The Central Pollution Control Board (CPCB) has issued a clarification regarding its air quality reporting in Delhi following public concerns over apparent data gaps and a perceived cap on the Air Quality Index (AQI) at 500. The board stated that discrepancies between official data and readings from private applications are rooted in established scientific methodology and technical limitations of monitoring equipment.
Addressing the reports of missing data during the post-Diwali period, the CPCB explained that older particulate matter analysers, deployed when the National Air Quality Index (NAQI) was launched in 2015, were calibrated to measure up to 1,000 micrograms per cubic metre. Because of these hardware constraints, the automated validation system flags any reading exceeding this range as an error. Consequently, these extreme readings are excluded from the station's 24-hour average.
Regarding the 500-point limit, the CPCB defended the ceiling as an intentional design feature of the NAQI, consistent with international standards such as the US EPA scale. The board noted that once the index reaches the 'Severe' category, further extrapolation does not change the associated health advisory. It emphasised that the category label is more significant for public communication than the numerical value itself.
The CPCB also distinguished its reporting from private platforms, which often rely on low-cost sensors that capture sharp hourly fluctuations. The official index is designed to assess sustained health risks by using a 24-hour rolling average. While private apps may show higher figures during brief pollution spikes, the CPCB stated that they often display lower readings when pollution levels decline because they lack the sustained exposure context provided by the NAQI.
Key facts
- The CPCB reported that the NAQI uses a six-category scale ranging from 'Good' to 'Severe' with a 500-point cap.
- Older particulate matter analysers have a measurement limit of 1,000 micrograms per cubic metre.
- The CPCB stated that the 24-hour rolling average is used to assess sustained health impacts.
- The board clarified that the 500-point ceiling aligns with international practices, including the US EPA methodology.
- The CPCB confirmed it is currently replacing older instruments and expanding its network to reduce future data dropouts.
Why it matters
The CPCB noted that the NAQI provides a consistent indication of health risks for public advisories. By explaining the difference between immediate hourly spikes and 24-hour averages, the board aims to clarify how official data is used to determine pollution health warnings.
Background
The National Air Quality Index (NAQI) was introduced in 2015 as a tool for communicating air quality status to the public through a colour-coded, easy-to-understand scale.
Source: Livemint, Times of India
Comments