Delhi is one of the most polluted cities in the world. PM2.5 pollution levels reach more than 10 times the World Health Organization’s annual limit. The city aims to tackle this crisis by installing a smog tower. Yet, an important question remains: Can Delhi’s air purifier tower effectively combat outdoor air pollution?
How the Delhi Smog Tower Works
Here’s Delhi’s smog tower.
It’s 24 meters tall and has 40 large fans. It sucks air in from the top and pushes filtered air out from the bottom of the tower. Inside, the tower has 10,000 filters to capture particle sizes up to 0.3 microns.
The Delhi government claims that this smog tower can deliver clean air up to one thousand cubic meters per second. It also uses 8 sensors to measure the air quality before and after filtration.
How Effective is the Delhi Smog Tower in Reducing Air Pollution?
To see how effective the Delhi smog air purifier is, the Smart Air India team went to the tower with a laser particle counter (the Kaiterra Laser Egg). This counter measures tiny pollution particles called “PM2.5.” We recorded air pollution farther and farther away from the tower.
We compared that to the data from the smog tower, which displays PM2.5 at the inlet on the top and the outlet on the bottom. Right at the filter outlet, the tower had about 50% less pollution than the top.
Sadly, even a 50% reduction meant that the air was still 12 times higher than the World Health Organization annual limit.
But hey, so far, so good, right? Fifty percent is better than zero.
The problem is that even this giant tower cleans just a tiny bit of air compared to all the polluted air in Delhi. That cleaner air is just a drop in the bucket. At just 100 feet from the tower, the air is back up to 66% from the outlet.
There, the effectiveness compared to the inlet is just 14%.
But let’s give the tower a chance. Maybe it’s cleaning the air in the neighborhood, so even the air at the inlet is cleaner than the rest of Delhi. We tested that by comparing the air here to the average on that day in Delhi according to the US Embassy pollution data. On that day, Delhi averaged 120 micrograms of PM2.5 (per meter cubed, download the data here).
In other words, air elsewhere in Delhi was just as polluted as the air at the tower inlet. That suggests the tower was not making the neighborhood air significantly cleaner than the rest of Delhi.
Not the First Ineffective Smog Tower
This isn’t the first outdoor air purification project. Similar smog towers were installed in Connaught Place, Delhi, and Xian, China. Data on the effectiveness of these “smog towers” was also not promising.
Dutch artist Daan Roosegaarde built an ionizing tower in Beijing and Tianjin, claiming it would clean the outdoor air. Independent tests found the air filter tower was not providing clean air even within 10 meters of the tower. A careful look at the team’s own modeling estimated only a 20% drop among large particles (PM10, not PM2.5), assuming zero wind, and only up to 20 meters from the tower. Thus, the tower was more art than science.
A Better Way to Reduce Smog
The best way to reduce air pollution is to curb emissions at the source. For example, China cut pollution in Beijing by 50%.
How did China do it? They didn’t plant trees. Trees have only a tiny effect of PM2.5 air pollution. And why would they? Trees didn’t evolve to suck up particles.
Instead, China restricted emissions in several national plans. It made gasoline cleaner. It phased out coal heating in cities. Beijing even banned street-side barbecue grilling. All of these will have a bigger effect for every dollar spent.
So instead of polluting in one place and trying in vain to clean it up down the street, let’s take that smog tower money and use it to stop the pollution in the first place.
Breathe safe!
How I Protect Myself
Smart Air is a certified B Corp committed to combating the myths big companies use to artificially inflate the price of clean air. To help people living in polluted cities protect themselves, Smart Air provides empirically backed, no-nonsense purifiers and masks, thereby helping to lower the cost of clean air.
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