A parallel plate wet denuder for acidic gas measurement

Abstract

in Wiley InterScience (www.interscience.wiley.com).A parallel plate wet denuder (PPWD) was designed and tested for acidic gas absorption in this study. The PPWD is composed of two frosted glass plates coated with nano-TiO 2 particles. The gap of the plates is 4 mm, the active surface is 7.5 cm in width and 15 cm in height. The DI water is flowing downward along the surfaces to form a uniform water film to absorb the gas flowing upward along the gap. The gas absorption efficiency and memory effect were tested using test gases of HF (3.57-3.80 ppb), HCl (0.48-15.63 ppb), and HNO 3 (8.43-20.92 ppb) generated from permeation tubes at the flow rate of 5-10 L/min, scrubbing DI water flow rate of 1.0 mL/min/ plate, and pH 5 6.8 6 0.3. The experiment was also conducted for HF and HCl with scrubbing water pH value of 3.08 and 4.10 to examine the effect of pH on the absorption efficiency. The experimental data at different flow rates match with the theoretical values very well assuming perfect absorption condition at the water film when the scrubbing water pH 5 6.8 6 0.3. The absorption efficiency of the three gases at the sampling flow rate of 5 L/min was nearly 100% when the scrubbing water pH value was 6.8 6 0.3, but was found to decrease slightly when the pH value of scrubbing water was reduced from 6.8 to 3.08, which indicates slight modification of perfect absorption condition at the water film. The memory effect test showed that the rise time was 15 to 25 min and the fall time was 10 to 25 min for the three gases. Good uniformity of the water film was observed during the 9-day ambient air sampling for HF, HCl, and HNO 3 , which indicates the applicability of the present PPWD for ambient air sampling.

Development of an Automated System (PPWD/PILS) for Studying PM2.5 Water-Soluble Ions and Precursor Gases: Field Measurements in Two Cities, Taiwan

“…The system mainly consists of four parts: (a) the gas collection unit (PPWD) -for the collection of water-soluble gases into aqueous samples; (b) the particle collection unit (PILS) -for the collection of water-soluble PM 2.5 into aqueous samples; (c) the sample unit (syringe pump) -for simultaneous storage of collected samples and sequential injection into the IC; (d) the sample analysis unitfor the analysis of anionic and cationic chemical species collected in aqueous solution. To operate the system at 12.3 L min -1 , the gap between the two parallel plates, h, of the present PPWD was decreased to 2 mm from 4 mm the original version which runs at 5 L min -1 (Tsai et al, 2008) to remain high gas collection efficiencies by keeping the dimensionless parameter µ the same according to the Gormley and Kennedy theory (Hinds, 1999). All gas tubing and valves of PPWD were made of Teflon to prevent the interaction between the gases and the tube and the fittings.…”

“…PM 2.5 water-soluble species are then collected by the PILS. For the present PPWD, sand-blasted (a microscaled surface roughness) glass plates coated with TiO 2 nanoparticles (P25, Degussa, Germany) were used as the collection plates to improve the wettability of the active surfaces for excellent capture of acidic and basic gases (Tsai et al, 2008;Ku et al, 2010). The water contact angle was measured to be as small as 4 ± 3.58° and the water film was found very uniform for long-term operation.…”

An Online Parallel-Plate Wet Denuder System for Monitoring Acetic Acid Gas

“…1) consists of two sand-blasted plates (17 cm × 7.5 cm, L × W) coated by the calcination process at 300°C with a thin layer of TiO 2 nanoparticles (Tsai et al, 2008), which were generated by the sol gel method. The gap between the two plates was 4 mm, providing a channel through which an upward gas stream flowed at a rate of 5 L/min (Fig.…”

“…Transportation time required for denuder effluent to travel between the PPWD and the injection valve is 2.47 minutes, as estimated by tubing volume and solution flow rate. The PPWD has a theoretical collection efficiency of 96-98% for acetic acid gas, as calculated using the gas penetration theory by Gormley and Kennedy (Tsai et al, 2008) with a diffusion coefficient of 0.103-0.133 cm 2 /sec (Bennett and Myers, 1982;Staudt et al, 1995;Bird et al, 2002).…”

“…Tsai et al (2008) designed a parallel-plate wet denuder (PPWD) and applied TiO 2 nanoparticles (P25, Degussa, Germany) on glass plates that were sand-blasted to give a microscaled surface roughness to further increase plate wettability. The accuracy of this method is excellent for capturing and detecting strong acids (Tsai et al, 2008). However, the accuracy of the PPWD coupled with an ion chromatography remains to be investigated for weak acids.…”