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 .
Measurement of Nitric Acid in Smog
The formation of nitric acid (HONO2) in the polluted atmosphere has been monitored using a newly developed analyzer. The analytical method, the operation and performance of the analyzer and some results of recent applications are described. The analysis consists of sample conditioning in combination with a Mast micro-coulomb detection cell adapted for sensing acids rather than oxi-dants. Results of calibration and interference testing are presented. The sensitivity of the instrument to HONO2 is about 2 ppb. Application of the analyzer for smog chamber and atmospheric studies is demonstrated. In simulated smog experiments with synthetic auto exhaust, the pattern of HONO2 formation parallels that of ozone formation. A similar formation pattern was observed during ambient sampling. Evidence is presented which suggest that these reactions, may both contribute to HONO2 formation in smog, but the relative importance of the two is yet uncertain. Atmospheric sampling in the Los Angeles area indicated 24 hour aver...