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Using a coupled LES-aerosol radiation model to investigate urban haze: Sensitivity to aerosol loading and meteorological conditions

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JournalAtmospheric Chemistry and Physics
DateAccepted/In press - 31 Jul 2020
DatePublished (current) - 22 Oct 2020
Volume20
Pages (from-to)11893-11906
Original languageEnglish

Abstract

The aerosol–radiation–meteorology feedback loop
is the process by which aerosols interact with solar radiation
to influence boundary layer meteorology. Through this feedback, aerosols cause cooling of the surface, resulting in reduced buoyant turbulence, enhanced atmospheric stratification and suppressed boundary layer growth. These changes in
meteorology result in the accumulation of aerosols in a shallow boundary layer, which can enhance the extent of aerosol–
radiation interactions. The feedback effect is thought to be
important during periods of high aerosol concentrations, for
example, during urban haze. However, direct quantification
and isolation of the factors and processes affecting the feedback loop have thus far been limited to observations and
low-resolution modelling studies. The coupled large-eddy
simulation (LES)–aerosol model, the University of California, Los Angeles large-eddy simulation – Sectional Aerosol
Scheme for Large Scale Applications (UCLALES-SALSA),
allows for direct interpretation on the sensitivity of boundary layer dynamics to aerosol perturbations. In this work,
UCLALES-SALSA has for the first time been explicitly set
up to model the urban environment, including addition of an
anthropogenic heat flux and treatment of heat storage terms,
to examine the sensitivity of meteorology to the newly coupled aerosol–radiation scheme. We find that (a) sensitivity of
boundary layer dynamics in the model to initial meteorological conditions is extremely high, (b) simulations with high
aerosol loading (220 µg m−3) compared to low aerosol loading (55 µg m−3
) cause overall surface cooling and a reduction
in sensible heat flux, turbulent kinetic energy and planetary
boundary layer height for all 3 d examined, and (c) initial
meteorological conditions impact the vertical distribution of
aerosols throughout the day.

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