21.   To use the devices, security guards usually wipe the handle of carry-on luggage with a piece of cloth to pick up microscopic particles.

22.   Unless it is in the form of microscopic particles that can be inhaled, she said, its radiation can be blocked by clothing, skin or even paper.

23.   Most of the studies about smog and babies came after former U.S. President Bill Clinton set new federal limits for ozone and microscopic particles.

24.   The substance adds to the water more microscopic particle around which snowflakes can form.

25.   The balls are impregnated with microscopic particles of metal which trigger a beep when the ball passes over the line.