Acidifying Precipitation: More about the data

Wet deposition is calculated from the composition of weekly precipitation samples collected at nine monitoring stations. Potential Acid Input (PAI) is the indicator used to represent wet deposition. PAI is calculated from the sum of all acidic components in the precipitation, such as sulphur and nitrogen compounds, excluding neutralizing components (base cations) such as sodium, magnesium, potassium and calcium.

There are nine precipitation quality monitoring stations in Alberta that measure pH and precipitation composition. However, seven stations are included in the analysis for this indicator. The other two stations (Fort Vermillion and Fort Chipewyan) do not have enough data for trend analysis. Only those stations for which long-term trends can be shown (i.e. five or more consecutive years of data) are included. Trends that are statistically significant (a=0.05) are identified with an asterisk.