Establishing ECFs

The ECFs reflect the cumulative annual human exposure associated with a given amount of chemical release from a given point source. As in the case of ground level ozone and PM, the region-dependent ECF is dependent upon the atmospheric residence time of the emitted chemicals, the release height, meteorologically dependent dispersion and deposition patterns, and the population density in the dispersion domains. Figure 3.8 shows examples of the cumulative exposure as a function of distance from the source of emission.

Figure 3.8. Cumulative exposure as percent of total according to dispersion models30 Source: Potting et. al. (2000).

The study results from Potting et. al. (2000) can be used to establish cumulative HEFs. In the study, two different models were used for the exposure calculations: the EUTREND31 Gaussian plume type model for short distances (up to about 10 km), and the WMI trajectory model for regional distances (up to over 2500 km distance).32 For these models, two substances were investigated: benzene, which has an atmospheric residence time of seven

30 _{References: European Commission (1998), ExternE: Externalities of Energy, Volume 7, Methodology 1998 Update,} Chapter 4: Models for Air Pollution Analysis. Potting, J., Trukenmüller, A., van Jaarsveld, H. and Hauschild, M. (2000); Site dependent assessment of human exposure from air emissions in life cycle assessment. In: Potting, J. (2000): Spatial differentiation in life cycle impact assessment, Doctoral thesis, Utrecht University, March 2000. 31 _{Van Jaarsveld J.A., W.A.J. van Pul and F.A.A.M. de Leeuw: Modelling transport and deposition of persistent} organic pollutants in the European region. Atmospheric Environment, Vol. 1997, Issue 31, pp 1011 – 1024.

32 _{Krewitt W., P.Mayerhofer, R.Friedrich, A. Trukenmüller, T. Heck, A.Gressmann, F. Raptis, F. Kaspar, J. Sachau, K.} Rennings, J. Diekmann, B. Praetorius. ExternE – Externalities of energy. National implementation in Germany (EUR 18271). Directorate-General XII for Science, Research and Development of the European Commission, 1997.

0 10 20 30 40 50 60 70 80 90 100 0 200 400 600 800 1000 1200 1400 1600 1800 2000

Distance from point of emission, km Hydrochloric acid Benzene

© 2009. Scientific Certification Systems, Inc. Page 3-19 days, and hydrochloric acid, with a corresponding residence time of seven hours. These two substances were used as surrogates for emissions of substances with similar chemical and physical properties, including atmospheric residence times. A whole class of low boiling point organic compounds emitted from coal operations would have exposure factors similar to benzene. Likewise, some compounds that are susceptible to wet deposition would have exposure factors similar to hydrochloric acid. In the case of radioactive substances, the radioactive decay half-life also must be considered when establishing the ECF.

To calculate the HEF, the Potting study used the EMEP grid in Europe for a region of 5500 x 5100 km divided into 150 x 150 km grid cells.33 When an emission of one gram per second (1 g/s) of the substance was located in any of the grid cells, the HEF, expressed as “person * (µg / m3_{)”, was obtained as a} result.

The HEF was calculated for various release heights and

meteorological/climatic conditions (e.g., maritime, central, South Europe and northern locations). In the case of hydrochloric acid, the average HEF was 2460 person * (µg / m3) per g/s. In the case of a longer-lived substance, benzene, the average HEF was 50,000 person * (µg / m3). Depending on the point of emission the HEF values varied as shown below in Table 3.9.

Table 3.9. Data required for establishing a site-dependent ECF for chronic hazardous chemical loadings – direct inhalation only

Source: Potting et al., 2000

Point of emission Exposure factor, person * (µg/m3_{) Population} Density*

1 g/s Benzene type

substance

Hydrochloric acid

type substance Persons/(km)2

The Netherlands 71 700 11 280 106

Austria 67 460 4 320 108

Italy 54 280 5 050 64

Finland 11 020 570 10

* This value was not given in Potting (2000). The values have been estimated roughly from statistical data for surrounding areas/countries within 300 km radius (the km2 includes sea and other

uninhabited areas).

The data in Table 3.9 can be used to calculate the HEC (the slope calculated through linear regression), which represents the rate that cumulative exposure varies by population density for hydrochloric acid-type chemicals and benzene type chemicals (Fig. 3.8). The product of the HEC and the average population density of any region within a known dispersion domain is the site- dependent ECF. Using the above data, and assuming an ECF = 1 for the highest values in the two columns, the regression analysis yielded the

33 _{EMEP, 1998.Transboundary acidifying air pollution in Europe. MSC-W status report 1998 – Parts 1 and 2.} EMEP/MSC-W Report 1/98, Norwegian Meteorological Institute, Oslo, Norway.

© 2009. Scientific Certification Systems, Inc. Page 3-20 following HECs for long-range chemicals and short-range chemicals within a given indicator group.

Figure 3.9. Determining the Human Exposure Coefficient for Chronic Hazardous Chemical Loadings, person * (µg / m3_{) * (g/s)}-1

The ECF values, therefore, were:

ECFs short-range compounds = 0.0011 * PD/(persons per km2)

ECFs long-range compounds = 0.0094 * PD/(persons per km2) Table 3.10 shows the ECF values for the regions relevant to the projects and baseline cases included in this study report.

Table 3.10. ECF Values for WECC states Chronic Hazardous Chemical Loadings Emission location Population

density (Persons/km2) ECF short-range ECF long-range Washington 28.2 0.031 0.265 Montana 2.1 0.002 0.020 Oregon 11.4 0.013 0.107 Idaho 4.7 0.005 0.044 Wyoming 1.8 0.002 0.017 California 73.7 0.081 0.693 Nevada 4.2 0.005 0.039 Utah 8.1 0.009 0.076 Colorado 12.3 0.014 0.116 Arizona 12.5 0.014 0.118 New Mexico 4.8 0.005 0.045

© 2009. Scientific Certification Systems, Inc. Page 3-21 The classification of radionuclides into short-range or long-range substances can be checked against the radioactive decay half-lives shown in Table 3.11. The nuclides Kr-85, Kr-88, Xe-135 and Rn-220 have decay half-lives below 10 hours, and therefore must be classified as short-range substances. However, given the non-ionic nature of these noble gases, the atmospheric velocity of transport may warrant a longer-range classification, pending further research. The nuclides H-3 and C-14, on the contrary, have a short atmospheric lifetime, despite the radioactive decay that is measured in years.

Table 3.11. Radioactive Decay Half-Life for Selected Nuclides

Nuclide + daughters Dominant nuclide half life

C-14 5730 years Pb-210 22.3 years H-3 12.4 years Po-210 138 days Xe-133 5.2 days Rn-222 3.8 days Rn-220 10.6 hours Xe-135 9.1 hours Kr-85 4.5 hours Kr-88 2.84 hours

© 2009. Scientific Certification Systems, Inc. Page 4-1

Section 4.