Canada Day fireworks cancelled over air quality fears

Persistently bad air quality over North America and worries about sparking more fires has led to the cancellation of some Canada Day firework displays.

There were also concerns over air quality around next week's Fourth of July celebrations in the US.

Smoke has drifted over large sections of the US and Canada this week.

On Friday, cities including New York, Toronto, Montreal and Washington DC were near the top of a list of major cities with world's worst air quality.

The first night of an annual fireworks competition in Montreal on Thursday was called off, and the city's Canada Day display, set for Saturday night, has also been cancelled.

However a celebration in Toronto is still scheduled to go ahead. The city was continuing to monitor the situation, a spokesperson said, but no changes were planned as of late on Friday.

The 1 July holiday commemorates the British North America Act, which merged four British colonies into a single new country in 1867. Like the Independence Day holiday in the US, it is traditionally marked with outdoor events, including fireworks.

A number of cities and towns in some of the worst affected areas cancelled their Canada Day pyrotechnics or moved them away from wooded areas.

The picture for the US Independence Day holiday is unclear. Long-term predictions of smoke drift are difficult, said Dave Roth, a forecaster with the US National Weather Service's Weather Prediction Center.

"The areas over the next day and a half that we expect the most smoke are across Minnesota, Wisconsin and parts of the north-eastern United States," he said on Friday afternoon, noting that weekend rain in New England would likely improve air quality in the region.

"Showers and thunderstorms are great for cleaning out the atmosphere," he said.

Another weather factor - extreme heat and drought - has led to the cancellation of fireworks displays in two Missouri towns, according to local reports.

The Canadian wildfires have brought bad air to the middle of the continent just in time for the holiday weekend.

"It's pretty well known that 4th of July tends to be one of the worst air quality days of the year," said Anastasia Montgomery, a researcher at Northwestern University in Chicago.

"It's not just the fireworks," she said. "There's a lot more traffic, a lot more grilling - the kinds of behaviours around the holiday combine with heat to make air quality really bad."

Smoke will persist until the Canadian fires are put out, Mr Roth said. And what's more, he says that wildfires in the western United States - Texas and Arizona - had been spotted in recent days. So far this year there have been relatively few wildfires in the region compared to the Canadian blazes, but that's subject to change.

"What ends the fire season in the US and Canada are cooler temperatures and ultimately rain and snow," which comes in September and October, he said.