An air quality alert has been issued for Wisconsin through Thursday. Here's why the smoke from Canadian fires continues to affect us.

It has been a summer of smoke so far in Wisconsin as the Department of Natural Resources has once again issued an air quality advisory across the state. Advisories like this one have been common throughout May and June as Canada struggles to corral massive fires across the country — but this week could be more severe.

Air quality advisories have typically lasted 12 to 24 hours when issued, however, the advisory issued Monday is expected to last until Thursday afternoon.

Paul Collar, a National Weather Service meteorologist, said the longer advisory could be because there is a chance that Wisconsin will see hazardous air — the most dangerous grade of air.

"It seems that this advisory is a bit more strongly worded, especially in regard to the possibility of hazardous air," Collar said. "This week the upper air pattern has shifted and is allowing the smoke from Canada to be funneled south into our area."

With air quality expected to be most severe on Tuesday and Wednesday, here is what you need to know about what these advisories mean, what effects the smoke will have and how to stay safe.

Smoky haze and smell is expected to hover over the Milwaukee area until at least Wednesday

On Monday, Milwaukeeans started to experience a hazy sky that was visible throughout the day and not just at sunrise and sunset like on other occasions. Moreover, the slight smell of smoke can be expected as the haze continues to sit in downtown Milwaukee.

The weather service said Tuesday and Wednesday are going to be the most severe days for smoke so Milwaukeeans can count on hazy skies in the near future.

What is an air quality alert, and how is smoke from fires causing one?

Jaclyn Anderson, a meteorologist with the National Weather Service, said an air quality alert is issued when air quality becomes unhealthy to inhale. Air quality is usually tainted by two things: particulate matter and high-levels of ground-level ozone pollution.

Monday the alert was issued until noon Thursday because of particulate matter from the Canadian fires polluting the air in Wisconsin. Ground-level ozone is the other cause of air quality alerts and often stems from pollutants like car exhaust and industrial fumes mixing with oxygen.

Is smoke in the air causing hazy skies?

Skies across Wisconsin will be noticeably hazy throughout the day but the haze will be especially evident during sunset. This haze is caused by the visible particulate matter from the Canadian fires that will continue to disperse south.

Is it safe to go outside during an air quality alert?

Polluted air can trigger asthma attacks and decrease lung function but, for most people, it is safe to go outside during an alert. Collar said northern counties in Wisconsin were immediately at the most risk but this will spread to the rest of the state in the following days.

The weather service has said “sensitive groups” can be more prone to the effects of polluted air and should be extra cautious when going outside during peak air quality alert hours.

How often do air quality alerts happen?

Air quality alerts usually take place in warmer months because fires can often be the cause of polluted air. For this reason, a handful of alerts have been issued over the last month across Wisconsin.

But it is not out of the ordinary to see air quality alerts in winter if pockets of air lay idle and start to accumulate ground-level ozone pollution.

In a typical year, one to five air-quality alerts are seen, but since spring has started there have been an abnormal amount of alerts in Wisconsin.

Where are the fires in Canada?

Fires in Canada are burning in the country's eastern Nova Scotia providence, which is having one of its worst fire seasons on record. Canada is also dealing with an onslaught of fires on its west coast where such events are more typical.

The Canadian government reports that over 200 fires are under control or "being held" but there are still about 80 that remain untamed in any way.

How did fires in Canada start?

Fires in Canada are thought to have started in late April and grew more severe in early May prompting a government response on May 6. It is thought that warmer conditions in eastern Canada due to global warming have increased the chances of natural fires in recent years.

These fires have traditionally occurred on the country's west coast, but this spring has seen historic fire numbers on Canada's east coast.

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This article originally appeared on Milwaukee Journal Sentinel: Why it is hazy in Wisconsin and what to know about air quality alerts