Did Delhi's AQI exceed 1,500? Decoding conflicting air pollution readings

The CPCB, India's official environmental watchdog, caps AQI readings at a maximum of 500, which signifies "severe" pollution levels. In contrast, international platforms often report AQI values exceeding 1,000 for the same locations, leaving the public perplexed.

In Short

• Delhi's air quality worsens in Oct-Nov with AQI discrepancies
• Central Pollution Board limits AQI to 500, but some platforms report over 1000
• PM2.5 levels are a more reliable air quality measure than AQI

During the transitional months of October and November, Delhi often finds itself shrouded in a thick haze of pollution. This period is one of the most challenging for air quality, as the Air Quality Index (AQI) frequently indicates hazardous pollution levels. However, significant discrepancies in AQI readings across different platforms have sparked confusion among residents and authorities alike.

The AQI in Chanakyapuri, New Delhi, has drawn global attention due to reports from the US Embassy showing remarkably high readings, especially in comparison to data from nearby stations monitored by the Central Pollution Control Board (CPCB). Several other platforms have also reported AQI values differing significantly from CPCB readings, despite using similar standards to those employed by the US Embassy.

For instance, data from the Swiss company IQAir indicated an alarming AQI exceeding 1,500 on Monday. This figure far surpassed the traditional Indian AQI cap of 500, raising questions about the accuracy and reliability of different monitoring systems.

IQAir, known for its real-time air quality data, does not impose an upper limit on AQI readings, unlike the CPCB's standards. This methodology offers a fresh perspective on pollution levels but has also highlighted the limitations of India's air quality monitoring systems. The staggering figures reported by IQAir have triggered global discussions on improving local air quality assessment methods.

VARIATIONS IN DATA COLLECTION METHODS

The differences in AQI readings can also be attributed to the methodologies employed by various agencies.

IQAir uses sensor-based monitoring, which provides real-time data and captures rapid changes in air quality. However, these sensors may be more susceptible to interferences or errors.

In contrast, the CPCB uses pollution analysers that deliver robust, albeit slightly delayed, results.

DIFFERENT STANDARDS, DIFFERENT RESULTS

The AQI is a vital tool for understanding how polluted the air is currently or is forecasted to become. The CPCB, India’s official environmental watchdog, caps AQI readings at a maximum of 500, which signifies "severe" pollution levels. At this stage, residents are advised to stay indoors and minimize physical activity.

In contrast, international platforms and websites often report AQI values exceeding 1,000 for the same locations, leaving the public perplexed. These discrepancies arise from differences in pollutant measurement techniques, data sources, and computational models.

For example, while the CPCB primarily relies on government-owned monitoring stations, foreign platforms may integrate data from satellite imagery, private sensors, and predictive models. Additionally, variations in pollutant metrics such as PM2.5, PM10, carbon monoxide, sulfur dioxide, and ground-level ozone, along with differing weightages assigned to each, contribute to the disparity.

AQI vs CONCENTRATION: WHAT’S MORE RELIABLE?

The complexity of AQI metrics often leads to confusion, especially when comparing international standards. For instance, the acceptable daily concentration for PM2.5 in the United States is 15 µg/m³, while in India, it is set at 60 µg/m³. Similarly, for PM10, the US standard caps the acceptable level at 45 µg/m³, whereas in India, it is 100 µg/m³.

Environmental activist Bhavreen Kandhari offers an analogy to simplify this comparison. She likens AQIs to stock market indices like Sensex or Nifty: while the indices may display different numbers due to varying methodologies, they are ultimately derived from comparable underlying data. Similarly, PM2.5 and PM10 levels remain constant as direct measures of pollutant concentration, regardless of the AQI framework.

CUTTING THROUGH THE CONFUSION

1. Focus on PM2.5 concentration: For a clearer understanding of air quality, prioritize PM2.5 levels over AQI values, which can vary due to differing formulas across countries.

2. Monitor health impacts: Recognise the health implications of PM2.5. Research shows that even minor increases in PM2.5 levels can significantly affect health. A 10 µg/m³ rise in PM2.5 concentration correlates with higher mortality rates, even at levels considered moderate.

3. Advocate for transparency: Push for air quality monitoring systems that present PM2.5 readings alongside AQI scores. This dual approach can enhance public awareness and facilitate better decision-making.

Addressing these issues can help demystify air quality data and empower individuals and policymakers to combat the challenges posed by air pollution effectively.