AP: Lesson - Photochemical Smog (Topic 7.2) 📖
⏳ Estimated Reading Time: 4 - 6 minutes
Explain the causes and effects of photochemical smog and methods to reduce it.
Photochemical Smog
Photochemical smog is produced when nitrogen oxides and volatile organic compounds (VOCs) in vehicle exhaust are acted upon by sunlight. The word “photochemical” can be broken down into two parts: “photo” refers to “light” and “chemical” refers to chemicals found in pollution. “Smog”, on the other hand, is simply short for “smoky fog.” So, photochemical smog is smog that develops from primary air pollutants reacting and changing to secondary air pollutants in the presence of sunlight.
The main culprits in the formation of photochemical smog are nitrogen oxides (NOx) and volatile organic compounds (VOCs). NOx is produced by vehicles burning fossil fuels, power plants that burn fossil fuels, and industrial activities that involve chemicals and fossil fuels. VOC emissions come from several sources including evaporating gasoline and other fossil fuels, paint applications, dry cleaning products, cleaning products, formaldehyde, and aerosol sprays.
Photochemical smog is formed when nitrogen oxides and volatile organic hydrocarbons react with heat and sunlight to produce a variety of pollutants.
Volatile Organic Compounds (VOCs), such as formaldehyde and gasoline, evaporate or sublimate at room temperature. Trees are a natural source of VOCs.
The production of photochemical smog mostly occurs in cities and usually begins in the early mornings as commuters hit the road and businesses, industries, and workers ramp up for the day’s work. The pollutants begin accumulating in the atmosphere and the rising sun then adds heat and light to kick off the chemical reactions.
One of the primary secondary pollutants formed from these reactions is tropospheric ozone (O3). This ozone has the same chemical formulation as stratospheric ozone (also O3) but it is considered a negative because of its proximity to living organisms residing on the Earth’s surface.
Nitrogen oxides are produced early in the day but ozone peaks in the afternoon. Typically, the summer months are times with the most smog formation due to the sun’s intensity. Days with thermal inversions are notorious for their high levels of photochemical smog formation (more on thermal inversions in the next lesson!).
Photochemical smog often forms in urban areas because of the large number of motor vehicles there.
Many environmental factors affect the formation of photochemical smog.
Nitrogen oxide is produced early in the day. Ozone concentrations peak in the afternoon and are higher in the summer because ozone is produced by chemical reactions between oxygen and sunlight.
Because many people get confused about “good ozone” (ozone in the stratosphere) versus “bad ozone” (ozone in the troposphere), it’s handy to remember the saying:
“Ozone: good up high, bad nearby.”
Human Health Effects
Photochemical smog can cause a slew of health effects. Below are some of the most common effects of smog. Have you ever experienced these effects? I have asthma and, as a high schooler, my family visited Los Angeles. My eyes were itchy, and I coughed the whole time we were there!
🫁 Respiratory Irritation (click to reveal)
Even brief exposure to photochemical smog can lead to painful irritation of the respiratory system. It causes reduced lung function and makes breathing difficult. Individuals may experience chest pain, headaches, and throat dryness.
🤒 Pneumonia and Fatigue (click to reveal)
Prolonged exposure to photochemical smog can result in pneumonia, fatigue, and heart palpitations.
😮💨 Asthma Aggravation (click to reveal)
High levels of smog trigger asthma attacks by increasing sensitivity to allergens. Those with pre-existing health conditions, such as respiratory diseases, are particularly vulnerable.
👁️ Eye Irritation (click to reveal)
When ozone interacts with the eyes, it leads to irritation, burning sensations, redness, and itchiness.
Photochemical smog can harm human health in several ways, including causing respiratory problems and eye irritation.
Preventing Photochemical Smog
There are a number of actions that can be taken to reduce photochemical smog. These actions revolve around reducing the production of nitrogen oxides (NOx) and volatile organic compounds (VOCs). Below are a few ways we can reduce photochemical smog:
🚙 Driving less and carpooling when possible.
🏭 Avoiding machinery that runs off of fossil fuels.
🚇 Using mass transit.
🚶 Walking when possible.
⛽️ Refueling your fossil fuel vehicle in the evening helps avoid evaporation of fuel into the atmosphere. Many states have devices that restrict the evaporation of fuel during the fueling process.
💨 Turn off your car instead of idling.
💅 Avoid using nail polish, oil cleaners, paint strippers, air fresheners, and insect repellent.
🔌 Be mindful of your energy consumption.
🏡 Use non-motorized equipment for lawn and gardening chores.
In short, avoiding the production of smog-producing chemicals is effective in reducing photochemical smog.
Photochemical smog can be reduced through the reduction of nitrogen oxide and VOCs.
Remember, we WANT ozone up in the stratosphere, where the ozone layer is located. We DO NOT WANT ozone down in the troposphere, where we are located.
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