The Carbon Family: Carbon Components and Their Relationships
Carbon is all around us, and it is a basic requirement for life as we know it. Everything now alive on the earth is impacted by carbon, and life could not exist without it. But lately terms like “Carbon Footprint” and “Total Inorganic Carbon” may have served to confuse the role of carbon in our everyday lives. Without a clear understanding of the carbon components it is difficult to interpret carbon measurements.
Why are we concerned about the measurement of carbon? Well, today more than ever, a better understanding of the carbon cycle and its impact on the planet, and consequently man’s impact on that cycle, leads us to see a better picture of the planet’s health. With that picture comes a direct impact on the human living conditions, something we all should be more aware of.
To look at carbon, we must examine the components of carbon and how they are derived for measurement. In this way, we can better measure the impact of inorganic and organic carbon compounds.
The Components of Total Carbon
Total Carbon is roughly comprised of two types of carbon, more or less defined by their source. Total Carbon is composed of both organic and inorganic sources, even though inorganic carbon may be a byproduct of a very organic process.
Total Organic Carbon
Total Organic Carbon (TOC) is the amount of carbon bound in an organic compound. Carbon in such a compound makes for a convenient way to measure the compound itself, and it is often used for that purpose. For example, carbon measurement in drinking water can be used to determine how much Natural Organic Material (NOM) is present in a given sample. Generally speaking, the source of NOM in water is from living organisms and decaying matter, although the purification process itself can contribute to carbon readings in water.
Water is considered cleaner with a reduced count of measurable NOM, and the United States Environment Protection Agency (EPA) regulates it in finished waters. Consequently, you want a lower reading of organic carbon in your drinking water.
To seemingly confuse the issue, TOC can also come from synthetic sources such as detergents, herbicides, fertilizers, and pesticides. But for the purposes of measurement, the components of TOC (see chart above) are as follows:
Non-Purgeable Organic Carbon (NPOC): This is the organic compound of TOC after purging it with gas for measurement purposes. The sample will be naturally acidic.
Purgeable (volatile) Organic Carbon (VOC): The organic compound that has been removed from a neutral sample by use of an inert gas, referred to as Volatile Organic Compounds (VOC).
The NPOC itself is broken down farther into its separate components:
Dissolved Organic Carbon (DOC): This is the organic compound remaining after a sample is filtered through a 0.45 micrometer filter.
Particulate Organic Carbon (POC): Also referred to as a suspended organic compound, it is organic material that cannot fit through the filter, i.e. larger than 0.45 micrometers.
The process of measuring TOC is often done by removing the inorganic carbon — an important part of the carbon cycle — and measuring the resulting compound. While we can see that the presence of TOC can be a good indicator that unwanted material can be present in consumables, the real component of carbon that we are concerned with, as it affects the environment, is in the next section, Total Inorganic Carbon.
Total Inorganic Carbon
Inorganic carbon can be found in several sources, including carbonic acid, bicarbonate anion, and most notably carbon dioxide (CO2). Since carbon dioxide, an inorganic carbon compound, is an important part of the carbon cycle, we can find it in abundant quantities throughout the Earth.
However, inorganic carbon can also be released outside of the carbon cycle through the combustion of materials in manufacturing and the burning of fossil fuels. This is unfortunate, since the typical automobile releases large amounts of carbon dioxide as it burns its fuel. This extra CO2 released into the atmosphere offsets the existing carbon cycle of life on Earth, and it also impacts the natural greenhouse effect of our planet, raising temperatures. This makes it very important to measure the presence of the compound.
In fact, even the Earth’s oceans include many forms of dissolved carbon dioxide. While this is a natural part of the carbon cycle, the ocean’s action of dissolving CO2 releases a hydrogen ion, decreasing the ocean pH. As we create more and more CO2, the ocean absorbs more of it, dropping the pH even more. The ocean’s lower pH has a negative effect on oceanic organisms, particularly on those that depend on calcification. That is, it could negatively impact creatures that create shells and plates. This in turn disrupts the natural food chain. Again, we see that it is important to measure the carbon components.
In measuring inorganic carbon, Total Inorganic Carbon (TIC) is defined as the sum of inorganic carbon in a given solution. As with TOC above, TIC is broken down into particulate and dissolved components. That is, the particulate (suspended) inorganic compounds are larger than the filtering threshold. The TIC is measured by acidification of a given sample to an equilibrium state, and then the resultant gas is trapped and measured.
As you can see, the process of measuring carbon is dependent on the components of carbon involved in the test, and consequently impacted by its sources. Through an understanding of these sources, it is easy to see how the complex carbon chain of both the life cycle and fuel expenditure is related to each other. And the better we understand this inherent relationship, the better we can accurately predict the impact our actions may have on future life on the Earth.
Photo Credit: St Stev via flickr (CC license)