Evaluation and Development of Procedures for Determination of Sulfuric Acid, Total Particle-Phase Acidity and Nitric Acid in Ambient Air-Phase II

摘要

Selective extraction of H2SO4 with benzaldehyde and titrimetry for strong acids were compared in atmospheric trials. Gaseous nitric acid was determined by (1) measuring the nitrate collected on nylon or NaCl-impregnated cellulose filters after removal of particulate matter with Teflon prefilters, and (2) the difference between total inorganic nitrate (TIN) and particulate nitrate (PN). TIN was measured by the sum of the nitrate collected with a Teflon prefilter and nylon or NaCl-impregnated after-filter, and PN, by the nitrate able to penetrate a diffusion denuder coated to remove acidic gases. The atmospheric HNO3 results were also compared to those by Fourier Transform Infrared Spectroscopy. A modified chemiluminescent NOx monitor converted to measure nitric acid continuously, was compared to the filter techniques in laboratory trials. Levels of H2SO4 up to 11 micrograms/cu. m were observed in California's South Coast Air Basin (SCAB) using selective extraction with benzaldehyde. HNO3 appeared to contribute to the particulate acidity together with the H2SO4. Gaseous nitric acid measurements using nylon or NaCl-impregnated after-filters were substantially higher than those by the difference technique. This correlated with losses of nitrate from the Teflon prefilters, which exceeded 50% at high ambient temperature and low relative humidity. Gelman A glass fiber filters retained essentially all the gaseous nitric acid sampled.