Delhi's air quality has become a pressing concern, leading the Supreme Court to question the adequacy of the air-quality monitoring systems in place. With 40 Continuous Ambient Air Quality Monitoring Stations (CAAQMS) strategically located across the city, the aim is to provide a comprehensive overview of air pollution levels.
These stations operate as automated laboratories, continuously measuring eight critical pollutants: PM2.5, PM10, NO₂, SO₂, CO, O₃, ammonia, and lead, as specified by CPCB's 2012 guidelines. Each unit is designed to withstand dust and maintain optimal conditions for accurate readings.
The monitoring equipment employs advanced CPCB-approved methods for assessing air quality. Particulate matter, including PM2.5 and PM10, is quantified using Beta Attenuation Monitors, which assess the reduction in beta-ray transmission caused by dust accumulation on filter tapes.
For gaseous pollutants, various methods are used: sulphur dioxide is measured via UV fluorescence, ozone through UV photometry, and carbon monoxide with Non-dispersive infrared (NDIR) absorption techniques. NDIR absorption specifically analyzes how much infrared light a gas absorbs, allowing for precise concentration measurements.
Nitrogen oxides are detected using chemiluminescence, while ammonia levels are gauged through optical spectroscopy, which studies the interaction of light with matter to derive chemical properties. These methodologies align with National Ambient Air Quality Standards, ensuring reliable and standardized data collection across India.
The accuracy of the Air Quality Index (AQI) relies heavily on the dependability of the monitoring equipment and the volume of validated data. Unfortunately, many stations struggle to meet CPCB's 16-hour data requirement due to various shutdowns from calibration, power outages, extreme weather, or data transmission failures.
A recent report from the Comptroller and Auditor General (CAG) highlighted that several stations in Delhi failed to log complete data or measure critical pollutants like lead. Technical issues can also skew readings: high humidity can inflate particulate measurements, while improper siting of stations can disrupt airflow, leading to inaccurate results.
Numerous studies indicate that particulate readings, especially from Beta Attenuation Monitors (BAM), may significantly overestimate pollution levels under certain conditions. Research conducted in 2021 revealed that beta gauge accuracy declines sharply when humidity exceeds 60%, resulting in a potential overestimation of more than 30% during high-pollution events.
The findings suggest implementing site-specific correction factors to adjust biases, which have been shown to decrease errors from 46% to below 2%. Similar warnings from the U.S. EPA note that heavy particle accumulation can disrupt airflow, further complicating accurate readings.
To maintain effective monitoring, Continuous Ambient Air Quality Monitoring Stations (CAAQMS) must adhere to stringent calibration schedules. The CPCB mandates that detailed calibration records be maintained for every monitor, as even minor drift can affect sensitive readings.
The CAG audit revealed significant gaps, including the failure of DPCC's 24 stations to measure lead, which is essential for accurate AQI calculations. Additionally, many stations reported incomplete AQI data for 12% of months between 2014 and 2021.
The CAG has suggested several measures to enhance the monitoring network, including:
Experts, such as Anumita Roychowdhury from CSE, advocate for regular independent audits to verify compliance with CPCB protocols and ensure the accuracy of data reporting standards.
Q1. What is the purpose of Continuous Ambient Air Quality Monitoring Stations (CAAQMS)?
Answer: CAAQMS are designed to monitor the levels of various air pollutants continuously, providing crucial data to assess air quality and inform public health decisions.
Q2. How does humidity affect particulate matter readings in Delhi?
Answer: High humidity can lead to overestimation of particulate matter concentrations, as moisture causes particles to appear heavier, distorting the data collected by monitoring stations.
Q3. Why is calibration important for air quality monitoring equipment?
Answer: Calibration ensures that monitoring equipment provides accurate readings. Even slight instrument drift can significantly impact the reliability of air quality data.
Q4. What are the major pollutants measured by Delhi's monitoring stations?
Answer: The major pollutants include PM2.5, PM10, nitrogen oxides, sulfur dioxide, carbon monoxide, ozone, ammonia, and lead, all of which are critical for assessing air quality.
Q5. What recommendations have been made to improve air quality monitoring in Delhi?
Answer: Recommendations include relocating obstructed stations, upgrading outdated equipment, and ensuring consistent data reporting to enhance the accuracy of air quality assessments.
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