Emission modeling, formaldehyde

Hawthorne, A., et al. (1987) Models for estimating organic emissions from building materials formaldehyde example. Atmos. Environ. 21, No. 2. Lewis, R. G., et al. (1986) Monitoring for non-occupational exposure to pesticides in indoor and personal respiratory air. Presented at the 79th Annual Meeting of the Air Pollution Control Association, Minneapolis, MN. 

The development of new models for the prediction of chemical effects in the environment has improved. An Eulerian photochemical air quality model for the prediction of the atmospheric transport and chemical reactions of gas-phase toxic organic air pollutants has been published. The organic compounds were drawn from a list of 189 species selected for control as hazardous air pollutants in the Clean Air Act Amendments of 1990. The species considered include benzene, various alkylbenzenes, phenol, cresols, 1,3-butadiene, acrolein, formaldehyde, acetaldehyde, and perchloroethyl-ene, among others. The finding that photochemical production can be a major contributor to the total concentrations of some toxic organic species implies that control programs for those species must consider more than just direct emissions (Harley and Cass, 1994). This further corroborates the present weakness in many atmospheric models. 

Brown (1999b) reported formaldehyde and VOC emissions from new, unfinished particleboard and MDF (both using urea formaldehyde resins) in Ausbalia. Formaldehyde emissions over the first three weeks exhibited first-order decay behavior that predicted little to no formaldehyde emission after 6 months. However, further emission measurements at 8 months showed the products sbll emitted formaldehyde at approximately one-half the new product rate (also further unpublished measurement at 2 years showed the same emission rate as at 8 months). It was concluded that the wood-based panels emitted formaldehyde by a double-exponen-ttal model, the early- to late-term emissions including the free formaldehyde in the products but the long-term emissions consisbng of only the formaldehyde... 

In contrast to this anti-maser action in formaldehyde, H20 and OH are observed in maser emission. Collisional or radiative pumping is thought to maintain the population inversion between the two levels. As photons pass through the cloud, they are amplified by stimulated emission of radiation. The maser emission of H20 is possibly the most unusual of the observed anomalies, both from an astrophysical and a spectroscopic point of view. This is not the place to discuss details of the various models suggested, we would refer to concentrate on some of the general features observed in the maser emission spectra. 

A limited number of sink effect studies have been conducted in full-sized environments. Tichenor et al. [20] showed the effect of sinks on indoor concentrations of total VOCs in a test house from the use of a wood stain. Sparks et al. [50] reported on test house studies of several indoor VOC sources (i.e., p-dichlorobenzene moth cakes, clothes dry-cleaned with perchloroethylene, and aerosol perchloroethylene spot remover) and they were compared with computer model simulations. These test house studies indicated that small-chamber-derived sink parameters and kj) may not be applicable to full-scale, complex environments. The re-emission rate (kj) appeared to be much slower in the test house. This result was also reported by other investigators in a later study [51]. New estimates of and were provided,including estimates of fca (or deposition velocity) based on the diffusivity of the VOC molecule [50]. In a test house study reported by Guo et al. [52], ethylbenzene vapor was injected at a constant rate for 72 h to load the sinks. Re-emissions from the sinks were determined over a 50-day period using a mass-balance approach. When compared with concentrations that would have occurred by simple dilution without sinks, the indoor concentrations of ethylbenzene were almost 300 times higher after 2 days and 7 times higher after 50 days. Studies of building bake-out have also included sink evaluations. Offermann et al. [53] reported that formaldehyde and VOC levels were reduced only temporarily by bake-out. They hypothesized that the sinks were depleted by the bake-out and then returned to equilibrium after the post-bake-out ventilation period. Finally, a test house study of latex paint emissions and sink effects again showed that... 

A recent survey of emission data from stationary and mobile sources was used as input for an atmospheric dispersion model to estimate outdoor toxic air contaminant concentrations for 1990 for each of the 60,803 census tracts in the contiguous United States (Woodruff et al. 1998). The average long term background concentration estimated for formaldehyde was 0.2 ppb (Woodruff et al. 1998). 

Another strong factor is age. Inasmuch as formaldehyde emission is due to the diffusion of residual material from the center core, the emission is proportional to the concentration, and decreases as the concentration decreases. If all formaldehyde were present as formaldehyde gas, or methyIenegIycoI, the emission process should be strictly exponential. It has indeed been proposed that one can model emission according to ... 

Matthews, T. G. Reed, T. J. Tromberg, B. J. Fung, K. W. Thompson, C. V. Hawthorne, A. R. "Modeling and Testing of Formaldehyde Emission Characteristics of Pressed-Wood Products," Consumer Product Safety Commission, CPSC-IAG-84-1103, 1984. 

There are more possibilities for measuring the two parameters and in principle there are two models to calculate the formaldehyde emission parameters. The two models that can be applied are the "ideal mixing model (Figure 6) and the "plug flow model (Figure 3). 

The effect on particleboard of an ammonia treatment can also be shown using this testing method. In figure 8 again the ideal mixing model is applied. Notice that the line with the lowest emission is the one on the top. The reason is that the reciprocal values and not the steady state formaldehyde concentrations as such, are plotted. Here the slope is different as well. 

Furnishing. The formaldehyde level in a room at actual conditions depends on several factors, and is not an arithmetical sum of various sources (10), (11). In order to estimate the contribution of formaldehyde emission from single pieces of furniture the test objects have been exposed in area to air volume proportions to which they can be found in a small room or a kitchen. The assumption that the formaldehyde level in the chamber and in the actual room is the same, is based on a theoretical model originally developed for particle boards (4). At constant climate the emission from a test object is determined of the relation between the loading factor and the air change rate. 

Grot, D. "Plan for Testing Model for Formaldehyde Emissions from Pressed Wood Products" National Bureau of Standards,... 

A. Berge et al. (3) and J.J. Hoetjer ( 4) have developed models for the formaldehyde emission from particleboard which can be presented as follows ... 

Groah, W. J. (2006). Predicting indoor-air formaldehyde concentrations from emissions of urea-formaldehyde-bonded wood products using the Versar model. Forest Products J 55, 97-100. 

In order to optimize the resins performance, in terms of internal bond strength and formaldehyde emission, the desirability method was used. An optimized resin was identified and produced. The properties obtained were within or close to the values predicted by the empirical models employed. 

Methanol is the typical fuel with one carbon (Cl) atom for fuel cells. Methanol was one of the first small molecules chosen to study the oxidation on platinum group metals in the very early beginning of electrocatalysis. In that time, the oxidation of other Cl molecules such as formic acid and formaldehyde (interest in CO oxidation came latter with the oxidation of reformatted gases) were investigated as a model oxidation because their elementary steps were supposedly present in the mechanism of methanol oxidation. From the point of view of CO2 emission, methanol has, among the other small molecules, the highest energy production per unit of produced... 

Meyer-Amek et al. (2005) examined CH2O column data over Africa for September 1997. They interpreted the data using a trajectory analysis coupled with a chemistry model. They found similar formaldehyde concentrations deriving from biomass burning and from biogenic emissions from woody savannah and tropical rainforest. The formaldehyde concentrations for the biogenic emissions were found to occur close... 

---