The National Environment Agency measures fine particles in the air called PM2.5. It is measured in micrograms of PM2.5 per cu m.
PM2.5 can be more dangerous than larger dust particles, as they can enter the lungs or bloodstream more easily.
There are no health advisories for PM2.5 readings between zero and 15.
When the reading is between 150 and 250, people with heart or lung disease, children and older adults should remain indoors and keep activity levels low. Everyone else should avoid all physical activity outdoors.