What are Greenhouse Gases?

Greenhouse Gases (GHG) in General

In the previous article How Greenhouse Effect works on our lovely Planet Earth?, we have gone through reading about the process of Greenhouse Effect, how it works and what are the consequences that the Greenhouse Effect is threatening us right now. However, in this article we shall concentrated more on the Greenhouse Gases or GHG.

Greenhouse gases or GHG are gases that can absorb and emit longwave, infrared radiation (IR radiation) in a planetary atmosphere.

  • From the total sunlight that falls on the Earth’s surface, approximately 40% of that energy is re-radiated upward into the atmosphere in the form of longwave radiation.
  • Then from that amount, approximately 75% of that upward radiated longwave energy is absorbed by water vapor, carbon dioxide, methane and other greenhouse gases.
  • Since this absorption process is molecular in nature, the subsequent re-radiation of energy by these gases is multidirectional. As a result, about 50% of the longwave emission is reradiated back toward the Earth where it is once again turned into heat energy.
  • Through this process, greenhouse gases contribute to the amount of heat energy released at the Earth’s surface and in the lower atmosphere.

Types of Greenhouse Gases

All greenhouse gases are molecules that contain at least three atoms which are bound loosely enough together to vibrate when they absorb heat. The most abundant greenhouse gases in Earth’s atmosphere are;

  • Water vapor
  • Carbon dioxide
  • Methane
  • Nitrous oxide
  • Ozone

Non-greenhouse gases

Approximately 98 to 99% of the atmosphere is composed mainly of Nitrogen (N2), Oxygen (O2) and Argon (Ar). These gases are each composed of two atoms which are bound together so tightly that they do not vibrate, or absorb heat. Therefore, they are not greenhouse gases and do not contribute to the greenhouse effect.

The remaining percentages of atmospheric gases are mostly greenhouse gases. Although the ratio seems small, we know that the greenhouse effect brought on by these gases has a very large impact on our sustainability of our environment.

Greenhouse Gases: Water Vapor

 Water vapor is the most abundant greenhouse gas in the atmosphere, contributing approximately 36%-72% to the greenhouse effect. Water vapor is a naturally occurring gas, created by the hydrologic (water) cycle where human contribution is very small compared to the natural occurrences.

Although the water vapor is the highest contributor to GHG however it doesn’t contribute anything to global warming. Water vapor is a “reactive” GHG with a short atmospheric lifetime of about 1 week. If you pump out a whole load of extra water vapor it won’t stay in the atmosphere; it would condense as rain or snow and we’d be back to where we started. If you suck the atmosphere to dry of moisture, more would evaporate from the oceans. The balance is dynamic of course: humidity of the air varies by place and time, but it’s a stable balance.

Greenhouse Gases: Methane

On the other hand, methane, or CH4, is a fairly potential greenhouse gas which capable of trapping 20 times more heat than carbon dioxide.  However, its atmospheric presence is lower than CO2 and, when this is combined with a relatively short atmospheric lifetime of approximately 8-12 years, methane ultimately has a smaller effect on global warming than carbon dioxide.

Global methane emissions derived from natural sources are estimated to be around 225 Tg per year. These numbers are rather uncertain, however, as they depend on many different environmental variables. A more concrete number regarding methane emissions is from IPCC which is estimated that more than 60% of global methane emissions are the result of human-related activities.

According to IPCC the amount of methane in the atmosphere has been increased up to 150% since the pre-industrial era year of 1750.

Greenhouse Gases: Nitrous Oxide

Nitrous oxide or N2O is actually produced by either natural or human-related sources. Primary human-related   sources of   N2O   tend to be agricultural soil management, animal manure management, sewage treatment, combustion of fossil fuel, adipic acid production, and also nitric acid production.

Nitrous oxide can be also made naturally from a wide variety connected with biological resources in soil as well as water, particularly microbial action in wet tropical forests.

Nitrous oxide emission amounts may differ substantially from a country or location to another, depending on many elements for instance industrial, agricultural production characteristics, combustion systems, waste management practices, and climate.

As an illustration, heavy utilization of synthetic nitrogen fertilizers in crop production typically results in significantly more N2O emissions from agricultural soils than that occurring from fewer rigorous, low-tillage techniques. In addition the absence of control devices on combustion sources, such as catalytic converters on vehicles, can increase the level of N2O pollutants.

Besides from being the third most significant greenhouse gas, Nitrous Oxide is also a main contributor to the destruction of atmospheric ozone. This greenhouse gas possesses an atmospheric lifetime that could reach over 100 years and it’s also 300 times stronger than carbon dioxide. Considering that they exist far less within the atmosphere thus the contribution to global warming is smaller than that of CO2 or methane.

However, according to information provided by NOAA, nitrous oxide has increased from 270 parts per billion in pre-industrial 1750, to nearly 320 parts per billion today, with a continuous growth rate of 0.2% – 0.3% annually.

According to the 2007 IPCC AR4, WG1: “The Physical Science Basis of Climate Change“, the two main natural sources of nitrous oxide are soils and oceans, which together account for over 90% of natural nitrous oxide emissions.

Greenhouse Gases: Fluorinated Gases

The United States, EPA established SNAP, stands for Significant New Alternatives Policy to evaluate and regulate substitutes for the ozone-depleting chemicals that are being phased out under the stratospheric ozone protection provisions of the Clean Air Act (CAA).

The program is under section 612 of the Clean Air Act and the SNAP program specifies acceptable uses for alternatives to Ozone Depleting Substances (ODSs) like CFCs, HCFCs, and halons, which are in the process of being phased out in accordance with the Montreal Protocol and Clean Air Act Amendments of 1990.

This policy requires manufacturers to find solutions to remove chlorine from the molecular structures that were in use prior to 1990, because the chlorine was severely depleting the stratospheric ozone. Thus, some new fluorinated gases have been created to replace them. These include HFCs, PFCs, and SF6. These fluorinated greenhouse gases have no natural source and all of them are man-made. Thanks for reading.

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