Across India, 70% of stations reported ‘severe’ PM2.5 readings

Why in the News

‘Severe’ PM2.5 peaks spread from 96 air quality monitoring stations before Deepavali to 375 during it, nearly 70% of the stations that reported. An analysis of all Continuous Ambient Air Quality Monitoring Stations (CAAQMS) of the Central Pollution Control Board (CPCB) also found that many stations stopped reporting during the festival. The Board’s explanation for the missing data does not fully account for those gaps.

How is air quality monitored, and what counts as ‘severe’?

1. What a CAAQMS is: A CAAQMS is an automatic station that measures air pollutants round the clock and reports readings every hour. It works like a weather station for pollution.
2. PM2.5: PM2.5 is fine particulate matter small enough to reach deep into the lungs.
3. ‘Severe’ category: A PM2.5 reading of 250 micrograms per cubic metre or above falls in the ‘severe’ category.
4. Network size: The CPCB network has 634 stations, of which only 571 were live and reporting during Deepavali, as per its data portal.
5. The takeaway: A peak is recorded only if the monitor keeps reporting when pollution is highest.

How widespread was the Deepavali spike?

1. Reporting stations: The share of ‘severe’ stations is counted out of the 551 stations that reported PM2.5 at least once in the hourly readings taken during Deepavali.
2. Delhi: All 59 stations in Delhi recorded ‘severe’ peaks.
3. Seven other States: Among States with at least 20 stations, more than two thirds of stations reported ‘severe’ peaks in Maharashtra, Uttar Pradesh, Rajasthan, Haryana, Madhya Pradesh, Gujarat and Andhra Pradesh.
4. Tier 2 cities: The analysis also ranks tier 2 cities, excluding State capitals and cities in the National Capital Region (NCR), by their median (middle value) PM2.5 readings.

Why is the missing data contested?

1. CPCB’s explanation: CPCB analysers for particulate matter are calibrated to measure a range of 1,000 micrograms per cubic metre. Automated data checks ignore values outside that range, which “may appear as a data gap” during “extreme episodes“.
2. Silence before the limit: Many stations partly or fully stopped reporting PM2.5 even though their reading in the preceding hour was not close to the analyser limit.
3. Last readings before silence: The number of stations that failed to report PM2.5 for at least one hour rose during Deepavali. Most of them last reported 500 micrograms per cubic metre or less.
4. Tamil Nadu: Of 37 stations in Tamil Nadu, only nine reported PM2.5 at least once in the Deepavali window. The State stood out for absent data, not for lower pollution.

What do sulphur dioxide readings say about ‘green crackers’?

1. Expected effect of green crackers: The push towards ‘green crackers‘, which are designed to pollute less, was expected to bring down emissions, especially of pollutants such as sulphur dioxide (SO2).
2. No decline in three cities: Stations in Delhi, Mumbai and Kolkata show no drop in SO2 values during Deepavali over the last five years.
3. Chennai: Chennai shows a sharp decline this year. It is unclear whether the fall is real or reflects the absence of accurate readings.

Challenges

1. Unmeasured peaks: Analysers with a fixed upper range cannot record the worst hours, so true peak exposure stays unknown.
2. Late health response: Without live readings, authorities cannot issue timely health advisories or emergency curbs.
3. Uneven network: Monitors are concentrated in large cities, so smaller towns and rural areas are thinly covered.
4. Weak cracker enforcement: Conventional crackers are hard to tell apart from certified green crackers at the point of sale.

Way Forward

1. Higher range analysers: The CPCB should install analysers that measure beyond the present range at known hotspots.
2. Flagged data: Automated validation should publish out of range values with a flag, not remove them.
3. Uptime audits: State Pollution Control Boards should publish station wise uptime for every high pollution episode.
4. Cracker testing: Regulators should test samples of crackers on sale against green cracker norms before the festival.

Conclusion

Severe festival pollution now extends well beyond Delhi, and the monitoring network loses data when readings are highest. Whether the CPCB accounts for stations that stopped reporting below its stated limit remains unresolved.

Back2Basics: Green crackers

1. Developer: Green crackers were developed by the National Environmental Engineering Research Institute (NEERI), a laboratory of the Council of Scientific and Industrial Research (CSIR).
2. Emission claim: They are designed to emit about 30% less particulate matter than conventional crackers.
3. Legal position: The Supreme Court, in Arjun Gopal v. Union of India (2018), permitted only green and reduced emission crackers.

Matching Previous Year Question

“[2021, GS3, 10 marks] Describe the key points of the revised Global Air Quality Guidelines (AQGs) recently released by the World Health Organisation (WHO). How are these different from its last update in 2005? What changes in India’s National Clean Air Programme are required to achieve these revised standards?”