Ozone is a deceptively simple chemical that can have a tremendous amount of influence on living things. Understanding the mechanics of the ozone layer is crucial to recognizing the significance of problems caused by it. Knowing the facts is illuminating.
Ozone Layer Basics
The chemical formula for ozone is O3, according to the National Oceanic and Atmospheric Administration (NOAA). National Geographic (NatGeo) indicates that a molecule of ozone literally consists of a trio of oxygen atoms.
In some ways whether ozone is dangerous or beneficial depends on its location in the atmosphere. NatGeo indicates that ozone molecules are extremely reactive. The reactivity of ozone molecules has costs and benefits noted by NOAA:
- Lower and upper molecules - The lower and upper layers of the atmosphere both contain the same ozone molecules.
- Number of molecules - For every 10 million molecules of air, there are three ozone molecules.
- Good vs. bad ozone - Ozone in the upper atmosphere is called stratospheric ozone and helps protect living things from UV-B radiation and is widely called "good ozone." Ozone in the lower atmosphere, the troposphere, functionally acts as a contaminant, and is the "bad ozone."
As their name indicates more of good and less of bad ozone is ideal, however pollution has led to a reversal of this trend with various ecological and health impacts.
Tropospheric Ozone Facts
Only 10% of the ozone in the atmosphere is in the lower atmosphere where much of life on earth occurs, according to Penn State University. According to the Environmental Protection Agency (EPA Air Quality), ozone is one of the most common air pollutants. There was always some ozone in the lower atmosphere. It is human activities that have increased its concentration making it a problem.
The EPA (Ozone) explains that ozone is not released directly by any source. It is formed in the atmosphere when oxides of nitrogen (NOx) and other volatile organic compounds (VOCs) react in the presence of sunlight. It is for this reason that ozone production is higher in the afternoon. Emissions from fossil powered automobiles and power plants, and refineries that produce oxides of nitrogen and hydrocarbons lead to an increase in ozone.
Tropospheric ozone has many harmful effects on people and ecosystems.
Tropospheric ozone causes smog. Some important facts about it are:
- Concentration - Since human activities are responsible for the formation of ozone, its concentrations are higher in cities and villages compared to rural areas, notes Penn State University.
- Ozone paradox - The nitrogenous compounds that result in production of ozone also break it down, so there is more smog in villages than cities, because cities have higher concentrations of nitrogenous compounds in the air. This is called the "ozone paradox" by scientists, and is the reason for the "weekend effect," when ozone levels rise due to less traffic on weekends, according to a Belgian Environment release.
The bad ozone has deleterious effects on people.
- Worst affected - The Center for Disease Control and Prevention (CDC) states that children, elderly and people with lung problems are the worst affected by ozone. It can lead to breathing trouble, wheezing, asthma, lung damage and even death.
- Deaths per year - Berkeley Lab estimates that 150,000 pre-mature deaths every year can be attributed to ozone pollution.
- Harmful concentration threshold - The threshold level of 0.1 parts per million (ppm) of ozone concentrations can be harmful to people, according to CDC (Occupational Hazards) (pg. 1).
- Indoor pollution - Ozone pollution can occur also indoors where '45% to 75% of total exposures' occur according to Berkeley Lab
Environmental and Ecosystem Effects
Ozone impacts plants in more than one way. The USDA considers that bad ozone is the air pollutant that affects plant health more than "all other air pollutants combined."
- Plant growth - Iowa Department of Natural Resources notes that ozone affects the ability of plants to breathe by closing the stomata or small pores present on the underside of leaves. It is also through these stomatas that carbon dioxide necessary for photosynthesis and food production enter. So plant growth is affected.
- Tissue damage - Ozone damages and injury's the tissue of plants due to necrosis and chlorosis, as it is a strong oxidant, points out USDA. The result can appear as "stippling, flecking, bronzing, and reddening."
- Yield reduction - The combined result of both effects of ozone is a loss in crop yield. NASA reports around 5-10% yield reduction in crops. Dicots like soyabean are more susceptible to ozone than monocots like corn. For example, in 2014, India lost 6.7 million U.S. tons of crops to ozone pollution, which would have been enough to feed 94 millions, according to AtmosNews.
- Soil fertility - When plants produce less food due to less photosynthesis, they send and store less carbohydrates in the roots. When the plant dies, less carbon is released into the soil, decreasing populations of microbes dependant on it. Many of these microbes are necessary for recycling nutrients in the soil and maintaining fertility. So soil fertility also decreases when ozone levels are high according to NASA.
- Forest - NASA reports that forests are also affected by ozone pollution, but these have been more difficult to determine.
- Global warming - Tropospheric ozone is the third major greenhouse gas, after carbon dioxide and methane notes NOAA (GHG), that leads to global warming.
Stratospheric Ozone Layer
The good or stratospheric ozone layer is situated 9.3 to 18.6 miles above the planet's surface, according to NatGeo. Here lies 90% of the ozone in the atmosphere according to Penn State University.
Maintaining a functioning stratospheric ozone layer is essential for life on earth. A large portion of the sun's radiation is actually harmful, namely the ultraviolet radiations (UV rays). Life in all its present complexity would not have been able to develop without the protection of the ozone layer.
Damage to the Ozone Layer
Problems with the ozone layer have received a great deal of publicity and attention since they were first identified. In the 1980s scientists discovered that the ozone layer was thinning at the poles. Soon the connection between use of chlorofluorocarbons (CFCs) and ozone depletion was made, explains the Union for Concerned Scientists (UCS). This is how CFCs deplete ozone:
- CFCs which were widely used in refrigerators, air-conditioners and aerosols are compounds that contain chlorine and fluorine, explain the American Chemistry Society. Though CFCs were inert in the troposphere, they were broken down by the UV rays in the stratosphere, and released chlorine.
- Chlorine from CFCs reacted with the oxygen from ozone destroying the ozone molecules. This process is at its maximum in polar regions where ozone concentrates due to global wind movement. NatGeo indicates that the Antarctica has been especially vulnerable to ozone layer degradation, largely because the low local temperatures accelerate the chemical reaction that breaks CFCs down into chlorine.
- Ozone Hole reports that a single atom of chlorine from CFCs can destroy over 100,000 molecules of ozone.
Ozone depletion can have devastating consequences.
Climate in various parts of the world has been affected not so much by decrease in ozone as by the presence of polar ozone holes.
- Rainfall patterns - The presence of the ozone hole at Antarctica for example has altered tropical rainfall patterns according to a 2017 scientific study reported in Phys.
- Ozone hole and global warming myth - Contrary to common belief, the hole in the ozone layer over the two polar regions does not cause global warming, point out the UCS, even though both the phenomena are caused by the same causes.
Ozone depletion affects both terrestrial and marine life, because it increase the amount of UV radiation that reaches the earth.
- Lessened resistance to pests/diseases - The EPA (Effects) notes physiological and development processes of plants can be disturbed which in turn decrease plant growth, and their resistance to pests and diseases.
- Pollination and insect effects - NASA (Effects) (Effects) reports that flowering times of plants can be affected by UV rays, which if it does not occur in synchrony with insect life-cycles affects pollination and also the insects dependent on them.
- Phytoplankton survival issues - The effect on aquatic life depends on the depth at which they live. Unfortunately, phytoplanktons which live near the water surface to make use of sunlight, have been reported to be affected by UV radiation increases. Their survival is reduced which shrinks their populations note EPA (Effects). Since planktons are the basis of the marine food chain, their decrease affects all other trophic levels of marine life.
- Marine animal development hindered - Marine animals, like fish and amphibians, also suffer because their early development processes are disrupted by UV rays, explains EPA (Effects).
- Less carbon capture by plants - When plant production on land and aquatic systems is affected biogeochemical processes especially those connected to carbon production are also affected. Less plant growth means less carbon capture overall, adding to global warming notes EPA (Effects).
Health Concerns Related to Ozone Layer Depletion
Without a stable ozone layer, humans are that much more vulnerable to ultraviolet radiation.
- Cancer and immune system - According to the World Health Organization, ultraviolet radiation can decrease immune function and increase rates of cancer.
- Skin cancer - 1% increase in UV radiation increases skin cancer by 2-3% according to NASA (Effects).
- Eye problems - Over-exposure to UV radiation causes many eye problems, like cataract, and snow blindness, according to NASA (Effects).
Restoration Efforts for the Ozone Layer
Damage to the ozone layer has received considerable attention from environmental groups and political leaders worldwide.
- The international Montreal Protocol, was first signed in 1987, to ban use of CFCs and it has been modified numerous times since, according to United Nations Environment Program (UNEP).
- A new class of chemicals called dichloromethane used in solvents and paints have been found to damage the ozone as they can be broken down by sunlight to produce chlorine, a study in 2017 reports. Since they can rise to the stratosphere, they can slow down ozone restoration.
Ozone Layer Is Recovering
The Montreal Protocol which was strictly implemented by nearly all the nations of the world has paid off. The hole in the ozone layer over Antarctica has been decreasing according to the timeline expected by scientists, according to a National Geographic (2016) report.
The hole in the ozone used to start appearing in August and reach its maximum size in October. Scientists from MIT and Leeds found that in 2015 the hole started to appear later, and was not as deep as before, and had shrunk considerably. The ozone hole which was at its largest in 2000, had shrunk by 4 million square kilometers in 2015. The ozone layer is expected to recover completely by 2050.
Ozone in the Twenty-First Century
When the stratospheric ozone layer makes a full recovery, it is possible that the situation will be regarded as an environmental success story. However, the facts about the ozone layer demonstrate just how vulnerable it is, and just how much the ozone layer can be affected by changes in public policy and human habits. Meanwhile the problem of the tropospheric ozone remains with its level 30% more in the post-industrial era, according to NOAA (GHG).