B. What are the Greenhouse Gases?
The following shows the more significant Greenhouse Gases and their concentrations: [https://www.c2es.org/content/main-greenhouse-gases/]
- Water Vapor 30,000 ppmv
- Carbon Dioxide 407 ppmv
- Methane 1.7 ppmv
- Nitrous Oxide 0 .32 ppmv
- Ozone 0.025 ppmv
- Flourocarbons 0.0005 ppmv
This shows that water vapor dominates everything else combined by 98.3 percent. In addition to water vapor, the atmosphere supports a considerable amount of liquid water ice crystals in the clouds amounting to about 10% of the amount of water vapor.[Linacre E & Geerts B. (1999) Cloud liquid water content, drop sizes and number of droplets, University of Wyoming.] The liquid water and ice crystals have a much wider absorption ability, including capturing high energy sunlight radiation, as well as the ability to reflect radiation that is not present in molecular gases. Hence the total greenhouse effect from atmospheric water is 50 to 200 times greater than all other greenhouse gases combined. [Segalstad T (1996) The distribution of CO2 between atmosphere, hydrosphere, and lithosphere; minimal influence from anthropogenic CO2 on the global “Greenhouse Effect”, Emsley, J. (Ed.): The Global Warming Debate. The Report of the European Science and Environment Forum. Bourne Press Ltd., Bournemouth, Dorset, U.K. 41-50; 1996.]
Water vapor concentration diminishes with elevation and dropping temperatures. The figure below illustrates the relationship between water vapor concentration in grams per kilogram (multiply by 1.61 to convert to ppmv for water vapor/air mixture).
The above figure illustrates that after about 6 kilometers, the water vapor concentration begins dropping faster until it reaches about 15 km in the Stratosphere. The mixing ratio at 10 kilometers is 0.1 g/kg or 100 ppm (160 ppmv). The CO2 concentration remains relatively constant between the troposphere and the stratosphere at about 390 ppmv. However, the higher elevations has a significant drop in mass. For example, the troposphere contains between 75 and 80% of all mass in the atmosphere and the lower Troposphere contains 75 to 80% of the mass in that zone. This is because the higher atmospheric pressure the greater the mass density changing exponentially. Between sea level and 5 km (kilometers), the pressure and therefore density drops by half. In comparison the atmospheric pressure on Mars is about .1 atm (100 millibars) which occurs in the Stratosphere at about 16 km.
However, NASA reports that the thin atmosphere at 5-6 km allows the infrared radiation to escape unimpeded.
“Heat radiated upward continues to encounter greenhouse gas molecules; those molecules absorb the heat, their temperature rises, and the amount of heat they radiate increases. At an altitude of roughly 5-6 kilometers, the concentration of greenhouse gases in the overlying atmosphere is so small that heat can radiate freely to space.” Emphasis added https://earthobservatory.nasa.gov/features/EnergyBalance/page6.php
The Stratosphere starts at about 12 kilometers. At 5 to 6 kilometers, the pressure is about .5 atmospheres and the water vapor drops to about 1600 ppmv (mixing ratio of ~1 g/kg). This concentration dominates the CO2 concentration at 400 ppm.