Denuder difference method

Atmospheric NO2, SO2, and O3 were measured by various methods (1, 4, 5). light scattering was measured by integrating nephelo-meters. HNC g) and aerosol NC " were measured by the denuder difference method (6-8) using MgO-coated denuder tubes and nylon membrane filters, with ion chromatographic nitrate determination on alkaline filter extracts. Valid ammonia data were not obtained during any of the rain periods. 

NO, NO2, and 0 were monitored continuously with a Monitor Labs dual channel chemiluminescence NO analyzer and an AID portable ozone analyzer. SO2 was determined with the carbonate-glycerol impregnated filter technique. HNO was determined by the denuder difference method (J[2). HCl was determined with the Na2C0o impregnated filter technique (j[3). The oxalic acid impregnated filter method (j[4) was used to determine NH. Total particulate was collected on 1-ym pore size Ghia Tefweb filters. Aqueous extracts of the filters were analyzed to determine particulate NO, S0 J, Cl , NHjJ, Ca, Mg", Na , and K" " concentrations. 

Several different methods exist for measuring HN03, most commonly FTIR and TDLS, which were described earlier. Other techniques commonly used include filters, denuders, transition flow reactors, and scrubbers, followed by analysis of the collected material for nitrate, e.g., by ion chromatography. A modification of the luminol method has also been used. Finally, mass spectrometric methods look very promising as a sensitive and specific method of detection and measurement. A brief description of each of these methods that have not yet been treated follows. 

Continuous Sampling and Determination. There are no truly continuous techniques for the direct determination of sulfuric acid or other strong acid species in atmospheric aerosols. The closest candidate method is a further modification of the sensitivity-enhanced, flame photometric detector, in which two detectors are used, one with a room-temperature de-nuder and one with a denuder tube heated to about 120 °C. Sulfuric acid is potentially determined as the difference between the two channels. In fact, a device based on this approach did not perform well in ambient air sampling (Tanner and Springston, unpublished data, 1990). Even with the SF6-doped H.2 fuel gas for enhanced sensitivity, the limit of detection is unsuitably high (5 xg/m3 or greater) because of the difficulty in calibrating the two separate FPD channels with aerosol sulfates. 

Cochran, E.W, M.J. Joseph, S.S. Stinson, and S.S. Summers Apphcation of a diffusion-denuder method for the investigation of the effects of smoke pH on vapor-phase nicotine yields from different types of cigarettes Beitr. Tabakforsch. Int. 20 (2003) 365-372. 

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