California Air Resources Board

Good indoor air quality depends on several factors such as the reduction of indoor pollutant sources like smoking, consumer products and building materials that emit harmful chemicals, and minimizing emissions from sources such as cooking. The level of indoor pollutants can also be reduced through passive ventilation by opening windows, and with active ventilation and the use of high efficiency filtration to minimize outdoor pollutants coming into the home. Good indoor air quality is particularly important for people who may be more sensitive to air pollution effects, such as children, the elderly, and those with chronic conditions, like asthma or cardiovascular disease.

Selected Indoor Air Quality Studies

Below, you will find links to some of our more recent studies on indoor air quality, filtration and ventilation that have been funded by CARB. You can also view all CARB research projects, ongoing and completed, in our searchable research project catalog.

Benefits of High Efficiency Filtration to Children with Asthma

(Contract 11-324, Completed in 2018)

This study evaluated the use of high-efficiency filtration in homes with asthmatic children. The investigators found that portable air cleaners and central air systems equipped with high efficiency filters reduced indoor air pollution in the homes of children with asthma, and reduced their medical visits for asthma as well, but not their asthma symptoms.

News Release

Characterizing Formaldehyde Emissions from Home Central Heating and Air Conditioning Filters (Contract 14-303, Completed in 2018) Studies have shown that some fiberglass filters used in commercial heating, ventilation and air conditioning (HVAC) systems can be sources of formaldehyde. The investigators found that formaldehyde emissions from residential fiberglass filters also emit more formaldehyde relative to synthetic filters, and they estimated their contributions to indoor concentrations in California homes.

Reducing In-home Exposure to Air Pollution (Contract 11-311, Completed in 2016) This study evaluated eight combinations of ventilation and air filtration systems for pollutant removal and energy use installed in an unoccupied test home. The researchers found that all systems reduced indoor particle levels that originated from outdoor air, and that four systems reduced the level of indoor PM by more than 90 percent. 

Environmental Exposures in Early Childhood Education Environments and Follow-up: Evaluation and Identification of Volatile Organic Compounds in Early Childhood Education Facilities (Contract 08-305, Completed in 2012; and Contract 12-330, Completed in 2015) These studies examined environmental characteristics and contaminant levels in air and dust of 40 California early childhood education (ECE) facilities. The initial study detected over 40 volatile organic compounds (VOC) in the air of these child care facilities. The follow-up study analyzed many of the VOCs and their potential health risks and found 12 chemicals that warrant additional exposure and health evaluation due to their potential for carcinogenic, neurologic, or other health effects.

Indoor Environmental Quality and HVAC Survey of Small and Medium Size Commercial Buildings. Field Study (Contract 06-311, Completed 2011) This field study of 37 buildings throughout California obtained information on all aspects of ventilation and levels of indoor air pollutants. The study results showed that many of the buildings such as healthcare establishments, gyms, offices, and retail stores had low air exchange rates and were not getting enough outdoor air into the building. As a result, these buildings did not meet Title 24 ventilation requirements. However, the building shell did provide partial protection from outdoor particles.

Ultrafine Particles in Schoolrooms and Homes (Contract 05-305, Completed in 2010) This study identified and improved our understanding of the factors that influence ultrafine particle levels in schoolrooms and homes by characterizing the generation of ultrafine particles from indoor sources and measuring infiltration from outdoors (e.g. heavily traveled roadways). The study results showed that particle number (PN) counts in occupied classrooms and homes were much higher than unoccupied spaces. Also, PN exposures per person were higher for people in homes than in schools.

How CARB Uses the Findings from the IAQ Research Program

The findings from CARB funded research contracts have informed both regulations and policies at CARB, and provided the scientific basis for actions taken by other agencies and organizations as well.

Update to the New Building Code: Recently, CARB worked successfully with the California Energy Commission to increase the filter efficiency requirements in new buildings from the currently required MERV 6 to MERV 13, beginning in 2020. The updated standard will have a major impact because it effectively reduces PM2.5 that enters homes from the outdoor environment, and it is more health protective. This is a marked improvement compared to the requirement of MERV 6 filters in current building code.

New Building Energy Efficiency Standards on Filtration Requirements

Additional Information for Green Buildings & Energy Efficiency

Near Roadway Exposure Technical Advisory: The findings from our studies were also part of a 2017 technical advisory recommending that high-efficiency filtration be used as a mitigation measure to reduce indoor PM near busy roadways. This advisory, which summarizes strategies to reduce air pollution exposure near busy roads, provides planners and other stakeholders with information on science-based strategies that can be implemented to reduce exposures. This guidance provides evidence on the effectiveness of high efficiency filtration to remove particulate pollution, and recommends high efficiency filtration in new construction, especially in infill areas and near busy roadways, to reduce exposure to traffic emissions, protect public health and promote equity and environmental justice.

Guidance Documents: Air Cleaner Information for Consumers provides guidance to consumers on topics such as how to properly choose and use portable air cleaners and central system filters, and how to minimize exposure to wildfire smoke. CARB recommends high efficiency filtration in its guidance document for selecting air cleaners and central filters.

CARB also has collaborated with other state agencies and the U.S. Environmental Protection Agency to update the 2016 Wildfire Smoke Guide for Public Health Officials with current information and a fact sheet on the selection and use of indoor air cleaners. The updated guide was released in August of 2019 and can be found at Wildfire Smoke, Guide for Public Health Officials.