Air monitoring: Research needs.
Sampling and analyses difficulties encountered in the ambient, source and exposure monitoring areas of environmental data sampling of inorganic particulate matter, inorganic gases, organic particulate matter, and organic gases are discussed. Attention is given to instrumentation such as tunable lasers, ion chromatography, optical emission spectroscopy, fiber glass filters, dichotomous samplers, Teflon and other polymeric membrane filters, and electrostatic samplers. A lack of species-tailored devices is noted, as is a need to develop numerical and statistical models that will decrease the required sampling volume for reliable estimates. Finally, better characterizations of the effects that sampling has on the medium sampled are recommended. 8 references.
Simultaneous nitric acid, particulate nitrate and acidity measurements in ambient air
Abstract A laboratory and field study was conducted to evaluate measurement methods for atmospheric nitric acid and to elucidate the formation of artifact particulate nitrate on filter media. Nitric acid collection with nylon and NaCl-impregnated filters was compared employing Teflon pre-filters to remove atmospheric particulate matter. The two collection procedures provided > 97% collection of nitric acid at the levels expected under ambient conditions. At higher levels, the efficiency of the nylon filters decreased. Nylon filters supplied by Millipore and Ghia Corporations were shown to be equally effective. Clean Teflon pre-filters permitted passage of > 98% of the HNO 3 to the collection filters. However, atmospheric particulate matter on the pre-filters retained HNO 3 . Ammonium nitrate on otherwise clean pre-filters caused positive error in HNO 3 measurement (and a corresponding loss of particulate nitrate) when clean air was passed through the sample. Dissociation to NH 3 and HNO 3 is a likely source of these errors. A lower limit of 22 (ppb) 2 is obtained for the NH 4 NO 3 dissociation constant at 21°C. Atmospheric sampling was done in Pittsburg, California. On average, results with the two HNO 3 collection procedures agreed within 3% for levels in the range 0.3–1.5 ppb. Levels of HNO 3 and NH 3 were below those needed for saturation with respect to NH 4 NO 3 formation. A glass fiber filter was shown to serve as a total inorganic nitrate sampler, collecting both particulate nitrate and HNO 3 .
Simple method for microgram amounts of sulfate in atmospheric particulates.
Abstract A simple, manual procedure is described which is useful for the analysis of water-soluble sulfate in low volume ( = 20m3) filter samples. The technique uses an aqueous extraction and an exchange reaction between a barium-nitrosulfonazo III chelate and sulfate in aqueous acetonitrile. Decrease of absorbance at 642 nm is measured in a double beam spectrophotometer. The method has been evaluated for extraction efficiency, precision, accuracy, working range, equivalence to other methods, and interferences.