Was 'Delhi AQI between 1,300 and 1,600' a typo? Here's why it wasn't

A well-read article published two days ago on The Squirrels had an initial part that read: "As Delhi's air quality deteriorated to the 'severe plus' classification on Monday, with the city registering an Air Quality Index (AQI) between 1,300 and 1,600, the authorities enacted pollution control measures..." Since this website does not have a comment section, some readers who know columnist Surajit Dasgupta sent messages to him, asking whether he had added an extra zero to the figures by mistake. That couldn't have been the case, as AQI 130 or AQI 160 wouldn't be classified under the "severe" category. It was, therefore, assumed he had no idea of the range of the index!

The fact is that the Central Pollution Control Board (CPCB), which serves as India's official environmental authority, sets a maximum limit of 500 for AQI readings, indicating "severe" pollution conditions, but various international platforms frequently report values of the index surpassing 1,000 for the same areas, causing confusion among the public. Since The Squirrels is going global shortly, this columnist incorporated both indices, albeit elaborating on the Indian standard alone.

During the transitional months of October and November, Delhi frequently experiences dense pollution. This time of year poses significant challenges for air quality, with the AQI often reflecting hazardous pollution levels. The notable variations in the index readings from different sources have led to confusion among both residents and officials.

The index in Chanakyapuri, New Delhi, has gained international attention due to alarming reports from the US Embassy, which have shown exceptionally high readings compared to data from nearby stations operated by the Central Pollution Control Board (CPCB). Other platforms have also reported values of the index that diverge significantly from those of the CPCB, despite employing similar measurement standards as the US Embassy.

For example, data from the Swiss firm IQAir indicated a concerning AQI exceeding 1,500 on Monday, which surpasses the conventional Indian index limit of 500 by a huge margin, raising doubts about the precision and dependability of various monitoring systems.

IQAir, recognized for its real-time air quality information, does not set an upper limit on readings of the index, unlike the CPCB's guidelines. This approach provides a new lens through which to view pollution levels but also underscores the shortcomings of India's air quality monitoring frameworks. The alarming figures reported by IQAir have sparked global conversations about enhancing local air quality evaluation methods.

Differences in AQI-determining techniques

The discrepancies in AQI readings can also be linked to the different methodologies utilized by various organizations.

IQAir employs sensor-based monitoring, which delivers real-time data and captures swift fluctuations in air quality. However, these sensors may be more prone to interference or inaccuracies.

The CPCB employs pollution analyzers that provide reliable results, though they may be slightly delayed.

The AQI serves as an essential instrument for assessing current air pollution levels and predicting future conditions. The Central Pollution Control Board (CPCB), which acts as India's official environmental authority, limits readings of the index to a maximum of 500, indicating "severe" pollution. At this level, it is recommended that residents remain indoors and reduce physical exertion.

Conversely, various international platforms and websites frequently report values surpassing 1,000 for the same areas, causing confusion among the public. These inconsistencies stem from variations in pollutant measurement methods, data sources, and computational approaches.

For instance, while the CPCB mainly depends on government-operated monitoring stations, international platforms may utilize data from satellite observations, private sensors, and predictive analytics. Furthermore, differences in pollutant metrics, such as PM2.5, PM10, carbon monoxide, sulfur dioxide, and ground-level ozone, along with the differing importance assigned to each, further exacerbate the discrepancies.

What's more reliable?

The intricacies of AQI metrics can often lead to misunderstandings, particularly when comparing international benchmarks. For example, the acceptable daily concentration for PM2.5 in the United States is set at 15 µg/m³, while in India, it is established at 60 µg/m³. Similarly, the US standard for PM10 limits the acceptable level to 45 µg/m³, whereas India's threshold is 100 µg/m³.

Environmental activist Bhavreen Kandhari provides an analogy to clarify this comparison. She compares this environmental index to stock market indices such as Sensex or Nifty: although these indices may show different figures due to distinct calculation methods, they are fundamentally based on similar underlying data. In the same way, PM2.5 and PM10 levels consistently reflect the actual concentration of pollutants, irrespective of the index system used.

Clearing the confusion

1. Stress PM2.5 levels: To gain a more accurate perspective on air quality, it is essential to prioritize PM2.5 concentrations rather than relying solely on AQI figures, which may differ due to varying calculation methods in different regions.

2. Assess health effects: It is important to understand the health risks associated with PM2.5 exposure. Studies indicate that even slight increases in PM2.5 levels can have a substantial impact on health. For instance, a rise of 10 µg/m³ in PM2.5 concentration is linked to increased mortality rates, even when levels are deemed moderate.

3. Promote transparency: Advocate for air quality monitoring systems that display PM2.5 data in conjunction with values of the index. This combined approach can improve public understanding and support more informed decision-making.

By addressing these points, the air quality information gets clarified, which empowers individuals as well as policymakers to effectively tackle the challenges of air pollution.