Annular Denuder Sampling Research Articles

A compact porous-metal denuder for atmospheric sampling of inorganic aerosols

A novel approach has been undertaken to develop a high efficiency compact diffusion denuder utilizing a porous metal disc. The performance of a porous metal disc used as a compact diffusion denuder has been experimentally and theoretically evaluated. The porous media is made of 100 μm grade sintered stainless-steel. The disc is 4.7 cm in diameter and 0.23 cm in thickness. Experiments showed that it has high gas collection efficiency and low particle loss at 10 liter per minute (1 min −1). Using 1% sodium carbonate/glycerin coating, the collection efficiencies for the sulfur dioxide and the nitric acid gas are 99.6 ± 0.4% and 93.4 ± 2.5%, respectively. Comparisons to an annular denuder sampling simultaneously are found to be 106.3 ± 6.0% and 95.5 ± 15.8% for sulfur dioxide and nitric acid gas, respectively. The averaged loss for monodisperse aerosols in the particle size range of 0.015–2.5 μm in diameter is under 10%, with loss of less than 3% in the important size range of 0.1–2.5 μm. The sampling capacity of the denuder for 25 ppb sulfur dioxide at 101 min −1 is over 100 h. Membrane filtration theory was used to model the gas collection efficiency and particle losses. The result indicates that the porous metal used as a denuder is very efficient in collecting gas. Also, the small size of the denuder makes it possible to design a very compact atmospheric and/or indoor denuder sampling system.

Nitrous and nitric acid measurements at sites in South-East England

Measurements of HONO and HNO 3 have been made using annular denuder samplers at sites in south-east England. Whilst concentrations of HNO 3 exhibited a diurnal variation, with a maximum in mid-afternoon nitrous acid shows the opposite diurnal cycle with maximum levels at night due to daytime photolysis. Concentrations of HONO increase with those of NO 2, and elevated nighttime HONO level appear to be followed by high levels of HNO 3 the following day. Average concentrations of HONO (0.45± 0.26 ppb in 24 h samples are comparable to those of HNO 3 (0.56±0.36 ppb in 24 h samples), each representing about 5–10% of the concentration of NO 2. Although NO 2 oxidation provides the source of HNO 3 concentrations of the two compounds are not related, presumably since the formation of NH 4NO 3 aerosol limits HNO 3 concentrations at out site.

Design of a personal annular denuder sampler to measure atmospheric aerosols and gases

A personal sampling device has been designed to measure atmospheric gases and particles. This sampling system includes a glass impactor, an annular denuder and a filter pack. The glass impactor consists of an entrance section containing the inlet tube, the acceleration jet, and the impaction plate which is mounted at the entrance to the annular denuder. The impaction plate is a removable porous glass disk which can be impregnated with mineral oil to avoid bounce-off of the collected particles during sampling. The impactor has been designed to have a 50% aerodynamic particle cut-off point of 2.5μm, at flow rates of 4 and 2 ℓ min −1. For each flow, a different inlet has been designed with acceleration jet diameter of 0.250 and 0.190 mm, respectively. The annular denuder can be coated with citric acid to collect NH 3 and nicotine vapors. Also collection of SO 2, HNO 3 and HNO 2 is possible by coating the denuder with sodium carbonate. The last component of the designed personal sampler is a filter pack containing a 37-mm Teflon filter which is used to measure fine particle mass, aerosol strong acidity, sulfates and nitrates. The Teflon filter can be followed by a citric acid coated glass fiber filter used to collect nicotine which originates from the volatilization of the particle-phase nicotine collected on the Teflon filter. The ability of the personal sampler to collect fine particles was examined by conducting indoor aerosol sampling experiments. Also, ammonia collection efficiency tests were performed to characterize the personal denuder. The findings of these experiments showed that the designed personal sampler can be adequate for measuring human exposures to acid aerosols. In addition, the performance evaluation of the sampler to collect environmental tobacco smoke was investigated by conducting chamber tests.