by Paul Ehrlich , Air Quality & Clean Air Issues Coordinator

February 2019

In the April/May 2018 issue of the Jersey Sierran I wrote about a Science article* (summarized in The Changing Face of Urban Air Pollution**). The authors announced, and provided extensive evidence for, the increased contribution of volatile organic compounds to urban air pollution so that they are now the major source of toxic compounds. The bad news is that volatile organic compounds are to a large extent used indoors. Many products used in the home as well as commercial buildings are considered volatile chemical products, including cleaning agents, personal care products, paint, pesticides, inks, and adhesives. In this article I will summarize several recent studies of indoor air pollution.

Air Pollution Inside Schools and Day Care Centers

Children are more susceptible to toxic chemicals than adults because of the ongoing division of cells that contributes to their growth, the immaturity of major organ systems (including the immune system). and a higher metabolic rate. In addition, exposure to toxic compounds in childhood will add to the total burden of toxic substances that can result in adverse effects years, or even decades later. Many studies have provided evidence of higher concentrations of pollutants in classrooms than in air outside of the school. For example, an Australian study of 41 classrooms (20 heated by electric heaters, 21 by unflued natural gas heaters) showed that peak concentrations of nitrogen dioxide were 4-fold higher in the gas-heated rooms. Children in those rooms were more likely to be absent as well as experience more sore throats and colds during the monitoring period. More serious consequences are expected from high long-term nitrogen dioxide exposure. Researchers in Portugal showed that in four day care centers (children aged 1 to 5 years) carbon dioxide levels (which are correlated with the concentrations of other pollutants) increased as much as 8-fold above background. Of course, air pollution can vary widely due to school location, placement of a classroom relative to school facilities and nearby pollution sources, number of open windows, number of students in a classroom (especially relative to its size), chemicals in cleaning products, etc.

The Environmental Protection Agency website has an excellent summary of many aspects of indoor school conditions with links from the webpage Creating Healthy Indoor Air Quality in Schools. Many references are provided on webpages such as: Improve Academic Performance through Better Indoor Air Quality in Schools and Adopting Indoor Air Quality Best Practices.

Air Pollution in Homes and Offices

Indoor pollution in homes is generated mostly by fossil-fueled appliances (stoves, etc), personal care products, and smoking. Of course, pollution from outdoors leaks inside and depending on conditions, such as air pollution severity and number of open windows, can make a major contribution. While indoor pollution is generated from the sources mentioned above many complex reactions occur that affect air quality at time scales from seconds to months and distances from nanometers to the whole house. Some reactions result in pollutants similar to those found outside, such as particulate matter (called secondary organic aerosoles) that are formed from ozone and other gaseous pollutants. However, indoor pollutant complexity also arises from reactions at surfaces, which are chemically quite distinct from the outdoor gas-phase reactions. Further adding to the complex pollutant mixtures are the great variety of surface areas, including furniture, clothing, and human and pet skin. An example of the latter is ozone reacting with skin oils.

Offices differ from houses in the same way that houses vary: the nature of the appliances, design of the heating and cooling systems, type of furniture, number of people per square foot, etc. For example, most of the pollutants in one crowded university lecture hall were derived from the personal care products worn by students.

Given the difficulty in characterizing pollutant reactions accurate and detailed computational models must be developed to predict pollution levels in specific structures. Using model houses built to help generate relevant data scientists hope to have usable computer models within several years.

* McDonald et al., Science, 359, 760 (2018)

**Lewis, AC, Science, 359, 744 (2018)