Aerosol-Fog Interactions and Chemical Processing: Insights from the Grand Banks and Sable Island Regions during FATIMA 2022
TREVOR VANDENBOER, Leyla Salehpoor, Leigh Crilley, Cora Young, Gianina Giacosa, Phillipe Gauvin-Bourdon, Rachel Chang, Ed Creegan, Harindra J Fernando, York University
Abstract Number: 462
Working Group: Aerosol Chemistry
Abstract
Fog formation results from radiative, thermodynamic, microphysical, dynamical, chemical, surface conditions, and meteorological interactions. Aerosols can promote fog formation as condensation nuclei when the relative humidity (RH) exceeds 100%. There is an intricate relationship between aerosol and fog characteristics; physico-chemical characteristics of aerosol change by the occurrence of fog, and aerosol properties directly impact the life cycle of a fog layer. Sea fog study is critical in understanding fog formation, development, and dissipation to enable accurate forecasting and improve safe marine activities and transportation. During the Fog and Turbulence Interactions in the Marine Atmosphere (FATIMA) project, we explored the initiation and persistence of marine fog events.
We measured the chemical composition of aerosols during fog episodes and in the absence of fog to better understand how aerosol and aerosol chemistry affects (and are affected by) fog formation. Size-resolved aerosol samples were collected with two Micro Orifice Uniform Deposit Impactors on the Atlantic Condor research vessel in the northwest Atlantic Ocean from 3 July to 1 August 2022. Major water-soluble cations and anions, DEAH+, TMAH+ (diethylamine, trimethylamine), and MSA- (methane sulfonic acid) were quantified by ion chromatography with conductivity detection. Coarse mode ions Na+ and Cl- dominated under both conditions, as expected for sea salt. In some fog events, sea salt loadings increased before fog formation and then decreased or were entirely lost. This suggests that NaCl aerosols may act as initial fog condensation nuclei but do not sustain the fog droplet number. Fine mode NH4+ and nss-SO42- were the most abundant inorganics in both fog and non-fog aerosols. An increased sum of total concentration (neq m-3) of NH4+, DEAH+, TMAH+, MSA-, and nss-SO42- was observed in fine mode aerosols during the fog periods suggesting uptake of gaseous precursors was facilitated. We show that fog water and coarse aerosol pH differ, and that interstitial aerosol pH increases during fog events as a result.