1.   Although chlorofluorocarbons, or CFCs, have been blamed for the destruction of ozone, they actually do little harm until they come into contact with ice particles.

2.   Comprised of tiny ice particles, noctilucent clouds are so thin that stars shine brightly through them.

3.   Comprised of tiny ice particles, the clouds are so thin that stars shine brightly through them.

4.   However, significant areas are cold enough and contain enough water vapor for ice particles to grow, provided small particles are already present.

5.   The group plans particularly to study lee wave clouds, clouds of ice particles that form downwind of mountain peaks, in Scandinavia and the Urals.

6.   Then the small ice particles may collide with other water droplets.

7.   In the case of hail, ice particles tend to melt or fall to the ground before becoming big enough to cause damage.

8.   The aircraft bounced and creaked as it climbed, ice particles clanging noisily.