How Home Furnace Pollution Affects The Sunset

The vibrant colours of a sunset are the result of a phenomenon called Rayleigh scattering. During the day, when the sun is directly overhead, light travels a shorter distance through the atmosphere, and blue light wavelengths dominate, giving us a blue sky. However, as the sun sets, it has to travel through more atmospheric particles, and the longer red and orange wavelengths are more likely to reach our eyes. While some pollution particles can enhance the red hues of a sunset, large amounts of pollution can lead to a hazy, washed-out appearance.

Home furnaces can contribute to air pollution, particularly if they are unvented or poorly vented, releasing combustion pollutants directly into the home or the outdoors. Gas-fuelled home appliances, such as furnaces, have been found to worsen indoor and outdoor air quality by emitting pollutants such as carbon monoxide, nitrogen oxides, formaldehyde, and fine particulate matter.

So, while some pollution can make sunsets more vibrant, too much pollution can diminish the overall sunset experience. Therefore, it is essential to consider the type and amount of pollution when determining the impact of home furnaces on sunsets.

The impact of gas appliances on indoor and outdoor air quality

Gas appliances have a significant impact on both indoor and outdoor air quality. A UCLA Fielding School of Public Health report found that gas-fired appliances affect the air people breathe and have related health effects. The report, commissioned by the Sierra Club, highlights the adverse consequences of fossil fuel use in household appliances on indoor air quality and public health.

Indoor Air Quality

Gas appliances, particularly gas cooktops and ovens, can negatively impact indoor air quality. The UCLA report revealed that concentrations of carbon monoxide (CO) and nitrogen dioxide (NO2) during cooking can exceed national and California-based ambient air quality standards, especially for NO2. When using a gas stove and oven simultaneously for an hour, acute exposures to NO2 can surpass air quality thresholds in over 90% of modelled emission scenarios.

The Consumer Reports' tests further emphasised the importance of ventilation when using gas appliances. Their findings showed that using a range hood or downdraft hood helped lower nitrogen dioxide levels, but levels still exceeded the World Health Organization's 1-hour guidelines in several tests.

Outdoor Air Quality

The UCLA report also indicated the benefits of transitioning from gas to clean-energy electric appliances. By replacing residential gas appliances with electric alternatives, there would be a reduction in secondary nitrate fine particulate matter (PM2.5) and primary PM2.5, resulting in fewer deaths and cases of acute and chronic bronchitis. This reduction in negative health effects translates to approximately $3.5 billion in annual health benefits.

Gas-fuelled furnaces and water heaters that vent combustion gases outdoors were identified as the primary contributors to outdoor air pollution from gas appliances.

Recommendations

The UCLA study authors recommend converting buildings to using highly efficient and pollution-free induction cooktops and heat pumps. In the interim, ensuring adequate ventilation and appliance maintenance is crucial. Range hoods, exhaust fans, and proper ductwork can help reduce indoor air pollution levels.

For new appliances, consider choosing electric or induction alternatives, which often outperform their gas counterparts without the associated risks. Financial incentives and credits are available in some regions to promote the adoption of clean electric equipment.

The health risks of gas use in California

California is taking steps to address the health risks associated with gas use, particularly in relation to gas stoves and other gas appliances. About 70% of California households use natural gas for cooking, and the state has proposed measures to regulate and reduce the use of these appliances. Here are some key points regarding the health risks of gas use in California:

Health Risks of Gas Stoves

Gas stoves emit pollutants that can irritate the airways and cause or exacerbate respiratory problems. One of the primary concerns is nitrogen dioxide (NO2), which is produced when natural gas is burned at high temperatures. Studies have linked indoor gas stove usage to higher rates of childhood asthma, and NO2 is a known respiratory irritant. In addition, gas stoves can leak unburned natural gas, which contains benzene, a known carcinogen. Fine particulate matter (PM2.5) created during cooking is also a known irritant and can contribute to respiratory issues.

Legislative Action in California

California lawmakers have passed a bill, AB2513, which would require health warning labels on gas stoves sold in stores and online. The warning labels would inform consumers about the potential health risks associated with gas stove usage, including the release of harmful pollutants such as nitrogen dioxide, benzene, carbon monoxide, and formaldehyde. The bill also highlights the increased vulnerability of young children, people with asthma, and individuals with heart or lung disease to the toxic effects of combustion pollutants.

Reducing Health Risks

To reduce the health risks associated with gas stove use, experts recommend improving ventilation. Using vent hoods or exhaust fans while cooking can help reduce the concentration of pollutants in the kitchen. Additionally, switching to electric stoves or induction cooktops is an option for those who can afford it. The Inflation Reduction Act offers rebates for purchasing new electric appliances. Regular maintenance and inspection of gas appliances are also important to minimise the risk of pollutant exposure.

Broader Efforts to Reduce Gas Use

California has taken steps beyond warning labels to address the health and environmental impacts of gas use. The state plans to ban the sale of gas heaters by 2030. Additionally, several cities in California, including Berkeley, have passed bans on natural gas hookups in new buildings. These efforts are part of a broader campaign to reduce pollution and transition to cleaner energy alternatives.

The effect of Rayleigh scattering on sunset colours

The vibrant colours we see at sunset are the result of a phenomenon called Rayleigh scattering. During the daytime, the angle of the sun allows mostly blue light wavelengths to pass through the atmosphere, giving us the blue sky we see every day. However, at sunset, the angle at which sunlight enters the atmosphere changes significantly, and most of the blue and green (shorter) wavelengths of light are scattered even before reaching the lower atmosphere, leaving us with more of the orange and red colours in the sky.

The phenomenon is named after the 19th-century British physicist, Lord Rayleigh (John William Strutt). Rayleigh scattering is the scattering or deflection of light by particles with a size much smaller than the wavelength of the radiation. For light frequencies below the resonance frequency of the scattering medium, the amount of scattering is inversely proportional to the fourth power of the wavelength. This means that blue light is scattered much more than red light as it passes through the air.

The blue colour of the sky is a result of three factors: the blackbody spectrum of sunlight entering the Earth's atmosphere, Rayleigh scattering of that light off oxygen and nitrogen molecules, and the response of the human visual system. The strong wavelength dependence of Rayleigh scattering means that shorter (blue) wavelengths are scattered more strongly than longer (red) wavelengths. This results in the blue and violet light that we see in the sky during the day and at twilight.

At sunset, light has to travel through a greater distance in the atmosphere, so even more blue light, and some green and yellow light, is filtered out. This leaves us with the warmer hues of the visible light spectrum, the reds and oranges, and is why many sunsets look like fire.

However, the presence of large particulate matter in the atmosphere, often caused by the combustion of fossil fuels, can make sunsets hazy instead of colourful due to its absorption and scattering of light.

The sources of indoor combustion pollutants

Unvented combustion appliances, such as gas stoves, kerosene heaters, and charcoal grills, are significant sources of indoor pollution as they release combustion pollutants directly into the home. Using charcoal grills or gas stoves for heating can be especially dangerous and produce very high levels of indoor pollutants.

Vented combustion appliances, such as furnaces, wood stoves, fireplaces, and gas water heaters, usually exhaust combustion pollutants directly outdoors. However, if the vent system is faulty or not maintained, indoor pollutants can quickly build up. Leaks or blockages in flues, chimneys, or vents can cause pollutants to spill into the home. Operating exhaust fans, fireplaces, or forced air heating systems with unbalanced airflows can also cause spillage.

Environmental tobacco smoke (ETS) is a major source of indoor particles and PAHs and contributes to other toxic pollutants and irritants. Burning incense, grilling foods, using the oven's cleaning cycle, and hobbies that produce smoke or flame can also increase indoor pollution levels.

House dust and soil can contain particles and PAHs, which can be inhaled, absorbed through the skin, or swallowed, particularly by young children who often play on the floor.

Outdoor air pollution from nearby wood stoves, fireplaces, motor vehicle traffic, outdoor barbecues, and gasoline-powered lawn equipment can also contaminate indoor air.

To reduce indoor combustion pollutants, it is essential to keep sources of pollutants out of the home and garage. If this is not possible, ensure proper ventilation, avoid using unvented or poorly vented sources, and never use gas stoves or ovens for heating. Regular maintenance and inspections of combustion appliances are crucial to identify potential problems and reduce indoor pollutant levels.

The role of aerosols in enhancing sunset colours

The vibrant colours of a sunset are the result of a phenomenon called Rayleigh scattering. During the day, when the sun is directly overhead, light travels through a relatively thin section of the atmosphere. However, as the sun sets, the light must travel through a longer path and is scattered by more air molecules.

The colours of the sky result from sunlight interacting with molecules in the air, primarily nitrogen and oxygen, which cause it to be deflected in all directions. All wavelengths of light are scattered, but they are not scattered equally. According to John W. S. Rayleigh's approximate scattering law, colours with shorter wavelengths are scattered the most: violet, followed by blue, then green, and so on.

By the time the light from the sunset reaches our eyes, most of the blue light has been scattered out of the beam, leaving behind the warmer hues of yellow, orange, and red, which blend into the reddish-orange colours of a sunset.

However, scattering by nitrogen and oxygen can only explain reddish-orange sunsets, not blood-red sunsets. To get a blood-red sky, you need aerosols. Aerosols are solid or liquid particles suspended in the air that originate from both natural processes and human activity. Natural aerosols include forest fire smoke, mineral dust, sea spray, and volcanic eruptions.

Human-generated aerosols, such as soot from internal combustion engines and sulfuric acid aerosols from burning fossil fuels, can also contribute to redder sunsets. These particles scatter light in a similar way to oxygen and nitrogen molecules, removing cooler colours like violet and blue from the spectrum and enhancing red hues.

However, it is important to note that an excess of large aerosol particles can dampen the overall sunset experience. When there are too many large particles in the troposphere, the closest layer of the atmosphere to the ground, the sunset can appear washed out as these particles scatter all colours indiscriminately, increasing overall brightness but reducing colour contrast.

Therefore, while aerosols can enhance the redness of a sunset, the presence of too many large aerosols can diminish the vibrancy and intensity of sunset colours.

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