As the chill of November-December settles over India, the recurring crisis of air pollution once again grips the nation, with Delhi and its surrounding areas being the most affected. The Air Quality Index (AQI) in the national capital has reached hazardous levels, prompting the implementation of the Graded Response Action Plan (GRAP-4)—a set of emergency measures to tackle severe air pollution.
The Current Scenario: AQI Crosses Dangerous Thresholds
The Central Pollution Control Board (CPCB) reports that Delhi’s AQI has reached around 500, classified as “Severe.” However, the debate on air quality intensified after reports on social media claimed even higher figures, with some suggesting AQI levels near 1000.
Adding to the controversy, data from Swiss-based air quality monitoring company IQAir revealed an alarming AQI reading above 1500 for parts of Delhi on November 18. This discrepancy highlights a critical gap in air quality monitoring systems used in India and internationally.
Why the Data Discrepancy?
The divergence in AQI readings arises from differences in monitoring methodologies:
CPCB’s Pollution Analyzer System:
- Uses a more conventional, standardized system that measures pollutants like PM2.5, PM10, carbon monoxide, sulfur dioxide, and ozone.
- Use Analyzer to measure concentration of pollutants
- Reports consistent but delayed results.
- Caps AQI levels at 500, meaning any figure above this is not reflected in official data.
How CPCB’s AQI Calculated?
- Sub-Index Calculation: The AQI is determined by calculating sub-indices for individual pollutants based on their 24-hour average concentrations (8-hour average for CO and O₃) and comparing them to health breakpoint ranges. The highest sub-index becomes the AQI for that location.
- Minimum Data Requirement: AQI can only be calculated if data for at least three pollutants are available, including either PM2.5 or PM10. A minimum of 16 hours of data is needed to compute sub-indices.
- Incomplete Data Handling: If data for AQI calculation are insufficient, sub-indices for monitored pollutants are still provided to indicate air quality for those specific pollutants.
- Real-Time Reporting: An automated system collects data from continuous monitoring stations and provides real-time AQI updates based on a running 24-hour average. For example, the AQI at 6 AM includes data from 6 AM the previous day.
IQAir’s Sensor-Based System:
- Provides real-time data with rapid updates.
- Sensor based monitoring, less accurate than CPCB’s method
- Captures momentary spikes in pollution levels, sometimes registering extreme values like 1500.
- However, this system can be prone to interference or errors, as acknowledged by experts.
So, Data discrepancy in AQI readings arises from differences in CPCB’s standardized, delayed system and IQAir’s real-time, sensor-based method.
Understanding AQI and PM2.5 Levels
While AQI represents an aggregated score of various pollutants, PM2.5 levels (particles smaller than 2.5 microns) are particularly critical for health. Even a slight increase in PM2.5 can have severe implications, especially for vulnerable groups like children, the elderly, and those with pre-existing conditions. Experts recommend focusing on PM2.5 readings for more reliable assessments of air quality impact.
GRAP-4 Measures
To combat the crisis, Delhi has initiated GRAP-4, the highest level of emergency action under the Graded Response Action Plan. Measures include:
- Closure of construction activities to reduce dust pollution.
- Ban on entry of non-essential vehicles into Delhi.
- Intensified water sprinkling and dust suppression efforts.
- Promotion of work-from-home policies to minimize vehicular emissions.
- Shutting down industries that contribute significantly to pollution.
Health and Environmental Impacts
The health impacts of prolonged exposure to such hazardous air pollution are profound. High PM2.5 levels can cause respiratory diseases, cardiovascular issues, and aggravate pre-existing health conditions. The economic cost, in terms of healthcare and productivity losses, adds to the burden on Delhi’s residents and its governance.
Looking Forward: The Need for Systemic Change
While GRAP-4 is a necessary short-term measure, long-term solutions require a multi-pronged approach:
- Improved Monitoring: Bridging the gap between real-time and standardized systems to provide accurate, actionable data.
- Policy Implementation: Stricter enforcement of vehicular and industrial emission norms.
- Green Energy Transition: Reducing reliance on fossil fuels and adopting renewable energy sources.
- Public Awareness: Encouraging individual contributions like carpooling, use of public transport, and adopting cleaner technologies.
The ongoing crisis serves as a stark reminder of the urgency to address air pollution on a war footing. Only through collective efforts can Delhi hope to breathe easier in the coming years.
