Project at a Glance
Project Status: complete
Title: Dry deposition of acidic gases and particles.
Principal Investigator / Author(s): John, Walter
Contractor: Air and Industrial Hygiene Laboratory, California Department of Health Services
Contract Number: A3-108-32
Research Program Area: Atmospheric Processes
Topic Areas: Acid Deposition
Several techniques have been developed for the measurement of dry acid deposition. The deposition of particulate sulfate and nitrate on leaves, pine needles and surrogate surfaces was measured directly by washing off the deposits. Deposition velocities were derived from parallel sampling of airborne particle concentrations. Surface exposures ranging from 14 to 62 days under nearly unvarying meteorological conditions gave constant deposition velocities. Deposition velocities were approximately the same for all surfaces and somewhat higher for nitrate compared to sulfate. Surrogate surfaces had deposits on the top surface only. A surrogate Nuclepore "leaf" sampled sulfur dioxide at a rate consistent with a bubbler but much higher than predicted. The bubbler performed well, even under extreme conditions.
A method was validated for the measurement of the size distributions of acidic particles. The Berner cascade impactor was calibrated with monodisperse aerosols. A Halocarbon grease compatible with acid analysis was shown to suppress particle bounce. It was shown that ammonium sulfate particles are properly sized, even at high relative humidities. Evaporative losses of ammonium nitrate reach only 7% at 35įC. Ambient size distributions of strong acid, sulfate, nitrate, ammonium, sodium and chloride ions were measured at Oildale and Berkeley. Distributions vary between species and with ambient conditions.
For questions regarding this research project, including available data and progress status, contact: Heather Choi at (916) 322-3893
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