"A PM2.5 particle--a particle with a diameter of 2.5 microns or smaller--is extremely small," explains Yeh (1 micron equals 1 millionth of a meter). PM2.5 particles are even more damaging to the respiratory tract than PM10 particles, which are more widely discussed. These tiny airborne particles get lodged in the capillaries at the end of the respiratory tract and are almost impossible to remove.
「PM2.5 是直徑 2.5 微米、非常微小的粒子（1 微米相當於 10-6 公尺），」葉宣哲解釋，PM2.5 比已知的 PM10 影響呼吸道更甚，因為這種「飛沙」顆粒極小，會深入呼吸道末端血管而固著、堆積，幾乎無法清除排出。