National Benefit of Improved Particle Filtration
No published estimates of the national-level benefits of improved particle filtration in U.S. buildings were identified; however, one published paper  has estimated the per-person benefits of filtering the outdoor air supplied mechanically to office buildings, relative to not filtering this air. From a societal perspective, the annual benefits of reduced premature death ranged from $37 to $144 per office worker and the annual benefits of reduced illness ranged from $8 to $30 per worker. The estimated annual per person cost of providing the filtration was $2.6. (The authors point out that there is some evidence that dirty particle filters reduce work performance and that this effect, if real, could cause productivity losses from dirty filters that overwhelm the benefits of reduced particle exposures when filters are utilized.) If one subtracts the per-person costs from the benefits and scales up these estimates for the 41 million U.S. office workers , the net annual benefits are $1.4 to $5.8 billion for prevention of premature death and $0.2 to $1.1 billion for avoided illness. While we would expect smaller national-level benefits from simply improving particle filtration in offices, as opposed to adding filtration if totally absent, the benefits would still be large. Also, because of the larger population in homes and the larger time spent in homes, the benefits of improved filtration in homes may be substantially larger than the estimates provided above. Most filtration systems would also reduce indoor concentrations of particles from indoor sources, bringing additional health benefits. However, current information on the health effects of indoor-generated particles, other than those from tobacco smoking, are too limited to permit a quantification of the benefits.
Experimental demonstrations of many of the health benefits of reduced exposures to outdoor air particles from improved particle filtration are difficult because many of the health effects are rare (but severe), such as premature death and hospitalization. Very large study populations and long-term studies would be necessary to demonstrate these health benefits. One study has demonstrated in controlled experiments that the addition of particle filtration in homes improved vascular function, which is a predictor of cardiovascular health effects . Other research has found that increased use of central air conditioning in U.S. homes markedly reduced the adverse health impacts associated with outdoor air particles with a diameter of 2.5 micrometers or smaller . The authors attributed the benefits of central air conditioning to the particle filters in central air conditioning systems; however, homes with air conditioning may also have less opening of windows, which would also reduce indoor exposures to outdoor air particles. Several studies have evaluated whether use of portable air filter systems in homes reduce acute health symptoms of allergies or asthma in allergic individuals, with mixed results. While there is some evidence of reduced adverse health symptoms, the extent of improvement appears small . Another challenge is that outdoor air and indoor air particle concentrations often increase or decrease in sync with outdoor air gaseous pollutants such as ozone. Consequently, it has been difficult to fully isolate the impacts of particles on adverse health outcomes.
In many commercial buildings and homes, filter system improvements will be simple to implement. Particle filters with a wide range of particle removal efficiencies are commercially available. In many situations, higher efficiency filters can directly replace existing lower efficiency filters in air handling systems. In some air handling systems, the hardware holding the filters will need to be changed to allow installation of filters with a greater depth in the direction of airflow, so that the airflow resistance is not increased to an unacceptable level. In commercial buildings, the largest challenges will be to upgrade filters in existing rooftop air handlers, as some of these air handlers will not have sufficient space for installing a deeper filter. Often, however, filter efficiency can be upgraded moderately without increasing filter depth. The largest challenge to filter system upgrades in homes, will occur when the home does not have a forced air heating or cooling system, as these homes will not have an existing particle filtration system to upgrade. Also, filter upgrades in the air handling systems of homes will only be effective in reducing indoor particle concentrations when the air handlers operate during periods of space heating and cooling. Stand-alone fan-filter systems can be used in these homes, but with increased equipment and energy costs.
There is some evidence that dirty particle-loaded filters can decrease work performance . There is no evidence that using more efficient filters, in place of lower efficiency filters, diminishes work performance, but this effect cannot be ruled out. More frequent filter system replacement or use of particle filters containing some activated carbon have been suggested for reducing the potential adverse impacts of particle-loaded filters [22, 27].
The cost of filtration is increased when higher efficiency filters are used, but it is not necessary to use filters with a very high efficiency to significantly reduce indoor particle concentrations, thus, the cost increases are modest .