Reported here is a further evaluation of a Two-Week Sampler used to measure concentrations of acidic gases and fine particulate inorganic ions for the ARB-sponsored Epidemiologic Investigation to Identify Chronic Health Effects of Ambient Air Pollutants in Southern California. The Main Leg of the two weeks Sampler consists of a sodium carbonate-coated honeycomb denuder to remove nitric acid followed by a Teflon particulate filter and then a sodium carbonate-coated quartz filter to trap volatilized particuIate nitrate. The Organic Acids Leg of the sampler has a Teflon prefilter to remove particulate material followed by two potassium hydroxide (KOH) -coated quartz filters to trap organic acids.
Two-week collections using components of the Main Leg of the sampler in conjunction with filtered ambient air were made in Riverside in the fall of 1994, and Claremont in the summer of 1995, to evaluate the penetration of nitric acid. For both studies, the nitrate on the carbonate-coated denuders agreed quite well with the front nylon reference filter, although during the Riverside collection a positive artifact was indicated on the nylon reference filter. For the Riverside sampling, the carbonate-costed denuders were the only substrates that contained significant nitrite. While sodium chloride-coated substrates showed little artifact collection, the sodium chloride-coated denuder did not appear to remove nitric acid effectively. In all cases, carbonate-coated back filters collected much more nitrate than could be due to nitric acid, indicating an interference; this will cause particulate nitrate to be over-estimated. The denuder was also shown to remove nitric acid effectively at six times its design flow rate.
The Main Leg of the sampler was also evaluated for interferences from peroxyaceryl nitrate (PAN) and nitrous acid generated in the laboratory. An average of sixteen percent of the PAN was trapped by the denuder of the Main Leg and 3 percent by the back filters. With nitrous acid, the carbonate-coated denuder removed from 50-100 percent of this species as nitrite and the rest was removed by the back filters. With ozone present, essentially all of the nitrite was converted to nitrate. Sodium chloride-coated denuders and back filters showed no affinity for removing either PAN or nitrous acid.
The Organic Acids Leg was tested for PAN interferences under laboratory conditions and for sampling artifacts using ambient air. When exposed to PAN, the KOH-coated filters of the Organic Acids Leg of the Two-Week Sampler removed PAN as acetate with approximately 60 percent efficiency for each filter. When sampling filtered ambient air, approximately 20 percent of the acetate.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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