The results of research done with high-altitude aircraft flights showed significant amounts of ozone being destroyed outside the main hole, suggesting that the area of ozone loss may be considerably greater than once thought. Furthermore, this same research revealed that ozone destruction begins earlier in the year than expected.
--C. Donald Ahrens, Meteorology Today (modified)
Use this/that with singular nouns and these/those with plural nouns.
Although not everything is known about the reactions that take place among hydrocarbons and other gases, it is believed that this reactions disrupt the normal mechanism for ozone removal, and so the concentration of ozone is able to increase.
Although not everything is known about the reactions that take place among hydrocarbons and other gases, it is believed that these reactions disrupt the normal mechanism for ozone removal, and so the concentration of ozone is able to increase.
--C. Donald Ahrens, Meteorology Today
You can sometimes use demonstrative adjectives as demonstrative pronouns.
These tools are delicate.
[demonstrative adjective] These are delicate.
[demonstrative pronoun]
However, take care that you do not create broad pronoun reference.