Data wars: Should you trust PCB or private apps for AQI levels?

Experts caution Hyderabad residents against panicking over high AQI readings shown by car dashboards and private apps, saying official CPCB data remains reliable. They cite inaccurate low-cost sensors, confined cabin measurements and lack of regulation as reasons for misleading air quality readings.

Hyderabad: As you wait for the red light to turn green at a busy Hyderabad junction, a quick glance at your car’s dashboard or a private AQI app might send your heart racing. But before you panic and frantically roll up your windows because a screen displays an AQI level of 500, experts have a word of advice: breathe easy.

There is a high possibility that your car’s dashboard or the mobile phone might be utilising private sensors or apps that are not as scientific and accurate as that of the measuring instruments that are maintained by State and Central Pollution Control Board (PCB).

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The Reality Check

Officially, as on Monday, the Central Pollution Control Board (CPCB) recorded Hyderabad’s AQI at 102, placing it in the ‘moderate’ category. In stark contrast, New Delhi recorded an AQI of 377, falling under the ‘very poor’ category.

Despite the official figures, people in Hyderabad, while they commute or even browse, see much higher numbers on their personal devices. Experts familiar with this issue pointed out that a lot of car owners also equip their car interiors with car purifiers and even music systems that come equipped with AQI sensors.

Based on reports and experts from CPCB, such private applications are notorious for being inaccurate because they only measure the air inside the tiny car cabin and not the actual atmosphere.

AQI is capped at 500 in India

Once air quality crosses 400 it becomes severe and any number above that level will continue to be more severe. Whether the AQI level is 400 or 500, the general alert or advisory for the general public will always be ‘stay indoors’ and it will not change.

While Indian authorities have set a cap for AQI measurement, there is no such cap in the United States (US) or Europe. Mobile applications whose software is based on Europe and US will tend to display more than 500 AQI levels because of no regulation.

Another major reason why AQI levels of PCB are more accurate is the use of high-end measuring equipment. The PCB stations throughout the country monitor AQI levels by utilising Beta Attenuation Monitors (BAMs), which are massive high-end equipment costing anywhere from Rs 20 to Rs 30 lakh. There is so much stress on accuracy that scientists calibrate the machines every month.

A similar due-diligence in measuring AQI levels is not present in private mobile apps that are based on low-cost sensors, essentially on laser scattering technology that cost anywhere from Rs 5, 000 to Rs 15, 000.

According to reports, such small sensors can be fooled by other major weather parameters like humidity and water vapour, causing them to report massive spikes that usually do not represent the city’s AQI levels.

Some important points:

CPCB utilizes the 24-hour moving average of AQI.
Private mobile apps that claim live real-time data are volatile
A private sensor detects a person smokes and its AQI reading can make the entire neighborhood hazardous
Majority of AQI apps installed in air purifiers and sound systems in a car are not trustworthy
Unlike private mobile applications, the CPCB in India has capped AQI levels at 500 avoid panic