From Dalton's law of partial pressures, it is clear that a gas occupies the entire space available to it, whatever its atomic weight may be. Thus, the other gases present in the container do not hinder the gas to occupy the entire volume of the container by Brownian movement. So,is there any other force acting on ozone to stop it from reahing the Earth's surface? As since ozone's molecular weight(48)is much greater than the average molecular weight of air.

Some information on this page may also be found at The Ozone Hole Tour from the University of Cambridge.

The first thing to remember is that ozone formation and destruction are two sides of a dynamic process. Ozone is highly reactive, so no single molecule of ozone will survive for long in the atmosphere (as opposed to something inert, like carbon dioxide or nitrogen). What we are concerned with is net formation or destruction of ozone--that is, whether we get more ozone formation or ozone destruction at a particular altitude.

Ozone is formed when short-wavelength or "hard" ultraviolet light (wavelength <~ 220 nm) dissociates dioxygen molecules into oxygen atoms. These oxygen atoms react with more dioxygen to form ozone:

O₂ + hn ® 2O (1)
O + O₂ ® O₃ (2)

In the absence of other ozone scavengers (a long list), ozone can be destroyed either by reaction with yet more dioxygen or by absorbing ultraviolet light between about 220 and 240 nm:

O₃ + O₂ ® 2O₂ + O (3)
O₃ + hn ® O₂ + O (4)

The net effect is that ultraviolet light with wavelength <~ 240 nm is efficiently prevented from reaching the earth's surface. Notice that reaction 4 results in no net ozone destruction because the atomic oxygen produced just forms more ozone according to reaction 2.

In the upper atmosphere, reactions 1 and 2 (as well as reaction 4) predominate because the UV flux is high. However, as we get lower in the atmosphere (and density increases) ozone and dioxygen meet more often (reaction 3, not to mention reactions of ozone with other compounds like methane). Meanwhile, most of the hard UV light has been filtered out by reactions 1 and 4 at higher altitudes, resulting in less photochemical ozone formation at lower altitudes.

In summary, ozone formation is dominant in the stratosphere but negligible at lower altitudes, while ozone destruction occurs all the time and everywhere, and increases with atmospheric pressure. Ozone will not have time to get to ground level from the stratosphere!

Of course, we can get ozone formation at low altitudes via the photochemistry of nitrogen oxides, which are formed in flames and internal combustion engines. This is bad because ozone is highly corrosive.