Exposure to air pollution goes from outdoors to indoors – here’s why

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You may have seen the before and after lockdown photos of major cities that appear to show dramatic changes in air quality. In one, the India Gate war memorial in New Delhi is barely visible amid the smog. Then, during the lockdown, it is clearly visible in its grandeur of red stone from Bharatpur.

Getting vehicles off the road can do wonders in tackling smog, but there’s more to air pollution than that. The move away from fossil fuel-powered vehicles and improved outdoor air quality in urban areas, along with changes in buildings and lifestyles, mean indoor air pollution will become a lot. more important in the future. And there aren’t many easy answers about how much risk this will create or how to manage it.

Vehicles have been a dominant source of air pollutants for decades. But the age-old dominance of petroleum-based fuels is coming to an end with the increasingly rapid deployment of electric vehicles. A consequence of this will be a drop in the concentrations of highly reactive gases called nitrogen oxides, which in fact neutralize another pollutant of industrial origin, ozone. So fewer gasoline and diesel cars, coupled with lower emissions than the remaining ones, could actually lead to higher ozone concentrations in urban areas.

Unlike the stratosphere where ozone plays an important role in protecting us from harmful ultraviolet rays, on the surface it can act as a respiratory pollutant. This property makes life difficult for people suffering from respiratory diseases such as asthma and bronchitis.

But we are not only exposed to ozone outdoors, it can also enter buildings through windows, doors and cracks in buildings. So it follows that if ozone concentrations increase outdoors, they will also increase indoors. This is because computer models predicted that during lockdown, indoor ozone concentrations would increase by 50%.

Once inside, ozone reacts with the many chemicals emitted by common indoor activities, such as cleaning, to form new air pollutants, some of which are harmful to our health.

However, indoor ozone is not the only problem. There are many sources of indoor air pollution. When we cook, especially with natural gas, and when we fry meat at high temperatures, we produce nitrogen oxides and particles. Cleaning can produce scent compounds (called volatile organic compounds) as well as particles. Lighted candles can also produce nitrogen oxides and particulates, as well as volatile organic compounds if scented.

Some of these compounds are emitted directly and some of them may react further, such as with ozone, to form new air pollutants. Therefore, indoor air quality largely depends on indoor activities and the proper ventilation of a building.

Over the past 50 years or so, buildings have become more airtight thanks to increased energy efficiency measures, a trend that is expected to continue. Over the same period, in many countries people have been spending more and more time indoors, at home, on the move or at work. It has recently been estimated that British children spend just over an hour outdoors each day. As a result, most of our exposure to air pollution occurs indoors, even though the pollutants are formed outdoors.

Yet, while ventilation will dilute emissions from indoor sources, it will also allow more ozone indoors which could trigger chemical reactions. It is clearly a complex picture.

Exposure to air pollution is complex and dynamic

Changing the sources of air pollution can reduce the concentration of some pollutants, but could increase the concentration of other pollutants such as ozone. We are exposed to indoor and outdoor air pollution and mixtures of different air pollutants in each. Even on the same street in identical houses, the exposure is likely to differ in single-family houses due to the different behavior inside.

The main health effects associated with air pollutants come either from long-term exposure, such as cardiovascular and respiratory disease and lung cancer, or from short-term exposure, such as damage to the lungs or lung cancer. worsening of asthma. While we understand fairly well the health effects of certain air pollutants such as nitrogen dioxide and particulate matter, for many air pollutants there is little or no information on how they affect our health.

This lack of information is particularly acute for indoors, where research lags considerably behind the quality of outdoor air. For example, particles in indoor air are formed or emitted during cooking, and it would be useful to know if the toxicity of these particles is higher or lower than that of common sources outdoors, such as motor vehicles. .

All of this means that improving the quality of outdoor air will not necessarily reduce our overall exposure to air pollution. An important future step is to better understand our total exposure to air pollution, especially indoor, and its effects on our health.


Study examines indoor exposure to air pollution


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