Human life has always resulted in the emission of pollutants into the earth’s atmosphere, and natural pollutants have always existed as well. The ecological balance was maintained by the self-cleansing and recycling capacity of earth, however, because of the relatively small number of human processes leading to pollution.
The advent of the industrial revolution and the sheer speed of technological development have led to a dramatic upsurge in the level and variety of pollutants that are spewed into the atmosphere in the last 150 years. This trend is obviously disturbing, considering that there is only one planet available to us to live on!
What is a Pollutant?
A pollutant is any substance that is directly or indirectly harmful to mankind or to the environment.
Types of Pollutants
All pollutants can be classified into two categories: primary pollutants and secondary pollutants.
Primary air pollutants are pollutants that are released directly into the atmosphere, such as smoke or chemicals vented from manufacturing plants.
Secondary pollutants, on the other hand, are pollutants created when one or more primary pollutants react. These are are often deadlier than the primary pollutants. An example of a secondary pollutant is tropospheric ozone.
Natural ozone (O3) exists in huge amounts in our atmosphere: it is vital to life on the planet, because it blocks almost all of the ultraviolet rays from the sun. However, ozone is extremely toxic. Fortunately, almost all the ozone in the atmosphere is stratospheric, at between ten and fifteen kilometers above sea level - much too high for any significant interaction with earthbound organisms.
Ozone may be created when air pollutants such as carbon monoxide, hydrocarbons and nitrogen oxide interact in the presence of sunlight. This ozone is present near ground level, making it extremely dangerous to living tissues.
Hazardous pollutants are either primary or secondary pollutants that are severely toxic even at low concentrations. Most of these are strictly regulated by law: however, harmful concentrations have been reported in some regions.
Some common hazardous pollutants are mercury, benzene, dioxins, and lead compounds. All of these, except the last, are emitted during processes involving coal, gas, or waste combustion: lead compounds are produced by gasoline combustion. Mercury and dioxins affect the nervous system.
Benzene can cause acute irritation of the mucous membranes of the eye and lungs, as well as the skin, and chronic exposure can cause blood disorders. Lead is especially worrying as it can permanently damage intelligence and learning ability in children, and cause renal injury.
Another class of hazardous pollutants consists of polycyclic aromatic hydrocarbons, or PAH. PAH is a constituent of smoke, both vehicle smoke and wildfire smoke. Exposure to PAH can cause a range of transient and chronic problems, including irritation of lungs and eyes, blood and liver problems, and, possibly, cancer.
Greenhouse gases are not directly harmful to humans: however, in the long run, they may prove to be the deadliest of the atmospheric pollutants. The term refers to gases that trap heat from the sun and prevent it from being released back into space, thus increasing the Earth’s temperature. This can result in a variety of disastrous effects such as heat waves and a rise in the level of the oceans.
Water vapor is the most common greenhouse gas but it is not part of this discussion because its levels are not significantly affected by human activity.
The most important greenhouse gas affected by human activity is carbon dioxide (CO2). The average level of CO2 in the air was about 280 ppm prior to the 1700s, but following the industrial revolution it has been rising steadily to reach its present level of about 400 ppm. According to a survey done in 2014, 81% of the greenhouse gas emission from the USA is carbon dioxide.
Carbon dioxide is a product of combustion: burning anything at all produces carbon dioxide. Most of the CO2 produced today from human processes, however, is from vehicle emissions. In contrast, in the past it came chiefly from wood, coal or peat burning for fuel, volcanoes, respiration, and the natural decay of dead organic matter.
Methane is another major greenhouse gas. It is not emitted in nearly as high amounts as carbon dioxide, but it raises the global temperature even more efficiently, making it more dangerous, gram for gram. Its emission is due to agricultural activity, piping of natural gas and landfills, as well as from natural reservoirs like wetlands. The level of methane is more or less constant at present.
Nitrous oxide and CFCs
Nitrous oxide is another greenhouse gas released by fertilizers and fossil fuel use, among human activities. The chlorofluorocarbon (CFC) class is thousands of times more efficient than carbon dioxide at trapping heat and deplete stratospheric ozone dramatically. In 2016, more than 140 countries agreed to limit the use of CFCs, and eliminate them altogether gradually.
If successfully complied with, this level of HFC reduction is predicted to avoid the heat equivalent of 80 billion tons of carbon dioxide in 35 years.
Chemical waste from factory processes contains possibly the worst atmospheric pollutants. Billions of factories across the world manufacture industrial products for us to use, and almost all of them release harmful chemicals into the air as a side effect. Most of these are hydrocarbons from petroleum-based industries.
Hydrocarbons are not inherently harmful, but they undergo reactions when exposed to sunlight to form photochemical smog, forming thick clouds of pollutants close to the ground. Smog impairs visibility and causes severe irritation of the eyes and lungs, as well as asthma-like wheezing in many individuals.
Aerosols containing sulfur, organic and soot particles as well as increased atmospheric dust from mining and factories are other sources of air pollution by human processes. Soot, or particulate air pollutants, can enter the lungs and the blood and cause asthmatic bronchitis, cardiac damage and even premature death. Eye and throat tissues become irritated especially when the individual spends much time outside, or is older.
Sulfur dioxide is part of a family of air pollutants that cause acid rain, but they also reflect solar radiation back from the earth into the atmosphere. Whereas volcanic eruptions were formerly the major source of sulfur emissions, today human industrial activities have taken this place.
Recent studies have shown that every year, 64,000 people die prematurely because of air pollution. This number will only grow as population increases and lifestyles become more consumeristic. Climate change is already occurring, and its impact upon coastal life zones is still emerging. The need to regulate our activities and reduce the level of pollution from its present dangerous level is therefore urgent.