Tungstic acid for preconcentration and determination of gaseous and particulate ammonia and nitric acid in ambient air

Abstract

Tungstic acid surfaces chemisorb NH, and HNOa. Coilectlon of these gases is posslbie by sampling with a hollow tube, the interior of which is coated wlth tungstic acid. Under conditions of laminar flow, the gases diffuse to the wail and are chemisorbed while particles are carried through the tube. Particles are collected with an in-line tube packed with tungstic acid coated sand. Thermal desorption followed by a simple separation and detection by a chemiluminescent NO, analyzer permits analyses at the parts per bllllon and lower concentration range for gaseous and particulate forms of the analytes. Detection limits are 1-3 nglsampie. The precision of analyses of ambient air samples is in the 5-10% relative standard deviation range. Coated hollow tubes conform sufficiently to the mathematical model of tube gas dynamics so as to permit reasonable determination of gaseous diffusion coefficients at ambient concentrations.Ammonia, nitric acid, and sulfuric acid aerosol are important factors influencing the acidity of air and acidity of rain. Ammonium nitrate and ammonium sulfate are solid compounds resulting from atmospheric acid-base reactions of the three acid rain components. Thus, both gaseous and particulate forms of ammonia and nitric acid are expected to be present in air.The determination of gaseous ammonia and nitric acid at the trace concentrations (0.1-5.0 pg/m3) present in comparatively nonpolluted, ambient air as well as discrimination of gaseous from particulate forms is a difficult task. A number of workers have noted particle to gas or gas to particle conversion reactions on filters used to separate particles from the gas phase. A discussion of this aspect of previous work is given in our companion article (I).Analytical procedures for gaseous ammonia have involved absorption on an oxalic acid treated surface as in the ring oven technique of Shendrikar and Lodge (2) modified by Cattell and DuCross (3). Gillett and Ayers (4) report the detection limit of this method to be near 0.05 pg/sample in routine use. Ferm (5) has used an oxalic acid coated diffusion tube to collect NH3 later determined by ion-selective electrode. McClenny and Bennett (6) have reported a method for gaseous ammonia based upon absorption on Teflon beads after filtration to remove particulate ammonia. Collected gaseous ammonia was desorbed by heating and detected by using a photoacoustic detector. The detection limit was approximately 5 ng/sample.Gaseous nitric acid has been collected on sodium chloride impregnated filters after removal of particles by a nontreated prefilter (7,8). Total gaseous and particulate nitrates can be collected on filter combinations such as, for example, a quartz fiber filter and a nylon filter (9). Shaw et al. (IO) developed a method for nitric acid in air employing two parallel sampling lines, one of which includes a diffusion denuder tube to eliminate "OB.Both total and particulate HN03 are determined and the difference is gaseousThe work reported here started with a preliminary study of new approaches t...

Real-time measurements of ammonia, acidic trace gases and water-soluble inorganic aerosol species at a rural site in the Amazon Basin

“…The HNO 3 diffusion coefficient in air was experimentally determined by several investigators ranging from 0.04 cm 2 s −1 to 0.121 cm 2 s −1 (STP) (Braman et al, 1982;Eatough et al, 1985;Durham and Stockburger, 1986;and Deandrade et al, 1992). In this study, we used the highest value (0.121 cm 2 s −1 ).…”

Compilation and evaluation of gas phase diffusion coefficients of reactive trace gases in the atmosphere: volume 1. Inorganic compounds

“…The interaction of trace gases with surfaces, and therefore gas phase diffusion coefficients, are not only important in the investigation of atmospheric heterogeneous reactions, but are also important to describe the efficiency of diffusion denuders which are widely used to collect trace gases or to separate trace gases from aerosol particles. For example, denuder tubes in which inner walls are coated with adsorbents are widely used to capture trace gases such as HNO 3 (Braman et al, 1982;Durham et al, 1987;Eatough et al, 1985), HONO (Ferm and Sjodin, 1985) and NH 3 (Braman et al, 1982) for online/offline analysis, and to separate aerosol particles from gases (e.g. to separate NH 3 from particulate NH + 4 ).…”

Determination of Nitric Acid in Ambient Air by Gas Chromatography/Photoionization Detection after Collection in a Denuder

“…The HNO3 diffusion coefficient value used (0.12 cm 2 /s) was calculated by the method of Wilke and Lee. 10 Braman et al 4 found experimentally an approximating value and Ferm 3 a value of 0.116 cm 2 /s. The denuder preparation could be reproduced.…”

“…A denuder chosen for such a system should have a chemically stable coating with respect to regeneration and collection during ambient sampling runs to avoid frequent calibration of the system. The in situ monitoring of ambient HNO3 (and NH3) concentrations with a denuder system was described by Braman et al 4 and adapted to automatic operation.…”