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Characterisation Method Information
Characterisation Method Name:
NOx impact on Severe morbidity
Date Completed:
Principal Method Name:
EPS: secondary particles pathway, direct exposure pathway and oxidant pathway
Method Description:
Model 1, secondary particles pathway

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

Equivalency factor

Regional background levels of nitrates are about half the concentration of NOx. As
nitrates and NOx has about the same residence time in the atmosphere, we can roughly estimate an equivalency factor of 0.5 for NOx versus PM10 i.e. half of the regional NOx will become. As the effects of PM10 particles are believed to be mainly caused by particles less than 2.5 micron, as these are approximately half of the PM10 concentration and as nitrate particles are mainly less than 2.5 microns, the equivalency factor ought to be 1.0 instead of 0.5.

Calculation of pathway specific characterisation factor

The characterisation factor of PM10 for severe morbidity is -2.33E-06 person-years/kg, giving a characterisation factor for NOx of - 2.33E-06 person-years/kg NOx.

Model 2, direct exposure pathway

The characterisation factor is determined by the empirical method.

NO2 will give irritation in the respiratory tract. Asthmatics are the most sensitive group and respond to concentrations around 500 mg/m3 for one hour. The number of asthmatics varies considerably between different countries and time periods. From being a rather unknown type of symptom in the beginning of the 20th century asthma may be a reality for as much as 40% of school children. (Bråbäck, 1995) About 10-15% of the urban population in North America and Western Europe is assumed to be exposed to NO2 values exceeding WHO recommendations. The same figure is assumed to be true for all developed countries where 77% of totally 1.2 billion people lives in urban areas. 30% of these are assumed to be big cities and 10% of the overexposed is assumed to suffer from irritation in the respiratory tract (including asthmatics). 33% of 4.1 billion inhabitants live in urban areas in developing countries. 30% are assumed to live in large cities where air pollution is worse than in developed countries. 50% is assumed to be over-exposed to NO2. Thus, the same share of the urban population,15%, is over exposed in the non-OECD as in the OECD countries.

WHO recommends that 400 mg/m3 never should be exceeded. In the preparatory work for the Swedish air quality criteria, "never" is interpreted as the 99.9 percentile. People
living in areas with NO2 concentrations exceeding WHO guidelines, are thus exposed to
irritating concentrations in the order of 0.001 years per year. 10 % may be considered to be sensitive. This would give (0.77*1.2E+09 +0.33*4.1E+09 )*0.1*0.15*0.001 = 34000 person-years severe morbidity.

The global anthropogenic emission is estimated to 153 tg NOx/year (IPCC 1994). The natural is estimated to 180 tg NOx/year (Stern, air pollution, 3rd ed vol 6, AP 1986) but claimed by IPCC (Intergovernmental Panel on Climate Change)(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 NO2 exposure. The average contribution to NO2 is therefore 5.56E-12 per kg NOx.

Characterisation factor in this pathways is:

34 000*5.56E-12 = 1.89E-7 person-years/kg NOx

Model 3, oxidant pathway

The characterisation factor is determined by the empirical method.

The global average ozone concentration was estimated to 20 ppbv. The elasticity
is used, which is determined by ExternE (1995). It includes change in hospital admissions 1.095 cases per 100000 persons per year and change in emergency room visits for asthma by 2.63 cases per 100000 persons per year per annual change in ozone concentration in ppbv are used. Assuming an average duration of hospital visits of one week, and emergency room visits of one day, we obtain a total value for the indicator of
20*5.28×10 9 *(1.095×10 -5 *7/365+ 2.63×10 -5 *1/365) = 2.98×10 4 person-years per year

Characterisation factor in this pathway is thus :

2.98E+04 * 2.78E-12 = 8.28E-08 person-years/kg NOx

For all three pathways, the Characterisation factor is :

- 2.33E-06 + 1.89E-07 + 8.28E-08 = - 2.06E-06 person-years/kg NOx

Literature Reference:
1. Bråbäck, L., “Respiratory symptoms and atopic sensitization among school children in differnent settings around the Baltic sea”, Linköping University Dissertations No 442, Linköping 1995. 2. IPPC, “The 1994 Report of the Scientific Assessment Working Group of IPCC. Summary for policymakers”, WMO and UNEP, 1994
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 health 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 the default method, the environmental system of primary interest is the global one. As the emission flow groups considered are global, the system chosen is global and during the year 1990.

Existing Characterisation Factors of NOx 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 = *
NOx -2.06E-06 p yr/kg 3 pathways