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.