Dust is a ubiquitous collection of microscopic particles found suspended in the air and settled on surfaces. These fine fragments of solid matter originate from a variety of sources, both natural and human-made, and are present globally. While often invisible to the unaided eye, dust particles range in size from about 1 to 400 micrometers.
The Makeup of Indoor Dust
Indoor dust, found within homes, is a complex mixture primarily derived from occupants and their activities. A significant portion, estimated between 20-50%, consists of dead human skin cells. Each person sheds approximately 500 million skin cells daily, contributing to dust accumulation.
Beyond human skin, pet dander, which includes tiny flakes of skin, hair, or feathers from animals, is another major component. Textile fibers from clothing, carpets, upholstery, and other fabrics also break down and become airborne. These fibers, along with small food crumbs, paper fibers, and microscopic plastic particles, contribute to indoor dust. Microplastics, ranging from 1 to 5 millimeters, are increasingly found indoors, often at higher concentrations than outdoors.
Outdoor and Natural Dust Contributors
Dust particles also originate from external sources, entering indoor environments or persisting outdoors. Soil particles, lifted by wind through a process known as aeolian transport, are a common natural contributor. These include minerals tracked inside on shoes or clothing. Pollen from plants and mold spores, both microscopic biological particles, are seasonal additions to environmental dust.
Natural sources include volcanic eruptions, releasing fine ash into the atmosphere. Industrial emissions and vehicle exhaust also contribute to outdoor dust, including particles from tire and brake wear. Even cosmic dust, originating from outer space, contributes a small, albeit continuous, amount to the Earth’s dust composition.
The Journey of Dust: Formation and Movement
The various components of dust become airborne through processes like shedding, abrasion, and degradation of materials. For instance, shedding human skin and pet dander directly releases particles. Similarly, friction from walking on carpets or sitting on furniture can abrade textile fibers, making them airborne.
Once these particles are released, air currents and ventilation systems play a role in their suspension and movement. Airflow within a room can keep lighter particles aloft, distributing them. Eventually, these suspended particles settle onto surfaces due to gravity, forming visible dust layers. Static electricity can also influence dust accumulation, attracting particles to charged surfaces.