Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
7 Systems, Built Environment Past, Present, Futures Few areas of technological application are as ancient as "the built environ- ment" the structures and communities in which most of us spend our lives- and its relationship to our well-being. This area of human knowledge has never- theless been neglected in important ways. Although occupants of numerous buildings and residents of manifold communities have attested to the adverse environmental health impacts that chronically occur under present policies, and although dedicated organizations have been forming in the Pittsburgh area as elsewhere to pursue agendas for more healthful ways of designing and main- taining built environments, the field has not been the object of serious inquiry and has not seen advances on a grand scale. To remedy this situation, new partnerships have been forged between those who erect the built environment and those concerned about its health impact- including the people who live in it. Another set of environmental health partnerships needs to be established between the country's government, research universities, and communities in diverse socioeconomic and geographic settings. There is no federal research policy, much less a coherent federal research program, that addresses environ- mental health problems raised by built-environment practices. Such partnerships not only could help in financing environmental health research but also could ensure that the human capabilities for fruitfully directing such funds are avail- able. Research programs tend to produce professionals trained in the problems at hand, and especially in the case of built-environment issues such training must be tempered in experience. *This chapter was prepared from the transcript of the meeting by Steven J. Marcus as the rapporteur. The discussions were edited and organized around major themes to provide a more readable summary and to eliminate duplication of topics. 47
48 . ENSURING ENVIRONMENTAL HEALTH IN POSTINDUSTRIAL CITIES Federal and state government involvement can also help to modernize build- ing practices by providing advanced standards and streamlining regulatory regimens. Ultimately, however, it is the interface between the higher-level and com- munity readerships, and decision-making mechanisms within communities them- selves, where the main action must lie. The specific natures of regional climates, land use, neighborhoods, building design, transportation modes, energy systems, and extent and types of preserved natural environments are, in their combina- tions, as varied as the needs and preferences of diverse human communities themselves. Members of those communities should be environmentally informed and empowered to manage their civic affairs in pursuit of universal human goals. A panel of speakers discussed the broad parameters of sustainable built environments the need to reduce sprawl and incorporate walkable communi- ties, for example, and the desirable characteristics of healthy structures as well as approaches to critical decisions such as "smart-growth" communities, trans- portation alternatives, the specific criteria for "green buildings," and sustainable energy strategies for serving communities efficiently while guarding against global climate change. HEALTH AND THE BUILT ENVIRONMENT New principles of architecture and land-use planning must be applied, accord- ing to Vivian Loftness, professor and head of Carnegie Mellon University's School of Architecture, if we are to get beyond the obsolete industrial revolution paradigm and adopt the "human-ecological" approaches that produce healthful buildings and communities. First and most critically, she said, we must move away from single-use zoning i.e., sprawl which is harmful to human environments and human well- being, and move toward "live, work, walk communities" that are less dependent on the automobile and more amenable to social interaction and physical fitness. In a landmark study that has much impressed the design community, the CDC recently published relationships between obesity and land-use policy, recogniz- ing that neighborhoods with significant walking and bicycling have much lower obesity rates, as well as lower rates of depression and Ritalin usage! "We unfortunately only have two viable modes of transportation left in this country cars and airplanes even though almost all other forms of transporta- tion are far more energy- and environment-effective," Loftness said. "They use much less fuel and they put out much less pollution, they require less land and create less runoff and erosion." (See Figure 7-1.) Sprawl communities have higher infrastructural costs virtually across the board for water, electricity, even postal delivery, among others in compari- son to higher-density living environments (see Table 7-1~. Human-ecological design should prevail in the design and renovation of individual buildings as well. Here too, waste, inefficiency, relative neglect, and .
SYSTEMS, BUILT ENVIRONMENTPAST, PRESENT, FUTURE Single occupant automobile Airline Passenger truck Automobiles Transit Rail Transit busses Motorcycle Intercity bus School bus Walking Bicycle 49 6116 3598 3585 3415 2277 965 768 397 39 5074 4950 0 1000 2000 3000 4000 5000 6000 7000 Btu's per passenger mile FIGURE 7-1 Single occupancy vehicles and airplanes are the most viable modes of transportation in the United States and are the least safe energy-effective and environ- mentally safe. SOURCE: Lowe, 1989. Worldwatch Institute C) 1986. Reprinted with permission. TABLE 7-1 Cost of Sprawl in the Suburbs vs. Infille Suburbs (in dollars) Streets/roads 3,000 800 Utility extensions 5,000 950 Gallons H2O/day 400 200 Therms natural gas 150 60 Kilowatt hr./ year 10,000 6,000 Postal delivery (300 times the cost of infill- estimate was only supplied) SOURCE: Wilson, 2002. Urban Ecology ~ 1996. Reprinted with permission. d Areas of a City Infill (in dollars)
so ENSURING ENVIRONMENTAL HEALTH IN POSTINDUSTRIAL CITIES threatened health are the norm rather than the exception. "Over 30 percent of all U.S. energy use, 20-40 percent of U.S. pollution, and 30 percent of U.S. waste are caused by the built environment," Loftness said, "yet there is almost no federal funding to evaluate and reduce these costs." The Department of Energy, for example, devotes only 2 percent of its total budget to building research, despite the fact that 35 percent of United States energy use is in buildings. EPA has an equally small budget for building research, and NIH has no dedicated funding to study the effect of the built environment on health. Moreover, "there are almost no Ph.D. programs in this country dedicated to linking the built environment to health and productivity," she said. "We are looking at an incredibly starved field." Yet there is no shortage of investment opportunities, should funders and researchers decide to give higher priority to green-design principles. Improved and more extensive application of natural light, shading, passive technologies, and high-performance active technologies, for example, would allow for lower energy use and provide more healthful and productive human environments. Meanwhile, the impacts that HVAC (heating, ventilation, and air conditioning) systems, for example, have on health remains relatively unstudied, and short- comings of the past are perpetuated. "We are watching new hospital and office complexes being built with HVAC technology that was developed in the 1950s and has not advanced since," Loftness said. Better HVAC systems would pro- vide personal control, access for maintenance, and separation of ventilation and thermal conditioning. Although such ventilation strategies for improved indoor air quality have been shown to increase productivity and health (Figure 7-2), very few new office buildings even have "operable windows" that allow occu- pants to control outside air or moderate temperature. The advantages of improved HVAC design and of increased access to day- light and natural ventilation are beginning to be measured. A number of United States and Canadian studies have shown improved health and performance in schools and offices: from 5-10 percent reductions in sick-building symptoms to 10-25 percent higher reading and math test scores when workers have natural light (see Figure 7-3~. Nevertheless, "almost all policies are still driving us forward with very small windows, very dark glass, and sealed buildings and even workplaces with no windows at all," said Loftness. Finally, attention must also be paid to the design and renovation of building interiors, she said. "It is extremely important to recognize that the selection of materials and furniture inside buildings is as critical to our health as land-use patterns are." Studies have repeatedly shown, for example, that ergonomic furni- ture reduces musculoskeletal complaints and medical-claim rates, and improves task performance (see Figure 7-4~. Loftness called on the medical community in general, and the U.S. Centers for Disease Control and Prevention in particular, to initiate and publish research that is critical to improving the built environment. "We have the opportunity to
SYSTEMS, BUILT ENVIRONMENTPAST, PRESENT, FUTURE 14 ~ . ~ 12 10 . _ o O_ 6, / / O _ - ~ 3 Hi > o Q 1 Individually Controlled Ventilation System 11 o! ~ improvement in typing 3.25* ..! .~.. ...... _ -----1 Pollutants Increase Outdoor Air Ventilation Rate typing, addition proof reading creative thinking 1.1* 0 ~~ Y ~~ 0 ~~ _ _ T _ .. S _ 1 a' = Provide Task Air 33/ reduction 2 workdays in SBS lossfrom 2% 35d% 0.99~* ARD fPOm SBS in short term A, sick leave 46% improvement in vent. effectiveness 1.38~* 2 workdays I., lossfrom 20°/ improvement ................ symp redU ll iDt~ t in vent. self reported 1.76~ I m prove Filteration -1 1C ~ ssYO - reducecl Non-attendance 1 .65* - ON ~ ~,o;)O ~ ,,oOO ~ ~q>9c4 9~' HOOF `~ ~ ~9O<3 ~ ~ ~q>9C, At- ~ ~~> ~1,~° I' ~~'Q~ ~~ ~~ ~ I've ~ Amp 'I'm Case Studies Introducing Improved Indoor Air Quality ( ~ Performance improvement for specific tasks multiplied by estimated time at tasks ) ( AA Improved ventilation effectiveness calculated relative to productivity gains from other studies 51 :5 1/3 a m C) m hat m C) / _ FIGURE 7-2 Access to individually controlled ventilation or ventilation systems that removed pollutants increased worker productivity. SOURCE: Carnegie Mellon CBPD BIDS/ABSIC Report 2003. Reprinted with permission. dramatically improve the quality of the places we create," she concluded, "with positive impacts for our youngest to the ends of our lives." SMART GROWTH "We like to say that we want to move from building 'developments' to building healthier, safer, and livable that is, smart-growth communities," said Alex Graziani, executive director of the Smart Growth Partnership of Westmore- land County. To achieve that goal (in accordance with the dictionary definition of "economic growth that consciously seeks to avoid wastefulness and damage to the environment and communities"), the 10 Principles of Smart Growth must apply: 1. Mix land uses. Communities that combine land/work/walk tend to be attractively built and maintained places that we wish to travel to, or return to, Graziani said. 2. Take advantage of compact building design. "Compact" should apply not
52 ENSURING ENVIRONMENTAL HEALTH IN POSTINDUSTRIAL CITIES ·5 40 o - ~ ,' ~ ·> 20i f a) o Q . .... ~ 10 c Provide Daylight in Workspaces Sky-lighting stores 40 l o .~ ~ Daylit classroom ....... Provide Operable Windows Provide Mixed-mode Ventilation Daylit office Daylit office lb 15 ~ 1 ff~ Operable window Daviit classroom 7 5 ~ . a,\ User-controlled mixed-mode Ventilation Mixed-mode l 5 Ventilation 3.8 ....... Access to window 0.4 ' i' · of `~q>9~ ~ ~ ~99~ ~°°~ ~°~ ,~P~°~°~ ~~d,~ $~ .~ I ,; Case Studies Introducing Improved Performance with Access to Natural Environment / / ~ Mixed-m ode .....Ve~ntilatian...... 9.75 l rent Croon FIGURE 7-3 Access to natural environment increases productivity. SOURCE: Carnegie Mellon CBPD BIDS/ABSIC Report 2003. Reprinted with permission. Only to buildings per se but to the collection of buildings and other facilities that make up a community. Conventional development is land-consumptive, while smart-growth development uses the same amount of square feet for offices and houses much more efficiently and sustainably. For example, instead of every- one cutting his or her own one-acre lot, everyone can use the community green. Create a range of housing opportunities and choices. We should be accommodating all kinds of residences, Graziani said, "because we need to build communities, not single-use, single-type developments." 4. Create walkable neighborhoods. "If you are able to walk to work, walk to school, and walk to shop, recreate, or worship, you live in a smart- growth community." Foster distinctive, attractive communities with a strong sense of place. Communities should not be Anywhere, USA. Their architecture should have distinctiveness and be beautiful to behold, and they should be built for the future, not just for 10 years. 6. Preserve open space, farmland, natural beauty, and critical environ- mental areas. It's important that new-community developers have a strong
SYSTEMS, BUILT ENVIRONMENTPAST, PRESENT, FUTURE by ~ 45- cn 40 - 35- 2 O 15- ',: 30 - 25 - 20 - 10 - ii~ O 53 ''' 1 ''''''1'''''' 1 ''''''' 1'''''I 1 ~ 1'''''- 1'''''' 1'''''' 1'''''' 1'''''' 1 ''''''' 1 ~ BY z z · cn z Y ~ cn cn cn z ~ cn cn ~ cn z z · I O Z I z us ~ ~~, ~ Cl ~ e ~ ~ ~ Ill 0 I 0 Eli 0 ~ Z NEAR EXTERIOR WINDOW ~ MIDDLE OF THE OFFICE SPACE ~ NEAR INTERIOR CORE OF BUILDING FIGURE 7= Individuals who worked near an exterior window had fewer complaints across the range of sick-building symptoms as compared to those who worked in the middle of the office space or near the interior core of the building without access to windows. SOURCE: Carnegie Mellon CBPD DOE Forrestal/Germantown Field Studies, 1995. Reprinted with permission. sense of landscape architecture, not only to preserve key natural areas but to determine the most harmonious places for home sites and roads and to use parts of the landscape itself for benignly accommodating such needs as storm-water drainage. 7. Strengthen and direct development toward existing communities. By con- centrating growth where infrastructure already exists, natural areas can be preserved for present and future generations. "Someone once said that Yellowstone National Park exists because Manhattan exists," Graziani noted. "In other words, because people have chosen to live in that high- density community, Yellowstone is there to be enjoyed by all of us."
54 ENSURING ENVIRONMENTAL HEALTH IN POSTINDUSTRIAL CITIES 8. Provide a variety of transportation choices. "We should not be building our newest and best developments just for people who can drive, while neglecting people who are disabled or cannot drive because of age [or simply wish to travel by other means]. We need to be building for the entire community." 9. Make development decisions predictable, fair, and cost-effective. In reg- ulating developers, it makes sense to give "green lights for doing the right thing while making the wrong thing conventional development- the one that requires all the variances and conditions," Graziani said. Either way, development becomes more predictable, as well as fair and cost-effective, for the developers and for everyone else. 10. Encourage community and stakeholder collaboration in development decisions. Public involvement is essential, he maintained, and where the public doesn't make the right decisions at times, that doesn't mean it's incapable of doing so. Participants need to be helped and informed. This is consistent with Thomas Jefferson's view on the matter: "I know no safe depository of the ultimate powers of the society but the people them- selves. And if we think them not enlightened enough to exercise their control with a wholesome discretion, the remedy is not to take it from them but to inform their discretion." Public involvement also has practical advantages to all concerned. In that spirit, Graziani shared the following "key concept": "A community-based col- laborative process is a way to reduce confrontation and improve proposed projects by involving the citizens up front in the development process, using their energy positively instead of negatively." TRANSPORTATION'S IMPACTS ON ENVIRONMENTAL HEALTH Transportation and health have linkages across five major categories- physical activity, pedestrian safety, environment, economic, and quality of life- according to David Ginns, a coordinator for Transportation for Livable Communi- ties, which is a joint project of Sustainable Pittsburgh and the Surface Transportation Policy Project (STTP). "The goal of STPP," he said, "is to make our communi- ties more healthy by building transportation systems that serve citizens, not cars. If people can walk to school and work and walk for recreation we will have sound environmental health." Physical Activity The design of our communities the frequent lack of sidewalks, for exam- ple, and dependence on the automobile contributes to higher and higher rates of physical inactivity in the United States population. In 1991, only a handful of
SYSTEMS, BUILT ENVIRONMENTPAST, PRESENT, FUTURE 55 states had adult obesity rates of more than 15 percent; by 2000, all states except Colorado were in the greater-than-15-percent category. Physical inactivity and consequent obesity have been growing at an especially rapid rate among chil- dren. As shown in Figure 7-5, the percentage of overweight children increased during the l990s as the frequency of children's trips made on foot dropped. Communities where children cannot walk to school or to other activities contrib- uted to the problem. Pedestrian Safety "The lack of investment in pedestrian safety contributes to pedestrian deaths," Ginns said. "STPP stands behind an increase in dollars for pedestrian safety and bicycle/pedestrian facilities to resolve this problem and produce healthier and safer communities." Environment The environmental problems caused by motor vehicles are legion. For example, they emit 31 percent of the carbon dioxide in the United States, along with 81 percent of the carbon monoxide and 49 percent of the nitrogen oxides. Reducing such emissions, along with other motor-vehicle-related threats, can only be accomplished by investing in alternatives to the automobile. 20% 16% 12% 8% 4% 0% Percent of Children's Trips Made on Foot ,~ Percent of Children Who Are Overweight · .~~ ................ 1974 1978 1982 1986 1990 1994 Year FIGURE 7-5 The number of trips made on foot by children decreased from 1974 to 1996, while at the same time the percentage of children who were overweight increased. SOURCE: Surface Transportation Policy Project C) 2000. Reprinted with permission.
56 ENSURING ENVIRONMENTAL HEALTH IN POSTINDUSTRIAL CITIES Economics While walking is free, Ginn pointed out that technology-based transporta- tion comes at a price; however, the difference in cost between the bicycle and the automobile is large. The cost of operating a car for one year is approximately $5,170 opposed to $120 for operating a bike. An average family has to work more than 6 weeks to pay a year's car expenses whereas to cover a bike's expenses a family has to work for one day, and walking is free. "By promoting alternative modes of transportation and connecting our communities with bicycle and pedestrian facilities," Ginns said, "we can allow families to invest more dollars in recreational opportunities and, as a result, have healthier families." Quality of Life About 40 percent of adults say they would commute by bicycle if safe facilities were available, and STPP encourages investments that make those facilities a reality. "To make our communities healthier, safer, better connected, and less auto- dependent," Ginn said, requires well conceived and coordinated actions. STTP has formulated such a set of recommendations, which include: (1) collect better data and require more health research; (2) establish bicycle and pedestrian per- formance measures; (3) set aside targeted funds for bicycle- and pedestrian- oriented projects; (4) develop comprehensive bicycle and pedestrian plans; (5) provide safer and more frequent pedestrian crossings and bicycle routes; (6) require bicycle and pedestrian accommodations in every project; (7) create a "safe routes to schools" program; (8) develop a PR marketing campaign; (9) pro- mote compact growth patterns; (10) reward local governments with incentive grants; (11) suballocate/devolve transportation decision making to the local level; (12) provide a commute benefit for biking/walking; (13) improve public facility siting regulations, including schools. In a tribute to TV's Fred Rogers (one of several tributes at the symposium for the recently deceased Pittsburgh native), he compared the idealized "Mr. Roger's Neighborhood" to the real world of the city. "We all know we can't make our communities utopian," Ginns said, "but we can make them healthier and safer. This requires investment in public-transportation, bicycle, and pedes- trian facilities, as well as changes in how we plan and design our communities for environmental health." GREEN BUILDING Pittsburgh' s David L. Lawrence Convention Center the site of this sympo- sium has the distinction not only of being the first environmentally sensitive convention center in North America; it is, according to the "LEED" standard,
SYSTEMS, BUILT ENVIRONMENTPAST, PRESENT, FUTURE 57 "the largest green building in the entire world." So claimed Gary Goodson, deputy director of the Green Building Alliance, which has helped support the convention center's green design, construction, and operations efforts alongside the architects: Rafael Vinoly and Burt Hill Kosar and Rittelmann. LEED is an acronym for the Leadership in Energy and Environmental Design rating system, developed by the U.S. Green Building Council, which the council describes as "a voluntary, consensus-based national standard for devel- oping high-performance, sustainable buildings." Goodson pointed out that LEED has five categories sustainable sites, water efficiency, energy and atmosphere, materials and resources, and indoor environmental quality each of which he briefly discussed with respect to the "landmark effort" that produced the Pitts- burgh convention center. Sustainable Sites "We certainly did not win all the battles," Goodson acknowledged, but the center still won enough to garner its superlative green-building distinctions. For example, it satisfies the LEED requirement of 60,000 square feet of floor space per acre. With regard to transportation connections, it accommodates virtually all modes (excepting a helicopter pad and water landing). To play its part in reducing the urban heat-island effect, the center has a reflective roof and under- ground parking. And to reduce local light pollution, it is not illuminated on the outside. That way, Goodson said, Pittsburghers may better see the stars and migrating birds will be less distracted. Water Efficiency Nonpotable water alone is used on the landscaping, and with the aid of a water-reclamation system, the center's consumption of potable water has been reduced by over 80 percent. Energy and Atmosphere Energy efficiency has actually been increased over the standard by about 25 percent, but the team believes they could have gone even further with more efficient chillers. Materials and Resources Some 90 percent of the now-demolished old center, by weight, was recycled. And regional virgin materials were readily available in Pittsburgh; nearly all of the concrete and steel came from within a 500-mile radius of the city.
58 ENSURING ENVIRONMENTAL HEALTH IN POSTINDUSTRIAL CITIES Environmental Quality During construction, dust kick-up from building materials was minimized by keeping them clean. The finished center has an efficient HVAC system and carefully monitors its carbon dioxide emissions. Using PPG's Pure Performance paint, no volatile organic compounds are emitted. There are individual controls in every room, and all of the areas except meeting rooms enjoy daylight views. With the overall success of this monumental project across all these catego- ries, Goodson suggested, "The Pittsburgh region is a national leader in the green building field." REVOLUTIONIZING ENERGY SYSTEMS Electricity is quite inexpensive in the Pittsburgh area largely because most of it comes from burning coal, according to M. Granger Morgan, professor and head of the department of engineering and public policy at Carnegie Mellon University. But in Pittsburgh as elsewhere, some dramatic changes will have to be made in energy systems over the next few decades in order to deal effectively with carbon dioxide and climate change. Air pollution comes from a variety of sources, but "if you look for the industrial sector that produces the most pollution per unit of economic output, it is electric power, and it produces substantial amounts of oxides of sulfur, oxides of nitrogen, and greenhouse gases," Morgan said. The major greenhouse gas is CO2, which is created when fossil fuels are burned. But unlike most other air pollutants, which have relatively short residence times in the atmosphere, CO2 molecules can remain there for more than 100 years. The result, as is now well documented, is the greenhouse effect. Since the beginning of the industrial revolution, atmospheric concentrations of CO2 have risen by about 30 percent and the planet has already warmed in response by about 1.5° F. The Intergovernmental Panel on Climate Change (sponsored by the United Nations) estimates that over the next century the earth' s average temper- ature will continue to rise by 2.5-10° F. "The impacts of such warming on the economies of the United States and other developed countries will probably be quite small, maybe a couple of percent at most," Morgan said, "but the impacts on the economies of some developing countries will likely be much larger, and the impacts on many natural ecosystems will be really enormous." Such outcomes must of course be averted, but a confounding factor in CO2 buildup is that stabilizing emissions will not immediately stabilize concentrations. Given the gas's long residence time, massive reductions in CO2 emissions in excess of 80 percent will be necessary in order to stabilize concentration. Thus, while options such as conservation and renewables can help, Morgan said, "they can't probably get us 80 percent on time scales of a few decades." There has been a recent revolution in thinking about carbon capture and disposal
SYSTEMS, BUILT ENVIRONMENTPAST, PRESENT, FUTURE 59 (CCS) technologies, which take carbon out of fossil fuel, either before or after combustion and then sequester it deep underground or in the oceans. This is a major area of research at the moment, Morgan said, and its principal venue the National Energy Technology Laboratory happens to be located just south of Pittsburgh. Dramatic technological innovation would not be required for CCS, he main- tained, as we already produce a good deal of hydrogen fuel (which is what would essentially result after stepping fossil fuel, precombustion, of its carbon) and we move CO2 long distances in pipelines and inject large amounts of materials underground (Figure 7-6~. Also, CCS is comparable in cost to other serious options, such as large-scale wind, and far less expensive than long-term options such as solar photovolta~cs. There are no magic bullets, however. It will take a combination of different strategies to begin having serious impacts on CO2 emissions. Consequently, people in Pittsburgh and throughout the country must con- tinue to promote energy efficiency in buildings, transportation, and industrial 1 0000 1 000 en 100 10 1 Large quantities Gases Sub-seabed .4 i , ~ , Long Time Frame Cal w FLMunicipal Oilfield Hazardous Acid Wastewater Brine Waste Gas Natural Gas CO2for OCS water OCS Storage FOR injected for gases FOR and (e.g. NO) brine disposal, CO2from all US power plants 1 r i ...... ............ _ _ FIGURE 7-6 The mass of current United States fluid injections is greater than the mass of current power plant CO2 emissions. SOURCE: E. Wilson, Carnegie Mellon University and U.S. Environmental Protection Agency, unpublished. Reprinted with permission.
60 ENSURING ENVIRONMENTAL HEALTH IN POSTINDUSTRIAL CITIES processes fleet operators and public buildings can take the lead and we need to continue to work on mass transit and the development of renewables, Morgan said. We must also promote combined heat and power systems, which achieve remarkably high efficiencies (more than 80 percent) because they not only make electricity but also use the waste heat to warm (or cool) a building; this is "dra- matically better than the current strategy of making the electricity in one place and the heat for the building in another." Meanwhile, "we need to work to get some large demonstration activities for carbon capture and disposal located here in our area, inasmuch as the country's leading lab is here." Finally, he added, "while nuclear power clearly faces various problems, it is certainly the case that nuclear power is one way to make electricity without carbon dioxide."