Kindle Notes & Highlights
by
Tim Smedley
Read between
March 14 - March 22, 2021
Los Angeles, like Mexico City and Beijing, is a natural pollution trap. It sits in a geological bowl (of around 1,630 square miles) surrounded by a high rim of mountains which traps in the air below.
LA, Mexico City, Beijing
Air pollution has overtaken poor sanitation and dirty water to become the number one environmental cause of premature death in the world. The latest estimate from the WHO is that approximately 4.2 million people die from outdoor air pollution annually, far greater than the number from HIV/AIDS, tuberculosis and car crashes combined.
#1 public health
Clean air is made up of 78.09 per cent molecular nitrogen, or N2. The rest is 20.95 per cent oxygen, plus trace gases such as 0.93 per cent argon and 0.04 per cent carbon dioxide.
Clean air consisting of
But in our towns and cities, the biggest single contributor of the nitrogen oxides called nitrogen monoxide (NO) and nitrogen dioxide (NO2) – collectively referred to as ‘NOx’ – is transport fumes. Every car engine is, in effect, a mini lightning bolt, and our roads are filled with a never-ending storm. Nitrogen dioxide can cause significant health problems, and is therefore of the greatest concern, while nitrogen monoxide is less harmful but tends to react quickly in the air to form more NO2.
NOx
The UN’s 1985 Helsinki Protocol on the Reduction of Sulphur Emissions was very effective. In the US between 1980 and 2013, annual average sulphur dioxide concentrations decreased by 87 per cent, while in Europe, sulphur dioxide emissions decreased by 76 per cent between 1990 and 2009. However, removing sulphur from fuel is expensive, meaning that lower-grade fuel including sulphur remains the norm in many developing countries and in international shipping.
Sulphur dioxide
‘Laser Egg 2’ produced by the Beijing-based start-up Kaiterra. The reason why I decided to give this one a go was a recommendation by email from Frank Kelly at King’s College London – his colleague had tested a few against the expensive, finely tuned monitors in the lab, and found the Laser Egg 2 matched up rather well. It could fit in my hand luggage, and measures PM2.5 in micrograms (one-millionth of a gram) per cubic metre (mg/m3). During my travels for this book I could turn on my ‘Egg’ wherever I went, as a quick ‘pulse check’ PM2.5mg/m3 reading rather than anything scientifically
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Laser egg validation
Roughly four out of every five deaths caused by air pollution are caused by PM2.5.
PM2.5 prime suspect
I learn that there are broadly three sources of PM: natural aerosols,3 secondary PM and primary PM. The natural ones include sea salt, sand, dust, pollen and volcanic ash – basically any natural material that is fine enough to be whisked up by the wind and carried in the air.
PM categories
However, ‘natural dust’ doesn’t always mean the same as ‘natural causes’.
Natural causes vs natural dust
Secondary particles, however, are a little more complex. They are formed by chemical processes within the air itself.
Secondary PM
PM2.5 is mostly secondary. A big one is sulphur dioxide emitted from burning coal or in some cases high-sulphur diesel … That sulphur oxidises all the way to sulphuric acid and condenses into the particle sulphate. Most sulphate is secondary, the vast majority I’d say.’ I wasn’t expecting that response. It’s one worth bearing in mind whenever anyone talks about filters for trapping particulate matter, for car engines or anywhere else – filters may be able to trap solid particles, but they can do nothing about the ones that are emitted as gases and turn into particles later on. Ammonia gas, for
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PM2.5 is mostly secondary
A study by the US Federal Highway Administration suggests that the proportion of all PM2.5 in the US comprised of secondary PM varies anywhere from 30 per cent to 90 per cent.
Secondary PM2.5
Among the easier-to-understand primary pollution particles, emitted directly into the air as a solid, the undisputed heavyweight champ is ‘black carbon’.
Black carbon
huge amounts of black carbon are produced by forest fires it is a significant contributor to global warming.
Black carbon and global warming
A global black carbon inventory in 1996 estimated that annual emissions came from open burning (42 per cent), fossil fuels (38 per cent) and solid fuels (20 per cent).
BC sources
Charcoal has been used for centuries to purify water, because organic chemicals such as VOCs are chemically attracted to it.
Charcoal benefits
In pursuit of the perfect-looking living room, the UK’s largest single source of PM2.5 – 37,200 tonnes of it a year – is now domestic wood burning.
Wood burning sourcs of pm2.5
wood-stove epidemic either. In Maine, the use of wood as a primary heat source increased from 7 per cent of households in 2005 to 13 per cent by 2015,
Wood as primary heat source
wood burning contributes between 10 per cent and 39 per cent of winter PM2.5.
Wood burning contributing to winter pm2.5
Another form of primary PM is tiny shards of metal. Lead,
Lead as source of primary pm2.5
Lead, writes the epidemiologist Devra Davis, has the same electronic charge as calcium, and therefore competes with calcium throughout the body: ‘In the bones, the brain, and the blood and throughout the nervous system all of which depend on calcium, lead can trigger irreparable damage.’2 As a means of getting it into the bloodstream, she says, you couldn’t invent a better way than miniaturising it, putting it into a combustible liquid and releasing its fumes into the air.
Why lead is bad
Leaded petrol would be commonly used throughout the world until the late 1990s, when most major countries began to phase out its use.
Leaded petrol was common until 90s
All these nuances and different substances get rather lost in the catch-all term ‘PM2.5’. ‘They do, don’t they?’ agrees Ally, relieved that I’ve finally worked it out. ‘PM2.5 is just a convenient way of measuring. It’s a measurement of how much mass of particles is in the air, it tells you nothing about what the particle is, it doesn’t tell you whether it was from a forest fire, whether it’s black carbon, whether it’s a liquid aerosol, it tells you nothing at all. That metric was adopted in the 1970s because that’s all people knew … it seems a very poor measure if you’re working in this field
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Nuances of PM2.5
Working out the exact chemical composition of PM remains difficult given that a cloud of dust can come from multiple local and transboundary sources.
Identifying the chemical composition of pm2.5
Each city therefore has its own unique PM fingerprint. In Stockholm, Sweden, the first days of spring are heralded when up to 74 per cent of PM10 comes from road dust as winter studded tyres rip up the road surface exposed by melting snow. In Delhi in 2012, the biggest single source of PM2.5 was transport (17 per cent), followed by power plants (16 per cent), brick kilns (15 per cent), industry (14 per cent), households (12 per cent), waste burning (8 per cent), diesel generators (6 per cent), road dust (6 per cent) and construction (5 per cent).
Each city has a unique PM fingerprint
The most stomach-turning example is Mexico City in the late 1990s, when the inner city had more than two million stray dogs depositing 353 tonnes of dog poo a day: the PM10 in the air was found to include ‘dog dust’ – particles of dried faecal matter. As the LA Times nauseously put it in 1999, ‘The dog dust and other particulates settle on the tortillas, tamales and salsa being served up to customers at the open-air stands, feeding chronic intestinal miseries.’
PM10 shit particles
When Chinese journalist Chai Jing took a PM particle filter sampler with her during an ordinary working day in Beijing in 2012, it registered 305.91mg/m3 . The filter turned from pure white to pure black. To find out what the stuff was, she invited Dr Xinghua Qiu from Peking University to chemically analyse her sample. It contained 15 carcinogens, including biphenyl, acenaphthene, benzo(e)pyrene (one of the most potent known carcinogens) and fluorene (one of the key pollutants during the 1948 Donora disaster).
Carcinogens in PM
Even in London, it transpires that up to 75 per cent of PM can be transboundary, coming in from elsewhere.
Transboundary PM2.5
It spoiled the picture that had begun to build: that most pollution is local and can be dealt with through local action. Transboundary pollution was beginning to sound like climate change – that the actions of one city or even one country can ultimately be meaningless if others do nothing or emit even more.
Local VS global
‘Well, it depends if we are looking at an annual average or a peak. Usually a peak, or pollution episode, is because we are stuck in a meteorological condition of low boundary layer, no wind … and we are basically polluting ourselves. That is mostly local. But on a daily basis, on an annual level, we have wind and yes we are receiving pollution from our neighbour … Sometimes even the wind can circle around and bring our own pollution back to us, because we are a big emitter.’
Local VS global
‘When you talk about ambient particle exposure, there are two things you need to think about: one is the overall background levels, and that is going to be dominated by meteorological factors, which way the wind’s blowing and where it is blowing from … and yes it can be transported from miles away. But when we’re talking about city traffic, the particles are generated on the road, and they disperse quite quickly. It’s an exponential decay, usually from the roadside.
Types of ambient particle exposure
But in terms of where we actually live, work and travel, we spend far more time on or near roads than we do standing next to power stations. Within towns and cities, our proximity to vehicles exposes us to the smallest particles that can enter into our bloodstream. Particulate number (PN) – the total number of particles in any given gulp of air, rather than the mass or weight of particles – is therefore the final piece of the particulate jigsaw. Unlike the background sources of urban air pollution, vehicle emissions occur at ground level and near to us humans breathing it all in. The very
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Proximity to roads and vehicles VS background sources
“lung deposited surface area” – LDSA is a term that you’re going to hear much more of. So that tells us how much capacity the surface has for having nasty things on it, it tells us how many particles there are which is important, because the particles are becoming smaller.’
Lung deposited surface area (LDSA)
It had long been theorised that ultrafine particles smaller than PM0.1 could make their way almost anywhere in the body, including the lymph nodes, spleen, heart, liver and even the brain. Now Newby’s Edinburgh team had proved it.
PM0.1 can enter bloodstream, lymph nodes, heart
But the vast majority of nanoparticles below 30nm, the ones that swim around our arteries and cluster around our cholesterol, don’t come from transboundary pollutants. They come from our roads. More specifically, they come from the cars and vehicles burning fossil fuels – ancient lakes of decayed biological matter – for propulsion.
Nanoparticles from car emissions as more dangerous relative to transboundary sources
