Specific emission rate

Air measurement in a chamber or cell initially produces the concentration C(t) at the time t of the measurement. To enable better comparability of the measured data the specific emission rate (SER) independent of air exchange and loading is to be preferred. The SER describes the product-specific emission behavior, for example, as area-specific emission rate (SERA) with the unit pg/(rn h) or as unit-based specific emission rate (SERu) with the unit gg/(unit h). 

SER is the specific emission rate, D is the diffusion coefficient, 8is the thickness of the boundary layer, Cs is the concentration of the target VOC at the source surface and Q is the concentration of the target VOC in the air and fcg is the gas-phase mass transfer coefficient. 

The method of analyzing the vapor samples collected from the test chamber/cell exhaust stream plus guidance as to how to use that data to derive an area- or volume-specific emission rate for the product under test. Analytical methods used for testing vapor-phase emissions typically fall into two main categories ... 

Data are typically reported as mass emitted per unit surface area (or volume) per unit time. This is known as the area (or volume) specific emission rate (pg/m2/h.) Alternatively, some test protocols require results to be presented in terms of vapor concentration, either in the chamber/cell itself or in a specified model (reference) room. NOTE that specific emission rate data can be converted to concentration data (and vice versa) by means of calculation. 

In other words test stand investigations can be subdivided on the basis of two fundamentally different goals the principle focus of the test stand methods described below and the corresponding test protocol is to determine material-specific emission data with the aid of vehicle-specific emission rates (ER). If exposure is to be considered insofar as it affects health the boundary conditions of the investigations (air exchange, temperature) would need to be modified to correspond to a realistic exposure scenario. In principle investigations of this kind are also possible once the test conditions have been correspondingly adapted. 

Table 10.7 Area specific emission rates of VOCs.

The term area specific emission rate is used in parallel with the term emission factor. ... 

These results demonstrated that books and journals may release significant amounts of VOCs and must be regarded as typical point sources that are located close to occupants (Salthammer, 1999). Consequently, chamber concentrations are presented instead of unit specific emission rates. 

Tichenor and Mason (1988) have shown that m-dichlorobenzene and p-dichloroberizene are common ingredients of moth crystals. Thus, area specific emission rates up to 1.4 x 107pg/(m2h) of these compounds were measured by Sparks et al. (1990). Similarly, Sheldon et al. (1988a, 1988b) and Wallace et al. 

With the aid of emission test chamber measurements (see Chapter 5) emissions from electronic devices can be determined without any environmental influences affecting results. Such investigations aim at determining device-specific emission rates under standardized environmental conditions. Using these emission rates it is possible to make comparisons between the emission characteristics of different devices not only qualitatively (the composition of the emissions) but also quanti-... 

When using the unit-specific emission rate of the device with the highest emission (monitor 21, 14 d) in Table 17.6 as a basis for the total of POC (SERu = 2.6ggunit 1 h 1), a theoretical indoor air concentration of 0.3 igm"3 is obtained for the model room (DIN EN ISO 16000-9, 2006). The indoor air concentrations of all other devices are below this value by a factor of at least 10. The present results show that the POC emissions then result in a theoretical indoor... 

Table 17.6 Unit-specific emission rates, SERy (ng unir fr1), for POC of 4 monitors sampling after different times in operation (7d, 14d) in the test chamber (Wensing, 2004).

Kemmlein, S., Bergman, M., Jann, O. (2006) Emission test chamber study specific emission rates of PBDE from selected materials under various conditions. Organohalogen Cpds., 68 488-491. 

Another approach that is commonly used to evaluate the emission rates of VOCs in indoor microenvironments is to estimate an area-specific emission rate (SER). This approach assumes that VOCs are homogeneously mixed in the environment and that SER can be calculated with the following equation [10] ... 

Cork products can also emit considerable amounts of the aldehyde furfural (2-furancarboxaldehyde) with surface-specific emission rates SER, > 1,000 pg m - h [57], whereby the release of the furfural generally corresponds with that of acetic acid. The cause for the formation of furfural is the thermal decomposition of the hemicelluloses contained in the cork at temperatures above 150 °C, while acetic acid is formed by the separation of acetyl groups. Further by-products identified in the thermal treatment of natural cork were formic acid and hydroxymethylfurfural [58]. 

SERj area specific emission rate in micrograms per square metre per hour. SERp length specific emission rate in micrograms per metre per hour. 

Specific emission rate Product specific rate describing the mass of a volatile organic compound emitted from a product per unit time at a given time from the start of the test. The area-specific emission rate, SERg, is used in the standard. Several other specific emission rates can be defined according to different requirements, for example, length-specific emission rate, SERi, volume-specific emission rate, SER, and unit-specific emission rate, SER,. The term area-specific emission rate is sometimes used in parallel with the term emission factor. 

Fuel-specific emission rates of elemental carbon are shown in Table 14.1. These rates can vary significantly as they depend strongly on the conditions under which combustion takes place. Woodbuming fireplaces and diesel automobiles are effective sources of EC per unit of fuel burned (Mulhbaier and Williams 1982 Brown et al. 1989 Dod et al. 1989 Mulhbaier and Cadle 1989 Hansen and Rosen 1990 Burtscher 1992). 

The SER describes the product-specific emission behavior for selected chemical compounds (VOCx) or the sum of the emissions (TVOC), e.g. as an area-specific emission rate (SER ) measured in pg/(m h), or as a piece-related unit-specific emission rate (SERjj) measured in pg/(unit h). 

The FLEC is mainly used for the determination of area-specific emission rate, (SER ) at constant temperature, relative humidity and air exchange rate. 

A procedure for the determination of area-specific emission rates (SER ) from sources on site in buildings has also been developed (Nordtest, 1998). During such measurements the air supply may consist of pure synthetic air from, e.g., a mobile gas bottle. 

In another case study, Zellweger et al., (1997e) studied the emission of hexanal fi om linoleum in an office. SER measured with the FLEC (both on-site and in-lab) correlated well with the area-specific emission rates (SER ) calculated on ventilation rate and room air concentrations. The FLEC measurements also revealed that low-volatility compounds such as glycol ethers from the room air had absorbed on the linoleum, although the linoleum initially did not emit any glycols. Relatively often, low-volatility VOCs are subject to sink effects. 

Table 3.3-3. Area-specific emission rates for different types of furniture coating. The substrates are given in parentheses.

As a consequence, chamber concentrations are presented instead of unit-specific emission rates. 

Braungart et al. (1997) have also investigated emissions from 11 electronic devices in their desiccator. All products were operated during or immediately before the test. Unit-specific emission rates ranged from 5.9 pg/h (cellular phone) to 206 pg/h (electric shaver). Emission rates of 7 products were below 27 pg/h. Typical VOCs detected in the chamber air were aliphatic hydrocarbons (C10-C18), aromatic hydrocarbons (toluene, o-, m- and p-xylene, C3-/C4-benzenes), 2-ethyl-1-hexanol, BHT (2,6-di-tert- butyl-4-methylphenol) and cyclohexanone. One electric shaver emitted large amounts of methylnaphthalenes. Emission rates of single compounds were well below 10 pg/h apart from one case in which the emission of 23 pg/h naphthalene from an electric hair drier was measured. 

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