India Has 9 Of World's 10 Most-Polluted Cities, But Few Air Quality Monitors

India has nine of the 10 most polluted cities in the world, but with 200 particulate matter (PM) 2.5 monitoring sites in operation during the 2010-2016 period, India's air quality monitor density--about 0.14 monitors per million people--is below China (1.2), the United States of America (3.4), Japan (0.5) and Brazil (1.8), according to research from 2019.

As a consequence, India does not accurately know the spread of pollutants, including sulphur dioxide (SO2), nitrous dioxide (NO2), respirable PM 10, the finer particulate matter or PM 2.5, lead, carbon monoxide (CO) and ammonia. Chronic exposure to these pollutants contributes to the risk of developing ailments such as cardiovascular, respiratory diseases, as well as of lung cancer, according to the World Health Organization.

Further, since existing air quality monitors are concentrated in urban areas, health and environmental authorities cannot assess the extent of air pollution in rural areas due to biomass, fuelwood, stubble burning and spraying of pesticides.

Real-time air quality monitoring needed

Ambient air quality is monitored by observing pollutants, including SO2, NO2, PM 10, PM 2.5, lead, CO and ammonia, present in the air. Currently, the country's clean air programme has set a tentative national target of 20%-30% reduction of air pollution in 132 non-attainment cities by 2024, taking 2017 as the base year. The 'non-attainment cities', called so because they did not meet the national ambient air quality standards (NAAQS) at the time, are required to formulate city-specific action plans in order to reduce air pollution. So, while the thrust is on the most-polluted cities, rural and semi-urban areas are not being fully monitored for want of monitors and protocols.

In India, air quality has been traditionally monitored using manual readings. Data from 804 monitoring stations are used for monitoring ambient air quality. Even after the introduction of real-time monitors, the Central Pollution Control Board (CPCB) continues the practice of using data only from manual monitors to report compliance with air quality standards, according to a Centre for Science and Environment (CSE) report from 2020.

There are 261 real-time monitors whose data are updated on the central database. This network is technically part of the National Air Quality Monitoring Programme (NAMP) but its data are stored and treated separately because CPCB has not established a method of equivalence between the two monitoring techniques, the 2020 CSE report pointed out.

In the manual method, the monitoring of pollutants is carried out for 24 hours (four-hourly sampling for gaseous pollutants and eight-hourly sampling for particulate matter) with a frequency of only twice a week, whereas real-time monitors measure pollutants constantly. In simple terms, the readings from manual monitors are the ones the CPCB uses for ascertaining long-term air quality trends, including annual data on air quality. Data from real-time monitors are only included in calculating daily AQI (air quality index) of a location.

"These numbers from our 2020 report need updating but, in any case, coverage of overall urban population is inadequate and rural population is completely outside the ambit of monitoring today," said Anumita Roychowdhury, executive director at CSE and the report's author.

"Manual monitoring protocol requires readings from 104 days in a year but for some stations, we have found data was recorded only for 50-75 days," she said.

Manual monitors do not make sense for air quality monitoring anymore, said S.N. Tripathi, head of the civil engineering department at the Indian Institute of Technology, Kanpur and a member of the NCAP steering committee. "It is a very tedious procedure and readings once or twice a week are not very helpful for a day-to-day understanding of air quality. We need more frequent measurements--at least hourly readings are needed."

Experts have suggested that data from real-time monitors also be used for ascertaining long-term trends and not just for daily AQI.

In 2015, identifying this lack of monitors--there were even fewer at the time--IndiaSpend had launched its own network of low-cost sensors to measure the air quality in many Indian cities. You can read more about the project that ended in 2018, here.

India needs 1,500 air quality monitoring stations

The minimum number of stations to monitor suspended particulate matter where the area's population is less than 100,000 is four. The minimum number is three for SO2, four for NO2, one for CO, according to CPCB guidelines for ambient air quality monitoring released in 2003. The number of monitors required increases with the population.

The number of sampling sites depends on the size of the area to be covered, variability of pollutant concentration, data requirements related to monitoring, pollutant to be monitored and population figures which can be used as indicators of criticality both from view of likely air quality deterioration as also health implications, the guidelines state.

When scientists compared the density of India's monitoring network with that of other high-population countries, they found large differences.

"It is like when a person is ailing, the doctor will need to measure fever before deciding the course of treatment, otherwise treatment can go wrong. The number of monitors we have recommended [in the paper] is the basic, bare minimum requirement," explained Tripathi, who is also one of the authors of this paper.

India's six megacities (Mumbai, Kolkata, Bengaluru, Chennai, Hyderabad, Delhi) need at least 23 to 44 air quality monitoring stations each, while the existing number of stations range between nine and 12 [excluding Delhi], according to the CSE report from 2020.

The monitors that India has are also not evenly distributed. "More than 33 per cent of the real-time monitors are concentrated in Delhi-NCR. Delhi alone has invested over Rs 100 crore to set up 38 stations over time," said the CSE report. In several states, including Manipur and Arunachal Pradesh, station density is very poor and only two to five years of data are currently available, said another paper, titled 'Monitoring particulate matter in India' published in Springer journal in 2019. For comparison, there are 87 monitoring stations for PM 10 and 32 for PM 2.5 in the Greater London region, a city of nine million, it said. In 2021, Manipur, with a population of 2.7 million, has only one monitoring station and Arunachal Pradesh, with a population of 1.25 million has two.

Using CPCB criteria, an average city of one million-plus residents requires around 25 monitoring stations, and if this number is extrapolated across 60 [million-plus] cities, a total of around 1,500 stations would be required, the Springer journal paper said.

An environment ministry report on NCAP agreed. "With reference to the existing 4,000 cities in the country, 703 manual monitoring stations in 307 cities reflect limited numbers and need augmentation. It is proposed to augment it to 1500 stations from existing 703 stations," it stated in its 2019 report.

At its very launch, NCAP had promised to increase the number of monitoring stations in the country, including rural monitoring stations.

The cost of measuring pollutants

To address the data gaps in monitoring pollutants, India will require 1,600-4,000 monitors (1.2-3 monitors per million people), the Elsevier paper said, and warned that even at these densities, only relatively basic information on common air pollutants would be available more frequently, and would cover a relatively limited area.

The average cost of a monitoring station is around Rs 1 crore with around 10% for annual maintenance costs, the 2019 Springer paper had estimated. This would require an initial investment [of setting up 1,500 stations] of Rs 3,000 crore due to capital and operational costs for 10 years.

India has set aside a budget of Rs 470 crore for control of pollution in the financial year 2021-22, which includes funding for its ambitious National Clean Air Programme.

"On top of this, costs associated with infrastructure, personnel and training need to be accounted for; and this can be estimated as an additional Rs 3,000 crore; to cover other miscellaneous costs, an additional 50% is added to this, resulting in a total of Rs 7,500 crore. These estimates indicate that the average cost of running the Continuous Ambient Air Quality Monitoring [CAAQM] station network in each city over a 10-year period would amount to around Rs 12.5 crore per year," the paper read.

Rural areas should also be monitored

The NCAP report had itself pointed out the grave problem of air pollution in rural areas and proposed to set up 75 stations in rural areas.

Rural areas suffer from outdoor air pollution as well as indoor air pollution. Major sources of outdoor air pollution are indiscriminate use of insecticides/pesticides sprays and burning of wheat and paddy straw. Atmospheric concentration of ozone has been observed higher in rural areas as compared to urban areas, the report stated.

"Under NCAP, city-level action plans were to find out pollution sources within the city," said Sunil Dahiya, analyst, Centre for Research on Energy and Clean Air. "But instead of looking at just cities, look at airsheds [airshed is a region which shares similar air quality]. States were supposed to formulate their own state-level clean air plans based on cities' plans. Stubble burning, power plants, these are regional sources of pollution and not limited to a city or town. A hybrid of local and regional approach is needed. While we have formulated local city action plans, we are far away from state or regional plans."

Alternatives to expensive monitors

Procuring new air quality monitors is expensive and time-consuming.

"Apart from government monitors, there are monitors set up by industries. If that data is coupled with government data, it could give much more granular information for the situation of pollution across the country. It will also save the cost of setting up new stations," Dahiya said.

Another alternative to expensive monitors could be low-cost sensors. These sensors offer an opportunity to generate high-resolution data at a lower cost, and with fewer deployment and access limitations. But they have not been proven to provide long-term, accurate data yet and efforts are underway to improve precision in such sensors. Latest analyses are supporting the case for deployment of well-designed low-cost sensors for measurement of air pollution at the city level, according to the Springer paper.

"While it is true that we have to expand our monitoring network, procurement of monitors is very expensive. India needs to leverage its real-time monitoring network for long-term trends and have a hybrid model with satellite monitoring and low-cost sensors that help in mapping the pollution profile and exposure of a region," Roychowdhury said.

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