A Triple-Path Denuder Instrument for Ambient Particulate Sampling and Analysis

Abstract

A field instrument for sampling sulfate and nitrate particulate matter in a controlled chemical environment has been constructed and field tested. The instrument contains HNO3 and NH3 denuders and an ambient air path, all connected by manifold to a PM-10 size-selective inlet. Ambient aerosols are collected on acid-washed quartz filters mounted in the front compartment of dual stainless steel cassettes. The rear cassette chamber contains backup filters which allow denuder breakthrough detection and specific gas measurements. The aerosol collection system has been designed specifically for use with x-ray diffraction analysis methods. An investigation of denuder coating reactions reveals that multistage reactions take place with ammonia absorbed by oxalic acid, and that nitromagnesite is formed by reaction of nitric acid with magnesium oxide coatings. Reference intensity constants needed for quantitative x-ray diffraction analysis of denuder reactions, filter pack reactions, and ambient atmospheric particulate products have been measured. They have been used in several applications, including the estimation of ammonia gas concentrations in the system gas stream and quantitative analysis of compounds observed in field ?shakedown? tests. These field tests demonstrated that the system is mechanically reliable, although improvements to this system might include an increased pumping capacity and use of teflon filters to increase the signal-to-noise ratio of x-ray diffraction analysis.