How successful are anti-smog weapons, sprinklers, and dust suppressants as immediate cures for air pollution?

 By Abinaya Sekar & Bhargav Krishna

Jan 10, 2023 

An employee uses an anti-smog gun at a New Delhi construction site.

Anti-smog weapons have emerged as a key representation of New Delhi's initiatives to reduce wintertime air pollution in recent years. Anti-smog weapons are becoming more common in Indian cities as a way to cut pollution.

Anti-smog cannons, which are mounted on trucks and resemble missile launchers, release water droplets into the air to scatter suspended dust particles. However, as they create traffic congestion, these massive cars that circulate on city roadways also add to pollution.

Along with their relatives, the smog towers, they serve as a striking reminder of the technical solutions that litter the landscape of air pollution and attempt to retrospectively solve a problem that should be addressed at its root. Deploying such technology also poses threats to the environment and human health, and its effectiveness is called into doubt.

Anti-smog Weapons 

High-pressure propellers in anti-smog cannons spray a thin, nebulized mist of water into the air, giving it the appearance of rain. By increasing their bulk, the suspended air particles are compelled to settle.

Construction sites utilise anti-smog guns with coarse nozzles, whereas urban areas benefit more from anti-smog guns with finer nozzles for regulating airborne particles. Anti-smog guns designed for construction sites must not be used in urban areas because nozzles are matched to the particle size and should not be cross-applied. However, in the winter of 2022, the nation's capital saw the usage of anti-smog weapons from construction sites in populated areas.

The environment department of the Delhi government released recommendations in 2021 regarding the use of anti-smog guns during building and demolition projects, but there are no equivalent restrictions for their usage in public areas.

Guidelines for the use of anti-smog weapons at building projects in the National Capital Region needing environmental clearance and having built-up areas bigger than 20,000 square metres were released by the Central Pollution Control Board in September of last year.

This was in accordance with the Union Ministry of Environment, Forestry, and Climate Change's recommendations and a January 2021 Supreme Court ruling. The Delhi government required the deployment of anti-smog weapons at building sites with an area larger than 5,000 square metres in September.

When the Air Quality Index hits Stage 1, between 201-300, and is deemed "bad," the Commission for Air Quality Management suggests using anti-smog guns at building sites. Water misting and dust suppressants are advised in hotspots, high-traffic corridors, and "sensitive" locations when the Air Quality Index deteriorates to stage II, which is between 301 and 400, and is deemed "extremely bad."

Experts have questioned the effectiveness of anti-smog weapons to reduce air pollution during the past two years.

High Water usage

Water is utilised at a rate of 40–250 litres per minute in anti-smog weapons intended for use in cities. Anti-smog guns are intended to be used at building sites to control dust for around 30 minutes every two to three hours. Depending on the site circumstances and the style of building, these needs may change.

Gopal Rai, the environment minister for Delhi, claims that the city has 521 sprinklers, 233 anti-smog weapons, and 150 mobile anti-smog weapons. 233 anti-smog cannons operating three times daily for 30 minutes will consume 21 lakh litres of water each day, assuming a flow rate of 100 litres per minute.

Similar calculations would show that installing 150 mobile anti-smog guns and 521 water sprinklers for four hours each day would require 36 lakh litres of water for the anti-smog guns and 125 million litres for the sprinklers.

Without taking into account water loss from leaks or spills, these measures account for the daily usage of 182 lakh litres of water. Anti-smog weapons are a short-term solution to the problem of air pollution in Delhi given the city's ongoing water shortages.

Quality of water

The water quality utilised in an anti-smog gun must be free of biological pollutants due to public health imperatives. In accordance with Delhi's government regulations, the water utilised must be devoid of coliforms, viruses, bacteria, and unwanted substances that might clog the nozzles.

The recommendations forbid the use of treated sewage water in active activity zones, such as building sites. Class A and Class B water, or water of comparable quality to municipal supply water, should be used instead of treated sewage. Class A water is suitable for drinking after disinfection, but Class B water is suitable for outdoor swimming. These are a few of the categories according to surface water standards.

However, according to press sources, purified sewage water has been sprayed in Delhi. According to studies, sewage treatment facilities in India are unable to adequately handle rising contaminants like microplastics and antibiotics, which is likely why antibiotic-resistant bacteria are becoming more widespread. Spraying cleaned sewage water around cities will increase air pollution.

Chemical dust supperssants

Typically, water is used alone to suppress dust, or water is used in conjunction with chemical dust suppressants. When dust suppressants are employed, the efficacy lasts for five to six hours as opposed to just 15 to 30 minutes when simply water is utilised. As a result, less dust suppression is needed, conserving water.

However, research across the board has revealed that dust suppressants are not very effective in preventing the inhalation of tiny particulates (such as PM2.5, which is less than 2.5 micrometres in size). The Delhi government advised using the chemical magnesium chloride hexahydrate as a dust suppressor in a November 2019 guideline. But there are serious problems with it.

First, using water can provide moisture to the air in semi-arid places like Delhi, which encourages the growth of microorganisms. The use of dust suppressants might increase pollution. Strong winds, for instance, may cause dust suppressants that stick to soil particles to get resuspended in the air. Additionally, volatile organic chemicals that are released into the air by dust suppressants are possible. This may have a negative impact on air quality and help create more ozone, a pollutant gas that harms human health.

Second, exposure to these chemical compounds is increased for municipal employees who apply dust suppressants. In urban settings, dust suppressants may potentially contact nearby people's skin. The danger of exposure is disproportionately high for commuters, rickshaw drivers, street sellers, pedestrians, and especially people from socioeconomically deprived backgrounds.

Third, despite the fact that both magnesium and chlorides are necessary for plant growth, a rise in their concentration in the soil may be detrimental to plant development. It becomes challenging for plants to absorb water and other nutrients from the soil when magnesium and chlorides levels are high. Chloride toxicity is indicated by sections of a leaf becoming yellow or wilting when chlorides build up in the margins of leaves.

Finally, the extremely soluble calcium and magnesium chlorides can permeate the soil and contaminate the groundwater. One of the main exposure routes for ingesting these chemical compounds might be through the intake of groundwater.

Better Solutions?

Anti-smog weapons are not a sustainable pollution control technique because to the potential health impacts, high water requirements, and danger of poor water quality. Additionally, they are unable to lessen exposure to tiny or ultra-fine particles without a smaller nozzle size. In contrast, the effectiveness of dust suppressants is substantially influenced by their composition, pace of application, and interactions with the air, soil, and groundwater.

Civic and governmental authorities should engage specialists and make sure that such judgements are backed by solid scientific data before adopting these solutions.