Even your own house isn’t immune from air pollution. A group of researchers in Colorado has carried out one of the world's first large-scale research studies into the chemistry of indoor environments and found that even the most basic household tasks can increase levels of pollution far more than previously thought.
Led by Marina Vance, an assistant professor of engineering at the University of Colorado Boulder, a group of researchers cooked and cleaned in a manufactured three-bedroom house at the University of Austin, Texas. These manufactured houses are built like residential houses but are also fitted with highly sensitive sensors and instruments so that researchers can measure the environment inside. Throughout the course of the experiment, the researchers cooked various meals, from toast to a full Thanksgiving dinner, and they cleaned the rooms in the house with a variety of products.
"Homes have never been considered an important source of outdoor air pollution and the moment is right to start exploring that," says Vance. "We wanted to know – how do basic activities like cooking and cleaning change the chemistry of a house?"
They found that there were extremely high levels of PM2.5 particulates – fine particulates which measure 2.5 micrometres and are too small to be filtered by our nose – in the air after cooking, as high as 200 micrograms per cubic metre. To put that into context, the air in central London has a concentration of PM2.5 particulates of 15 micrograms per cubic metre, which is already considered to be harmful by many standards.
Levels of fine particulates and pollutants from gas, soot and vegetable oils increased after cooking a meal using a gas stove and combined to create the PM2.5 particulates, which have also been proven to exacerbate respiratory diseases. The scientists found that substances which were left in ovens, or even on pans during cooking, could have an effect on the indoor air chemistry as well.
“When something is released directly from a foodstuff, or from a car exhaust or something, we call those primary pollutants, as they’re directly from the source,” says Julia Fussell, who is a member of the Science Policy and Epidemiology team at the King’s College London Environmental Research Group. “Those pollutants can then partake in complex chemical reactions.”
This area of research is relatively new. Measuring the chemistry of indoor environments is difficult because of the scale and complexity of the challenge – every residential unit, whether a house, flat or trailer, already has a unique mixture of various particulates, which these researchers found can also change depending on the individuals present (fine particles can stick to people's clothes). So extrapolating measurements from specific buildings will paint an inaccurate picture – particularly as a house in the countryside will have different pollutants when compared to a high-rise flat in the city. Even then, this can be compounded by, for instance, different kinds of hobs or the cleaning liquids used.
One particular area of concern for researchers is how volatile organic compounds (VOCs) can affect the indoor air environment. These are often released not just from cooking or cleaning, but also from aerosols (for example, spraying perfume) and can be found in building materials that are common not just in houses, but in most buildings.
"One of the reasons this is attracting more attention is that buildings have become more airtight, to reduce heat loss and increase comfort. But this means they rely much more on the designed ventilation provision to achieve good levels of ventilation," says Tim Sharpe, a professor in the Mackintosh Environmental Architecture Research Unit at the Glasgow School of Art. “At the same time, there are more and more sources of pollution in the home – chemicals from building materials, furniture and household products, particulates from cooking, and moisture from washing and clothes drying.”
The design of the houses and construction materials used can also have a significant effect on the amount of pollutants within a building – for example, ventilation in older buildings is significantly worse than in new builds. But new buildings that emphasise energy efficiency will be airtight, and this can keep pollutants circulating, as well as reduce their ability to react with other harmful substances.
“When the chemical reactions happen indoors, the primary pollutants get converted into secondary pollutants, and some of those are the volatile organic compounds,” says Fussell. “A lot of the chemistry occurs between ozone and particles that come in from the outside, so the things that we cook and clean with, like a household chemical or an aerosol.”
Tom Woolly, a professor of architecture at Anglia Ruskin University and the author of Building Materials, Health and Indoor Air Quality, says a major problem in the UK is that there are minimal indoor air quality standards for buildings. “There is some kind of limit for VOCs in building regulations, which is based on a standard invented many years ago, but I’ve spoken to building control inspectors and not one of them was aware that this was in the building regulations,” he says.
“Say you’ve decided to buy a new home, somewhere in the home counties for example – and that house will have been tested for energy efficiency and for being airtight, but it doesn’t come anywhere near the standards that it has to, because there are these toxic chemicals which have been emitted from the building materials.”
“In airtight buildings with low exchange rate, the risk of exposure to indoor contaminants is considerably higher,” says Grainne McGill, also at the Mackintosh Environmental Architecture Research Unit. “Architects can reduce the risk of poor indoor air quality by specifying low-emitting, non-toxic building materials and finishes.”
But even if new flats are built with air tightness as a primary aim, this doesn’t address the potentially harmful chemicals which are emitted from all kinds of building materials – such as insulation and cladding which supposedly contains flame retardants. However, as the interest in the area rises – and as more people have become aware of the problem – architects and manufacturers are implementing new standards and testing procedures to reduce the uptake of harmful substances.
Even ways to act on the findings of the experiment can have unintended consequences. For example, opening the windows while cooking, or after, will be useful in airing out the pollutants, but it does expose the indoor environment to ozone particles and other outdoor substances, which could exacerbate air pollution problems.
While the findings from this study may be worrying, there are some other changes that individuals can make if they want to reduce the level of pollutants that they're generally creating. “Anything that burns (eg gas cookers, toasters, stoves) produces particulates and pollutants," says Sharpe. “Therefore using extractor fans and cooking on the rear rings where possible is helpful, and people should think about the materials that they use in their homes - some of which are labelled as low VOC. Some things are not well labelled, but people with health issues should take a precautionary approach.”
A more impactful change would be to switch from cooking with gas to cooking with electricity – researchers found that a great amount of the pollutants were released from cooking with gas, as a byproduct of the chemicals involved. Another would be to eat less meat, which contains a lot of fat, and switch to steaming vegetables instead of frying or cooking them.
However, if you're waiting for more sweeping change, you'll be waiting for a while. There's not enough evidence, currently, for policy makers to create regulations on air pollution indoors, or what kind of stove top is best.
“In outside terms, we can say categorically that air pollution causes respiratory and cardiovascular problems, but in the indoor environment, it’s still pretty new,” says Fussell. “The important thing here is that we can say that there’s potential to cause health effects, but there’s a lot more research that needs to be done before it's certain.”
This article was originally published by WIRED UK
