The Sky's Orange Hue: Why?

Wildfires can cause the sky to turn orange. In 2023, cities in the Midwest like Chicago and Detroit, as well as much of the Great Lakes region, experienced orange skies due to smoke from Canadian wildfires. The smoke particles in the air blocked certain colours of sunlight from reaching our eyes, leaving behind reds and oranges. This phenomenon typically occurs at sunrise and sunset, when the sun's light has to travel through more particles in the atmosphere.

Wildfires in British Columbia and Alberta, Canada

In early May 2023, more than 100 wildland fires raged across Western Canada, with the provinces of Alberta and British Columbia being the worst affected. The fires destroyed homes and forced tens of thousands of people to evacuate. The thick smoke from the wildfires blanketed a long stretch of Highway 43 in Alberta, turning the sky a garish blood orange. One resident, Nicole Clarke, described feeling a sense of terror as she fled her hometown of Fox Creek with her two young children.

The fires in Alberta have been so intense that they have produced towering chimneys of smoke that reached the upper troposphere. Using remote sensing, researchers at the University of Wisconsin-Madison observed the formation of a pyrocumulonimbus (pyroCb) cloud billowing from a wildfire west of Edmonton on May 4. Temperatures at the top of the cloud were as cold as -61°C (-78°F), indicating that the smoke may have reached an altitude of about 12 kilometers (39,000 feet).

On May 8, there were 29 fires burning out of control in Alberta, with 75 active wildfires by May 17, 23 of which were considered out of control. The smoke from these fires blanketed much of Canada and even reached parts of the US. The early start to the wildfire season and the sharp rise in temperatures have fuelled concerns about more fires to come.

British Columbia has also experienced wildfires and evacuations. A wildfire burned near the town of Fort St. John, close to the BC-Alberta border. By June 2023, about 160,000 hectares had burned in the province since the start of the year. Dry and windy conditions contributed to the spread of unusually large fires in the region.

Wildfire smoke and its effect on sunlight

Wildfires can cause the sky to turn orange due to the smoke they produce, which affects how sunlight reaches us. Sunlight is composed of white light, which contains all the colours of the rainbow. When there are smoke particles in the air, they block certain colours of light from reaching our eyes. In the case of wildfire smoke, blues, purples, and yellows are blocked, leaving behind reds and oranges. The intensity of the orange hue can vary depending on the amount of smoke and the time of day.

The presence of wildfire smoke in the atmosphere can lead to a more noticeable orange appearance during sunrise and sunset. This is because the sun's light has to travel through a greater amount of atmosphere, and consequently, more smoke particles, resulting in an enhancement of the orange colour. The wind patterns throughout the day also play a role in the accumulation of smoke, with lighter winds in the morning and stronger winds in the evening.

The orange sky serves as a visible indicator of poor air quality. The smoke particles that cause the orange hue can have negative effects on human health, even for individuals who are generally healthy. Exposure to the smoky air can lead to coughing, eye irritation, fatigue, and throat irritation. For people with respiratory conditions such as asthma, the impact can be more severe, and health experts advise limiting exposure to the outdoor air as much as possible during these conditions.

The impact of wildfire smoke on sunlight and the resulting orange sky has been observed in various regions, including Midwest cities like Chicago and Detroit, as well as the Great Lakes region. These areas experienced the effects of smoke from Canadian wildfires, leading to hazardous air quality and eerie orange skies. Similar incidents have occurred in San Francisco during California wildfires in 2020 and in New York City, resulting in comparable "Blade Runner 2049"-esque scenes.

Air quality and health implications

Air quality is a significant determinant of health, and poor air quality can have adverse effects on well-being. When the air quality is orange or "unhealthy for sensitive groups", as indicated by the Air Quality Index (AQI), it is essential to understand the potential health implications and take necessary precautions.

The AQI is a system designed to warn the public about dangerous levels of air pollution. It tracks various pollutants, including ozone (smog) and particle pollution from sources like smoke, power plants, factories, and vehicle exhaust. On orange days, the air quality is generally acceptable for most individuals. However, sensitive groups, including children, older adults, pregnant women, and people with chronic illnesses, are at an increased risk of experiencing health issues.

For those in sensitive groups, it is recommended to limit prolonged or intense outdoor activities. This is because they may immediately feel the health effects of poor air quality, such as respiratory symptoms, breathing discomfort, coughing, shortness of breath, and throat irritation. People with asthma or other lung conditions need to be especially cautious, as their risk of adverse health effects is heightened.

Additionally, even healthy individuals may experience negative health consequences with prolonged exposure to orange-level air pollution. While they may not be as severely affected as those in sensitive groups, they can still develop symptoms such as difficulty breathing and throat irritation. Therefore, it is advisable for everyone to reduce their time spent outdoors, especially in high-traffic areas, to minimize the potential health risks associated with poor air quality.

To protect your health during periods of poor air quality, it is essential to stay informed about the AQI levels in your area. You can do this by checking newspapers, listening to the radio, or visiting websites that provide real-time air quality data. By taking proactive measures, you can help safeguard yourself and your loved ones from the potential health implications of poor air quality.

Visibility issues and travel disruptions

The phenomenon of orange skies is often an indication of poor air quality, specifically caused by smoke particles in the air. In this case, the orange skies in Midwest cities like Chicago and Detroit, as well as in the Great Lakes region, are a result of smoke from Canadian wildfires.

The presence of smoke particles in the air can cause significant visibility issues. The smoke blocks certain colours of the white light spectrum from reaching our eyes, leaving mainly reds and oranges. This can give the sky a more greyish or orangeish hue, depending on the time of day and the amount of smoke present. The wind tends to be lighter in the morning, resulting in less smoke buildup. However, as the day progresses, the smoke accumulates, and by sunset, the light travels through more atmosphere and smoke particles, enhancing the orange appearance of the sky.

This reduced visibility caused by the smoke can have a significant impact on travel, particularly for drivers. The haze and murkiness caused by the smoke can decrease visibility on roads, making it difficult for drivers to see obstacles, other vehicles, or pedestrians. It is advisable to drive with extra caution during such conditions, reducing speed and using headlights to improve visibility. Additionally, those operating aircraft or watercraft may also experience visibility issues due to the smoke, potentially leading to flight or sailing disruptions.

The poor air quality resulting from the smoke particles can also cause health issues, particularly for individuals with respiratory conditions like asthma. It is recommended that people limit their exposure to the outdoor air during these conditions and seek medical attention if they experience symptoms such as coughing, eye irritation, throat irritation, chest tightness, headaches, dizziness, or wheezing.

Overall, the orange skies caused by the Canadian wildfires can lead to both visibility issues and travel disruptions, affecting daily life and potentially causing health concerns for those in the affected regions. It is important for residents in these areas to stay informed, take necessary precautions, and follow the advice of local authorities and health experts.

Recommended precautions for vulnerable individuals

Air pollution is a serious global health problem, with certain groups of people being more vulnerable to its adverse effects. These groups include children, pregnant people, older adults, and individuals with pre-existing heart and lung diseases, such as asthma, COPD, and cardiovascular disease. People of color and those with lower incomes are also disproportionately affected by air pollution. Therefore, it is important for vulnerable individuals to take extra precautions to protect their health during periods of high air pollution, such as when the sky turns orange due to wildfire smoke or other factors. Here are some recommended precautions for vulnerable individuals:

• Stay indoors: Limit your time outside, especially when air pollution levels are expected to be high. Avoid outdoor activities, such as exercising or working, that can increase your exposure to pollutants.
• Reduce indoor air infiltration: Keep windows and doors closed to minimize the entry of outdoor air pollutants into your home. Use air conditioning or air filtration systems to improve indoor air quality if possible.
• Monitor air quality: Stay informed about the air quality forecast in your community. Check for air quality alerts or warnings, and be aware of any advisories for vulnerable groups.
• Limit physical exertion: Reduce physical activity, especially outdoors or near sources of air pollution. Strenuous activities can increase the inhalation of pollutants and exacerbate respiratory issues.
• Use respirators or masks: Consider wearing a respirator or a well-fitting mask when outdoors to reduce the inhalation of particulate matter and other pollutants. Look for masks that are specifically designed to filter out fine particles, such as N95 or P100 respirators.
• Consult a healthcare provider: Discuss your individual circumstances with a healthcare professional. They can advise specific interventions or precautions based on your health condition and susceptibility to air pollutants.

It is important to note that these precautions are meant to reduce exposure to air pollutants and potential health risks. However, the best way to protect vulnerable individuals is to address the root cause by advocating for collective action and policies that reduce emissions and improve air quality at the source.

Frequently asked questions