First clean water, now clean air
We don't think twice about our drinking water being free from disease. What about the air we breathe?
I wrote this a year ago, but I haven’t yet posted it to my Substack. You can listen to a narration of the article here.
Clean water
In the mid 19th century, London had a sewage problem. It relied on a patchwork of a few hundred sewers, of brick and wood, and hundreds of thousands of cesspits. The Thames — Londoners’ main source of drinking water — was near-opaque with waste. Here is Michael Faraday in an 1855 letter to The Times:
Near the bridges the feculence rolled up in clouds so dense that they were visible at the surface even in water of this kind […] The smell was very bad, and common to the whole of the water. It was the same as that which now comes up from the gully holes in the streets. The whole river was for the time a real sewer […] If we neglect this subject, we cannot expect to do so with impunity; nor ought we to be surprised if, ere many years are over, a season give us sad proof of the folly of our carelessness.
That “sad proof” arrived more than once. London saw around three outbreaks of cholera, killing upwards of 50,000 people in each outbreak.
But early efforts to address the public health crisis were guided by the wrong theory about how diseases spread. On the prevailing view, epidemics were caused by ‘miasma’ (‘bad air’ — a kind of poisonous mist from decomposing matter. Parliament commissioned a report on the ‘Sanitary Condition of the Labouring Population’, which showed a clear link between poverty and disease, and recommended a bunch of excellent and historically significant reforms. But one recommendation backfired because of this scientific misunderstanding: according to the miasma theory, it made sense to remove human waste through wastewater — but that water flowed into the Thames and contaminated it further.
But in one of these outbreaks, the physician John Snow has spotted how incidence of cholera clustered around a single water pump in Soho, suggesting that unclean water was the major source of the outbreak. A few years later, the experiments of Louis Pasteur helped foster the germ theory of disease, sharpening the understanding of how and why to treat drinking water for public health. These were well-timed discoveries —
Because soon things got even worse. Heat exacerbated the smell; and the summer of 1858 was unusually hot. 1858 was the year of London’s ‘Great Stink’, and the Thames “a Stygian pool, reeking with ineffable and intolerable horrors” in Prime Minister Disraeli’s words. The problem had become totally unignorable.
Parliament turned to Joseph Bazalgette, chief engineer of London’s Metropolitan Board of Works. Spurred by the Great Stink, he was given licence to oversee the construction of an ambitious plan to rebuild London’s sewage system, to his own design. 1,800km of street sewers would feed into 132km of main interconnecting sewers. A network of pumping stations was built, to lift sewage from streets below the high water mark. 18 years later, the result was the kind of modern sewage system we mostly take for granted: a system to collect wastewater and dump it far from where it could contaminate food and drinking water; in this case a dozen miles eastwards to the Thames estuary. "The great sewer that runs beneath Londoners”, wrote Bazalgette’s obituarist, “has added some 20 years to their chance of life”.
Remarkably, most of the system remains in use. London’s sewage system has obviously been expanded, and wastewater treatment is much better. Bazalgette’s plan was built to last, and succeeded.
As London built ways of expelling wastewater, it also built ways of channelling clean and running drinking water. New canals, plumbing infrastructure, and water supply companies piped water from springs, wells, and rivers straight into houses and public drinking fountains; replacing wells, collecting rainwater, or unclean water pumps.
One of the nice things about living in London today is that it is very, very easy to find running water, and it’s reasonable to basically never worry about whether the water that comes out of taps is safe to drink. In the last century, 7 people have died of cholera in the United Kingdom.
The same story unfolded nearly everywhere in the developed world, and it marked the beginning of a so far effectively permanent end to waterborne disease in wealthy countries. I naively but conservatively estimate clean water measures saved more than 130 million people in the 50 years since 1973 alone1. Of course these improvements to sewage and plumbing and water treatment were expensive, but very clearly paid for themselves many times over, and it is clearly worth expanding those measures until everyone in the world has access to them.
That’s not mentioning the improvements from sanitation and hygiene, which are different from just having access to clean drinking water. Unsafe sanitation and lack of access to handwashing facilities, treated as risk factors, together look responsible for nearly 1.5 million additional deaths annually.
I just think this is worth dwelling on: in about half a century, developed countries effectively ended waterborne disease.
Clean air
You probably guessed from the title but the punchline is that now’s a good time to do the same thing with airborne disease.
The basic analogy:
Unclean water imposed an enormous human toll, until we built ways to deliver clean water, dispose of unclean water, and keep the two separated. Now nearly everyone in at least developed countries has access to safe drinking water, and in those places most waterborne diseases are very rare.
Unclean indoor air continues to impose an enormous human toll, even in developed countries. Almost nowhere in the world do we adequately treat, monitor, or even circulate the air we breathe: we breathe untreated air pretty much all the time. But we know how to build measures to effectively end airborne diseases, too.
I think the first step here is just noticing the price we pay for unclean indoor air. Consider: most people just have to factor in a ~single digit number of days per year recovering from some airborne disease like the flu or common cold. In the US alone, this costs double-digit billions of dollars in direct healthcare costs and foregone wages. Ventilating air helps to eliminate biological pathogens, but it also just makes it fresher and less stuffy — where some studies tentatively show double digit percentage improvements in productivity from just getting rid of stuffy (CO2-rich) air. But likely the biggest cost is now also the most obvious. Every few decades a pandemic with airborne transmission pathways will tear through the world, and the world will be mostly powerless to stop it. The most recent example took around 20 million lives so far. The next could be even worse.
Part of the problem with making these facts salient might be that our disgust reactions aren’t firing in helpful ways: unclean water is visibly (and olfactorily) unclean, but bad air is perfectly disguised as clean air, and contextual cues are needed. So the first step is bringing the human costs of unclean air into the open. How about visualisations which make the mechanisms of unclean air visually salient?
In the hopeful story, these costs become historical. Covid could be to airborne diseases like London’s cholera outbreaks and Great Stink were to waterborne diseases: a confluence of (i) “wow, as long as we know how to end this, we should”; and (ii) “huh, looks like we do increasingly know how to end this”.
I don’t know whether that is the story we’re in, but I think we know enough to describe many of the practicalities. So here’s how the hopeful story could play out, across a handful of technologies:
The high-level plan
We’ll focus on indoor air quality, largely because respiratory pathogens are much more likely to spread indoors than outdoors (and also because treating indoor air is achievable and affordable). For instance, this study estimates more than 90% of Covid infections occurred indoors.
The world we want to end up in is a world where we massively slow the spread of airborne pathogens, primarily to reduce the vast expected cost of catastrophic biorisk, and also to reduce the yearly toll of (non-pandemic) respiratory diseases.
How do we reach that point of safety? Practically, we’ll need technology that does two things. Either: straightforwardly blocking the spread of pathogens in crowded indoor spaces. If patient zero coughs, and the aerosolized pathogen is sterilised or ventilated away before it can spread to anyone else, then a potential outbreak is stopped dead. Or, at least: slowing transmission. If Rt drops and stays below 1, you don’t have the conditions for an epidemic. And in any case, slowing transmission buys time for other medical countermeasures — like the time to develop and deploy vaccines.
On a social level, we’ll need ways to make sure these safety-promoting technologies are deployed as widely, cheaply, and quickly as they need to be. With two tools: (i) standards and other regulations to capture the externalities from unclean air; and (ii) major R&D initiatives like prizes, FROs, or advanced market commitments to speed up wide rollouts of these safety-promoting technologies.
Which technologies?
Ventilation
Ventilation just means getting rid of the stale air in a room and replacing it with air from outside the room. If the air from outside the room is cleaner, then you’ve now got cleaner air.
This metaanalysis finds strong evidence that ventilation helps reduce infection rates. There’s also some evidence for more general health benefits, like less inflammation, sick leave, and fewer asthma and allergy symptoms.
The V in HVAC is ventilation, so many AC / heating systems ventilate air already. A DIY version of a ventilation system is to open two roughly opposite windows in a space, and place a fan moving air out one of the windows.
There are some drawbacks: it’s often noisy, often energy-consuming, and it relies on outdoor air being significantly fresher than indoors, which isn’t always the case (especially in cities).
Filtration
Then there’s filtration: passing air through a filter to remove small particles, including pathogens. Quoting from this Rethink report on indoor air quality:
Standalone filtration units […] have been shown to reduce the exposure to pathogenic aerosols under controlled conditions, with 5 eACH HEPA filtration in classrooms enough to cause a 4-5 fold drop in pathogen dose.
[…] Addition of filters to existing ventilation systems in a typical model scenario has been shown to reduce relative risk of infection of influenza by up to 47%, at a total annual cost of $352 for HEPA filters[.]
[…] In addition to reducing pathogen transmission, filtration has benefits for respiratory health and cognition, due to its ability to remove harmful particulate, gaseous, and chemical pollutants. Given these benefits, widely investing in improved filtration in built environments is likely to help the population even in non-pandemic years.
The way filters work — even the advanced ones — is almost embarrassingly simple. Get some kind of foamy/spongy/fibrous material with lots of small holes; put many layers of that material into a box; and force air through that box with a fan. During the pandemic, Richard Corsi proposed a design for a DIY air purifier which is more or less as simple as I made out, enabling people to cheaply build their own air purifiers for homes and schools and offices. It’s called the Corsi-Rosenthal box, and it takes about $100 and 15 minutes to build. Here is Corsi in a radio interview: “People are now reporting 600 cubic feet per minute (280 L/s) in clean air delivery rates. That’s phenomenal. That’s actually better than a lot of the more expensive HEPA-based portable air cleaners”. Even more than ventilation systems, air filters are low-tech, and already very cheap to install and maintain (I’d guess typically less expensive than fire safety systems).
An aside: ventilation plus filtration is the major reason that the risk of Covid infections on flights was and is so relatively low: air in the cabin is replaced every couple minutes, fresh air is drawn from outside the plane, and mixed with recycled air passed through HEPA filters. Airbus says that the risk of infection is lower on a plane than people sitting six feet apart in an office.
Germicidal UV (GUV)
Like antibacterial soap, it turns out that certain wavelengths of light can effectively sterilise pathogens (without sterilising humans). There are roughly two kinds:
Upper-room UVC illuminates the top of the room and avoids illuminating people. This means you can use relatively lower frequencies of UV light which are currently easier to produce with lamps, but which can cause eye damage in humans. Upper-room UVC is cheap and well-understood. This study found an 80% reduction in TB transmission in guinea pigs. So it will also keep pets safe.
Far-UVC is a narrow band of UV wavelengths at higher frequencies than are currently economical to produce with lamps. The key advantage of Far-UVC is that early studies show no indications that it harms humans, even at very high doses. But it is effective at stopping pathogens: for example this study finds that Far-UVC light inactivated 99.9% of aerosolized coronaviruses. As long as longer-term studies on the safety of Far-UVC agree, then this is some extremely exciting technology.
Currently, Far-UVC is too expensive to scale to a significant fraction of all the indoor spaces in a country. And current versions produce small amounts of a kind of smog that can be harmful (without attendant ventilation). So I’m not advocating for installing current UVC tech in every room — we’ll need a few years of figuring out how to produce it more cheaply and with fewer side-effects (ideally with LEDs).
In the hopeful story, new PhDs and R&D labs begin a concerted program to first make the breakthroughs which would enable Far-UVC to become cheap, and then major manufacturers introduce the technology to wider and wider markets. It might parallel the story of solar photovoltaic tech2: between 1975 and 2021, the cost of a watt of solar energy fell by more than 40,000%; and by more than 600% in the past decade alone. The process from now to real maturity — where Far-UVC is cheap enough to be ubiquitous — needn’t last much longer than Bazalgette’s 18-year sewage project.
Standards and monitoring
The expectation of clean water in wealthy countries is enabled by technology and infrastructure; like effective sewage systems and water treatment facilities. But to a large extent it is also enabled, and was initially bootstrapped, by sound policymaking and regulation.
Regulation requires verification. In the UK the Water Supply (Water Quality) Regulations 2016 say things about how much lead can be in my tap water (< 10µg/litre), and water test kits exist to check for lead concentrations, giving those regulations teeth. Similarly, UK building standards say things about how new builds should handle drainage and waste disposal and other exciting things, all easily verifiable.
So is it easy to measure air quality? Pretty much. The concentration of CO2 in a room can be a good proxy for how well ventilated it is (and therefore for risk of transmission without filtration or germicidal light). Plus, CO2 buildup itself can be cognitively impairing. CO2 monitors can cost less than $20. Only a notch more expensive are gauges for different sizes of particulates. Again, particulate matter in general can both proxy well for the effectiveness of filtration, and cause breathing problems of their own. Metagenomic sequencing technology could also survey the air for actual pathogenic material, but it needs to become cheaper first. So we have multiple easy ways to measure air quality, which is good news for straightforward, boring, scalable kinds of air quality guidelines.
Think about water safety regulations again: I don’t really know what they say, and I don’t need to. I just trust that they make sure the water that comes out of my taps is safe. I imagine the story where we achieve a world of clean indoor air would look similar.
Some places where it might be possible to make near-term improvements to regulations and guidelines:
The WHO Guidelines for Indoor Air Quality mention dangerous chemicals and gases, but not particulate matter or (crucially) pathogens and their transmission potential
Most buildings in the US fall under ASHRAE Standards 62.1 and 62.2, which do not consider airborne pathogens
The Occupational Safety and Health Administration in the US can regulate indoor air in workplaces, but its regulations are a little thin on the ground, don’t mention pathogens, and rely on self-certification in most cases
Encouragingly(sidenote: In other good news, the American Society of Heating, Refrigerating and Air-Conditioning Engineers recently announced that they were committing to developing a national indoor air quality pathogen mitigation standard.), the Biden administration announced initiatives to support clean indoor air, including a revised “Clean Air in Buildings Challenge” listing a bunch of sensible suggested upgrades to air quality, and offering funds from the American Rescue Plan and Bipartisan Infrastructure Law funds. But funds could be more explicitly earmarked for this purpose, as they were planned to be in the Pandemic Preparedness Plan (AP3) which did not pass
Thinking further ahead with a wealthy country like the US or UK in mind, we might imagine:
Air quality guidelines have been introduced, plus the means to easily monitor air quality. Subsidies are set up for adding filtration, ventilation, and even UVC into homes and workplaces. More robust standards are established for new builds
As a consequence, much like how plumbers will fit houses to a boiler by adapting some of the plumbing, there are also services to adapt houses for cleaner/sanitised air; such as by installing a system of air ducts, rather than just putting a HEPA filter in the corner of a room
Getting started
When we have such a successful precedent in the story of clean water, there is something so transparently worthwhile about this prospect of creating clean indoor air.
I’m not sure I emphasised this enough: if a country installed all the measures I mentioned, it could more or less end respiratory disease in that country. A world in which clean air measures are as widespread as clean water measures are in rich countries is a world which has effectively ended respiratory disease everywhere. It’s just totally possible to stop worrying about a relative catching a cold, or the flu, or pneumonia.
That’s a huge deal: ignoring pandemics, even halving deaths from respiratory disease means saving hundreds of thousands of lives every year. Not ignoring pandemics, the numbers are of course much starker. It’s hard to quantify how bad truly worst-case pandemics could be, given that they could have civilisation-spanning consequences. But these basic measures would help stop or slow many of them.
Like with waterborne diseases, the wealthiest countries will probably get there first. A ballpark upper-bound estimate for the cost of comprehensively installing the measures I’ve described in buildings across the US is about $200 billion, or about $50 billion for a more targeted program focusing on buildings like schools, preschools, hospitals. But this would surely be worthwhile: even in economic terms, it would save tens of billions in healthcare costs, tens of billions of dollars from lost productivity due to illness, and further further tens of billions from the continued risk of another pandemic.
But we needn’t rely on government spending forever and for every part of the plan. Technologies become cheaper when people build lots of instances of them. To give one example, there may come a point where Far-UVC technology is affordable enough to past the cost-benefit test for businesses looking to protect their employees from disease. This is win-win-win territory: employees would prefer to work in an environment where they don’t get semi-regularly sick; employers benefit because fewer employees get sick; and the world benefits because that is one less office-sized petri dish spawning airborne disease for everyone else. In many cases, it’s about supporting a one-time lift to get to that self-sustaining state where everyone’s incentives are aligned.
In short: practical measures to improve indoor air quality seem like an historically good deal.
The story of spreading access to clean water and sanitation is not over. Unsafe water causes more than a million deaths a year — the 13th leading risk factor on one way of slicing things up. Almost all the deaths from unsafe water are concentrated on poor countries, especially sub-Saharan Africa and India. And a solid 25% of the world lacks access to safely managed drinking water. But full access to clean water is no longer encumbered by knowledge about how diseases spread, or how to properly treat water: we have the blueprints. We know how to bring this story to a happy, if belated, ending.
If the project of spreading access to clean water, then let’s do the same for clean air. What’s stopping that from happening? Surely not that it’s impossibly expensive: the cost-benefit analysis already tips in favour for many countries. Nor feasibility: we either already have the technology at scalable prices, or we have clear precedent for similar technologies plummeting in price with R&D. So maybe what’s stopping the story repeating are things like awareness, political will, the visibility of early adopters, and funding for foundational research. And — hopefully — those things are changeable.
Read more:
This excellent report from Rethink Priorities and 1Day Sooner was my main source (here’s a summary)
The Global Burden of Disease estimates that unsafe water sources are still responsible for 1.2 million deaths each year. Very roughly three quarters of the world have access to a clean water source, and 6% of the world population did not have access to an improved water source of any kind. So let’s conservatively guess that clean water measures reduce the deaths attributable to unsafe water by 75%, compared to a world with the same population but no clean water technology, on average from 1973 to the present day (i.e. over the last 50 years). In other words, we’re guessing that without clean water measures, deaths from unsafe water would be $1.2 million / (1-75%) = 4.8 million and so counterfactual lives saved per year is 4.8-1.2 = 3.6 million per year. Average world population over that period was about 75% of today. So a naive and conservative guess at the lives saved from clean water measures = 75% × 3.6 million × 50 = 135 million people.
In a nutshell: (1) Solar cells were pioneered in R&D labs, often backed by governments. E.g. the US wanted to put solar cells on spacecraft; (2) Then they began being sold to private buyers in niche markets. E.g. Japan subsidised solar cells for calculators, toys, and watches; (3) Then Germany began a major subsidy program to develop domestic solar power capacity in the early 2000s; (4) Then other manufacturers took the grid energy solar tech and drove down costs through building a ton of it; especially in China. As a result, between 1975 and 2021, the cost of a watt of solar energy fell by more than 40,000%; and by more than 600% in the past decade alone. Solar PV also did not majorly benefit from philanthropic funding, in the form of e.g. prizes or advanced market commitments. So it’s a story which demonstrates how costs can fall quickly and dramatically with (i) major investment and (ii) the ability to learn from building millions of units (unlike e.g. nuclear power plants). Both those factors can apply to Far-UVC, and we have the option to supercharge the process with early incentives.
Very interesting read! I agree pretty much that it would be good to have air purification systems everywhere.
However, im a little skeptical about all the costings as you mentioned them. If even today, the air purification systems dont cost all that much, why are we not seeing large scale research in this field? Something like choose 10,000 homes at random, fit 5000 with good air purification systems, wait a year and compare aggregate performances across various health indicators.