**2. Traditional methodologies to estimate GHG emission factors from the electricity generation sector**

There are two main methods to estimate pollutant and GHG emission Factors from the electricity generation sector: 1) direct measurement or 2) estimation. Direct measurement is considered to be the most accurate since it uses real-time data from the generation sector. However, these data are not readily available and historically, GHG emissions have been estimated from fossil fuel and process-related activities. Estimation is the method used by several countries when preparing their national GHG inventories (ICPP, 1997). In the past, GHG emissions from the electricity generation sector were calculated using the Average GHG Intensity Factor (GHGIFA) (Guler et al., 2008). The GHGIFA is the amount of GHG emissions per kWh electricity produced. This method assumes that the reduction in electricity demand is uniformly distributed amongst all types of electricity generation. For example, the GHGIFA estimated in 1993 was 136 g/kWh for the Province of Ontario. Table 1 shows the GHGIFA values for the years 2004, 2005, and 2006 for the Province of Ontario from the electricity generation sector (EnvCan, 2006).


Table 1. Annual Emission Factors

The combustion of fossil fuels produces several major greenhouse gases. The amount of emissions from CO2, CH4, SO2, NO, and N2O varies from one fuel to another, and they are calculated using emission factors. These emission factors are commonly expressed in tons of CO2 per MWh or grams per kWh of electricity produced (Gordon & Fung, 2009).
