Special Feature: What are Ultrafine Particles?

Particulate matter (PM) is the principal component of air, of which ultrafine particles (UFP) are those with a diameter of 100 nm or less. There is a growing concern in the public health community about the contribution of the UFP to human health. The potential for UFP to cause harm to health is great. However, its source, mechanism, and precise role in many illnesses are still largely unknown. The special issue provides comprehensive reviews of the UFP and related effects on human health and disorders, which is an invaluable resource for understanding the current status and future perspectives of UFP management.