The air that we breathe

When you look out the window, you can often see the pollution. It forms a thick haze, obscuring our view. That haze is made up of millions of little particles.

Hong Kong's Air Pollution Index (API) tells us how bad the pollution is. The API measures the number of small particles suspended in the air.

But a recent report by scientists say that's not good enough - we need to consider the number of very fine particles, which are even more dangerous.

The API only measures particles in the air that are 10 microns or less in diameter. It is the ones that are even smaller - 2.5 microns and less - that cause worse damage. These ultrafine particles can enter the body far more easily, scientists say. And they are being linked to serious health conditions, like cancer, strokes, heart disease and diabetes.

A new report commissioned by the Environmental Protection Department has urged the government to begin reporting fine-particulate levels as part of the API and tighten all current pollution standards.

Young people are among the worst affected by poor air because their lungs are still developing.