Influence of aerosol optical properties on surface temperatures computed with a radiative-convective model

Abstract

Calculations on the effects of aerosols (i.e. suspended particles) have been shown to lead to heating or cooling in atmospheric models, depending on the size distribution of the aerosols, the height of the aerosol layer, and nature of the underlying surface. This work reports a study of the influence of different aerosol optical properties on surface temperature. The calculated surface temperatures are shown to be relatively insensitive to the real part of the refractive index and to the aerosol size distribution assumed. The sensitivity to surface albedo is similar for three aerosol types characteristic of marine aerosols, continental aerosols and stratospheric aerosols. For an aerosol composed of limonite or silicate, an increase in the absorptive component of the refractive index n 2 increases the calculated surface temperature for a constant global average airborne aerosol density as shown below. Surface albedo Surface temperature change for 0.1 increase in n 2 0.07 (oceans) 0.4 K 0.60 (snow and ice) 1.0 K It can be seen that the heating is increased 2–3 times as the surface albedo is increased by an order of magnitude. A 0.1 increase in n 2, corresponds very roughly to a factor of two increase in the percentage of solar absorption by an average particle. It would be useful to be able to determine from the results of this study, if global average aerosols heat or cool the atmosphere. Unfortunately our knowledge of the actual global aerosol distribution, optical properties and optical density is inadequate to make this determination.