Most people are already keenly aware of primary pollutants.
These include everything from carbon monoxide to highly reactive organic compounds released through incomplete industrial fuel combustion. Notwithstanding the political difficulty of getting legislation passed, these pollutants are generally easy to control.
By obliging industrial concerns to limit emissions, nations can control the level of primary air pollutants that end up in the atmosphere. This is why having a multinational accord like the Paris climate deal – which includes 195 individual nations – is such a valuable step forward.
However, secondary pollutants are notably more difficult to control. These are not the pollutants directly emitted by cars, engines, power plants, and the like. These are the noxious gases synthesized by photochemical reactions occurring in Earth’s atmosphere.
Examples of Secondary Pollutants
Some of the most common secondary air pollutants are also the most well-known:
Controlling Secondary Air Pollutants
Of the three secondary air pollutants listed above, nitrogen oxide is the easiest to control. This is because it only lasts about one day in the atmosphere before it gets deposited in the ground. However, even ground-based nitrogen oxide can cause environmental damage.
Ozone and sulfuric acid, however, represent far greater challenges to the environmental community. Smog created by ground-level ozone, for instance, tends to persist far beyond the original lifetime of the primary pollutants that cause it. Even eliminating the industrial sources of these pollutants does not entirely eliminate the ozone problem.
1. Ground-Level Ozone
For instance, while nitrogen oxides produced by combusting coal, gasoline, and oil are known to generate ground-level ozone when exposed to air and sunlight, volatile organic compounds also contribute to the problem. These compounds come from a broad variety of sources, including residential wood combustion. Creating enforceable legislation that covers homeowners’ decision to burn their own wood is difficult in most regions.
2. Sulfuric Acid
Sulfuric acid is also a challenging pollutant to eliminate. Industrial controls can only do so much to prevent the combustion of sulfur-containing fuels. Completely eliminating harmful sulfur dioxide from reaching the atmosphere could be achieved by a massive-scale movement towards alternative and renewable energy sources, but this idealistic situation is far from the pragmatic realities of energy lobbying.
Instead, many industrial concerns contain sulfur dioxide and treat it with powered limestone, creating calcium sulfate. Calcium sulfate is useful to the construction industry, generating an economic incentive for this system.
Another method for reducing the amount of sulfur dioxide that escapes to the atmosphere is the seawater scrubbing process. This process uses the natural alkalinity of seawater to absorb and neutralize sulfur dioxide, removing up to 99 percent sulfur in the process and depositing the resulting water back in the sea. However, the resulting seawater contains heavy metals and chlorine, which present their own long-term environmental issues.
There are also methods for reducing the amount of sulfur present in combustible materials before combustion occurs. For example, the Fluidized Bed Combustion method uses mechanical energy and heat transfer to create ideal conditions for sulfur dioxide extraction. Once the fuel is properly prepared, limestone is added as a sorbent, leading to 80-90 percent absorption of sulfur pre-combustion.
Unfortunately, this method creates a large quantity of alkaline waste destined for landfills. For this reason, it is not a widely adopted commercial practice in modern industrial facilities. Nevertheless, new technologies may soon provide better and more efficient ways to remove sulfur from fuels before combustion takes place.
If successfully treated fossil fuels generate fewer primary and secondary pollutants, the entire world stands to benefit. At least, until the global move towards clean, renewable energy becomes reality.