Particles larger than 10 micrometers generally get caught in the nose and throat, never entering the lungs. If these particles are soluble in water, they pass directly into the blood stream within minutes. These are the particles that can enter the human lung directly. If particles are 10 micrometers in diameter, then 1600 particles can fit on the dot. If the particle diameter is 2.5 micrometers, then 25,600 particles can fit on the dot.
Particle size is everything when it comes to air pollution and health.
The study of fine particles and their effects on human health has been under way in earnest since 1975. The new study also controlled for changes in outdoor temperature. Researchers have shown that fine particles cause death and disease, but the mechanism by which this occurs has remained a mystery. This hypothesis is proposed as the biological mechanism by which fine particles cause respiratory and heart-related diseases and death. One might ask why steps weren't taken long ago to prevent the disease and death associated with fine-particle pollution.