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Characterisation Method Information
Characterisation Method Name:
SO2 impact on YOLL
Date Completed:
Principal Method Name:
EPS: direct acute effect pathway, corrosion pathway and secondary aerosol pathway
Method Description:
YOLL stands for Year of Lost Life.

Model 1, direct acute effect pathway

The characterisation factor is determined by an empirical method.

One way to estimate the category indicator value is to identify those groups for which
threshold limits for health effects are exceeded. Excess mortality occur at 500 mg/m 3 among elderly chronically ill people (WHO, 1987). These concentrations are very rare as
daily means. UN environmental data report 91/92 indicates only a few cities with annual
means above 200 mg/m 3 (Shenyang, China and Teheran, Iran). A rough estimate is that 5
million persons live in areas where the SO2 concentration every third year as a daily
average exceeds 500 mg/m 3 . (Obtained from extrapolation of log-normal frequency
distribution). Assuming an increase in death rate of 1% in respiratory diseases (less than
10% of all mortality causes) and a life shortening of 3 years, a normalised death
incidence would be 375 YOLL per year.
Another way of estimating the excess mortality is to use elasticity figures obtained from epidemiological studies. Lipfert and Wyzga (1995) has reviewed various such studies.
They find an elasticity of about 0.02 for SO2, which means that if the concentration of
SO2 is decreased by 1% of the average, there is a decrease of 0.02% in the mortality rates. Taking away 100% would (if the dose- response function were linear) give a 2%
reduction. The effect is mainly detected for elderly above 65 years and on a time scale of
0-4 days. Using one week of life shortening SO2 would be responsible for about 5.28E+09 /65(average mortality per year)*1/50(YOLL/case) *0.02(part of population
affected) = 32500 YOLL per year.
Although some epidemiologists seem to consider the elasticity figure for SO2 showing something else than a causal effect of SO2, the figure 32500 YOLL will be used as it still is small compared to changes in the category indicator induced via other pathways.

The global emission of SOx (SO2 + SO3 + H2SO4) is 170 million tons per year. SO3 and
H2SO4 have similar but not identical effects as SO2. Their emissions are only a few
percent of the SO2 emissions. Thus the average contribution is estimated to 5.88E-12 per kg SO2.

Calculation of pathway specific characterisation factor

The pathway specific characterisation factor is 32500*5.88E-12 = 1.91E-07 YOLL/kg SO2.

Model 2, secondary aerosol pathway

The characterisation factor is determined by an empirical method.

Category indicator value in system considered

The total indicator value for PM10 is determined in "PM10 impact on YOLL" to be 6.3410 7 YOLL per year for the chronic effect pathway. For all pathways it would be 4.24/4.23* 6.34E+07 =6.35E+07 YOLL per year, where 4.24E-4 is the added characterisation factor for all pathways and 4.23E-4 is the characterisation factor for the chronic effect pathway.
In "PM10 impact on YOLL" the global average population exposure to PM10 is estimated to 46 mg/m 3 . According to Brook et al. (1997), who studied the Canadian ambient aerosol, about 10% of the PM10 mass consist of sulphates. If used as a global average, the average exposure would be 4.6 mg/m 3 and the total indicator value allocated to sulphates 0.1*6.3510 7 =6.3510 6 YOLLs per year.

Contribution to category indicators value from a flow unit

In model 1, the contribution was estimated to 5.8810 -12 per kg SO2.

Calculation of pathway specific characterisation factor

6.35E+06 * 5.88E-12 = 3.74E-05 YOLL/kg SO2.

Model 3, corrosion pathway

The characterisation factor is determined by a combined empirical and equivalency
method using emissions and resources in steel production as a reference.

Category indicator value in system considered

The global replacement of steel caused by corrosion due to SOx is estimated to 3.5 10 9
kg/year. The estimations is based on assumptions of a 5 % reduction in the usage time for steel constructions, and a world steel production of around 700E+09 kg. (UN 1996)

As the global SOx-emission is 170 million tons per year the contribution is at an average 5.88E-12 per kg SO2. The average demand of new steel is therefore 0.021 kg/kg SO2.
When producing and disposing1 kg of steel, the net CO2 emission is estimated to around 1.72 kg.

Calculation of pathway specific characterisation factor

The characterisation factor of CO2 for YOLL is 7.93E-05 . This will give a characterisation factor of SO2 for YOLL of 0.021*1.72*7.93E-05 = 2.81E08 YOLL/kg

Calculation of characterisation factor

Considering all three pathways, the total characterisation factor for SO2 is 1.91E-07 +
3.74E-05 + 2.81E-08 = 3.76E-05 YOLL/kg SO2

Literature Reference:
1. WHO, Air Quality Guidelines for Europe, WHO Regional Publications, European Series, No 23, 1987. 2. Lipfert and Wyzga, 1995, J.Air &Waste Management Ass., Vol 45, p 949
Methodological Range:
The system is global and the time period is 1990.

Existing Characterisation Factors of SO2 impact 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 = *
SO2 3.76E-05 p yr/kg 3 pathways