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Characterisation Method Information
Characterisation Method Name:
NOx mipact on YOLL
Version:
1999
Date Completed:
1999
Principal Method Name:
EPS: secondary particles and oxidants pathway
Method Description:
YOLL stands for Year of Lost Life.


There are at least four mechanisms through which nitrogen oxides influence life expectancy and two of them will be modelled.

Model 1, pathway via human exposure to secondary particles

The characterisation factor is determined by an empirical method.

The average US concentration of nitrates is in the order of 1-2 mg/m 3 . (Spengler and
Wilson 1996). In Sweden similar concentration have been measured at a rural site (Ferm, 1984). In Mexico City, the concentration is around 3 mg/m 3 in winter-time contributing to 3% of the PM2.5 mass. (Vega et al., 1997) and the annual mean concentration of PM10 is estimated to around 200 mg/m3 (WHO, 1992).
The dose-response function associated with PM10 and YOLL is estimated to 2.61×10 -4 YOLL/mg/m 3 per person per year.

As nitrates are secondary particles, the correlation of general urban pollution components and nitrates are comparatively low. This means that regional levels as much as local determine the global average urban. Based on this a global average of 1.5 mg/m 3 is assumed, giving a total category indicator value of 2.61E-04 *1.5*5.28E+09 = 2.07E-06 YOLL/year.

The global anthropogenic emission is estimated to 153 tg NOx/year (IPCC 1994). The natural is estimated to 180 tg NOx/year (Stern, 1986) but claimed by IPCC (1994) to be much below the anthropogenic. Until better knowledge is gained, the figure 180 will be used for the sum total NOx-emissions. Both natural and anthropogenic emissions contribute to nitrate exposure. As most of the PM10 impact is assumed to be caused by PM2.5 and as the PM2.5-concentration is about half of the PM10, the contribution will be twice as high. The average contribution to the total cattegory value in the system is therefore 2*5.56E-12 per kg NOx.

Calculation of pathway specific characterisation factor

2.07E+06 YOLL*2*5.56E-12 per kg = 2.30E-05 YOLL/kg NOx

Model 2, pathway via oxidants

The characterisation factor is determined by an empirical method.

The ozone concentration in central part of urban complexes normally decrease on a short
time basis as a consequence of NOx emissions, which mainly are NO. However, the regional background seems to have increased compared to pre-industrial levels. In
Europe the regional pre-industrial levels were just below 10 ppbv (Volz, 1988). Today
rural and city levels are around 25-30 ppbv 1990 in Scandinavia (TemaNord, 1994). In a
global perspective the concentrations may vary considerably. Mexico city has annual average levels around 100 ppbv, while Jakarta has 1–7 ppbv, Seoul 10 ppbv and Tokyo
20 ppbv (UNEP/WMO 1992). Considering the population distribution on the globe it
seems likely that the global average ozone concentration is around 20 ppbv.

ExternE use an estimate of the dose-response function of ozone on mortality of 0.015 %
per ppbv change of ozone concentration. As for acute effects of PM10, it is assumed that the average shortening of life is 2.5 years per case. This would mean that for the global population, we would get 5.28E+09 *1/75*0.015E-02 *2.5*20 = 5.28E+05 YOLL per year.

The mechanisms for production of ozone is fairly well mapped although the complexibility in the photochemical reactions between numerous different VOC’s and NOx make model simplifications and approximations necessary. Depending on the
situation NOx or VOC may be rate limiting for the production of ozone. Until better
knowledge has been gained on a global level, half of the ozone is allocated to NOx and
half to VOC.

In model 1, the average contribution to was determined to 5.56×10 -12 per kg NOx. If we
allocate half of the oxidants to NOx we obtain half the contribution, i.e. 2.78E-12 per kg NOx

Calculation of pathway specific characterisation factor

5.28E+05 *2.78E-12 = 1.47E-06 YOLL/kg NOx

For both pathways we thus obtain 2.30E-05 + 1.47E-06 = 2.45E-05 YOLL/kg NOx
Literature Reference:
1. Spengler, J. and Wilson, R., “Emission, Dispersion and Concentration of Particles” p. 51 in Wilson and Spengler, “Particles in Our Air: Concentration and Health Effects”, Harvard University Press, 1996. 2. Ferm, M., Samuelsson, U., Sjödin, Å., and Grennfelt, P., Atmospheric Environment, Vol 18, pp. 1731-1735. (1984) 3.Volz, A. and Kley, D., (1988), “Evaluation of the Montsouris series of ozone measurements made in the nineteenth century. Nature 332, p. 240-242. 4. TemaNord (1994) “Critical Levels for Tropospheric Ozone”, Nordic Council of Ministers 1994:592.
Methodological Range:
NOx as a molecule has a residence time in air of several days to a week. When NO2 is oxidised it may stay gaseous as nitrous or nitric acid, but most of it is found in the atmosphere as nitrate salt in particles. This means that the impacts on life expectancy due to NOx occur on a regional scale. In some cases it may be of interest to define regional environmental systems, but for many whose products are spread and transported internationally, the environmental system of primary interest is the global one. As the emissions considered we thus define the system as global and during the year 1990.
Notes:

Existing Characterisation Factors of NOx mipact on YOLL
Characterisation Parameter Category Indicator Impact Indication Principle Aspect Substance Quantity Unit Notes
CFactor YOLL EPS/2000
Type = Emission
Direction = Output
Media = Air
Geography = *
NOx 2.45E-05 p yr/kg 2 pathways