How effective are anti-smog guns in Delhi? Here’s what experts have to say

How effective are anti-smog guns in Delhi? Here’s what experts have to say

Subject: Environment

Context-

• Vehicle-mounted ‘anti-smog guns’ have begun their rounds of the city, spraying water in a fine mist, in what is an effort to get suspended dust to settle as air quality begins to take a turn for the worse.

Anti-smog guns-

• Anti-smog gun is a device that sprays nebulised water droplets into the atmosphere to reduce air pollution.
• Connected to a water tank and mounted on a vehicle, the device could be taken across the city to spray water to settle the dust and other suspended particles.
• It can spray water up to a height of 50 metres and the results was positive as the spray acts like rain and settles dust particles and also PM 2.5.
• According to the CPCB’s guidelines on anti-smog guns, the water throw distance ranges from 30 metres to 100 metres depending on the device.
• Anti-smog guns can also be rotated.
• Treated waste water is not to be used in the anti-smog gun.
• The guns that are “customised for urban areas” use 40 to 250 litres of water per minute depending on the device, according to the guidelines.

Anti-Smog Guns for Delhi-

• This winter, Delhi will have more anti-smog guns than in previous years.
• While only large construction sites of 20,000 sqm or more needed them last year, they have now been mandated by the Delhi government at smaller construction sites of 5,000 sqm or more.
• The number of anti-smog guns that are required to be placed varies according to the size of the site, with a maximum of four being required at sites of 20,000 sqm or more.
• The Public Works Department is also rolling out more vehicle-mounted anti-smog guns this year than it did last year.
• The vehicles that are being used to mount the anti-smog guns are either CNG or BS-VI engines.

But how effective are these devices in mitigating air pollution?

• There has been no thorough scientific analysis so far to determine what impact they have, and there could be some brief effect at best.
• In winter, conditions are dry and with repeated action on the topsoil, it gets lifted. Due to low humidity, this dust is unable to settle.
• If the anti-smog gun is used along the roadside, the particulate matter may settle.
• It may reduce particulate pollution, but it is not a permanent solution.
• In emergency situations, where there is a fire or construction and demolition dust, this can be applied so that the situation is not aggravated in nearby areas.
• For the entire city, it is not possible. Water itself is an important resource.
• In China, they tried artificial rain to control haze. But that works at scale.
• Rain droplets remove pollutants, water has that ability which is called wet scavenging.
• That is the idea that is being pursued.
• Whatever comes beneath the droplets, the droplets will carry the particles and gases.
• But how many guns can you employ? You’re firing at a small place, and the overall volume is small, so it’s almost inconsequential whether you look at removal or other effects.

Supreme court’s directive-

• In November 2019, the Supreme Court asked the CPCB to ascertain the efficacy of anti-smog guns and submit a report in 10 days.

A Supreme Court order from January 2020 then mandates the use of anti-smog guns at large construction sites, road construction stretches and dust-prone traffic corridors.