Air purifiers are essential for keeping the air in our homes and offices clean and free of allergens, bacteria, and viruses. But how exactly are air filters made? In this article, we'll explore the different types of air filters and how they are manufactured. An air cleaner is generally made of a spun glass fiber material or of pleated paper or cloth enclosed in a cardboard frame. Its basic function is to clean the air circulating in the heating and cooling system.
Air purifiers evolved in response to people's reactions to allergens such as pollen, animal dander, dust, and mold spores. Reactions such as sneezing, runny nose, irritated eyes, and even more serious consequences like asthma attacks are the result of antigens found in the home. These antigens are the main triggers of asthma, and there are more than 17 million asthmatics in the United States alone. Air purifiers remove some of these particles, reducing allergic-type responses.
Due to their extremely small size, allergens can pass through a standard vacuum bag and redistribute into the air, where they stay for days. Even a single microgram of cat allergens is enough to provoke an allergic response in most of the six to 10 million Americans who are allergic to cats. Other airborne particles, such as bacteria and viruses, can cause diseases, some of which are fatal. There are many reasons why millions of air purifiers are sold in the United States each year for allergies, asthma, and deadly diseases. HEPA filters are made of very fine glass wires with a diameter of less than 1 micron (one micron is 0.00004 in., 0.001 mm).
In comparison, a human hair has a diameter of approximately 75 microns (0.003 in., 0.07 mm). The fine glass strands are entangled and compressed to form a filter mat. Because the individual yarns are so microscopic, most of the carpet is composed of air. Mat openings are very small, generally less than 0.5 micron (0.00002 inch, 0.0005 mm).
HEPA filters will collect particles up to 0.3 microns (0.0003 mm) in diameter. Even if the filter is only 2.5 mm (0.10 inch) wide, it would consist of 2500 layers of glass strands. Electrostatic precipitators rely on electrostatic forces to remove particles from the air. They work by creating a cloud of free electrons through which dust particles are forced to pass. As dust particles pass through the plasma, they are charged, making it easy to collect. Electrostatic precipitators can collect particles up to 0.01 micron (0.00001 mm) in diameter. Air purity has been a concern ever since humans have lived in groups.
One of the reasons hunter-gatherers are nomads is that they periodically need to get away from their garbage cans and latrines. In 1306, King Edward I of England banned the burning of coal in London because of the heavy pollutants left in the air. The industrial revolution of the 18th and 19th centuries only worsened the problem. The burning of coal to produce electricity and fuel trains produced a dark cloud of smoke over all the world's major industrial centers and covered entire cities with soot. To address this problem, engineers built taller smoke stacks to keep debris in the air away from the source. Regardless of the height of the piles, downwind people complained that ash and acid gases from the combustion of coal (the source of acid rain) destroyed their crops. Air pollution worsened again after World War II when cars became the main mode of transport in industrialized world.
Car smog has provided Los Angeles with some of the worst air quality in the world. HEPA filters are designed based on the size of particles to be removed and required air flow rate. The finer pores on HEPA material mean finer particles removed from air but also means that filter material will become clogged sooner and need replacing more frequently. The designer will specify diameter of glass fibers and density of mesh filter cloth that sets pore size for filter. HEPA filters may contain binders that provide additional strength but this also results in filter that clogs up sooner. By-products from manufacturing include non-carbonaceous materials distilled from manufacture activated carbon, specification filter material and excess material that must be discarded in production HEPA filters. Most other manufacturing waste like plastic channels from injection machines and excess sheet metal can be recycled. Additional debris occurs during operation air filters - ions produced by electrostatic precipitators interact with oxygen in air to produce ozone at high concentrations which is poisonous. Ozone levels produced in domestic electrostatic precipitator unlikely reach dangerous levels but some people sensitive even low ozone levels - collector plates electrostatic precipitator should be cleaned periodically. HEPA filters have limited lifespan depending on amount air being filtered through them and amount particulate matter in air - most manufacturers recommend they be replaced every few years. Used filters cannot be recycled so end up landfills - activated carbon can be recycled but cost handling small amount carbon contained household air purifier would be prohibitive so usually also ends up landfills after fully used. As scientists learn more about environmental pollutants and their impact on human health need provide cleaner air homes offices will only increase. Current generation HEPA filters can only remove particles up 0.3 micron (0.0003 mm) diameter whereas believed particles up 0.1 micron (0.0001 mm) diameter can cause mechanical damage lung tissue - viruses can have diameter as small as 0.02 microns (0.00002 mm).Clearly progress still be made indoor air pollution control - current direction technology towards ever finer filter materials - new standard filtration ULPA filter which stands Ultra-Low Penetration Air required remove particles up 0.12 microns (0.00012 mm) diameter approximately one-third diameter smallest particle HEPA filter can remove.