A technique using high‐flow, dichotomous filter packs for measuring major atmospheric chemical constituents

Abstract

We developed a high‐resolution technique to measure major reactive trace gases and the chemical composition of size‐segregated aerosols in the troposphere as part of the 1988 Global Change Expedition/Coordinated Air‐Sea Experiment/Western Atlantic Ocean Experiment. We sampled air over the western North Atlantic Ocean from the NOAA King Air research aircraft and NOAA ship Mt. Mitchell during July. Our system used filter packs containing an upstream, 90‐mm quartz filter to collect particles followed by two 90‐mm rayon filters impregnated with 10% K2C03‐10% glycerol to collect alkaline reactive gases. Paired filter packs were exposed when the aircraft sampled the boundary layer. An upstream cyclone with a 50% aerodynamic cut radius of approximately 0.4 μm removed large particles from one of the filter‐pack inlets. Air was sampled at an average rate of 0.12 m3 STP min−1 for the fine filter packs and 0.26 m3 STP min−1 for the total over intervals of 45 min to 90 min. Particulate‐phase concentrations of major anions (SO42−, CH3SO3−, NO3−, Cl−) and organic species (HCOOt [HCOO− and HCOOH] and CH3COOt [CH3COO− and CH3COOH]) were measured by gradient elution ion chromatography; base cations (Ca2+, Mg2+, Na+, K+) by atomic‐absorption spectroscopy; NH4+ by automated colorimetry; and H+ by glass electrode. We quantified SO2, HNO3, and HCl using two isocratic ion chromatography methods. This technique provided higher signal‐to‐noise ratios allowing increased temporal and spatial resolution, pH determination of particulate‐phase filter extracts, and measurement of HCl on gas‐phase filters.