How much solar radiation does atmospheric mineral dust absorb?

Abstract:

Mineral dust particles are critical to the Earth’s climate system because they account for approximately a quarter of the shortwave radiation scattered and absorbed by all aerosols in the atmosphere. But despite the importance of their radiative effects, the amount of shortwave radiation absorbed by atmospheric dust remains largely unclear. This is because knowledge of dust absorption properties, characterized by the dust aerosol absorption optical depth, primarily depends on the dust size distribution and the complex refractive index, which are difficult to observe from remote-sensing platforms. As a result, climate model simulations and retrieval algorithms rely on certain assumptions about dust properties that have led to significant uncertainties in their estimation of the global dust absorption optical depth. In this study, we obtain a more accurate constraint on global dust absorption optical depth by developing a framework that leverages dozens of in-situ measurements of the dust size distribution and single-scattering albedo. We find that dust is much coarser but has a lower value of dust imaginary refractive index than represented in climate models. Our results suggest that the net effect of these two competing influences is a larger global dust absorption optical depth than represented in current models. As such, the atmospheric dust absorbs more shortwave radiation than climate models simulate, which has potentially important implications for Earth’s energy balance and the hydrological cycle.