DETERMINATION OF ATMOSPHERIC CONCENTRATIONS OFSULFURIC ACID AEROSOL BY SPECTROPHOTOMETRY COULOMETRY AND FLAME PHOTOMETRY

Heretofore, nonspecific and insensitive methods were used to measure sulfuric acid aerosols in the atmosphere. We have developed a precise, sensitive, and highly selective method for determination of these toxic pollutants. The aerosols are collected by impaction or filtration, which separates the sulfuric acid from sulfur dioxide. The sulfuric acid is decomposed at controlled temperatures under a stream of nitrogen to separate the acid from other sulfates. The liberated sulfur trioxide in nitrogen is converted to sulfur dioxide by reaction with hot copper. The sulfur dioxide produced is analyzed either spectrophotometrically, coulometrically, or flame photometrically. The method can measure sulfuric acid in the presence of 10 to 100 times as much sulfur dioxide and other sulfates. Ammonium sulfate interferes quantitatively with the determination of sulfur acid. We do not, however, consider this a serious interference, because this compound forms in the atmosphere from sulfuric acid and gaseous ammonia. The relative standard deviation with standard samples is 5% or less. The sensitivities of the method for colorimetric, coulometric, and flame photometric analysis are 0.3, 0.03, and 0.003 μg of H2SO4 per sample. © 1969, American Chemical Society. All rights reserved.