Air Quality Index (AQI) and Particulate Matter

The AQI is an index for reporting daily air quality. It tells you how clean or polluted the air is, and what associated health effects might be. The AQI focuses on health effects you may experience within a few hours or days after breathing polluted air.

The easiest way of measuring this is via Particulate Matter (PM) also known as soot, which consists of microscopically small solid particles or liquid droplets that can either be emitted directly into the air, or formed from secondary reactions involving gaseous pollutants that combine in the atmosphere.

PM is usually measured in two size ranges: PM10 and PM2.5.

PM10 refers to particles with diameters that are less than or equal to 10 microns in size (a micron, or micrometer, is one-millionth of a meter), or about 1/7 the diameter of a human hair

PM2.5, also called “fine particulates,” consists of particles with diameters that are less than or equal to 2.5 microns in size. PM2.5 is a more serious health concern than PM10, since smaller particles can travel more deeply into our lungs and cause more harmful effects.

Our PurpleAir monitor uses laser beams to detect the particles going past by their reflectivity, like dust shimmering in a sunbeam. The PM 2.5 and PM 10 micro-gram weights are calculated from the counts. The values are averaged every 20 seconds and the latest results are graphically below – we also have a more detailed set of statistics here and you can see even more on a Google map here

Easiest way is to look at both the AQI and the PM2.5 levels and then consider what type of activity you should (or shouldn’t do) and the consequent Health effects .