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. To combat air pollution, the Delhi government recently installed a new smog tower in the center of the city. But will this Delhi smog tower have an effect on reducing outdoor air pollution?
How the Delhi Smog Tower Works
The Delhi smog tower is 24 meters tall and includes 40 large fans. The air is sucked in from the top and the filtered air comes out from the bottle of the tower. The tower consists of 10,000 filters to filter out 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, Dharyiash from the Smart Air India team took a Kaiterra Egg PM2.5 air pollution sensor to the tower. Dhariyash recorded air pollution levels at varying distances from the tower: 15 feet, 25 feet, 45 feet, and 100 feet.
The smog tower has a display on it showing the PM2.5 levels of the air at the inlet of the tower (before purification) and at the outlet (after purification). The air entering the tower at the time had PM2.5 levels of around 120 micrograms. As seen below, the air coming out of the tower was around 61 micrograms, still 12 times higher than the WHO recommended limit. This means the air purifier tower removed around 50% of PM2.5 pollution from the air, which is far worse than a typical HEPA air purifier which removes at least 95% of PM2.5.
As shown below, the effectiveness of the smog tower lowers quickly from the original 50% the further you go from the tower.
The effectiveness of the smog tower lowers quickly from the original 50% number as you get further from the tower. The PM2.5 level just 15 feet out from the tower was 81 micrograms, which is a reduction in effectiveness from 50% to just 33%. At just 100 feet out, there was nearly no benefit from the smog tower, with effectiveness reducing to 14%.
Not the First Innefective 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. Even 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.
In 2020, Delhi’s annual PM 2.5 concentration was 89 ug/m3 and it’s highly unlikely that installing these smog towers would have any significant effect on Delhi PM2.5 levels.
The best way to reduce air pollution is to curb emissions at the source. This would require a systematic approach and collective efforts both at the government level and citizen level. More pollution control equipment in power plants and industries with heavy penalties for breaching the air pollution laws are needed. The government should improve public transportation and electric vehicles in tier-2 and tier-3 cities to reduce air pollution across India.
Studies Document Protective Effects of Purifiers, Masks
Despite the harms of PM2.5, studies have found that wearing masks prevents harmful effects on blood pressure and heart rate variability. Similarly, placebo-controlled studies of air purifiers have found that reducing particulate in the home prevents harm to blood pressure, inflammation, and immune response—even among young, healthy twenty-year-olds.
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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