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The discrepancy in Delhi's air quality index (AQI) readings, with the Central Pollution Control Board (CPCB) reporting 494 and IQAir showing 1600, highlights a crucial issue: the lack of standardization in AQI measurement across international agencies. This difference stems primarily from the varying methodologies and scales employed by different countries and organizations. India's AQI, as calculated by the CPCB, uses a scale capped at 500, with levels above 500 categorized as 'severe plus'. This scale is based on specific national standards that weigh different pollutants according to their potential health impact within the Indian context. Conversely, IQAir, an international air quality monitoring platform, utilizes a model based on the US Environmental Protection Agency's standards. This system, while also considering various pollutants, might employ different weighting factors and a different upper limit to its scale, potentially explaining the significant difference observed in the reported AQIs. The higher IQAir reading doesn't necessarily mean the CPCB's data is inaccurate; rather, it emphasizes the limitations of comparing data across systems using different scales and methodologies.
The fundamental difference lies in the standardization and calibration of the AQI scales. Various countries and organizations adopt different scales for measuring the AQI based on their specific environmental conditions and health concerns. Factors influencing this variation include the types and concentrations of pollutants considered, the weighting factors assigned to each pollutant (reflecting their relative harm), and the upper limits of the AQI scale. The WHO provides guidelines for AQI calculations, but adherence to these guidelines is not universally consistent. Many countries choose to adapt these standards to better reflect local realities and health priorities. This lack of standardization makes direct comparisons between AQIs reported by different organizations difficult, requiring careful consideration of the underlying methodologies employed.
Furthermore, the spatial distribution of monitoring stations also contributes to the discrepancies. The CPCB utilizes a network of monitoring stations across Delhi-NCR, providing a broader representation of the air quality across the region. The locations and technology used by these stations are standardized according to the CPCB's protocols. However, international agencies like IQAir may rely on a smaller network of sensors, potentially located in areas with higher concentrations of pollutants, or using different sensor technology with different sensitivities. This difference in spatial coverage and the density of measurement points can affect the overall AQI readings reported, leading to variations, especially when localized pollution events occur.
The question of which AQI to trust is complex. While IQAir provides a valuable perspective on global air quality, Indian citizens should primarily rely on data from the CPCB, given that the CPCB's data reflects the nationally standardized AQI and is based on a comprehensive network of strategically placed monitoring stations across Delhi-NCR. This allows for a more representative assessment of the region's overall air quality. However, it is crucial to acknowledge the limitations of the CPCB's scale, namely its 500 cap. While this is designed to signify critically dangerous air quality, it doesn't provide a nuanced understanding of pollution levels that might exceed that value. The comparison of readings from multiple sources, while recognizing their methodological differences, could provide a more complete picture of the air quality situation. This might also necessitate a wider discussion on harmonizing international standards for AQI reporting to facilitate more effective comparison and cooperation.
The imposition of Stage 4 of the Graded Response Action Plan (GRAP) in Delhi underlines the severity of the air pollution crisis. The implementation of measures like restricting vehicular traffic, reducing office occupancy, and mandating online schooling reflects the urgent need to control pollution and protect public health. However, the effectiveness of GRAP and similar initiatives hinges on consistent monitoring, accurate data reporting, and enhanced public awareness regarding the nuances of air quality indices. The discrepancies observed between different AQI reporting agencies emphasize the importance of transparent and standardized reporting methods to ensure that policies and public health measures are based on a consistent and reliable understanding of the air pollution situation.
Source: Explained: Why Delhi's AQI Was 494 Today But International Monitor Said 1,600