When I first read about this topic, there was a chemical product that directly came up in my mind: ozone! Ozone gas consists of three oxygen atoms (O3) and is found in two different sites: in the atmosphere (stratosphere) and on the ground level. Its location determines the role of ozone and the formation process is different too. Ozone formed in the atmosphere is called stratospheric ozone. This is naturally created from the interaction of ultraviolet radiation from the sun with oxygen molecules (O2). On the other hand, ground-level ozone is called tropospheric ozone. This is formed mainly from photochemical reactions between two air pollutants, nitrogen oxides (NOx) and volatile organic compounds (VOC). As the term “photochemical” indicates, sunlight and heat is a major component that determines the concentration of tropospheric ozone, meaning typically a higher ozone concentration in summer months. 

Then, what is the positive effect of ozone on the environment and the earth? Good role of ozone is carried out by stratospheric ozone. It is a sunscreen of the Earth as it forms the ozone layer that is 9 to 22 miles above the ground, blocking harmful UV radiation from reaching the earth surface. This protects living things including humans from too much exposure to UV light, which could cause skin cancer and cell damage and inhibits the growth of almost all green plants. Also, there is concern that depletion of ozone may lead to a reduction of plant species and global food supply. However, as well known, ozone has been damaged and made “holes” from the emission of ozone depleting substances (ODS) such as chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, and methyl bromides, introducing more UV lights into the atmosphere and the geosphere. One good news revealed by a recent study is that ozone is healing itself. In 2016, scientists observed that stratospheric ozone concentration kept increasing and the size of the ozone hole in Antarctica has decreased by half between 2000 and 2015.

The negative side of ozone can be found in tropospheric ozone. As it is formed due to emission of ODS, it is more likely to occur in urban cities, but it can also travel long distances by wind, meaning rural areas can experience high ozone concentration. Tropospheric ozone is more common to us than stratospheric ozone is since it contributes to haze, also known as “smog”. The Environmental Protection Agency explains that exposure to ozone levels greater than 0.00000007 for more than 8 hours is unhealthy, which entails bronchial issues such as lung and throat irritation or aggravation of asthma. Considering such ozone concentration normally occurs in cities during warm periods, it is pretty harmful to humans. Ozone also affects some sensitive vegetations and ecosystems like wilderness areas, forests, and parks especially during the growing season. For example, ozone reduces photosynthesis rate, which slows the plant’s growth and increases the risk of disease and effects of other pollutants.

Citation

“Ground-Level Ozone Basics.” EPA, Environmental Protection Agency, 13 July 2020, www.epa.gov/ground-level-ozone-pollution/ground-level-ozone-basics.

“Ozone-Depleting Substances.” EPA, Environmental Protection Agency, 31 July 2018, www.epa.gov/ozone-layer-protection/ozone-depleting-substances#:~:text=ODS include chlorofluorocarbons (CFCs),,ultraviolet light in the stratosphere.

“Ozone Layer Protection.” EPA, Environmental Protection Agency, 19 Mar. 2020, www.epa.gov/ozone-layer-protection.

“What Is Ozone?” EPA, Environmental Protection Agency, 23 June 2020, www.epa.gov/ozone-pollution-and-your-patients-health/what-ozone.