Unit-specific emission rate

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. 

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).

SER volume specific emission rate in micrograms per cubic metre per hour. SER, unit specific emission rate in micrograms per hour per unit. t time after start of the test, in hours or days. 

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. 

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). 

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. 

X 10 pg/(m h)) when spread on surfaces. Knoppel and Schauenburg (1987, 1989) have identified 84 VOCs in ten different waxes and detergents. Area-specific emission rates ranged from 1.2 x 10 pg/(m h) to 2.6 x 10 pg/(m h). Colombo et al. (1990) have determined unit-specific emission rates of 2.7 x 10" pg/hand 1.9 x 10 pg/h for furniture spray polish and floor wax paste, respectively. Sparks et al. (1990) have published an emission rate of 1.4 x 10 pg/(m h) for a wood floor wax. 

SER or SERJ t) unit specific emission rate [pg/(unit h)]... 

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). 

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. 

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). 

Table 15.2 Area specific (SERa) and unit specific (SER ) emission rates for different household and consumer products. See original references for analytical details.

For the assessment of the contribution of the emission categories to the observed NMVOC concentrations the Chemical Mass Balance (CMB) modelling technique, version 8 from United States Environmental Protection Agency (Watson et al., 1998 Watson et al., 2001) was selected. The method uses source specific ratios between the emission rates of certain set of compounds and aims to recognise these fingerprints, or soiuce profiles, in the profile measured at the receptor point. As a result the CMB model delivers contributions from each source type to the total ambient NMVOC and individual hydrocarbon species at receptor points and their uncertainties. 

An estimate of emissions of a species from a source is based on a technique that uses emission factors, which are based on source-specific emission measurements as a function of activity level (e.g., amount of annual production at an industrial facility) with regard to each source. For example, suppose one wants to sample a power plant s emissions of SO2 or NO, at the stack. The plant s boiler design and its BTU (British thermal unit) consumption rate are known. The sulfur and nitrogen content of fuel burned can be used to calculate an emissions factor of kilograms (kg) of SO2 or NO, emitted per metric ton (Mg) of fuel consumed. 

Radioisotopes are unstable and decay by particle emission, electron capture, or y-ray emission. The decay is a random process, i.e., one cannot predict which atom from a group of atoms will decay at a specific time. The decay of radioisotopes, therefore, is described in terms of the average number of radioisotopes disintegrating during a period of time. The disintegration rate (or the number of disintegrations per unit time), -dN/dt, of a radioisotope at any time is proportional to the total number of undecomposed radioisotopes present at that time. This may be expressed as follows ... 

Atoms and molecules absorb only specific frequencies of radiation dictated by their electronic configurations. Under suitable conditions they also emit some of these frequencies. A perfect absorber is defined as one which absorbs all the radiation falling on it and, under steady state conditions, emits all frequencies with unit efficiency. Such an absorber is called a black body. When a system is in thermal equilibrium with its environment rates of absorption and emission are equal (Kirchhoff s law). This equilibrium is disturbed if energy from another source flows in. Molecules electronically excited by light are not in thermal equilibrium with their neighbours. 

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