Using aircraft measurements to characterize subgrid-scale variability of aerosol properties near the Atmospheric Radiation Measurement Southern Great Plains site
Authors: Fast Jerome D. , Bell David M. , Kulkarni Gourihar , Liu Jiumeng , Mei Fan , Saliba Georges , Shilling John E. , Suski Kaitlyn , Tomlinson Jason , Wang Jian , Zaveri Rahul , Zelenyuk Alla 
Published: September 2022

Abstract. Complex distributions of aerosol properties evolve in space and
time as a function of emissions, new particle formation, coagulation,
condensational growth, chemical transformation, phase changes, turbulent
mixing and transport, removal processes, and ambient meteorological
conditions. The ability of chemical transport models to represent the
multi-scale processes affecting the life cycle of aerosols depends on their spatial resolution since aerosol properties are assumed to be constant
within a grid cell. Subgrid-scale-dependent processes that affect aerosol
populations could have a significant impact on the formation of particles,
their growth to cloud condensation nuclei (CCN) sizes, aerosol–cloud interactions, dry deposition and rainout and hence their burdens, lifetimes, and radiative forcing. To address this issue, we characterize
subgrid-scale variability in terms of measured aerosol number, size,
composition, hygroscopicity, and CCN concentrations made by repeated
aircraft flight paths over the Atmospheric Radiation Measurement (ARM)
program's Southern Great Plains (SGP) site during the Holistic Interactions
of Shallow Clouds, Aerosols and Land Ecosystem (HI-SCALE) campaign. Subgrid
variability is quantified in terms of both normalized frequency
distributions and percentage difference percentiles using grid spacings of
3, 9, 27, and 81 km that represent those typically used by cloud-system-resolving models as well as the current and next-generation climate models.
Even though the SGP site is a rural location, surprisingly large horizontal
gradients in aerosol properties were frequently observed. For example,
90 % of the 3, 9, and 27 km cell mean organic matter concentrations
differed from the 81 km cell around the SGP site by as much as
∼ 46 %, large spatial variability in aerosol number
concentrations and size distributions were found during new particle
formation events, and consequently 90 % of the 3, 9, and 27 km cell mean
CCN number concentrations differed from the 81 km cell mean by as much as
∼ 38 %. The spatial variability varied seasonally for some
aerosol properties, with some having larger spatial variability during the
spring and others having larger variability during the late summer. While
measurements at a single surface site cannot reflect the surrounding
variability of aerosol properties at a given time, aircraft measurements
that are averaged within an 81 km cell were found to be similar to many, but
not all, aerosol properties measured at the ground SGP site. This analysis
suggests that it is reasonable to directly compare most ground SGP site
aerosol measurements with coarse global climate model predictions. In
addition, the variability quantified by the aircraft can be used as an
uncertainty range when comparing the surface point measurements with model predictions that use coarse grid spacings.