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When is cloud condensation nuclei activity sensitive to particle characteristics at emission?
Author(s) -
Fierce Laura,
Riemer Nicole,
Bond Tami C.
Publication year - 2013
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/2013jd020608
Subject(s) - supersaturation , cloud condensation nuclei , aerosol , particle (ecology) , condensation , chemistry , particle size , particle number , meteorology , physics , thermodynamics , organic chemistry , volume (thermodynamics) , oceanography , geology
The cloud condensation nuclei (CCN) activity of an aerosol population depends on individual particles' size and composition. However, these properties are modified shortly after emission by condensation of semivolatile substances and coagulation with other particles. It is, therefore, unclear to what extent particle characteristics at emission affect CCN activity after aging by condensation and coagulation. We present a process‐level analysis of particles emitted from a particular source, diesel engines, in which we isolate the separate effects of condensation and coagulation on the CCN activation of primary aerosol. We simulated aerosol dynamics in a polluted area with the Particle Monte Carlo model coupled to the Model for Simulating Aerosol Interactions and Chemistry and evaluated three factors influencing particle CCN activity shortly after emission: (1) particle characteristics at the time of emission, (2) aging conditions near the emission source, and (3) the water vapor supersaturation at which CCN activity is evaluated. CCN concentrations were sensitive to particle properties at emission only under specific environmental conditions. Diesel emissions did not strongly influence local CCN concentrations at low cloud supersaturation thresholds ( s <0.2 % ), regardless of particle characteristics at emission or aging conditions. At higher supersaturation thresholds ( s >0.2 % ) and under conditions of rapid secondary aerosol formation, changes in CCN concentrations showed a greater sensitivity to particles' emission size than composition.