System for dosing formaldehyde vapor at the ppb level

Abstract

Formaldehyde is one of the most relevant compounds for indoor air pollution. It is toxic, allergenic and carcinogenic and acts already at the ppb level. State-of-the-art detection methods are based on the wet chemical analysis of formaldehyde derivates. This is a complex and time-consuming approach and hinders the collection of real-time data. However, the use of wet chemistry allows for the simple calibration based on formalin solutions. By using gas sensors, online monitoring of indoor air quality is, in principle, possible. To find out whether their performance is good enough, calibration is the first issue to be resolved. Formaldehyde vapor at low concentrations has to be used, and temperature, humidity and flow rate have to be kept constant. This paper discusses the different possibilities of dosing formaldehyde and how to better meet the gas sensor calibration demands. The authors favor the use of an aqueous formaldehyde solution obtained by the depolymerization of paraformaldehyde in combination with a permeation tube used as external reference. Moreover, in the paper it is demonstrated that metal oxide sensors are appropriate detectors to calibrate the system for concentrations even down to 20 ppb. Consequently, the presented system is able to characterize gas sensors and can be used for the development of new devices which monitor indoor air quality.

Standard Formaldehyde Source for Chamber Testing of Material Emissions: Model Development, Experimental Evaluation, and Impacts of Environmental Factors

“…As a result, the diffusion of formaldehyde in the tube headspace can be neglected. On the basis of this assumption, the formaldehyde concentration in the LIFE tube headspace is assumed to be homogeneous and can be calculated by Henry’s law: − H = exp ( 6548.6 / T − 13.816 ) where, H is the Henry’s law constant (M/atm), and T is the temperature in the chamber (K). The equilibrium formaldehyde concentration in the tube headspace can be calculated as follows: C normalb , normalF = m 1 , normalF p 0 M V normalW H R T where M is formaldehyde molar mass (g/mol), V W is the volume of the solution (L), m l,F is the formaldehyde mass in the solution (g), P 0 is the atmospheric pressure (Pa), and R is the gas constant (J/mol·K).…”

Models for assessment of volatile organic compound diffusivities in leather or leather imitates by mercury intrusion porosimetry test

“…Compared to the diffusion of FA molecules in leather, the diffusion of FA molecules in the air layer inside tubes can be neglected. The equilibrium FA concentration ( C b , g/m 3 ) in the tube headspace can be computed by Henry’s law 41…”

A measurement strategy for non-dispersive ultra-violet detection of formaldehyde in indoor air: spectral analysis and interferent gases

“…It is toxic, allergenic and a potential human carcinogen [1][2][3]. It has been shown to cause inflammation of lung epithelial cells [4] and to be dangerous at the ppb level (parts-per-billion, 1 molecule in 10 9 of air) [5]. The World Health Organisation (WHO) has set a guideline level of prolonged formaldehyde exposure at 80 ppb, and many countries have set theirs in line with this [6,7].…”