Friday 14 May 2010

Misconceptions

1. CFC molecules are too heavy so they cannot reach the stratosphere
Even though CFC molecules have larger atomic mass than nitrogen or oxygen molecules, the mass of the molecules does no determine the composition of air in the atmosphere. The wind in the troposphere is strong enough to carry the air to the atmosphere. As there are no natural processes which break down CFCs, they remain uniformly distributed vertically and horizontally along the atmosphere.

2. Manmade chlorine is does not cause ozone depletion as much as natural chlorine
Manmade chlorine causes more ozone depletion than natural chlorine. Forms of natural chlorine include hydrogen chloride (HCl) released from volcano eruptions and sea salt which is 50% chlorine.

Despite the large amounts of chlorine which are produced naturally, natural chlorine can be depleted. Even though volcanoes release large amounts of hydrogen chloride during eruption, the gas has only enough energy to reach the troposphere and not the stratosphere. Sea salts are released very low in the atmosphere, as such they take 2 to 5 years to reach the stratosphere. Rain from the troposphere will dissolve the chlorine gas, thus the chlorine gas does not contributes minimally to ozone depletion.

On the other hand, CFCs (manmade chlorine) cannot be dissolved by water, and no chemical method can help to remove CFCs. So, CFCs deplete naturally and will have a long lifespan in the atmosphere.

Pie Chart showing percentages of different sources contributing to ozone depletion

3. Ozone layer depletion occurs only in Antarctica
The ozone hole is above Antarctica. However, ozone depletion does not only occur in Antarctica. Ozone levels vary seasonally and according to latitude. Ozone levels are greater at high latitudes (more depletion), and as such, Artic regions also experience ozone depletion. Antarctic region experiences more ozone depletion because low temperatures due to polar vertex allow polar stratospheric clouds to form. Stronger westerly winds circulate around the region – more chlorine molecules. Since the latitudes at tropical regions are lower, Ozone at the tropics do not deplete as quickly.

1 comment:

  1. Um.. Does global warming slow down Ozone Depletion? It was only said that CFCs need low temperatures in order for them to deplete the ozone layer. So does Global Warming help in anyway?

    ReplyDelete