Climate Change.
The average temperature of the earth has risen by 1.4°F over the past 100 years and will continue to rise, causing large shifts in the climate. Over this same time period, human activities have released increasing amounts of carbon dioxide (CO₂) and other greenhouse gases into the atmosphere. Activities that release CO₂ include burning coal to produce energy and deforestation. In the intermountain west, temperatures have increased by 2°F in the last 30 years (WWA, 2008). Climate models predict that this region will warm by 4°F by 2050, relative to a 1950-1999 baseline. To reduce the serious impacts of climate change, humans must begin to reduce their emissions of greenhouse gases and use less energy.

Building Energy Use.
In the US, commercial (19%) and residential (22%) buildings accounted for 41% of primary energy consumption in 2010, directly translating into CO₂ emissions (DOE 2011a). For residential buildings, space heating accounted for 45% of site energy consumption (DOE 2011b). In Colorado, space heating accounts for more than half of household energy use (54%), compared to air conditioning, which accounts for 1% (EIA 2009). Much of this energy is lost by escaping through unintentional openings in the homes, like cracks around doors and windows. Weatherization home improvements can save up to 30% energy.

Home Weatherization.
More than 7 million US homes have received energy efficiency improvements since the start of the Weatherization Assistance Program in 1976. These improvements include heating and cooling upgrades, improved insulation, air sealing, caulking, weather-stripping to doors and windows, and window replacement. Weatherized households are now seeing $250-$480 annually in energy savings. Homes that are weatherized under federal programs are required to have added ventilation if the home becomes too tight. This is typically done by adding a continuous exhaust ventilation system to the home, which increases ventilation by infiltration through the building shell.  Many homes are not retrofitted with federal funds, but by state funds or industrial programs. Unfortunately, tightening up a home can also have negative impacts on the IAQ within a home.

Indoor Air Quality Changes with Weatherization.
Outdoor pollutant levels, indoor sources, natural infiltration or mechanical ventilation, pollutant transformation, and surface deposition determine indoor pollutant levels in homes (IOM 2011). Indoor sources produced by occupant behavior are episodic (cooking, showering) or intermittent (painting, pesticide use), whereas sources produced by the home construction are mainly continuous (emission from furnishing, materials, stored products).

Home energy retrofits, or weatherization improvements, can improve IAQ by remediating existing hazards such as lead or radon, reducing air exchange with outdoor air lowering outdoor pollutant levels indoors, removing pollutant sources such as water leaks and unvented heaters, and by adding functional ventilation and/or filtration (IOM 2011; Nazaroff 2013). On the other hand, weatherization can worsen IAQ by disturbing legacy pollutants such as lead or asbestos, reducing ventilation leading to an increase in indoor pollutants, introducing new formaldehyde-emitting construction materials, and failing to install mechanical venting when it is needed or installing unreliable systems. Specifically formaldehyde (HCHO) is a toxic air pollutant and classified as a human carcinogen, which is pervasive in homes (Hun et al., 2010; IARC 2006). Lower ventilation rates in homes are an important determinant of HCHO levels in homes (Gilbert et al. 2005). There are numerous indoor sources of HCHO, such as pressed-wood products and consumer products. Emissions are continuous over time and levels could be significantly impacted by weatherization.

Indoor air quality studies of weatherized residential buildings have shown that some pollutant levels increase, while others decrease. A recent study by Noris et al. (2013) conducted energy retrofits on 16 low-income multifamily apartments that were designed to save energy and improve IAQ. Particulate levels, CO₂, and volatile organic compounds (VOCs) generally improved whereas (HCHO) and nitrogen dioxide (NO₂) varied by building. Larger decreases in indoor sourced pollutants were realized with larger increases in ventilation rate and IAQ improved more in buildings with added mechanical ventilation (excluding particles). A modeling study of weatherization impacts on IAQ showed that air tightening by 40% (reducing leakage area from 12.5 to 7.5 ACH50) worsened occupant exposures to all pollutants (Emmerich et al. (2005). Most interventions reduced some pollutants and increased others. Kitchen exhaust had the broadest positive effects. et al. (2005).

Health Impacts Related to Weatherization.
People spend a majority of their time indoors, and much of that time is at home. Weatherization has the potential to worsen IAQ, possibly resulting in adverse health effects. Health impacts of poor IAQ depend on the pollutant. The top four indoor air pollutants that have the highest chronic adverse health impact are particulate matter with diameters less than 2.5 microns (PM_2.5), secondhand smoke, radon (smokers), and formaldehyde (Logue et al. 2012). Exposures to pollutants from indoor sources, or as the result of occupant behavior, have the potential to increase when a home becomes tighter, resulting in higher exposures. Exposure to pollutants originating outdoors would decrease.

Adverse health impacts due to indoor air pollutant exposures is difficult to measure. Many health impacts are chronic and occur after years of exposure (i.e., early mortality from PM_2.5, cancer from formaldehyde exposure). Other health effects are acute, such as an asthma attack or sick building syndrome symptoms. Health effects studies, which have mostly been done recently on multifamily residential buildings, have shown varying outcomes. Wilson et al. (2013) showed that self-reported respiratory symptoms were more frequent after retrofit (-26%), residents had greater sleep disruption due to asthma (-28%), and improvements in general health were reported (reduced asthma medication usage, hypertension, sinusitis). There was no provision of mechanical ventilation in the retrofits. Breysse et al. (2011) reported on a green renovation of three multifamily affordable housing buildings that resulted in adults reporting significant improvement in overall, asthma, and non-asthma respiratory health, and significant improvement in non-asthma respiratory health. Renovations included adding continuous and spot ventilation. Energy reductions of 45% where realized. A draw back to this study was that pre-retrofit health was reported retrospectively one month after moving into renovated apartments.

Lower-Income Community Impacts.
Low-income communities are disproportionately exposed to poor indoor and outdoor air quality as well as hazardous housing conditions (Bashir 2002; Houston et al. 2004; Krieger et al. 2002; Litt et al. 2010) Rates of asthma, including incidence and asthma morbidity are higher in low-income populations (IOM 2000). While low-income populations may have the most to gain financially from reduced heating and cooling bills that weatherization can provide, they may also be most vulnerable to adverse health effects.

Wildfire Impacts.
While tightening a home has the potential to increase pollutant levels indoors, particularly for those pollutants that originate indoors, it also may have a protective effect by keeping out unhealthy outdoor air pollution. A major concern in the western US is smoke from wildfires, which are a significant source of particulate matter and carbon monoxide (CO). Climate change is expected to increase the frequency of wildfires and area burned (Yu et al. 2013; Westerling et al. 2006; Spracklen et al. 2009). Figure 1 shows the increase in number of wildfires per decade in Colorado (CSFS 2014).

Reducing exposure to wildfire particulate matter will be protective for public health. Studies of health and wildfire incidence report significant adverse health outcomes. Kunzli et al. (2006) investigated self-reported symptoms of children ages 6–18 years old exposed to smoke from a large wildfire in Sothern California and found that symptoms were associated with self-reported level of exposure and PM10 concentrations (PM with diameters less than 10 μm). Statistically significant fire-related increases were observed in respiratory hospitalizations, for COPD and asthma by Mott et al. (2005). During the Hayman fire in Colorado in the summer of 2002, Sutherland et al. (2005) found that self-reported adverse symptoms from COPD patients significantly increased on days with elevated PM_2.5.

Frequency of Forest Fires in Colorado.
In the last decade the average number of fires has risen to more than 2400 per year (Figure 1), with the vast majority of the fires in the warmer months. These fires routinely affect the air quality of Colorado front-range communities. Larger and more frequent fire events have become more common in Colorado in the last few decades (CSFS 2014). In 2012, there were 1,498 fires and 246,000 acres burned in Colorado (NIFC 2014). In 2012 (most recent data available), over 5000 fires were started in the Rocky Mountains, burning over 1 million acres (http://wildland-fires.findthedata.org/l/53/2012).

The location of households relative to the fire may have important implications for both indoor and outdoor air quality measures. PM emissions from wildfires are carried over large distances increasing PM concentration in communities hundreds of miles from the event. Larger particles (greater than 10 μm) tend to settle closer to the source due to gravitational settling while fine particles (2.5 μm or less), which are of primary concern for IAQ and health) can be transported over long distances (Sapkota et al. 2005; Zhu et al. 2002).

What to do next.
There is an urgent need to understand the impacts of climate change and weatherization on resident health and IAQ. It is important to understand how home energy retrofits, which are being done all over the US impact the complex indoor environment.  Weatherization has the potential to both increase the levels of indoor sources of pollutants while also decrease the levels indoors of outdoor pollutants. It is a move in the right direction for weatherization programs that use federal funds to require assessing ventilation rates and if they do not meet the guidelines from ASHRAE 62, then mechanical ventilation must be installed. This should also probably be required for all weatherization efforts.

References.

• Bashir, SA (2002). Home is where the harm is: inadequate housing as a public health crisis, Amer J Public Health 92:733-738.
• Breysse, J, et al. (2011). Health Outcomes and Green Renovation of Affordable Housing. Public Health Reports 126(Suppl 1):64–75.
• CSFS (2014). Colorado State Forest Service. http://csfs.colostate.edu/pages/documents/COLORADOWILDFIRES_reprt_table_cb_000.pdf, accessed Jan 2014.
• DOE (2011a). 2011 Buildings Energy Data Book, Chapter 1: Buildings Sector. http://buildingsdatabook.eren.doe.gov/ChapterIntro1.aspx.
• DOE (2011b). 2011 Buildings Energy Data Book, Chapter 2: Residential Sector. http://buildingsdatabook.eren.doe.gov/ChapterIntro2.aspx.
• EIA (2009). Household energy use in Colorado, http://www.eia.gov/consumption/
• residential/reports/2009/state_briefs/pdf/co.pdf.
• Emmerich, S, et al. (2005) Modeling the IAQ Impact of HHI Interventions in Inner-City Housing, NIST. NISTIR 7212.
• Houston, D, et al. (2004). Structural disparities of urban traffic in Southern California: implications for vehicle-related air pollution exposure in minority and high-poverty neighborhoods, J Urban Affairs 26:565-592.
• Institute of Medicine (IOM). (2000). Clearing the Air, Asthma and Indoor Exposures. National Academies Press. Washington DC.
• Institute of Medicine (IOM). (2011). Climate Change, the Indoor Environment, and Health. Eds. D. Butler and J. Spengler. National Academies Press, Washington DC, ISBN: 0-309-20941-2.
• Krieger, J (2002). Housing and health: time again for public health action. Am J Public Health 92(5):758-768.
• Litt, JS (2010). Housing environments and child health conditions among recent Mexican immigrant families: a population-based study, J Immigrant Minority Health 12:617-625.
• Logue, JM, et al. (2012). A method to estimate the chronic health impact of air pollutants in U.S. residences, EHP 120:216-222
• NIFC (2014). National Interagency Fire Center. http://www.nifc.gov/fireInfo/fireInfo_statistics.html, Accessed Jan 2014.
• Noris, F, et al. (2013). Indoor environmental quality benefits of apartment energy retrofits. Build Environ 68:170–178. doi:10.1016/j.buildenv.2013.07.003
• Sapkota, A (2005). Impact of the 2002 Canadian forest fire on particulate matter air quality in Baltimore City, Environ Sci Technol 39:24-32.
• Spracklen, DV, et al. (2009). Impacts of climate change from 2000 to 2050 on wildfire activity and carbonaceous aerosol concentrations in the Western United States. J Geophys Res-Atmos 114:Article D20301.
• Westerling, AL, et al. (2006). Warming and earlier spring increases western US forest wildfire activity. Science 313:940-943.
• Wilson, J, et al. (2013). Watts-to-Wellbeing: does residential energy conservation improve health? Energy Efficiency, 1–10. doi:10.1007/s12053-013-9216-8
• WWA (2008). Climate Change in Colorado, A Synthesis to Support Water Resources Management and Adaptation. Report for the Colorado Water Conservation Board. University of Colorado Boulder, http://wwa.colorado.edu/publications/reports
• /WWA_ClimateChangeColoradoReport_2008.pdf.
• Yue, X, et al. (2013). Ensemble projections of wildfire activity and carbonaceous aerosol concentrations over the western United States in the mid-21^st century. Atmos Environ 77:767-780.
• Zhu, Y, et al. (2002). Concentration and size distribution of ultrafine particles near a major highway, J Air Waste Manage Assoc 52:1032−1042.