Dust pollution and ultrafine dust are frequently mentioned topics recently. It is probably not difficult for you to recognize normal dust, passing by a construction site with trucks carrying raw materials, we will probably all understand what dust is like.

However, ultrafine dust is not usually that intuitive. Based on the size of the dust particles, they are classified as PM10, PM5 or PM2.5. PM10 is the content of dust with a size of 10 micrometers or less while PM2.5 is the content of dust with a size of less than 2.5 micrometers. Thus, PM10 will include PM5 and PM5 itself includes PM2.5. If compared to the diameter of your hair, the largest dust particle in the PM2.5 group is about 30 times smaller.

Why do we care about ultra-fine dust? Studies show that larger dust particles are often retained in the nose, mouth or throat, while dust particles under 10 micrometers can penetrate deep into the airways. The finer the dust, the deeper the penetration. PM2.5 dust has a high potential to enter the bloodstream after going deep into the lungs. Therefore, ultra-fine dust not only causes diseases due to direct contact such as eye pain, rhinopharyngitis, but can also have long-term effects on your entire body when they carry toxins from the outside environment circulating with the blood throughout the body.

So what is ultra-fine dust and where does it come from? The most obvious direct source is traffic smoke from incompletely burned fuel, smoke from fuel-burning factories, especially coal-burning factories, forest fires, post-harvest straw fires or dust from construction sites, road dust, etc. Ultra-fine dust is also formed in the atmosphere from secondary sources such as NOx, SO2, ammonia or volatile organic gases through complex chemical reactions.