The climate of the Earth is changing. As it does, we are experiencing some very immediate, visible and dramatic consequences. Increases in atmospheric air and ocean water temperatures have resulted in the melting of polar ice caps, a rise in storm intensity and a record numbers of forest fires. The Natural Resources Defense Council estimates that one million species could become extinct by mid-century as a result of these tremendous disruptions to the Earth's ecosystems.
The culprits responsible for this devastation are greenhouse gasses (GHGs) that are being emitted into and trapped in the Earth's troposphere—that part of the Earth's atmosphere closest to the planet's surface. The build-up of these GHGs is causing the air above the Earth's surface to warm at a significant rate. Life as we know it on the Earth is changing as a result.
THE SOURCES OF GREENHOUSE GASSESWhere do these greenhouses gasses come from? Largely from buildings and vehicles, both of which enjoyed a spectacular rise in numbers here in the United States in the time period following World War II. As American cities expanded into the surrounding greenfields to form suburbs (a phenomenon we now call urban sprawl), a significant increase occurred in the number of buildings constructed. This was subsequently followed by an increase in private vehicle ownership to provide access into the newly-built suburbs.The energy consumed by all these new buildings and vehicles, however, began to cause havoc with the atmosphere. Buildings consume energy for long-term space heating and cooling, water heating, lighting, and for power. Vehicles consume energy to power their engines. In the past, both buildings and vehicles have primarily depended on energy sources produced by burning non-renewable fossil fuels such as coal and oil. The output of combustion is a combination of inorganic gasses and particulate matter that contribute to GHGs. Buildings consume about 42 percent of the U.S. energy supply for operation and construction, and contribute to about 40 percent of U.S. GHG emissions. Together, buildings and transportation account for about 73 percent of the total U.S. GHG emissions. The United States is the world's largest producer of GHGs and contributes about 25 percent of the world's GHG emissions. As GHG levels rise, the atmospheric carbon dioxide (CO2) concentration has risen from a pre-industrial level of 280 parts per million (ppm) to today's level of 380 ppm. If we continue with "business as usual," and we account for the anticipated global population growth, the CO2 level will rise above 450 ppm in the latter half of the 21st century, which is not desirable for the long-term health of the planet and its occupants.
Energy is produced by burning fossil fuels in the troposphere. When we burn these fuels, the output is a combination of GHGs, including carbon dioxide, sulfur dioxide, nitrous oxides, diesel particulates, and diesel gasses. These GHGs are trapping heat in the air above the Earth's surface—causing the temperature to rise, which results in climate change. This rise will place additional loads on a building's cooling systems, which in turn will require more energy and emit more GHG at the source.
This temperature increase is also causing a buildup in the troposphere ozone level. Ozone is formed through a complex series of chemical reactions involving sunlight on nitrogen dioxide and hydrocarbons. So as the air above the Earth's surface warms up, we see an increase in ground-level ozone known as environmental smog.
A CHEMICAL SOUPThe air in buildings is made up predominantly of outdoor air brought in through mechanical ventilation (fans) or natural ventilation (operable windows). When the outside air enters a building, it brings with it high levels of outdoor ozone, which then combines with indoor ozone produced by equipment such as photocopiers and laser printers, and increases the indoor air ozone concentration.U.S. Environmental Protection Agency (EPA) studies show that the concentration of chemicals is two to five times higher indoors than outdoors. Indoor air is a complex chemical soup made up of volatile organic compounds (VOCs); semi-volatile organic compounds (SVOCs); microbial organisms and microbial volatile organic compounds (MVOCs); and inorganic chemicals and particulate matter (see "Special Report: The Air We Breathe," Interiors & Sources, March 2008). When ozone, a strong oxidizing agent, is added to this mixture, secondary reactions with the chemicals already in the indoor air soup occur, producing "secondary" products or chemicals in the air. Many of these secondary products have irritation and health impacts that are different from, and in some instances, more harmful than the initial compounds.
A quick review of the scientific literature reveals some interesting information about ozone's effects on indoor air:
- Ozone reacts with unsaturated compounds such as terpenes emitted from wood-based materials, including medium-density fiberboard, to produce strongly irritating compounds and aldehydes.
- Ozone reacts with the oils found in linseed oil—made up of esters of linolenic, linoleic and oleic acids—to produce a strong and persistent odor and aldehydes commonly found in buildings where linoleum and other linseed oil products (e.g., paints, polishes) are used.
- Some cleaning agents, including the newer, so-called "green" cleaning agents, contain compounds that react with ozone to form irritating indoor contaminants. For example, pine and citrus oil cleaners are a source for terpenoids, including a-terpinene, d-limonene, terpinolene, and a-terpneol that react with ozone to produce secondary compounds, including formaldehyde (a known carcinogen and respiratory irritant with a very low threshold for health effects) and ultra-fine particles, which can potentially harm human health. Other cleaning products contain ethylene-based glycol ethers, terpenes and other ozone reactive compounds.
- Ozone reacts with the emissions from photocopier toner, printed paper, and movable office partition systems to produce compounds that may persist for months after the reaction has occurred.
- Some latex paints emit monomers that react with ozone to form formaldehyde.
- Once secondary compounds are formed, they may become absorbed into the more porous building materials such as ceiling tiles, insulation materials, and carpets, and then may emit (called "desorbed") these secondary compounds into the indoor air over a long period of time.
Because Americans spend about 90 percent of their time indoors, their exposure to ozone and the chemicals produced by these secondary reactions occurs primarily within the four walls of the buildings they occupy. Inhalation of ozone itself directly affects human health, including reduced respiratory system function and mild lung inflammation. Studies show that exposure to secondary compounds could be as much as twice that for ozone itself, and that these secondary compounds will also have health effects, including an increase in respiratory diseases, asthma and allergies. Children and the elderly also may be more susceptible. If we connect just a few of the compounds identified above with potential health hazards, the list might look like this:
- Formaldehyde—classified by the World Health Organization as a known carcinogen; it also affects the respiratory system and eyes.
- Acetaldehyde—long-term exposure to this compound may have an impact on the respiratory system.
- Ozone and fine particles—predicted to increase the severity of asthma symptoms in children.
The obvious solution starts with reducing the amount of GHG that we produce. The big picture suggests that we think carefully about compact urban and transit-oriented development and walkable communities as described in a recent book by Christopher B. Leinberger, The Option for Urbanism, Investing in a New American Dream. Buildings should be designed to be energy efficient for the long term by using good site design to optimize the local climate impact on the building; improving the thermal performance of the building envelope using high-performance insulation and glazing; utilizing high performance heating, cooling and ventilations systems; capitalizing on natural ventilation where the outdoor air quality is acceptable for use indoors; and by using natural daylighting supplemented with efficient electric lighting. The next step is to explore the opportunities to change the energy production mix to reduce the use of fossil fuels, and to find more renewable energy sources as much as is feasible. Currently the menu of renewable energy sources includes the use of solar electricity generation using photovoltaic panels, solar hot water heating, wind energy generation, and geothermal heat sources.
At a more detailed building level, following the design principles outlined in "The Air We Breathe" provides good overall guidance. Applying the four principles—and taking into account the goal of reducing indoor ozone concentrations and secondary chemical reactions—a number of sustainable building strategies should be evaluated on a project by project basis:
1. SOURCE CONTROL- Since the major source of indoor ozone is outdoor ozone, building designers should obtain as much information as is available on the project-specific local outdoor ozone concentrations. This information will assist in establishing a baseline for understanding the effectiveness of mechanical or natural ventilation systems, and the level of ventilation and air filtration that might be needed.
- When selecting indoor materials, select those with low-VOC and low-formaldehyde emissions in order to reduce the indoor chemical concentration and to reduce the potential for ozone-generated secondary reactions. Building materials should be tested for VOC emissions and should comply with the requirements of the California Special Environmental Requirements Section 01350.
- When selecting indoor materials, select those with low embodied energy as verified with a formal Life Cycle Assessment (LCA). The LCA data provides information on the energy and water used to: mine the raw materials and manufacture the component materials and final products; transport the product; and recycle the product. The data is also useful because it requires energy to transport the product from the source to the use location.
- Increase the building ventilation rates to remove the indoor ozone and reduce the chemical concentrations. However, manipulating the ventilation rates has not proved very effective in the long run. Increased ventilation increases the building's energy use, and on very hot days, may increase the amount of outdoor ozone introduced into the indoor air. One solution is to temper or cool the air before distributing it throughout the building.
- New methods for energy-efficient and low-cost ozone air filtration are now being proposed to remove ozone from incoming outside air prior to use inside a building, especially in regions of the country that experience high outdoor ozone levels. Ozone reacts with and uses up the carbon molecules, and as such, research shows that filtration media containing quantities of activated carbon is effective at removing ozone from the incoming air.
- Pre- and post-occupancy air testing for indoor chemical compounds should be performed to detect the currently known indoor contaminants and to detect predicted and suspected secondary compounds.
- When selecting indoor materials, select those that can be cleaned with low-emitting cleaning agents that are known to have low reactivity with ozone, thus limiting the formation of secondary compounds. Avoid the use of cleaning products that contain pine or citrus oils, and those that are pine or citrus scented.
- Provide adequate ventilation while cleaning indoor spaces, and maintain high ventilation rates for several hours after cleaning.
- Provide dedicated ventilation to the outdoors for spaces where cleaning products are stored.
- If ozone filtration media are used, regular maintenance and replacement of the media will be necessary.
During the past decade, much has been written about global climate change based on science, reports, research, and actual observations. The movie, "An Inconvenient Truth," was able to publicize the issue in a way that scientists could not. The result is a highly elevated national awareness of the global challenges facing the Earth's citizens and ecosystems.
Quite a number of studies about the impact of GHGs and ozone on the indoor climate and building occupant health have also been produced. These, however, have not been as widely publicized as they are more scientific and dense in nature. It is imperative, however, that we recognize the important correlation between global climate change and indoor building occupant health—a vital connection which clearly indicates that human health will decline. That puts the onus on design professionals, who have the ability to design buildings to improve human health. One key action is to improve building design, including selecting appropriate materials and ventilation systems that reduce ozone concentrations within buildings and that reduce the potential for secondary chemical reactions to take place.
Now is the time to acknowledge this trend and take appropriate action.
Anthony Bernheim, FAIA, LEED AP, is principal, Sustainable Design Solutions, for HDR Architecture Inc. Bernheim has nearly 30 years of experience as an architect, with a unique expertise in integrating sustainable and high-performance building techniques and methodologies. He is especially recognized for his expertise in indoor air quality; his leadership and participation was key in the development of an innovative green building Special Environmental Requirements specification (now known as section 01350) that established nationally recognized standards for improved indoor air quality and material resource efficiency. Bernheim is a member of the National Board of Directors for the U.S. Green Building Council. In 2004, he received the AIA California Council's Nathaniel A. Owings Award in "recognition of a lifetime of service, commitment, and advocacy for the principles of sustainable design and preserving the Earth's natural resources." He can be contacted at [email protected].
