alternative – adj. offering or expressing a choice

respiratory – adj. the movement of air or dissolved gases into and out of the lungs

filter – n. a device that is used to remove something unwanted from a liquid or gas that passes through it

particle – n.

PM2.5 – n. fine inhalable particles, with diameters that are generally 2.5 micrometers and smaller

allergy – n. a medical condition that causes someone to become sick after eating, touching, or breathing something that is harmless to most people

nail – n. the hard covering at the end of a finger or toe the hard covering at the end of a finger or toe

affordable – adj. having a cost that is not too high

start-up – n. a fledgling business enterprise

consumer – n. a person who buys goods and services