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Project Status: complete

Title: Evaluation and development of procedures for determination of sulfuric acid total particle-phase acidity and nitric acid in ambient air-phase ii

Principal Investigator / Author(s): Appel, B R

Contractor: Air and Industrial Hygiene Laboratory, California Department of Health Services

Contract Number: A8-111-31

Topic Areas: Acid Deposition, Monitoring


Methods for measurement of sulfuric acid, strong acids and nitrate in atmospheric particulate matter, and for gaseous nitric acid were evaluated. Selective extraction 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. PN was measured by the nitrate able to penetrate a diffusion denuder coated to remove acidic gases including HN03. Losses of nitrate from Teflon prefilters were determined by comparing the nitrate retained by these filters to the nitrate penetrating the acid gas denuder. TIN was compared with the nitrate collected on glass fiber filters to assess the origin of the artifact particulate nitrate on the latter. A modified chemilumineseent NOx monitor converted to measure nitric acid continuously, was compared to the filter techniques.

Levels of H2SO4 UP to 11 pg/m3 were observed in California's South Coast Air Basin (SCAB) using selective extraction with benzaldehyde. Strong particulate acid measurements by titrimetry generally supported the H2SO4 determinations. However, EN03 appeared to contribute to the particulate acidity together with the H2SO4. Gaseous nitric acid measurements in the SCAB 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. Heating the filter samplers was shown to increase sampling errors. Atmospheric nitrate results obtained in short-term, low volume sampling with Gelman A glass fiber filters approximated those with the TIN samplers. Accordingly, these glass fiber filters retained essentially all the gaseous nitric acid sampled.


For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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