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Dependence of Aerosol‐Droplet Partitioning on Turbulence in a Laboratory Cloud
Author(s) -
Shawon Abu Sayeed Md,
Prabhakaran Prasanth,
Kinney Greg,
Shaw Raymond A.,
Cantrell Will
Publication year - 2021
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2020jd033799
Subject(s) - aerosol , turbulence , adiabatic process , saturation (graph theory) , particle size , particle (ecology) , atmospheric sciences , chemistry , mechanics , environmental science , meteorology , thermodynamics , physics , mathematics , combinatorics , oceanography , geology
Activation is the first step in aerosol‐cloud interactions, which have been identified as one of the principal uncertainties in Earth's climate system. Aerosol particles become cloud droplets, or activate, when the ambient saturation ratio exceeds a threshold, which depends on the particle's size and hygroscopicity. In the traditional formulation of the process, only average, uniform saturation ratios are considered. However, turbulent environments like clouds intrinsically have fluctuations around mean values in the scalar fields of temperature and water vapor concentration, which determine the saturation ratio. Through laboratory measurements, we show that these fluctuations are an important parameter that needs to be addressed to fully describe activation. Our results show, even for single‐sized, chemically homogeneous aerosols, that fluctuations blur the correspondence between activation and a particle's size and chemical composition, that turbulence can increase the fraction of aerosol particles which activate, and that the activated fraction decreases monotonically as the concentration of aerosol increases. Taken together, our data demonstrate that fluctuations can have effects equivalent to the aerosol limited and updraft limited regimes, known from adiabatic parcel theory.