Indoor Air Pollution

What's the most polluted atmosphere to which most of us are exposed? One clue—it's not the outdoor air that we've spent zillions of dollars to clean up. The answer? It's the air in our homes and offices. Enormous attention has been paid to outdoor pollution and it's impact on health, but people spend up to 90 percent of their time inside, making indoor air quality extremely important. 

Many people perceive that the risk from outdoor air is substantially higher than indoor air. In fact, the home environment is rarely considered to be a risk in this regard. In terms of regulation and control, the principal sources of pollution, such as vehicles and factories, lend themselves to formal legislative control. By contrast, exposure in the home is very much dominated by personal choice and behavior. 

Scientists have shown that the levels of many substances, such as volatile and semi-volatile organic compounds, are substantially higher indoors than outdoors. Indoor emissions come from many sources, such as stoves, smoking, cleaning products, home furnishings and even people. These chemicals can react with others to form new molecules. Sunlight from windows and emissions from gas stoves often accelerate these reactions. Houses also contain many surfaces including windows, carpets, walls and furniture that can absorb react and re-emit compounds. And people themselves emit volatile organic compounds from their breath, skin and personal care products.¹

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Considering the plethora of compounds in indoor air, it's not surprising that chemists have had a hard time figuring out when, where and how the substances arise. In 2018, a 4-week field study called HOMEChem—House Observations of Microbial and Environmental Chemistry—sought to answer some of these questions. In a manufactured house at the University of Texas at Austin, dozens of researchers, from across the country systematically studied how different human activities influenced indoor air composition. Among many interesting findings, the researchers observed that the order of activities—such as mopping and then cooking or vice versa—influenced air chemistry. These and other studies aim to establish a baseline of what's in indoor air, so that eventually researchers can assess the potential health effects of specific compounds or groups of compounds. ²

One example of past studies: William Nazaroff and Allen H. Goldstein at UC Berkeley studied two houses in Northern California. The vast majority of chemicals that they could measure in air were substantially higher indoors than outdoors. Out of approximately 200 detected chemicals, about half had concentrations about 10 times as high indoors as outdoors, and about 80% had concentrations at least twice as high indoors.³

Some of the most interesting indoor chemicals come from spices used in cooking. A lot of flavor compounds in spices are actually terpenoids—monoterpenes and sesquiterpenes and terpene alcohols. It turns out many of those chemicals are quite reactive in air.

Tobacco smoke is a problem all by itself, and anyone who is not aware of this issue is brain dead. More than 2000 compounds have been identified in cigarette smoke. Many of these are know carcinogens and irritants.⁴

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Smokers are prohibited from lighting up in workplaces, public buildings and now even in some bars. They aren't prohibited from lighting up in their own homes, where they can do serious harm to their family and friends.

Next to smoking, carbon monoxide is the most obviously identifiable problem. In the US around 250 to 300 people are killed every year by carbon monoxide from space heaters, furnaces or other household devices. Another 5,000 to 10,000 victims do not die, yet suffer acute carbon monoxide poisoning.⁵

Even more alarming, several World Health Organization (WHO) studies have shown that the average daily indoor air pollution in developing countries is 1,000-2,000 percent more above the recommended maximum threshold.⁶

An estimated 2.8 million people die annually because of indoor air pollution worldwide, mainly because of the burning of solid fuels (coal wood, or dung) for heating and cooking in the home in developing countries. ⁷

One question is, how concerned should folks in developed countries be about this issue? Charles Dinerstein reports, "Air pollution remains a contentious issue. While everyone is in favor of cleaner air, there is less unanimity over which pollutants, in what concentrations, can harm our health. The linkage between air pollution and disease is beset with problems of accurately identifying a dose-response, a clear temporal connection, and most importantly, biologic plausibility—how does a pollutant cause a disease." ⁸ 

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What is the impact of air pollution on our health?

He adds:

- Studying air pollution is difficult and ever changing. Our increasing understanding, especially about how factors relate to one another, means that our target questions keep changing and are more refined.

- What is the impact of air pollution on our health? The short answer is we do not know, although, it is hard to argue against cleaner air. Nor do we understand the underlying biological plausible mechanisms and their relationship to one another. Our understanding is in its infancy, and perhaps we should be more humble in our declarations.

Control Measures

The first control measure is to remove all smokers from your house, because all other potential indoor pollutants pale by comparison with tobacco smoke. Clearly much easier said than done. Then make sure you have no potential problems with carbon monoxide. Buy carbon monoxide detectors and place them near potential sources of toxic fumes, such as the hot water heater or furnace. Another important step is to make sure you have a vacuum cleaner that really vacuums.

Now that you've eliminated smoking, CO, and have a vacuum cleaner that doesn't recycle the dust, other strategies include a combination of ventilation, source removal or substitution, source modification and air purification changes. 

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References

1. "Atmospheric chemists move indoors," eurekalert.org, December 4, 2019
2. Delphine Farmer and Marina Vance, "HOMEChem: house observations of microbial and environmental chemistry," indoorchem.org, 2018
3. Celia Henry Arnaud, "Chemists move indoors to measure the air quality in our homes," cen.acs.org, November 24, 2019<
4. D. W. Moeller, Environmental Health, Harvard University Press, 1992
5. B. Goldfarb, ChemMatters, October 1997
6. B. Lomborg, The Skeptical Environmentalist, Cambridge University Press, 2001
7. J. Morris, Rethinking Risk and the Precautionary Principle, Butterworth Heinemann, 2000<
8. Charles Dinerstein, "Linking health to air pollution- easier said than done," American Council on Science and Health, December 27, 2019

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