relative humidity effects are included in the backscatter fraction the radiative forcing is found to be a more sensitive function of near infrared wavelengths compared to visible wavelengths. For increasing relative humidity, sulfuric acid is found to have a larger effect on radiative forcing compared to the forcing by ammonium sulfate or ammonium bisulfate. Also, as relative humidity increases, forcing increases to higher values for smaller mode size distributions compared to forcing by larger mode distributions. These parameterizations will enable climate forcing studies to be performed with radiative transfer schemes that more accurately represent sulfate influences on the radiation balance.

Aerosol Properties and Chemical Apportionment of Aerosol Optical Depth at Locations off the U.S. East Coast in July and August 2001

“…Assuming that Kotchenruther et al's results provide a lower bound for the RH growth in CLAMS, we can estimate an upper bound using Li et al's (2001) theoretical RH growth curve parameterizations for pure sulfate aerosols. We base our choice of the degree of acidity of the pure sulfate aerosol on a study by Brook et al (1997), who found that sulfate aerosol acidity increased in maritime locations on the Canadian Atlantic coast compared to the generally neutralized sulfate aerosol encountered further inland.…”

“…The upper bound to aerosol growth with increasing RH based on Li et al (2001) and Brook et al (1997) was applied to Eqs. (3) and (5), and to our calculations of the apportionment of AOD.…”

Aerosol Optical Properties and Particle Size Distributions on the East Coast of the United States Derived from Airborne In Situ and Remote Sensing Measurements

“…As will be discussed later, values of 0 and various size parameters were virtually identical in the two campaigns, but the aerosol composition differed as discussed by Magi et al (2005), who explain that we can assume the Kotchenruther et al (1999) results provide a lower bound for the RH growth for CLAMS and use the theoretical growth curve parameterizations for pure sulfate aerosols as determined by Li et al (2001) to estimate an upper bound. Since Magi et al (2005) show that aerosol composition during CLAMS was dominated by sulfate, we can determine the degree of acidity of the pure sulfate aerosol based on a study by Brook et al (1997) and air parcel back trajectories during CLAMS.…”

How the Inhomogeneity of Wet Sea Salt Aerosols Affects Direct Radiative Forcing

“…The relation of size distributions of dry and wet aerosols was explicitly discussed in Li et al (2001). The relation of size distributions of dry and wet aerosols was explicitly discussed in Li et al (2001).…”