Rio Tinto BC Works believes calm wind conditions and inversion may have been responsible for a spike in the sulphur dioxide (SO2) level over Kitimat on Monday.

The B.C. Ministry of Environment and Climate Change Strategy issued three alerts, starting at 2 p.m. with a reading of 36.9 parts per billion (ppb), followed by another alert at 3 p.m. with a reading of 66.8 ppb.

At 4 p.m. the ministry issued a third alert confirming that the SO2 level dropped to 40.8 ppb.

A Rio Tinto spokesperson said the raised SO2 level was not as a result of a change in smelter operations.

“The raised level was most definitely related to wind conditions, possibly an inversion,” said the spokesperson.

The ministry guidelines stress that certain precautions must be taken when the SO2 level passes 30ppb.

“Persons with asthma should consider reducing or rescheduling strenuous activities outdoors if experiencing symptoms,” reads the ministry guideline.

An inversion occurs when warmer air is held above cooler air, trapping air pollution such as smog, close to the ground.

The levels rose at 3 p.m.

The levels dropped to 40ppb by 4 p.m.

Any level above 36 parts per billion (ppb) requires people take steps to safeguard their health.