Size distributions and statistical analysis of nitrate, excess sulfate, and chloride deficit in the marine boundary layer during GCE/CASE/WATOX

Abstract

A high‐volume sampler and a two‐stage cascade impactor were used aboard the NOAA ship Mt. Mitchell to obtain a fine‐particle‐fraction and two coarse‐particle‐fraction size cuts of atmospheric marine boundary layer aerosol samples. Ion chromatography analysis yielded NO 3 − , S0 4 = , Na + , and Cl − concentrations and, by calculation, excess sulfate (XSO 4 ) and chloride deficit (Cl d ) concentrations. Statistical analysis of the July 1988 sample sets from the Bermuda and U.S. east coast areas showed that most of the observed coarse‐particle Cl d in the Bermuda‐area samples may be associated with the equivalence sum of NO 3 − and XSO 4 . However, the coarse‐particle Cl d observed in the U.S. east coast samples is substantially greater than the equivalence sum of NO 3 − and XSO 4 observed at this location. It is concluded that for the east coast sampling, about 13% of the observed 16.9 nmol XSO 4 m −3 displaced Cl − in sea salt aerosol particles. For the Bermuda area, 15‐20% of the observed 11.1 nmol XSO 4 m −3 displaced Cl − in sea salt aerosol particles (nearly 30% of the observed Cl d ) despite a relatively low sea salt mass concentration under light wind speed conditions. Under more typical sea state and wind speed conditions for the western North Atlantic Ocean, substantially more XSO 4 may displace chloride ions in sea salt aerosol particles.