High levels of a chemical detected at two of Sydney's six air monitoring stations Feb. 9 probably came from home and office heating systems, officials say.

The Sydney Tar Ponds Agency issued a news release Tuesday that said excess levels of benzo(a)pyrene were detected at the Henry Street and Intercolonial Street locations last Wednesday.

But officials said there was no activity related to the tar ponds or coke ovens cleanup sites that would account for the increased levels.

"No activity was underway at the Domtar tank dismantling project on the day in question," the release said.

Although no excavation took place last Wednesday, the release points out that "all activity at the tank takes place within an enclosed structure equipped with a fan that draws exhaust air through massive filters."

It also said that although all six monitoring stations recorded higher than normal levels of the chemical, the Victoria Road and Frederick Street locations - the two closest to where contractors are emptying the derelict Domtar tank - actually had the lowest readings.

"The lack of wind probably prevented emissions from home and office heating systems from dispersing," Walter van Veen of Conestoga Rovers & Associates, project manager for the Domtar tank removal, said in the release of what was a calm and foggy day.

"It could also have come from some very remote source, but this is less likely," he said.

Despite the rise in benzo(a)pyrene readings Feb. 9, the release said Environment Canada's air quality index was in the "good" range that day.

The release said the Sydney Tar Ponds Agency collects 24-hour air samples every 12 days, and every six days when there is work going on at either the tar ponds or coke ovens site.

This coincides with a national air monitoring system, the release said.

The Ontario Ministry of the Environment "action level" for benzo(a)pyrene is 1.1 nanograms per cubic metre, the agency said.

The Henry Street station recorded a level of 1.54, while the Intercolonial Street location recorded a 1.38, the agency said.

The other four monitoring stations recorded levels ranging from 0.48 to 0.99, the release said.