Ozone is a pale blue gas formed via chemical reactions between natural and man-made emissions. It contains three oxygen atoms. There are two types of ozone in the earth’s atmosphere: ground-level ozone and stratospheric ozone.
Ground-level ozone (a.k.a. smog) forms around the lower atmosphere just above the earth’s surface. Also known as tropospheric ozone, it affects plant, animal, and human life in diverse ways.
Ground-level ozone’s concentration level is lower than that of stratospheric ozone. Still, it can hugely influence biological processes in a given environment. Ground-level ozone is weather dependent. Its concentration is often highest on warm days with low humidity and light wind.
Stratospheric or atmospheric ozone typically forms six to thirty miles above the earth’s surface. The ozone concentration in this portion of the atmosphere can reach 12,000 parts per billion (ppb).
To understand the scale of stratospheric ozone concentrations, you should keep in mind that the Environmental Protection Agency (EPA) has a limit of 70 ppb as the ozone threshold for human health and welfare.
Atmospheric ozone is vital to continued life on earth because it functions as a protective barrier. The ozone layer’s high concentration levels shield all life and inanimate objects from the harsh impact of the sun’s ultraviolet rays.
Without the ozone layer, UV radiation would increase the risk of skin cancer. Instead of being a source of warmth, the sun would lead to many harmful effects.
Is Ozone Good or Bad?
Stratospheric ozone is good because it protects the earth from ultraviolet radiation. It’s no surprise that maintaining stratospheric ozone concentrations is a primary concern when the EPA and other bodies push the importance of reducing pollution levels.
However, ground-level or tropospheric ozone is bad above the 70-ppb threshold following exposure to such ozone concentrations for eight hours or more. Beyond 70 ppb, tropospheric ozone can cause a range of health problems.
What Is Ozone Pollution?
Ozone pollution refers to unhealthy ground-level ozone concentrations. The EPA and like-minded legislative bodies continue to work hard to educate citizens on how industrial processes and other human activity cause ozone pollution.
What Is the Source of Ozone?
Oxygen atoms, volatile organic compounds (VOCs), nitrogen oxides (NOx), and ultraviolet rays interact to produce ground-level ozone.
The gases that escape smokestacks, tailpipes, and other such sources react with three oxygen atoms in the presence of ultraviolet rays to form ozone (smog). The nitrogen oxides (NOx) and volatile organic compounds (VOCs) that combine to form tropospheric ozone come from:
- Power plants
- Motor vehicles
- Chemical plants
- Gas stations
The oxygen molecules come from various biochemical processes taking place in nature, such as photosynthesis. Under the right conditions and in the presence of sunlight, the ingredients will combine to form tropospheric ozone.
Stratospheric ozone forms naturally following the interaction between ultraviolet radiation and molecular oxygen.
Who Is Most at Risk From Breathing Tropospheric Ozone?
Everyone outdoors in areas where ozone air pollution levels are very high is at risk of breathing in tropospheric ozone and experiencing negative effects. However, the following groups of people are most vulnerable to the effects of breathing ozone:
- Children and teenagers
- People aged 65 and older
- People with existing respiratory problems such as chronic bronchitis, emphysema, asthma, and other chronic obstructive pulmonary diseases (COPDs)
- People who exercise outdoors regularly
- People living with obesity
The impact on your health following exposure will come down to several factors. For example, people exercising or working out will breathe in more air and, consequently, more ozone.
Second, ozone concentrations will fluctuate from time to time. It’s impossible to experience the same levels over prolonged periods.
Are Tropospheric Ozone Levels Higher in Urban Areas?
The concentration of tropospheric ozone levels is not just high in urban areas. The reaction that leads to ozone formation takes place in the atmosphere. Thus, ozone concentrations can spread anywhere.
In many cases, the ozone moves downwind from the origin of the gases. So, the winds can carry the ozone far from where it formed originally—sometimes across international borders.
Therefore, while we expect large metropolitan areas like New York City, Atlanta, and Los Angeles can have high levels of ozone, small cities and rural areas are not immune. In areas with high levels of ozone, the concentration is at its peak during the afternoon when the sun is also at its strongest.
However, areas downwind from cities that are the main sources of NOx and VOCs may experience higher ozone concentrations in the evening. Ground-level ozone levels may be high at any time of the day for people living in big cities and those in rural areas.
How Tropospheric Ozone Exposure Occurs
Tropospheric ozone exposure happens when people breathe in ambient air that contains a high level of ozone. The level of exposure for any individual comes down to the volumes of air they are breathing per minute, the tropospheric ozone concentrations in the surrounding air, and the exposure duration.
Ozone exposure levels will also vary across different microenvironments. For example, the exposure levels while exercising outdoors will vary compared to the levels obtainable while inside a vehicle or relaxing in an indoor space.
Keep in mind that people tend to breathe more deeply during physical activity. Consequently, uptake can reach deeper parts of the respiratory system faster when breathing ozone-laden air. The result is faster development of adverse health effects.
In many cases, the difference between outdoor and indoor ozone concentrations can be as high as 80%. Your exposure to ozone is the lowest if you’re indoors for most of the day in an airconditioned space with limited air exchange.
The Impact of Short-term Tropospheric Ozone Exposure
The main physiological effect of exposure to tropospheric ozone in the short term (up to eight hours) is a significant reduction in lung function that bars you from breathing to full capacity.
Several experiments show that exposure to high tropospheric ozone concentrations can reduce the volume of air you exhale per second. Other respiratory symptoms may follow, such as:
- Chest tightness
- Throat irritation
- Shortness of breath
- Pain, discomfort, or burning sensation when breathing
Ozone reacts with neurons in the respiratory pathways to cause these changes. These effects generally reverse, and respiratory function reverts to baseline levels 48 hours after exposure to ozone.
Research shows that the changes in lung function and the symptoms that follow prolonged exposure are due to ozone’s stimulation of neural receptors in the airways. It may also affect the central nervous system.
How Tropospheric Ozone Reacts in the Respiratory System
Tropospheric ozone doesn’t dissolve fully in water. Therefore, the upper respiratory tract can’t remove ozone from inhaled air with the same efficiency as water-soluble pollutants like chlorine gas or sulfur dioxide.
On days of high ozone concentrations, the bulk of the inhaled ozone will reach the lower respiratory tract.
Inside the lower respiratory tract, ozone dissolves into the epithelial lining of the lungs. Once inside, the compound reacts quickly with several biomolecules. The result of the reaction can trigger myriad long-term and short-term respiratory problems.
Impact at the Cellular Level
Ozone injures the epithelial cells in your airways in addition to other knock-on effects. Medical practitioners measure the effect of the damage by using a technique known as bronchoalveolar lavage (BAL) or bronchoalveolar washing.
The one administering the procedure collects samples of the epithelial lining fluid (ELF). The biochemical markers and cells in the sample provide insight into the level of exposure. Some of the key signs of airway inflammation after exposure to ozone are:
- A clear redness of the airway
- An increase in the presence of neutrophils in the ELF
- An increase in the levels of the enzyme lactate dehydrogenase (LDH)
Airway injury and inflammation cause the following responses:
- An increase in small airway obstruction
- Increased nonspecific airway reactivity
- Decreased airway epithelium integrity
Some of these responses to airway injury and inflammation may be of little significance in healthy individuals. On the other hand, the responses can be problematic for people with respiratory problems. For example, increased airway reactivity can lead to strong asthma symptoms (more on this later), lung tissue problems, and more.
Does Short-term Exposure to Tropospheric Ozone Affect All Individuals the Same Way?
Reactions to short-term exposure vary significantly between individuals. For instance, for a group of people exposed to the same amount of ozone and under the same conditions (perhaps 30 minutes of exercise), the results aren’t likely to be the same.
The least affected from the exposure will not show any reactions at all. On the other hand, the most affected will experience up to a 50% drop in lung function, shortness of breath, severe coughing, painful inspiration, and more. The results are the same at different levels of exposure.
People who react heavily to exposure at any point will likely have strong reactions following re-exposure at similar levels. Conversely, people with small or muted reactions to exposure at one point are unlikely to show any strong reactions following re-exposure.
Some research attributes the varied exposure reactions to factors such as age and body mass index (BMI). Younger adults (< 40 years) and people with a high BMI show stronger reactions to exposure than older adults (> 50 years) and other people with a low BMI.
However, other researchers suggest that we can link the level of ozone responsiveness to environmental or genetic factors.
Early evidence from research on different strains of mice suggests that some people may have genes that allow the body to better control the inflammatory response.
A further example of how people react differently to exposure is visible in the drug intervention research around the problem:
- Vitamin C and E supplements can reduce the lung function effects of ozone in some people without reducing the inflammatory responses.
- Non-steroidal anti-inflammatory drugs (NSAIDs) can prevent lung function decrease and symptoms in non-asthmatics but will not reduce the inflammatory responses.
- Inhaled steroids reduce the symptoms of exposure in people with asthma but not those without asthma.
The Impact of High Levels of Tropospheric Ozone on Society
Studies have shown that high concentrations of tropospheric ozone in an environment over a specific period lead to more emergency room visits. There’s usually an increase in hospital admissions due to respiratory problems.
People living with underlying respiratory diseases are at an increased risk of hospital admissions during this period. Most such patients show signs of worsening asthma, existing lung diseases, and, in some cases, chronic obstructive pulmonary disease (COPD). These patients often require medical treatment.
Other patients present varying subcategories of respiratory diseases. However, researchers have yet to make the connection to these diseases because of the insignificant number of hospital admissions.
Some studies have also linked ground-level ozone to increased hospitalization for cardiovascular diseases. Others have tried to establish a link between high ozone levels over a given period to changes in heart rates. However, all the findings remain inconclusive.
Some studies have drawn parallels between high ozone concentrations over a given period and increased school absences. However, these studies are inconclusive because some of the absent students didn’t have any illnesses.
At What Levels of Exposure Does Tropospheric Ozone Become Harmful?
The level of exposure that can cause visible symptoms will vary from person to person. We all have different ozone sensitivity levels. Also, the actual dose delivered to the respiratory tract will vary.
The exact dose will come down to the duration of exposure, the activity level, and the tropospheric ozone concentration levels. Therefore, you may react to lower ozone concentrations while engaging in strenuous activities like hiking. On the other hand, you can also relax indoors in an air-conditioned space on days with higher ozone concentrations with little or no reaction.
Keep in mind that people with a higher ozone sensitivity can feel the effects of ozone inhalation at lower concentrations. Less sensitive people will only experience the effects of ozone inhalation at higher concentrations.
The Effects of Long-term Exposure to Tropospheric Ozone
The effects of chronic exposure to ground-level ozone are a contentious issue. Despite an increasing amount of research on the topic, the findings remain inconclusive.
Some studies show that chronic exposure to high ozone concentrations for four days can reduce the severity of symptoms following new exposure weeks down the line.
Therefore, some health professionals believe that individuals living in areas with high levels of ozone may already have some protection against prolonged exposure.
However, BAL tests show that the process of inflammation, airway injury, and subsequent repair continues with repeated exposure.
Even after multiple days of exposure, the signs of cell injury remain high. Some studies also found that the depression of airway function continued through the period of exposure.
Various studies using laboratory animals showed that long-term exposure to high ozone levels leads to morphological changes consistent with chronic respiratory disease. Some of these changes include:
- Epithelial cell hyperplasia
- Mucous cell metaplasia
- An increased presence of fibrous tissue in the lower airways
- Modification of the distal conducting airways
However, despite the inconclusive findings about the long-term effects of ozone, it clearly does some harm.
The cycle of inflammation, injury, and repair in humans and the morphological findings in animals suggest that it’s best to avoid repeated exposure to high ozone concentrations.
Prolonged exposure can cause lung diseases, respiratory infections, and more.
How Tropospheric Ozone Affects People Living With Asthma
Patients living with respiratory conditions like asthma tend to have a stronger reaction following exposure to ground-level ozone.
There are two reasons for such a strong reaction. First, the response to ozone can interact with the underlying disease’s pathophysiology. Second, the impact of asthma on the respiratory system makes the effect of ozone a lot stronger.
Thus, asthma patients can’t cope with decreased lung function, which is one of the first symptoms of excessive ozone inhalation. People with asthma experience the following when ozone levels are high:
- Increased use of health care services
- Increased frequency of asthma attacks
- Increased medication usage
- Increased respiratory symptoms
- Decrease in lung function
Children are most at risk when looking at ozone’s impact on asthma. The prevalence of the condition is especially high in this demographic, and they spend a lot of time exercising outdoors. Therefore, their asthma episodes may worsen on days when the ozone in the atmosphere is at very high levels.
Some epidemiological studies suggest that long-term exposure to ozone may cause otherwise healthy individuals to develop asthma. The data from these studies remain inconsistent, but long-term exposure to ozone in young laboratory animals led to significant changes in their respiratory tracts.
In adult animals, ozone exposure increases their sensitivity to asthma-causing allergens.
How To Protect Yourself From Ground-level Ozone Pollution
There is no one-size-fits-all solution to protecting yourself from ground-level ozone pollution. As we covered above, ozone level sensitivity varies from one person to another. However, there are general guidelines you can follow, which we detail below.
Check the Air Quality Index Frequently
As the name implies, the air quality index is a tool United States government agencies use to communicate the pollution levels of the air around you. You should make it a habit of checking the index before you head out for any particular day.
Pay attention to the colors of the air quality index:
- Green and yellow: The air quality in the lower atmosphere is good or moderately polluted. Anyone can inhale the air with almost no worries.
- Orange: The air quality is unhealthy for sensitive populations.
- Red: The air is unhealthy for the general population.
- Purple: The air quality is very unhealthy for the general population.
- Brick red: The air is extremely hazardous to breathe in, with a high level of particle pollution.
Stay Indoors on Days of High Tropospheric Ozone Concentrations
If the color on the air quality index is orange or worse, you should consider staying indoors. You can work from home if you have that option or simply limit the number of hours you spend in unconditioned spaces to the barest minimum on days of peak concentrations.
Don’t Exercise in High-traffic Areas
You are sure to find near-peak concentrations of air pollutants in high-traffic areas. Even when the air quality index is green, inhaling the fumes and dust in such areas can increase your sensitivity to ground-level ozone.
Increased sensitivity can make days with moderate to high ozone concentrations more challenging than usual.
Use Air Quality Improvement Products
Tropospheric ozone, volatile organic compounds (VOCs), and nitrous oxides (NOx) are constantly floating around the atmosphere, even within indoor spaces. You can make the air inside your home healthier by investing in air quality improvement tools.
Air cleaners, energy recovery ventilators, humidifiers, and UV light can help lower the ozone within your indoor air. They can also lower the quantity of volatile organic compounds (VOCs), nitrous oxides (NOx), and other air pollutants within any indoor space.
The Importance of Stratospheric Ozone
Stratospheric ozone in the earth’s upper atmosphere (ozone layer) is essential for life to exist. The molecules act as a shield, protecting the earth from solar radiation. When the radiation reaches the stratospheric ozone, the layer deflects some of it, making sure that only a minimal amount of radiation can reach the earth.
However, in recent times, some holes have formed in the stratospheric ozone layer due to natural ozone fluctuations and human activity.
Gases from chemical plants, power plants, vehicles, and other such sources end up in the stratosphere. Once there, they degrade the ozone molecules, increasing the size of the ozone hole.
The Environmental Protection Agency, the United States government, and other governments worldwide are taking action and driving policies to prevent damage to the ozone layer.
Excess UV light or solar radiation can cause skin cancer and many other health problems. It can also destroy plant and microbial life.
Substances Responsible for Ozone Layer Depletion
The substances responsible for the depletion of the ozone layer in the earth’s upper atmosphere include:
- Chlorofluorocarbons (CFCs)
- Carbon tetrachloride
- Hydrochlorofluorocarbons (HCFCs)
- Methyl chloroform
- Halons (brominated fluorocarbons)
Halons can deplete the ozone layer ten times faster than other substances on the list. Fortunately, there is a limit to their usage. You can only find the substance in certain fire extinguishers.
Natural Causes of Depletion of the Ozone Layer
Scientists have noted that certain natural phenomena, including stratospheric winds and sunspots, affect the ozone layer. However, these natural causes only contribute to one to two percent of ozone depletion, and the effects are often temporary.
Major volcanic eruptions also contribute to ozone depletion.
Places With Thin Ozone Layers Around the World
Parts of the world where the ozone layer has depleted a great deal include:
- Australia and the rest of the mid-latitudes. Scientists estimate that the ozone layer in these regions has depleted by up to 10%.
- Antarctica. The layer over Antarctica is significantly thinner compared to other areas. The thinness is more pronounced between September and November when ozone holes appear over the region.
The Health and Environmental Impact of Stratospheric Ozone Layer Depletion
As mentioned above, ozone depletion means we have less protection from the sun’s rays across the earth’s surface. We are also more exposed to ultraviolet B (UVB) radiation. Increased levels of UVB radiation affect life on earth in diverse ways.
Impact on Human Health
Many studies show that high levels of UVB play an important role in the onset of malignant melanoma. They also cause non-melanoma skin cancer and cataracts, which can cloud the eye’s lens.
Without enough ozone, the incidence of these health conditions will increase.
Impact on Plant Life
UVB radiation entering the earth’s atmosphere affects developmental and physiological processes in plants. Some plants have developed mechanisms to fight the impact of these effects, but increased levels of UVB can significantly affect plant growth. Some of the indirect changes to plant life due to higher levels of UVB include:
- Changes in plant form
- Changes to nutrient distribution within the plant
- Changes to the timing of developmental phases and secondary metabolism
The changes will invariably affect the plant’s competitiveness, rendering it vulnerable to disease. These changes in structure can also make the plant more attractive to herbivores.
Impact on Marine Life
Phytoplankton are at the heart of aquatic food webs. However, they only thrive in the upper layer of the water bodies (also known as the euphotic zone), where there is just enough sunlight to support their productivity.
Exposure to UVB radiation affects the motility of phytoplankton. It’s harder for these organisms to survive under such conditions. Scientific research has highlighted a direct reduction in the phytoplankton population due to higher UVB levels following ozone depletion.
UV radiation also causes damage to shrimp, fish, amphibians, crabs, and other marine organisms in their early development phases. The most common effects include impaired larval development and reduced reproductive capacity.
Impact on Natural Chemical Reactions
Increased UVB Radiation affects a wide range of chemical reactions on land and in the water, thus changing the natural sources and sinks for greenhouse and other important trace gases such as:
- Carbon monoxide
- Carbon dioxide
- Carbonyl sulfide
- Single oxygen atoms
The changes can alter the biosphere-atmosphere feedback for these gases. This leads to a change in their concentration levels within the atmosphere.
What Are the Ways To Protect the Stratospheric Ozone Layer?
We can protect the ozone layer by working together to reduce carbon emissions. The United States government and other official agencies worldwide have committed to lowering our collective carbon footprint. However, we can all do more.
Below are some of the things you can do.
Stop the Consumption of Gases That Are Dangerous to the Ozone Layer
These gases are dangerous because of their manufacturing process and content and include nitrous oxide, methyl bromide, halogenated hydrocarbon, and CFCs (chlorofluorocarbons). Some such gases combine in the presence of sunlight to form ground-level ozone, while others lower the stratospheric ozone concentrations in the affected areas.
Avoiding processes that require the use of these gases or seeking alternatives will help the ozone concentration on both atmospheric extremes.
Minimize the Use of Cars
Cars contribute significantly to air pollution. Consider alternatives whenever possible, including public transport, cycling, and walking. In scenarios where you have to drive to a location, you should consider carpooling to decrease the number of cars on the road and avoid worsening pollution.
Stop Burning Fossil Fuels
Burning fossil fuels leads to NOx emissions. You should look to cleaner sources of energy whenever possible. Consider installing solar systems to harvest some UV radiation and power your systems.
You should also choose electric appliances wherever possible, from your choice of lawnmowers to your HVAC systems. For example, furnaces can contribute to NOx emissions, while heat pumps are eco-friendly.
If you can afford it, consider buying an electric car. Apart from the fact that it will help you navigate these times of high fuel costs, you will reduce your carbon footprint significantly.
Many antagonists of electric vehicles (EVs) have questioned the claims that they are more eco-friendly. They argue that EVs still consume a lot of electric energy, which often comes from burning coal.
However, there is no denying that switching from a combustion engine to an electric variant reduces your carbon footprint.
Use Eco-friendly Cleaning Products
Harsh cleaning products are harmful to your health and the environment. Most of them contain solvents and other corrosive substances. Look for eco-friendly products or use homemade cleaning agents containing baking soda, vinegar, and bicarbonate.
Buy Local Produce
You can reduce your carbon footprint and contribution to air pollution by buying local products. This way, you will get fresh products and discourage transportation across long distances.
As vehicles and airplanes travel more, they contribute to higher levels of nitrous oxides (NOx) in the atmosphere. This worsens ozone layer depletion and contributes to higher ground-level ozone concentration. By shopping locally, you can do your part in reducing the problem.
Maintain Your Air Conditioners
Leaking refrigerants and general AC malfunction contributes to higher levels of CFCs in the atmosphere. Call an HVAC maintenance expert to look over your air conditioners at least once a year.
Avoid the Use of Pesticides
Pesticides are effective at getting rid of farm pests and weeds. However, they adversely affect human health and can contribute significantly to stratospheric ozone depletion. Consider weeding your farm manually and only use eco-friendly weed removal products when manual weeding just can’t cut it.
Avoid the Use of Nitrogen Oxides
Some of the actions and campaigns against gases and compounds that cause stratospheric ozone depletion focus on limiting the use of chlorofluorocarbons (CFCs).
However, nitrous oxide doesn’t receive the same level of attention, and it’s a major ingredient that reacts with oxygen atoms to form ground-level ozone.
You need to do your part by avoiding the use of nitrogen oxides or any other products that will lead to their release as much as possible.
Join Climate Change Pressure Groups
The impact of stratospheric ozone depletion and ground-level ozone pollution on the world means we need all hands on deck to help more people rethink their carbon footprint.
With millions more people understanding the need to save the planet, we can continue the march toward a greener and safer earth.
If you don’t want to worry about breathing ozone or the increased risk of UV radiation, you need to push the climate change message within your circle of influence and encourage others to do the same.
Refineries, chemical plants, power plants, and other such establishments need to be more eco-friendly.
Ozone concentrations in the stratosphere and troposphere are important for very different reasons. High levels of tropospheric ozone cause many respiratory problems, while lower levels of stratospheric ozone jeopardize all biological processes.
Awareness is just the first of many steps toward making a genuine difference. By turning knowledge into action, we can leave this world better than when we found it for generations to come.