Air Quality: Sulphur Dioxide (SO2)

Since its inception in the 1960's the Association's air quality program has tracked sulphur dioxide levels in local air. For the past 20 years, sulphur dioxide levels in Sarnia and Corunna have also been an integral part of the unique Lambton Industry Meteorological Alert (LIMA) regulation.

LIMA is an area-wide approach to maintaining acceptable air quality during periods when emissions under poor dispersion conditions could lead to locally high concentrations of SO2. The regulation is designed to maintain the daily average SO2 concentration below the Ontario Ambient Air Quality Objective of 100 parts per billion (ppb).

When it appears that the 24-hour average at a monitoring station will rise above 70 ppb, industries which emit quantities of SO2 that are capable of impacting the air we breathe, switch to fuels that contain less sulphur dioxide. Rates of manufacturing products may also be cut back in order to reduce SO2 emissions. Higher than average hourly SO2 concentrations generally occur when southerly to southwesterly winds greater than 15 km/h persist.

 

When levels trend towards the 24-hour average of 70 parts per billion at one of the regulation monitoring stations, industries that emit quantities of the compound are directed to switch to lower-sulphur fuels, or reduce production. Historical annual average levels of SO2 at monitoring stations in Sarnia and Corunna, including those obtained during 2008, are presented in Figure 1. Levels have remained relatively constant over the last 20 years, and are well below Ontario’s acceptable annual average concentration level.

Long-Term Summary of SO2 Alerts (LIMAs)

In 2008, there were two LIMA alerts; during both of these, on January 5th and January 7th, the 24-hour criterion of 100 ppb was exceeded.  The average SO2 concentrations were 108 and 189 ppb, respectively.

Over the past 27 years, there have typically been six events per year, each lasting approximately 16 hours in duration. A long-term summary of SO2 Lambton Industry Meteorological Alerts and daily exceedances is shown in Figure 2.