Within the stratosphere resides our biosphere's naturally formed shield against the sun's harmful ultraviolet rays, the ozone layer. Ozone, (O₃), is naturally formed when oxygen atoms join oxygen molecules and has a natural average concentration of only .002% by volume in the stratosphere. The level of maximum concentration is observed around 25 km above the surface. Such a thin skin, it is necessary to life on our planet. The mid-1970's bred the beginning of public awareness over our fading ozone shield. Since then, scientists have picked up the pace on compiling databases of what surface products end up in the atmosphere.

Ralph J. Cicerone wrote an article for Science in March of 1994, (vol. 263, pp.1243-1244), that addressed the global phenomenon of biomass burning. So central to human history, biomass burning has more of an effect on our atmosphere's chemistry than has been traditionally thought. While he discusses notable chemical compounds such as the nitrogen oxides, CO and CH₃Cl in his article, (“Fires, Atmospheric Chemistry, and the Ozone Layer”), Cicerone emphasizes the negative effect that bromine atoms are having on the ozone layer, especially when housed by MeBr, (methyl bromide).

Cicerone points out that burning biomass is a form of non-industrial pollution, most notably done by developing countries. The United States, similar to all developed nations, was a large producer in the early-to-mid 1800's when European immigrants slashed and burnt large tracts of forest and prairie.

Burning produces the nitrogen oxide molecules NO and NO₂ along with CO, which combine to produce ozone in the troposphere through the net reaction:

This troposphere-born ozone has the same effect as that produced in polluted, smoggy urban air, through photochemical smog. It damages vegetation and irritates the eyes and lungs of city dwellers. Another molecule, CH₃Cl, is produced in burning vegetation and is largely destroyed through photochemical reactions in the troposphere. But a few percent survive the ascension and when CH₃Cl pierces the stratopause, ozone-destroying chlorine atoms are released.

More damaging to ozone than any of the fore-mentioned is gaseous MeBr. Thirty percent of the atmosphere's MeBr is contributed by burning biomass. Though most ozone loss to date is attributed to CFC-delivered chlorine, bromine atoms have 20-60 times the ozone-destroying capacity of chlorine atoms. Cicerone adds that 25% of the ozone atoms lost in the Antarctic spring are due to bromine atoms wrought by synthetic halon compounds and CH3Br.

Bromine atoms catalyze stratospheric ozone destruction by a series of reactions simplified by the net outcome of:

Bromine atoms also come to the stratosphere in stable organic compounds such as halon 1301, (CF3Br), and halon 1211, (CF2BrCl). Almost 100% of perhalogenated halon compounds reach the stratosphere intact because they have molecular lifetimes of 65 and 20 years, respectively. The halons are much less reactive, however, considering MeBr's expected two-year life span in the stratosphere. Worldwide production of methyl bromide has also increased, with a 50% rise between 1984 and 1991.

So, how much good would it do the fading shield of ozone if we halted MeBr production today, asks Cicerone. Will concentrations of MeBr decrease accordingly in the atmosphere in time, even without the continuous surface feed? According to the article, the answers depend on:

1) The relative sizes of natural and anthropogenic input of MeBr, (SN and SA, respectively);
2) Whether other natural sinks besides OH are significant;
3) Details of the stratospheric chemistry that control the chain length of the cycle comprising the reactions:
Br + O₃ --> BrO + O₂
Cl + O₃ --> ClO + O₂
BrO + ClO + light --> Br + Cl + O₂
which yield the net equation mentioned before:
2O₃ + light --> 3O₂

But ClO levels will decrease slowly, even in the wake of strong guidance by global production laws. Cicerone says that it might take decades for levels to completely purge. And as for the Clean Air Act classification of MeBr, we still have glaring questions about present concentrations and their staying power. A later paper published in Science , “Ozone Destroying Chlorine Tops Out,” (5 Jan.1996, vol. 271, p.32), stated that although chlorine has peaked and is decreasing, a gap in the protocol exists due to the presence of bromine atoms. According to the article, in fact, ozone losses to bromine may temporarily offset gains from chlorine reduction. Meeting in December of 1995, member nations of the Montreal Protocol agreed to phase out use of MeBr by the year 2010.

Addressing the input of biomass burning to ozone depletion, Cicerone further illustrated the fragility of our thin shield from lethal ultraviolet rays. There is no doubt that although the most successful depleting agent, chlorine, is on the decline, bromine is going to be a serious block to atmospheric recovery. Biomass burning contributes problems in the forms of nitrogen oxides, CO, CH₃Cl and the halons CF3Br and CF2BrCl, as well. The focus article most importantly raised legitimate questions to guide current research. Why is MeBr released both during the flaming and smoldering phases of burning while CH₃Cl only results from smoldering fires? How do Br quantities vary in plants? How should we go about taking inventory of Br released from burning annually? Do the oceans serve as a buffer in the global MeBr system? What is the true ratio of MeBr production between natural and anthropogenic sources, (SN and SA)? And how do we know that halting our MeBr production will similarly affect atmospheric concentrations in time to save the ozone layer?