Aerosol Total Volume Estimation From Wavelength‐ and Size‐Resolved Scattering Coefficient Data: A New Method

Abstract

While the importance of supermicron particles on human health and climate is well recognized, knowledge of their size-related properties remains elusive. Many routine near-surface in situ measurements of aerosol properties include size spectra of submicron particles and aerosol total scattering coefficient at three visible wavelengths and two size cutoffs. These properties are collected, for example, at the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) user facility. Our study illustrates how these conventional measurements can be used to predict total particle volume (particle size <10 μm). The well-known fact that small and large particles scatter sunlight very differently forms the basis of a new method. Our study demonstrates a good agreement between estimated and measured total volumes for five climate-important locations. The agreement suggests that the new method can be used to predict the total particle volume from the routine data collected at numerous sites around the world. Plain Language Summary Particles in the air are astonishingly diverse in terms of size. Determining their size distribution, which characterizes the number of particles for every size of interest, is a difficult technical problem due to an extremely wide range of sizes (several orders of magnitude) and lack of a single instrument that can measure over the entire size range. For example, most conventional particle sizing techniques cannot measure large particles (size >1 μm) despite their recognized importance for human health, environment, and climate. Here, a new method is introduced to indirectly estimate the volume of large particles, which is closely related to their size distribution. This method combines (1) routinely measured size distributions of small particles and (2) the well-known fact that small and large particles scatter sunlight very differently as a function of wavelength. The performance of this method is demonstrated for data collected at five sites characterized by continental, alpine, coastal, and marine environments. The good agreement between the estimated and the measured values of the total volume of small and large particles demonstrates the credibility of this method and highlights its potential application to routine aerosol measurements made at numerous locations around the world.

Measurements and Approximations for Submicron‐Aerosol Size Distribution Functions

“…Fine dust‐aerosol fractions (less than 2 m in diameter) are especially important for the atmospheric radiation budget, because such fractions (having a significant lifetime) most efficiently interact with short‐wave solar radiation (Spyrou et al., 2013; Tegen & Lacis, 1996; Tegen et al., 1996). The size spectra of submicron particles and aerosol total scattering coefficient can be used to predict total particle volume (particle size 10 m) (Kassianov et al., 2020).…”