Aerosols aloft lift, thicken winter fog over North India: IIT-M study

North India's winter fog is a perennial challenge, disrupting daily life, transport, and public health. Every year, from late November to February, the Indo-Gangetic Plain (IGP) experiences dense fog episodes, often leading to flight delays, train cancellations, road accidents, and increased respiratory illnesses. This phenomenon is not merely a natural climatic event but is significantly exacerbated by anthropogenic factors, particularly air pollution. The interaction between pollution and meteorological conditions creates a complex web, the understanding of which is crucial for effective mitigation strategies.

An IIT-Madras study has shed new light on this intricate relationship, revealing that aerosols 'aloft' – meaning those suspended at higher altitudes, not just near the ground – play a crucial role in lifting and thickening winter fog over North India. Traditionally, fog formation is understood as the condensation of water vapor around tiny particles (condensation nuclei) when the air cools to its dew point. This research highlights that aerosols, which are fine particulate matter originating from various sources like vehicular emissions, industrial activities, stubble burning, and biomass combustion, act as these condensation nuclei. The study's key finding is that this aerosol-induced 'invigoration' of fog is more pronounced during night-time, when atmospheric conditions often favor stable layers and reduced dispersion of pollutants, and tends to weaken after sunrise as the sun's warmth helps dissipate the fog and disperse aerosols.

Key stakeholders in understanding and addressing this issue include the research community, led by institutions like IIT-Madras, which provides the scientific basis for policy. Government bodies such as the Ministry of Earth Sciences, the Ministry of Environment, Forest and Climate Change (MoEFCC), the Central Pollution Control Board (CPCB), and state pollution control boards are responsible for monitoring air quality, formulating policies, and enforcing environmental regulations. Citizens are direct stakeholders, bearing the health and economic brunt of pollution and fog. Industries and agricultural sectors are significant contributors to aerosol emissions, making them crucial in implementing cleaner technologies and sustainable practices. International bodies and agreements also play a role in setting global environmental standards and facilitating technological exchange.

This finding holds immense significance for India. Firstly, on the health front, prolonged exposure to polluted fog exacerbates respiratory and cardiovascular diseases, leading to increased hospitalizations and mortality. Secondly, economically, dense fog severely impacts transportation networks – railways, roadways, and aviation – causing delays, cancellations, and significant financial losses. Agriculture also suffers due to reduced sunlight penetration. Thirdly, from an environmental perspective, it underscores the urgent need for comprehensive air quality management. The study provides crucial data for improving weather forecasting models, allowing for better prediction of fog events and their intensity, which can aid in disaster preparedness and operational planning.

Historically, the problem of air pollution in the Indo-Gangetic Plain has intensified with rapid industrialization, urbanization, and agricultural practices post-independence. The region, being a low-lying basin, often traps pollutants, creating a 'pollution bowl' effect. Policies like the National Clean Air Programme (NCAP), launched in 2019, aim to reduce particulate matter concentration by 20-30% by 2024, focusing on 132 non-attainment cities. The Commission for Air Quality Management (CAQM) in the National Capital Region and Adjoining Areas Act, 2021, established a statutory body to coordinate pollution control efforts across states.

From a constitutional standpoint, the right to a clean environment is implicitly derived from Article 21 of the Indian Constitution, the 'Right to Life and Personal Liberty.' Article 48A, a Directive Principle of State Policy, mandates the State to 'endeavour to protect and improve the environment and to safeguard the forests and wildlife of the country.' To fulfill these constitutional obligations, India has enacted several laws, most notably the Environment (Protection) Act, 1986, and the Air (Prevention and Control of Pollution) Act, 1981, which provide the legal framework for combating pollution.

Looking ahead, this study's implications are profound. It suggests that pollution control measures may need to be more spatially and temporally targeted, possibly focusing on reducing emissions that contribute to aerosols aloft, especially during night-time hours in winter. It also emphasizes the need for a regional approach to air quality management, as aerosols can travel across state boundaries. Future research could explore the specific chemical composition of these aloft aerosols and their exact mechanisms in fog formation. As climate change continues to alter meteorological patterns, understanding these complex interactions will be vital for India to build resilience against environmental challenges and ensure a healthier future for its citizens.