India, Bangladesh: Periods of air pollution to disrupt transport in India's Indo-Gangetic Plain through March

Fog and air pollution routinely affect transport services in the Indo-Gangetic Plain, encompassing Bangladesh and most of northern and eastern India, during winter. Flight delays, diversions, and cancellations occur regularly, especially during early morning hours. Fog also disrupts rail service and other ground transportation. Visibility problems are typically worst in December and January, but periodic disruptions are likely November-March.

Air pollution levels often spike in urban centers in the Indo-Gangetic Plain during winter, with Delhi and surrounding areas of the National Capital Region (NCR) being the worst affected. Cold air over Bangladesh and northern India often traps pollution near the surface, where it has the highest impact on health and can cause travel disruptions. The intensity and duration of the smoggy period have been increasing annually due to a rise in vehicle-produced pollution, among other factors. Conditions are classified as "severe" when PM 2.5 air pollution (airborne particulate matter with a diameter of 2.5 microns or less, small enough to penetrate the lungs deeply) exceeds 250. Local authorities may issue health warnings in the affected areas during periods of severe air pollution and could impose vehicular and commercial restrictions. Officials could also suspend all outdoor construction projects during periods of severe air pollution and force some factories to cease operations. Such closures typically do not lead to severe supply chain disruptions but may delay some time-sensitive orders and deliveries. Schools often remain closed when air quality deteriorates; higher employee absenteeism is also probable.

Transportation
Fog and air pollution-related flight disruptions are likely at Indira Gandhi International Airport (DEL) in Delhi despite upgraded instrument landing systems, lighting, and surface-movement tracking systems. Multiple operational runways and reduced minimum visibility requirements for departing planes have helped alleviate some delays at DEL in recent years, but problems are inevitable during the winter months. Air traffic controllers may divert DEL-bound flights to airports in Jaipur (JAI), Ahmedabad (AMD), Lucknow (LKO), Kathmandu (KTM), and other regional cities if visibility is poor. These diversions can delay flights by several hours.

Schedule changes could also affect flights to Mumbai's Chhatrapati Shivaji International Airport (BOM) that have stopovers in Delhi. Periodic flight delays due to fog and air pollution-induced poor visibility are also possible at other airports in the Indo-Gangetic Plain, including Kolkata's Netaji Subhas Chandra Bose Airport (CCU) and Patna's Jay Prakash Narayan International Airport (PAT) in India, as well as Bangladesh's Hazrat Shahjalal International Airport (DAC) in Dhaka and Shah Amanat International Airport (CGP) in Chittagong.

Fog routinely disrupts long-distance rail service in the Indo-Gangetic Plain during winter. Lengthy delays and cancellations, especially on Northern Railway's passenger routes serving Delhi, Haryana, Himachal Pradesh, Punjab, Uttar Pradesh, and Uttarakhand, are likely. Poor visibility also affects freight train movements throughout the region.

Heavy fog poses a significant road safety hazard and can cause severe congestion in Delhi and other cities in the affected areas, particularly during morning rush hours. Delhi officials could restrict private car use in the event of severe air pollution; only vehicles with even-numbered plates may drive on even calendar days and odd-numbered plates on odd calendar days. Road accidents increase drastically, especially in northern India, during foggy conditions due to low visibility. Companies that rely on commercial trucking to move goods should consider fog problems when scheduling wintertime deliveries; periodic delivery delays are possible.