Are outdoor purifiers the answer to Bengaluru’s air problem? The answer is a simple NO.

The Bruhat Bengaluru Mahanagara Palike (BBMP) in its recent budget had announced that it would be allocating INR 5 crore for the mitigation of air pollution in the city by installing outdoor air purifiers. This was followed by the Mayor of Bengaluru Gangambike Mallikarjun inaugurating the first such outdoor air purifier at Hudson Square last month. This might well be the fastest implementation of a promised budget item in history! On a more serious note, this approach to address the problem of air quality is extremely misdirected. Ignoring basic logic, the administration is taking the easiest, most gimmicky approach to negotiate the highly complex issue of deteriorating air quality. In this note, we elaborate on why outdoor air purifiers are not the answer.

Air purifiers are basically glorified vacuum cleaners, they suck in air, and along with it they also suck in the pollutants in the air, and keep them inside. This may work in a closed space, like a closed room, or in a hall if there is a very large air purifier, but it won’t work outdoors! This is like using an air conditioner in an open space.

A study by Urban Emissions in 2015 calculated that the total emissions in Bengaluru are 21,300 tonnes, ie 2,13,00,000 kg. BBMP says that the air purifier will collect about 2.5 kg of dust in 20 days, which amounts to 45.6 kg in a year. To actually clean up all of the city’s dust, we would then need 4,67,105  air purifiers, which would cost us INR 1,16,77,63,15,790! (based on Sarath Guttikunda’s methodology for Delhi)

The silver lining in this exercise is the BBMP has realised first that air pollution is serious enough to need intervention, and second (this may be knowingly or unknowingly) that exposure at hot-spots is key problem, which marks a definite shift from earlier focus on ambient air quality levels.

The problem lies in the manner in which the BBMP is approaching the problem, and this reflects the governance challenge in tackling air pollution. There has been no thought given to actually understanding the causes of air pollution in Bengaluru and prioritising the solutions.

Particulate matter is the main cause of air pollution in the city – this consists of particles so fine that they escape the body’s defence mechanisms like nasal hair, mucous, etc and make their way through the lungs into the bloodstream. Depending on the size of the particles, particulate matter or PM can be PM 10 (particles less than 10 microns) or PM 2.5 (particles less than 2.5 microns). The sources of PM 10 and PM 2.5 in Bengaluru are below.

PM 10

PM 2.5

Source Contribution Source Contribution
Road dust 50.60% Transport 49.90%
Transport 19.00% Diesel generators 24.70%
Diesel generators 13.00% Secondary sources 12.70%
Secondary sources 8.70% Domestic 5.80%
Industry 4.50% Road dust 3.50%
Domestic 4.20% Industry 3.50%

Source: TERI, 2010

Given this information, the BBMP can easily act upon the sources to reduce pollution which are within its jurisdiction. Although one can argue that vehicular emission standards are beyond the BBMP’s control, being part of the C40 cities, Bengaluru can learn from cities like London on how creating low emission zones. Ensuring better public transport, incentivising shared cabs and car-pooling, and ensuring we have encroachment-free safe footpaths for pedestrians and cyclists can reduce the vehicles on road. Other sources are well within the BBMP’s jurisdiction – like road dust. Fast-tracking the deployment of mechanised sweepers in hotspots, which reduce resuspension of dust by vehicles is a first step. It is very evident for anyone travelling on the major roads that cleaning of major roads and intersections is completely absent in Bengaluru. Cracking down on garbage and leaf burning is a second. Sand from construction activities has been found to be a large portion on road dust in the city, and the BBMP has failed to enforce regulation on transport, storage on site and disposal on construction material.

As an immediate mitigation measure, the BBMP must ensure that susbsidised air pollution masks are available at the 121 primary health centres  in the city, so that the most vulnerable like the pourakarmikas, traffic police-persons and bus drivers and conductors can buy these at affordable prices.

Delhi’s experiments with outdoor purifiers were cut short twice in the past – once before the Commonwealth Games in 2010, and another time in 2016, but in 2018 the national capital rolled out a plan of 50 such machines. Whether outdoor air purifiers are effective at all and if so to what extent, has not been corroborated by any scientific evidence. Bengaluru must ensure that the limited resources are used wisely and effectively to tackle the air quality problem, rather than focus on gimmicky experiments that have been widely debunked.


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