Analysis and Solutions
In this edition!
How many tons of air pollution are in Delhi?
How many air purifiers to clean Delhi?
How many industrial scale purifiers to clean Delhi?
Why not just emit less pollution?
The thing that stood out most on my trip to Delhi, Jaipur, Mumbai and Dhaka (Bangladesh) was pollution. I can’t overstate how unpleasant it makes cities that are beautiful underneath. I would blow my nose and find black specs on the tissue. I went around wearing a mask, but most locals didn’t.
I think the pollution is tragic on so many fronts. Pollution is terrible for the health of locals. Pollution darkens the cities, robbing them of sunlight. My hunch is that tourism is negatively affected. Mumbai is a beautiful coastal city that is safe to walk around in, but the pollution is a killer.
How many tons of air pollution are in Delhi?
In the chart below you can see Delhi pollution as of December 8th 2022. Everywhere is unhealthy, some places are very unhealthy and some are hazardous. When I was there the previous week, most of the areas were hazardous:
If you drill in (see the graph below), you can see that a) the pollution is seasonal and b) most of the issues are with 2.5 micron particles and 10 micron particles. Ozone, nitrous oxide and carbon monoxide are not quite so bad. Here’s the chart for PM 2.5 (dust smaller than 2.5 microns):
Let’s do a rough calculation of how much PM 2.5 there is in the air based on an average annual AQI (US method) of 200. The calculator (here) gives 150 micrograms of particles per cubic metre.
Running the same (also assuming an AQI of 200) for PM 10 gives about 350 micrograms of particles per cubic metre.
Taken together, that’s 500 micrograms of particles smaller than 10 microns (including less than 2.5 microns) per metre cubed of air.
I don’t have a great reference for the height of smog, but I’m guessing – based on what I saw approaching in an airplane – that the smog could be over 2,000 metres high.
Conservatively, let’s take a 25 km radius around Delhi. That’s 25,000*25,000*3.14 = ~2 billion square meters. Multiplying that by height gives 2 trillion metres cubed of pollution above Delhi. Multiplying that by 500 micrograms per cube gives about 1,000 tons of pollution floating in the sky above Delhi.
How many air purifiers to clean Delhi?
Let’s estimate how many air purifiers would be needed to clean 2 trillion metres cubed of pollution in one month. I chose one month because that seems roughly the characteristic time for pollution to accumulate.
Let’s consider this air purifier, which costs $150 and purifies about 2,250 cubic feet per hour. There are about 27 cubic meters per thousand cubic feet, so this air purifier does about 50 cubic metres per hour. 50 cubes per hour X 24 hours per day X 30 days per month is 36,000 cubes of air per month.
Alright, 2 trillion divided by 36,000 is about 55 million air purifiers. If every household in Delhi got a large (say 10X the purifier size we chose), then it might be possible to remove the pollution.
The industrial scale solution
What about building larger units?
Someone has thought of it. There’s the “Smog Free Tower” that can process 30,000 cubic metres per hour. That’s 30,000 cubes per hour X 24 hours X 30 days per month = 21 million cubes per month.
2 trillion divided by 21 million is about 100,000 Smog Free Towers. It’s pretty unclear how much one of those towers costs (it’s fancy because it uses ionisation to remove the dirt). Let’s say each tower costs $250,000. That would be a $25 billion investment. Probably worth it for making the city clean!
Why not just emit less pollution?
It would seem that a better solution to stop polluting in the first place. Anecdotally, when I asked locals whether they thought pollution would be better in 20 years, they didn’t think so. Much as it would be nice to stop the emission, if the emissions can’t be stopped it would seem better to at least clean the air up.
We’re spending on CO2 capture, why not air pollution?
Direct air capture (DAC) is a method of sucking carbon dioxide out of the atmosphere. This is highly expensive because carbon dioxide is a very small molecule, just a few angstroms in size. Dust particles that are microns in size are 10,000 times larger!
Cleaning the air of dust particles is a much easier (and cheaper) problem than cleaning air of CO2.
So, if there is willingness to subsidise CO2 capture (which there is in the US under the inflation reduction act in the US), shouldn’t we also be funding solutions for Direct Pollution Capture?
I’m Unsure
What I’m suggesting above is a very top-down approach, i.e. getting people or governments outside of where I live/work to make massive investments in air purification. Superficially, it seems better to try and tackle the root causes of pollution.
I don’t have a detailled understanding of the specific causes of pollution in India and the challenges in solving it. I also don’t have a good feel for the competing problems and needs that are there.
What I now better appreciate is that hazardous pollution is highly unpleasant, unhealthy, and my sense is that the indirect and negative side effects are probably being underestimated globally. (And it’s not just India, but India is mostly where I was.)