Toronto could get vibrant orange sunsets from wildfire smoke this week

You might notice Toronto's sunsets looking a little more dramatic than usual this week, and there's actually a scientific explanation behind why you'll see more vibrant colours in the sky.

Wildfire smoke from blazes burning across northern Quebec is continuing to drift into parts of southern Ontario this week, which is affecting air quality and creating the potential for vivid orange and red skies during sunrise and sunset in Toronto.

Wildfires have significantly expanded across Quebec over the past few weeks, with the total area burned growing from roughly 9,300 hectares at the end of June to more than 530,000 hectares as of this past Saturday.

Smoke from the wildfires first moved into parts of Ontario on Saturday, and additional smoke pushed south on Sunday, moving towards eastern Ontario, the Ottawa region, and parts of southern Ontario.

The smoke arrives as Ontario is preparing for its second major heat wave of the summer. This week, temperatures are expected to climb into the mid-30s this week, with humidex values reaching the mid-40s during the peak of the heat.

According to Air Quality Ontario, Toronto is currently sitting at a level 4 on the Air Quality Health Index (AQHI), which represents a moderate risk, and is expected to remain at that level through Tuesday.

An index rating between 4 and 6 means at-risk populations who experience symptoms like coughing or throat irritation should consider reducing or rescheduling strenuous outdoor activities, while the general population does not need to modify any outdoor activities unless symptoms occur.

Although the smoke can lead to hazier skies and reduced air quality, it can also produce some spectacular sunsets.

Wildfire smoke can transform everyday sunsets into deep orange, vibrant red, or even fiery-looking displays simply because of how smoke particles interact with sunlight.

While the atmosphere normally appears blue because tiny air molecules (like oxygen and nitrogen) scatter shorter wavelengths of light more effectively than longer wavelengths.

Wildfire smoke changes how sunlight travels through the atmosphere, as it contains tiny particles of soot, ash, and other aerosols that are much larger than individual air molecules. As a result, these larger particles scatter light differently through a process that's known as Mie scattering.

According to The Weather Network, Mie scattering occurs when sunlight interacts with particles that are similar in size (or larger than) the wavelength of visible light. Instead of strongly favouring blue light, these particles scatter colours more evenly while also reducing the amount of blue and green light that reaches our eyes.

"This process scatters all wavelengths more equally, not favouring blue like Rayleigh does. This leads to whiter or greyer appearance in the sky, especially when it's hazy," the weather channel notes.

"It can also make the sun look milky or red, especially during wildfire smoke events. Light hitting smoke or fog gets muddled, everything's scattered evenly, and you lose the vibrant blues — leaving warmer tones like red and orange."

Warmer colours, like reds and oranges, then become more dominant, and give the sky a fiery appearance. The effect is normally strongest during sunrise and sunset because sunlight has to travel through more of the atmosphere when the sun is low on the horizon.