How Pollution Affects Sunsets And Sunrises

The vibrant colours of a sunset are the result of a phenomenon called Rayleigh scattering. During sunset, light travels through more atmospheric particles, and shorter blue and green wavelengths scatter more easily, while longer wavelengths, which produce orange and red colours, make it through, creating those rich, vibrant colours. While pollution can indeed change the appearance of a sunset, the effect of pollution on sunsets depends on the type and amount of pollution in the air.

The scattering of light

The vibrant colours of sunsets are the result of a phenomenon called Rayleigh scattering, where particles in the atmosphere scatter light from the sun. This scattering process filters out shorter blue wavelengths, allowing longer red and orange wavelengths to pass through and intensify the colours of the sunset.

During sunrise and sunset, light must travel through more atmospheric particles to reach us. The shorter blue and green wavelengths scatter more easily, so they have a harder time making it through. On the other hand, the longer wavelengths, which produce orange and red colours, do make it through, giving us those rich vibrant colours.

The same scattering process is responsible for the colour of the sky during the day. Sunlight is made up of all the colours of light, and it appears as white light when all the colours are together. However, when sunlight encounters particles in the atmosphere, different colours of light are scattered in different ways. Blue light, for example, has shorter, smaller waves, so it is scattered more than other colours. This is why the sky often appears blue during the day.

When there is more pollution in the atmosphere, there are more particles to scatter sunlight, which can lead to more colourful skies. However, if there is too much pollution, the sunset colours can become muted and washed out. The size of the particles also matters. If the particles are of uniform size, they might impart a reddish or bluish cast to the sky. On the other hand, if the particles are of varying sizes, they may scatter all colours indiscriminately, increasing the overall brightness of the sky but reducing the colour contrast.

While pollution can enhance the beauty of a sunset, it is important to remember that it is also an indication of poor air quality. The vibrant orange and red sunsets observed in polluted cities like Los Angeles and Beijing are a result of the high levels of human-made aerosols in the atmosphere. These aerosols can come from factory and coal-power exhaust, car exhaust, leaking gas, and the by-products of burning plastics and aerosol spray cans.

The impact of smog

Smog is a type of air pollution that can have a significant impact on sunsets. It is caused by a variety of human activities, including factory and coal-power exhaust, car exhaust, leaking gas, and the burning of plastics and aerosol spray cans. These activities release a mixture of chlorofluorocarbons (greenhouse gases), hydrocarbons, sulfuric acid, and other harmful pollutants into the atmosphere. While it is commonly believed that smog enhances the beauty of sunsets, the reality is more complex.

The effect of smog on sunsets depends on several factors, including the size and concentration of aerosol particles in the atmosphere. Aerosols are solid or liquid particles suspended in the air, originating from both natural processes and human activities. In the case of smog, the particles are primarily a result of human activity. When these aerosol particles are small, they can contribute to the deep crimson sunsets observed in polluted cities like Los Angeles. This is because smaller particles scatter shorter wavelengths of light, such as blue and violet, more than longer wavelengths like red.

However, when there is a high concentration of large aerosol particles in the atmosphere, the sunset can appear washed out. This is because larger particles scatter all colours of light indiscriminately, increasing the overall brightness of the sky while muting the colour contrast. As a result, the sunset may lose its vibrant hues. Additionally, at extremely high levels of pollution, the sun may not even be visible, and the sky may appear hazy and saturated.

The effect of wildfires

Wildfires are a significant contributor to air pollution, and their smoke can have a notable impact on the appearance of sunsets. The smoke from wildfires contains numerous particles, which can include solid or liquid aerosols, chlorofluorocarbons (greenhouse gases), hydrocarbons, sulfuric acid, and other unpleasant pollutants. These particles are often very small, with a length of one-millionth of a metre or less.

When wildfire smoke fills the sky, it introduces a high concentration of particles into the atmosphere. These particles scatter sunlight, affecting the colours that reach our eyes. The particles scatter shorter wavelengths of light, such as blue and green, more than longer wavelengths, such as red and orange. This phenomenon is known as Rayleigh scattering. As the sun sets, its light must travel through more atmospheric particles to reach us, and the shorter wavelengths of blue and green light are scattered more easily, while the longer red and orange wavelengths persist, resulting in vibrant sunsets.

The smoke from wildfires can enhance this effect by adding even more particles to the atmosphere. The larger particles in wildfire smoke can also cause Mie scattering, which scatters the longest wavelengths of light the best, resulting in very reddish sunsets. The combination of Rayleigh and Mie scattering caused by wildfire smoke can create intense red, orange, and yellow hues in the sky.

While the visual impact of wildfires on sunsets can be striking and even inspiring, it is important to remember that wildfire smoke is unhealthy to breathe. The particles in the smoke can have negative effects on air quality and human health, and the impact on those living near the fires can be devastating. Therefore, while wildfires may create awe-inspiring sunsets, they also serve as a reminder of the destructive effects of human activity and climate change on our environment.

The role of aerosols

Aerosols are solid or liquid particles suspended in the air, originating from both natural processes and human activities. Natural aerosols can come from forest fires, mineral dust, sea spray, and volcanic eruptions. Human activities, on the other hand, contribute man-made aerosols through factory emissions, car exhaust, and the burning of fossil fuels and plastics. These man-made aerosols tend to be smaller in size compared to natural aerosols.

The size of aerosol particles plays a crucial role in their impact on sunset colours. Smaller aerosols, when present in high concentrations, can contribute to the deep crimson sunsets observed in polluted cities like Los Angeles. This is because smaller particles scatter shorter wavelengths of light more than longer wavelengths, allowing the red hues to dominate. However, if the concentration of large aerosol particles in the atmosphere is high, it can lead to a washed-out effect, muting the colours of the sunset. This is because larger aerosols scatter all colours of light indiscriminately, increasing the overall brightness of the sky while reducing colour contrast.

While moderate levels of pollution from aerosols can enhance sunset colours, excessive pollution can create hazy and muted displays. This is evident in highly polluted cities, where the sky may appear brown or grey due to the high concentration of particles scattering and absorbing light. Additionally, while the presence of certain aerosols can intensify sunset colours, it is important to consider the negative impacts of pollution on the environment and human health. Wildfires, for example, contribute to air pollution and can create colourful sunsets, but the fine particles in wildfire smoke can have detrimental effects on respiratory and cardiovascular health.

In summary, aerosols play a significant role in shaping the colours of sunsets, but their effect depends on their size, concentration, and the overall level of pollution in the atmosphere. While pollution from aerosols can lead to vibrant sunsets, it is important to recognise the broader implications of air pollution and take steps to mitigate its negative consequences.

How pollution affects sunset colours

The colours of a sunset are the result of a phenomenon called Rayleigh scattering, or light scattering. During sunset, light must travel through more atmospheric particles to reach the eye. The shorter blue and green wavelengths scatter more easily, while the longer wavelengths, which produce orange and red colours, make it through, giving us those rich vibrant colours.

Air pollution, caused by human activity and natural processes, releases particles into the atmosphere that affect the way light scatters and, therefore, the colours we see at sunset. Natural aerosols, such as those from forest fires, mineral dust, sea spray, and volcanic eruptions, can create more dramatic sunsets. Similarly, man-made smog, composed of chlorofluorocarbons, hydrocarbons, sulfuric acid, and other pollutants, can also affect sunset colours.

However, the effect of pollution on sunset colours depends on the size and concentration of the particles in the atmosphere. Large particles, such as dust, smoke, or pollutants, absorb more light and scatter wavelengths of light mostly equally, muting the colours of a sunset. On the other hand, small particles, such as those in volcanic smog and forest-fire smog, block certain wavelengths of light, allowing other colours to dominate.

While moderate air pollution can enhance sunset colours, excessive pollution can create hazy, washed-out displays. The transition from day to night might be peachier and healthier without pollution, as the sky would be brighter and the colours more pure.

Climate change has also impacted sunsets, with shifting weather patterns and increased wildfires creating the conditions for more dramatic sunsets in some regions.

Frequently asked questions