A Fabric Denuder for Sampling Semi-Volatile Species

Abstract

A new style of diffusion denuder has been evaluated specifically for sampling HNO 3 . A coated fabric is used as the denuder substrate, which can be loaded directly into a standard filter holder. This approach allows direct denuder sampling with no additional capital costs over filter sampling and simplifies the coating and extraction process.Potential denuder materials and coatings were evaluated in the laboratory to test the removal efficiency. NaCl coatings were used to assess more than 20 materials for HNO 3 collection efficiency. Particle retention, which would cause a denuder to have a positive bias for gas concentration measurements, was evaluated by ambient air sampling using particulate sulfate as the reference aerosol. Particle retention varied from 0 to 15%, depending on the denuder material tested. The best performing material showed an average particle retention of less than 3%.Denuder efficiency of four fabric materials was tested under ambient conditions to determine removal efficiency. The fabric denuder method was compared with a long path-length Fourier transform infrared (FTIR) spectrometer, a tunable diode laser absorption spectrometer (TDLAS), and a denuder difference sampler to independently measure HNO 3 . HNO 3 collection efficiency was typically 90% for the denuders, whether coated with NaCl or not. For 10-L/min sampling rates with the fabric denuder, the square of the correlation coefficient with IMPLICATIONS A simple fabric material used as a diffusion denuder has been shown to be an effective and inexpensive method to measure species such as HNO 3 and NH 3 which partition into both gaseous and particulate phases. The low cost of this approach compared with other types of denuders may encourage more measurements of these air pollutants. With a larger database available, the environmental and health effects of these species may be better assessed.the FTIR spectrometer was 0.73, compared to 0.24 with the TDLAS. INTRODUCTIONBackground HNO 3 in the atmosphere may pose a significant health risk and environmental hazard. In the atmosphere, HNO 3 and NH 3 are in equilibrium with NH 4 NO 3 particulate matter. These particles are primarily in the PM 2.5 size range, a particulate range for which a new federal ambient air quality standard has been promulgated.

Particulate Nitrate Measurement Using Nylon Filters

“…Negative NO 3 Ϫ sampling artifacts are also common. 12,13,[25][26][27][28][29][30][31][32][33] Loss of NH 4 NO 3 as a result of changing ambient conditions (e.g., T, RH, and/or gas phase concentrations of NH 3 or HNO 3 ) during a sampling interval can lead in some cases to significant biases in measured NO 3 Ϫ concentrations. Such losses can be reduced by shortening sample periods, reducing filter face velocities, and limiting filter pressure drops, 34 but they remain problematic.…”

A Passive Flux Denuder for Evaluating Emissions of Ammonia at a Dairy Farm

“…Fabric denuders were first evaluated by looking at the removal efficiency of HNO 3 by sodium carbonate-coated examples. 26 Fitz and Motallebi observed that they could estimate denuder efficiency by estimating the fractional penetration of the gas and assume that the denuder is treated with a chemical that quantitatively removes a target gas when the gas in question comes in contact with the denuder surface. 26 They concluded that two denuders made of a cotton fabric, 47 mm in diameter, were required in series to ensure a collection of more than 95% of the HNO 3 in ambient air when sampling up to 10 L/min.…”

“…25 Fitz and Motallebi recently reported the successful use of fabric denuders to selectively remove HNO 3 . 26 The denuder sampling approach they proposed is based on diffusion batteries to remove very fine particles. The use of cloth fabric as the denuder substrate is analogous to the wire screen denuders for collecting very fine particles in diffusion batteries.…”

Development of a Novel Porous Membrane Denuder for SO2 Measurement

“…The fabric denuder has a relatively small loading capacity and suffers from significant particle loss (Fitz and Motallebi, 2000). Tsai et al (2001) developed a personal porous-metal denuder specifically for adsorbing acidic gases and ammonia gas in an occupational environment.…”

“…However, these denuders are connected to an Ion Chromatography (IC) system or other sizeable infrastructure which makes them infeasible for personal sampling. Proposed by Fitz and Motallebi (2000), the fabric denuder is another type of new denuder. Fabric filter paper is coated and loaded in a filter stack, and collected pollutants are extracted in the same way as common filters.…”