: Opinion: Clearing the air for policymakers #IndiaNEWS #News By Karn Vohra Each year, South Asian countries vie for a bleak distinction: having the world’s most polluted air. India scooped the pool

Opinion: Clearing the air for policymakers #IndiaNEWS #News
By Karn Vohra
Each year, South Asian countries vie for a bleak distinction: having the world’s most polluted air. India scooped the pool in 2021–22, with New Delhi the most polluted capital and Bhiwadi (Rajasthan) the most polluted city overall. Air pollution represents the region’s third-highest risk for premature death (compared to the ninth highest in Western Europe).
Tackling the problem starts with monitoring the pollution to identify its main sources, so they can be regulated. And the best way to monitor the pollution is to track it from all sides, bringing together ground-based observations, satellite data and atmospheric-chemistry modelling. Pollution causes and effects vary over time and across locations, so a one-size-fits-all approach is not helpful.
Tracking Quality
Surface-monitoring networks have provided valuable air-quality data for decades. They can monitor compliance with local or national air-quality standards, but they are costly to set up and maintain. There is less than one ground-based monitor per million people in most low- and middle-income countries, so this method cannot routinely track air quality and provide enough relevant information to develop policies and guidelines.
Surface monitoring is also hampered by large data gaps, data-quality concerns and limited access to data. For instance, there are inconsistencies in the units of air-quality measurement data hosted on India’s Central Pollution Control Board website. In recent years, low-cost sensors to monitor air quality have been used more often, but these are also susceptible to technical biases and need regular calibration.
Satellite Instruments
The eyes in the sky, satellite instruments provide long-term coverage of air quality. Satellite observations help assess the impact of economic development and policy measures on air quality over time. Satellite data on atmospheric components helps identify pollution hotspots, especially in regions with limited surface-monitoring capability. Space-based instruments monitor air pollution from the ground up, and this data is evaluated against the ground-based observations before it is used to investigate changes in surface air pollution.
Satellites can show long-range transport of pollutants across political boundaries, especially plumes from forest- and land-clearing fires, a dominant source of air pollution in South Asia. They have also been extensively used to monitor changes in air quality since the onset of Covid-19. But it is important to use this satellite data carefully. The air-quality improvements observed during the lockdown were not just because of lockdown-induced emission changes but also because of changes in meteorology and chemistry.

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