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Characterisation Method Information
Characterisation Method Name:
SO2 impact on severe morbidity
Version:
1999
Date Completed:
1999
Principal Method Name:
EPS: secondary aerosol pathway and corrosion pathway
Method Description:
Model 1, secondary aerosol pathway

The characterisation factor is determined by an equivalency method using PM10 as a reference.

The reason for using PM10 and not SO2 as a reference as in "SO2 impact on YOLL" is that the main contribution to severe morbidity is from global warming while the main contribution to YOLL was direct exposure for PM10. For global warming effects, the
local exposure patterns is of less importance, and the easiest model was chosen.

Equivalency factor

An equivalency factor with PM10 could be determined through the formula:

MSO4/MSO2 * htrans * CPM10/CPM2.5

where
MSO4 and MSO2 are the molecular weights of SO4 -- and SO2, respectively,
htrans is the transformation efficiency of SO2 to SO4 2- , i.e. what part of the SO2 entering the atmosphere that become particles (in the form of sulphates) and
CSO4 and CPM10 are the concentration of PM2.5 particles compared to that of PM10.
Many authors consider PM2.5 particles to be responsible for the impact found to correlate
with PM10 (Wilsson, 1996). As most of the sulphate particle mass consists of particles less than 2.5 the ratio CPM10/CPM2.5 is used as an approximation for the enhanced potency of sulphate particles.

CPM10/CPM2.5 has been determined in several studies. (Brook et al. 1997), (Haller et al., 1999). Brook et al. studied the PM10/PM2.5 ratio at 19 sites in Canada between 1984 and 1993, Their average value, 1.89 will be used here. (For arid areas, the ratio increase, e.g. to 2.5) On the regional scale the transmission efficiency is very close to 1. The transformation rate is in the order of 1-2 % per hour, giving a residence time of the gas of a few days. If
it would rain within that time, part of the SO2 could be washed out without transformation to sulphate particles. For average global conditions, this part is considered to be small and is not used in the modelling.
Thus the equivalency factor is 96/64*1*1.89 = 2.83

Calculation of pathway specific characterisation factor

According to "PM10 impact on YOLL" there is - 2.33×10 -6 person-years/ kg PM10. We thus obtain -2.33E-06 *2.83 = -6.59E-06 person-years of severe morbidity per kg of SO2.

Model 2, corrosion pathway


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

Equivalency factor

When producing and disposing1 kg of steel, the net CO2 emission is estimated to around 1.72 kg or 0.021*1.72 = 0.036 kg CO2/kg SO2.

Calculation of pathway specific characterisation factor

The characterisation factor for severe morbidity is 3.53E–07 person-years/kg CO2. We thus obtain the pathway specific characterisation factor for SO2 as 0.036*3.53E–07 = 1.27E–08 person-years/kg SO2.

Calculation of characterisation factor

Considering both pathways, the total characterisation factor for SO2 for severe morbidity is -6.59E-06 + 1.27E–08 = -6.58E-06 person-years/kg SO2.


Literature Reference:
1. Wilson, R. and Spengler, J., “particles in Our Air: Concentration and health effects”, Harvard University Press, 1996, Harvard School of Public Health. 2. Haller, L., Claiborn, C., Larson, T., Koenig, J., Norris, G. and Edgar, R., (1999) “Airborne Particular Matter Size Distributions in an Arid Urban Area”, J. Air & Waste Manage. Assoc., Vol. 49, p. 161-168.
Methodological Range:
The system is global and the time period is 1990.
Notes:

Existing Characterisation Factors of SO2 impact on severe morbidity
Characterisation Parameter Category Indicator Impact Indication Principle Aspect Substance Quantity Unit Notes
CFactor Severe morbidity EPS/2000
Type = Emission
Direction = Output
Media = Air
Geography = *
SO2 -6.58E-06 p yr/kg 2 pathways