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Project Status: complete

Title: Development of a modular system for acidic deposition monitoring

Principal Investigator / Author(s): Cahill, Thomas A

Contractor: UC Davis

Contract Number: A132-102

Topic Areas: Acid Deposition, Monitoring


In order to effectively monitor dry acidic deposition in the forests of California, a simple and inexpensive monitoring system is needed for large-scale deployment. While the current California Acid Deposition Monitoring Program (CADMP) monitor performs satisfactorily, it is cumbersome and expensive for statewide application, especially in remote sites. To simplify and reduce the cost of particulate and gaseous sampling procedures for the CADMP, the University of California, Davis (UCD), developed for the ARB the Modular System for Acid Deposition Monitoring (MSAM). This sampler provides continuous monitoring on a 14-day cycle and could reduce the cost and complexity of field operations. A large part of the UCD project involves establishing comparability between the MSAM and the existing CADMP sampler before considering large-scale statewide deployment of the MSAM sampler. The study was conducted in two phases. In Phase I, the MSAM was tested in Sacramento for three one-week periods from April 8 to 29, 1992. The data analyses showed good agreement between collocated MSAM units and the ratio for the two collocated MSAM samplers was nearly 1.00 (0.808 to 1.36, except for ammonium and nitric acid). The statistical comparisons between the MSAM and CADMP sampler were satisfactory (within 20 percent) for sulfate, sulfur dioxide, total nitrates, ammonia, and nitric oxide. However, the Phase I tests did find some discrepancies between MSAM and the CADMP samplers for particulate nitrate, ammonium, and mass. After review of the design of the MSAM sampler, the problems were identified and modifications were made. Phase 11 compared the MSAM and CADMP samplers under field conditions. From August 5 to November 6, 1992, the MSAM was deployed at an intensive study site at Barton Flats in the San Bernardino National Forest. The data analyses showed the improvement of the MSAM sampler in Phase II. ln the fist three periods, the results showed good agreement between the two units for mass concentrations. In the case of NH3, the species showed a marked improvement from Phase I to Phase II (CADMPMSAM = 0.33 for Phase I and 0.84 for Phase II). After examining the data from the Phase II trials, it was concluded that the MSAM sampler performed well except for the collection of total nitrate. Nitrate collection differences were due to the use of a Teflon filter to capture and retain nitrate particles. Data from Phase I, when the MSAM employed a single Nylasorb filter, showed that MSAM total nitrate measurements agreed very well with CADMP total nitrate measurements (CADMPMSAM = 0.90). During Phase II, the single Nylasorb filter was replaced with a Teflon-Nylasorb filter combination to reduce the chances of filter clogging. The filters were placed in a double cassette. It was later determined that because of the filter cassette's construction, the nitric acid that passed through the Teflon filter could be absorbed by the plastic support grid and the plastic filter cassette walls before reaching the Nylasorb filter. This would reduce the amount of nitric acid collected by the Nylasorb. In addition, the MSAM Teflon filters were not analyzed for at least eight weeks. This gave the nitrate particles time to volatilize off the Teflon filter. UCD


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

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