Air Filters

Use and Production

Air filters are used in vehicles to both filter the air for the passenger compartment and prevent the entrance into an engine's cylinders of abrasive particulates that will contaminate the oil and contribute to mechanical wear and tear. Both types are usually made of pleated paper, sometimes felt. Ford introduced a new long-life filter system for engines in 2003 that uses foam instead of paper: these filters are placed in the bumper of the car with a stated [Page 17]150,000-mile service interval. But apart from the use of these filters in the Ford Focus, nearly all engine air filters are made with pleated paper.

The paper used for filters is called “filter paper” and is similar to the paper used for coffee filters and tea bags. The material, usually made with high-cellulose bleached wood pulp, called “dissolving pulp,” may be treated with chemical reagents and impregnated to increase moisture resistance before being pleated. It is semipermeable and placed perpendicular to the expected airflow, and many heavy-duty filters may be rinsed periodically in order to extend their life.

Dissolving pulp is made from pulpwood (timber grown specifically for paper production). Most pulpwood forests are reforested as standard practice, making them a renewable resource. Pulpwood can also be harvested from mixed forests, in which the better-quality trees are used for lumber production, while pulpwood is made from the four types of trees inferior for lumber: open-grown trees, which have heavy branches low on the trunk; dead or diseased trees; treetops; and trees too small for logging. Salvage cuts after natural disasters are often used for pulpwood. Typical tree varieties used for dissolving pulp include aspen, paper bird, red maple, balsam fir, jack pine, and white spruce, all of which have high cellulose content.

Health Effects

On the face of it, the production of air filters is largely environmentally friendly. The bleaching, however, can be considered problematic. Whiteness is considered desirable in most filters because it makes it easy to visually ascertain how dirty the filter has become. Various chemicals are used to reduce the chromophores (color-causing substances) in the pulp, including chlorine dioxide, hydrogen peroxide, sodium dithionite, magnesium salts, and sodium silicate. Ozone is sometimes promoted as an oxidizing agent for bleaching because it can achieve results without any chlorine (in products designated “totally chlorine free”) or without any elemental chlorine (in products designated “elemental chlorine free”). The main way in which bleaching pulp can damage the environment is through the release of materials into waterways, which are usually located near pulp mills because significant amounts of water are required for their operation. The substances released include chlorinated dioxins, which are recognized as a persistent environmental pollutant with significant human health effects. Most human exposure to dioxins is through food because they accumulate in the food chain through the fatty tissues of animals.

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