PM stands for particulate (微粒的)matter: the term for a mixture of solid particles(粒子) and liquid droplets in the air. Some particles are large or dark enough to be seen by our eyes. Others are so small that they can only (discover) with a microscope.
These particles come in many sizes and (shape) and can be made up of many different chemicals. Some come directly from a source, such as fields or fires. Most particles form the atmosphere as a result of complex reactions of chemicals, are pollutants from power plants, industries and automobiles.
Particulate matter (contain) microscopic particles that are so small that they can be breathed in and make one (serious) ill. Some particles less than 10 micrometers in diameter can get deep into your lungs some may even get into your bloodstream. Of these, particles less than 2.5 micrometers in diameter, also known as PM2.5, create the (great) risk to health.
Fortunately, every day the Air Quality Index (AQI) tells you how clean or (pollute) your outdoor air is, along with associated health effects that may be of concern. The AQI translates air quality data into numbers and colors that help you understand when (take) action to protect your health.
