Scented candles and stir-fries were worse than traffic fumes: My week with an air pollution monitor – Published in “i”

Using a pollution monitor for a week produced some surprising results for Etan Smallman



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To misquote one of The Police’s most famous songs, this week “Every breath I take, and every move I make… I’ll be watching it.” The “it” is the air pollution monitor that I have been carrying around with me, indoors and out, to determine the quantities of invisible particles that are making it into my body. I clutch it on the Tube and gaze at it while ambling past traffic. I even brandish it while making toast.

In 2019, the director-general of the World Health Organisation (WHO), Tedros Adhanom Ghebreyesus, said particulate levels in cities worldwide were “at crisis level”.

And last month, the most comprehensive research into the effects of air pollution on adolescents found that prolonged exposure can significantly increase their risk of developing high blood pressure in later life – with obese youngsters especially vulnerable. Professor Seeromanie Harding, of King’s College London and the lead author, said: “Reducing air pollution is an urgent public health priority to protect our children’s futures.”

My Temtop P200 (£42.99, tests air quality using a laser particle detector. As its digits slowly rise, my heart sinks; the higher the reading, the more microscopic particles that are passing into my lungs, bloodstream – and even brain.

It measures PM2.5, fine particulate matter with a diameter less than 2.5 micrometres (that is one 400th of a millimetre, or about 3 per cent of the width of a human hair). Coming from sources such as wood burning and tyre and brake wear from vehicles, it is thought to be the air pollutant that poses the biggest danger to human health. Chronic exposure increases the risk of developing cardiovascular and respiratory diseases – anything from asthma to lung cancer.

“Every day we’re inhaling something like five to 15 billion particles,” Zongbo Shi, professor of atmospheric biogeochemistry at the University of Birmingham, tells i. “Assuming maybe 20 per cent of those particles will be deposited into our lungs, we’re still talking about having to deal with 1 to 3 billion particles every day.”

“There’s no safe level of air pollution,” according to the British Lung Foundation, which estimates that up to 40,000 premature UK deaths a year are caused by exposure to toxic air. The WHO does have a recommended guideline limit: an annual mean concentration of 5 micrograms per cubic metre (µg/m³). But the UK’s air quality regulations allow for a yearly average of four times that.

When dealing with pollution on the roads, Shi points to Birmingham research from 2020 that found that PM2.5 exposure could be cut in half for those in cars by closing windows and having recirculation and air conditioning switched on. He says that a pedestrian should head for quieter streets, even if it means a detour, because walking a bit longer is also good for health, “so you have a double benefit”. And if you are on a slope, make sure to walk on the opposite side to traffic that is going uphill, “because the engines will be working really hard and the emissions will be a lot higher”.

Although he finds them too uncomfortable, Shi says anyone concerned about visiting a highly congested area – particularly vulnerable people such as those with asthma or chronic obstructive pulmonary disease – could opt to wear a mask. But it would need to be an N95, fitted tightly to the face, to have any impact.

My bedroom (in a London suburb) is a fairly harmless 3 µg/ m³. A five-minute walk to the local high street only pushes the reading up to 5 µg/m³ – though the light traffic and breeze help explain that. Another 15-minute stroll takes me on to a section of the North Circular that ranks as the sixth most congested road in Britain. In moderate midday traffic, the range is 3 to 26 µg/m³.

But it is the indoor figures that shock me. On the Underground, I detect pollution levels I fail to find on any London roads. Even though I am at the very back of the train (away from the window at the end of the carriage), I only record 9 µg/m³ when I get on, above ground, at West Finchley. However, the digits creep up once we enter the confines of the tunnel and reach 100 µg/m³ five stops in, at Tufnell Park. As I stand on the platform at Camden Town, with a gust from the passing train, my monitor gives me 173 µg/m³. But as the air settles, this rises to 209 µg/ m³. And even with the airflow as I come up on the escalators at King’s Cross, I’m recording over 100 µg/ m³ (compared with just 9 µg/m³ outside on Pentonville Road).

The particles have accumulated over more than a century: iron from the brakes, wheels and rails and fine dust from passengers’ clothing and skin, a potentially noxious brew that is stirred up every time a train whooshes through the tunnel. For the first time in a lifetime of living in the capital, I become acutely conscious of the subterranean smell of the Tube. What I had previously regarded as an innocuous metallic background haze now makes me realise my nasal passages are filling up with toxic particulates.

It is a handy rule of thumb when it comes to PM2.5, says Nicola Carslaw, professor in indoor air chemistry at the University of York (who admits that many of her students – reading degrees in environmental science – are surprised by the very concept of indoor pollution). “A really good way to think about it is, whenever you’re indoors and you can smell something, that’s obviously creating something, because you’ve got an emission you’re aware of.”

Believe it or not, most of your exposure to air pollution happens inside – in homes, offices and cars – because that is where we spend, on average, 90 per cent of our time.

It is in my kitchen, with windows closed and extractor fan off, where I record the highest reading of the week, 899 µg/m³ while stir-frying (and ever so slightly burning) some peppers and tomatoes.

This does not surprise Carslaw. “One of the things we’ve been looking at, at York, is stir-frying meat,” she says. “You have emissions from frying the oil itself. But when you start throwing in meat, you make particles very efficiently. Frying is worse than boiling or steaming, and frying meat is worse than frying vegetables.” I suppose I should be thankful I’m vegan.

If I swapped my electric hob for a gas one, matters would be even worse – as combustion of any fuel produces PM2.5, before you even stick anything in the pan. “Having gas in your house also means there’s a carbon monoxide risk if your boiler is faulty. And with the drive towards net zero, one thing that we could do – I’m not saying it’s cheap, but in terms of a solution that’s quite simple – is getting gas out of homes.”

To reduce emissions during cooking, open your windows, turn your extractor fan on and place pans at the back of the hob, where the fan tends to work most effectively. Also make sure it is actually taking the extracted air outdoors, not just funnelling it back into the kitchen (though for most renters, of course, this will be out of their control). Windows are also the answer for anyone whose home faces a busy road or building site – close the ones at the front and open any at the back. Carslaw says she is concerned that the increasingly air-tight buildings designed to achieve energy efficiency are a backwards step when it comes to airflow.

Candles are another source of indoor emissions. “This is where you sound like the Grinch that stole Christmas, isn’t it,” says Carslaw when I ask if we should be avoiding them. “I think it’s about moderation, so I wouldn’t say you should never burn a candle, but best to do it in a ventilated space and not to have too many burning at the same time.” She adds that scented candles – and air fresheners of any kind – are even worse, because the fragrance compounds add to the particulates being released into the air.

When I burn a candle containing hibiscus, patchouli, tuberose, musk and cacao, I get a reading of 12 µg/m³. However, this rises, briefly, to 835 µg/m³ with the smoke that billows after I blow it out. To get to a similar level with unscented tealights, I have to extinguish 20 of them.

Cleaning is another major source of trouble. Carslaw again recommends avoiding fragranced products wherever possible – for example, opting for plain bleach, rather than a pine variety.

“They’re not doing anything in terms of cleaning, so I think avoiding those additional compounds is a sensible thing to do.” Scrubbing my loo with lemon bleach only pushes my monitor up to 9 µg/m³, but it briefly jumps to 254 µg/m³ when I spritz my TV with an aerosol cleaner.

“I always suggest that people avoid sprays if they can,” Carslaw says. “You’re basically vaporising the components, which are then much easier to breathe. If you have a liquid cleaner and you put it on to a cloth and rub it in, that’s better in terms of what gets into the breathing zone.”

Then there are the furnishings themselves. New sofas and floorings can emit chemicals for months after purchase (think of that “new carpet” smell). Furniture can also act as a “reservoir”, soaking up pollutants, which are slowly released back into the air over time. Carslaw cites a US study of former drug dens turned into social housing. The fumes continued coming off the walls and furniture, leaving the residents with high levels of methamphetamine in their bloodstreams. It is why you should never buy second-hand beds or bookcases from a smoker. And remember the golden rule: ventilate, ventilate, ventilate.

I am now going to surrender my pollution detector, for fear I will end up as glued to it as I am to my smart meter. But its readings have provided a salutary lesson: when it comes to our air, clarity begins at home.

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