You might think being tucked up indoors means you’re safe from the peril of London’s air pollution problems.

But you’d be wrong, at least according to one study which has been carried out.

Four volunteers in different parts of the capital, including Bromley and Croydon in outer London, used air quality monitors to measure the carbon dioxide (CO2) levels in the places they visit every day.

Carbon dioxide is naturally present in the air at around 400 ppm (parts per million) but all the participants measured levels well above this during the research.

The highest CO2 reading of 2,284ppm was recorded inside a packed train at Baker Street station, almost five times the threshold for normal CO2 levels.

Elsewhere, Cecile, a mother and teacher who was staying at home in Bromley during the school holidays, recorded 1,172 ppm at home, taken after her son had gone to bed.

The CO2 levels stayed high into the next morning, with Cecile and her son starting the day recording levels at 770 ppm.

Perhaps surprisingly, the amounts of CO2 were much closer to normal when she was outside at Bromley town centre and train station.

Meanwhile, construction worker Owen recorded higher CO2 levels at home in Croydon than at his work in King’s Cross.

Owen commented that at his workplace, and in the building industry in general, they take precautions to reduce the levels of pollution that workers are exposed to.

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Elevated CO2 levels can be found where there is overcrowding or poor ventilation.

Exposure to high levels of indoor air pollution can lead to health problems including asthma, respiratory irritation, heart disease, cancer and sick building syndrome.

Indoor air quality expert Professor Ian Colbeck from the School of Biological Sciences at the University of Essex, who was working with Currys PC World and Dyson on the research, said CO2 levels between 1,000 and 2,000 ppm can cause drowsiness, while levels above that lead to headaches, sleepiness, poor concentration, nausea and increased heart rate.

Prof Colbeck has the following tips for limiting exposure to indoor air pollution:

Smoke outside

If you need to smoke, do it as far away from your home and any open windows as possible to prevent the smoke from seeping back indoors.

Ditch the rugs

Choose hard-surface floors for every room to help prevent allergenic or harmful particles from building up. Then just use a microfibre mop to clean the floors every week.

Shoes off

Help prevent dirt and debris from entering your home by placing a doormat outside your front door, and introducing a no-shoes-inside policy.

Cook without leaving a trace

Use an extractor fan whenever you cook to protect yourself from harmful levels of nitrogen dioxide (NO2) caused by gas cooking.

Banish condensation

Prevent condensation from creating harmful mould and damp by increasing ventilation in your home. Cover boiling pots and pans, open windows, keep the kitchen door closed when cooking, and use a humidity monitor to ensure the humidity level in your home is kept between 30 per cent and 50 per cent.

Go all-natural

Limit your exposure to volatile organic compounds (VOCs) that can be hazardous to your health by using products based on natural ingredients. If you do need to buy products that contain VOCs, buy just enough to use immediately so you don’t build up a stockpile. Products can include personal care items and aerosol sprays.

Embrace the green stuff

Houseplants can help improve indoor air quality naturally and effectively. Plants recommended for removing air pollutants include English ivy, philodendron, bamboo palm, peace lily and mother-in-law’s tongue.

Purify the air

Houseplants work particularly well when paired with an air purification system that uses activated carbon filters and a fan. An air purifier can work wonders for improving the air quality in your home by capturing even the smallest allergens and pollutants from the air.