Estimation of Sea Spray Aerosol Surface Area over the Southern Ocean
Using Scattering Measurements
Abstract
This study focuses on methods to estimate dry marine aerosol surface
area (SA) from bulk optical measurements. Aerosol SA is used in many
models’ ice nucleating particle (INP) parameterizations, as well as
influencing particle light scattering, hygroscopic growth, and
reactivity, but direct observations are scarce in the Southern Ocean
(SO). Two campaigns jointly conducted in austral summer 2018 provided
co-located measurements of aerosol surface area from particle size
distributions and lidar to evaluate SA estimation methods in this
region. Mie theory calculations based on measured size distributions
were used to test a proposed approximation for dry aerosol SA, which
relies on estimating effective scattering efficiency (Q) as a function
of Ångström exponent (å). For distributions with dry å<1, Q=2
was found to be a good approximation within ±50%, but for distributions
with dry å>1, an assumption of Q=3 as in some prior studies
underestimates dry aerosol surface area by a factor of 2 or more. We
propose a new relationship between dry å and Q, which can be used for
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