Lahore  -  As winter descends on South Asia, residents in Pakistan’s Punjab brace themselves for the thick, murky blanket of smog that, more often than not, wafts over from neighboring India. But this journey across borders is not as simple as it might seem. The speed and spread of smog from Indian Punjab to Pakistani Punjab are influenced by a combination of wind patterns, atmospheric conditions, and even particle size.

Winds Carrying Smog Across Borders

Wind patterns play a crucial role in transporting pollution across the 500 to 1,000 kilometers (310-620 miles) separating the two Punjabs. For smog to cross the border, wind speeds between 5 to 20 km/h (3-12 mph) are ideal, with westerly or northwesterly directions acting as a kind of highway for airborne particles. When these conditions align, smog can travel from one side of the border to the other in anywhere from one to eight days, depending on wind speed:

At 5 km/h: Particles might take 4-8 days. At 20 km/h: Smog could arrive in just 1-2 days.

Why Particle Size Matters

Larger particles, like PM10 (10 micrometers), don’t travel as far or as long in the air. They settle within a day or so. Smaller particles, particularly PM2.5 and PM1, are different. They can stay suspended for days and travel far greater distances. These finer particles are more likely to make the full journey from Indian farms and fields to Pakistan, carrying with them serious health risks, especially for those with respiratory conditions. The Right Conditions – or the Wrong Ones, Depending on Perspective.

It isn’t just the speed and direction of the wind that affect smog transport. If the atmosphere is unstable, with shifting temperatures or turbulent mixing, smog can spread vertically as well as horizontally, expanding across wider regions and drifting into Pakistani cities at a faster rate.

Notable Pollution Events of Recent Years

A few years have offered striking examples of just how fast – and how far – smog can travel. In 2017, westerly winds at about 15 km/h carried pollution from Indian Punjab to Lahore in roughly two days. In 2019, stubble-burning emissions from India reached Islamabad in around three days when wind speeds were around 10 km/h. These events are vivid reminders of how air quality in Pakistan can be affected by activities across the border, particularly during stubble-burning season in India.

The Health Toll on Pakistani Residents

As the smog season thickens, health warnings rise. Airborne particles exacerbate asthma, bronchitis, and other respiratory conditions, making the smog season particularly challenging for the elderly, children, and people with chronic health issues. With pollution sources not easily controlled across borders, Pakistani health officials urge caution and protective measures for residents facing another season of hazy, polluted air.

This annual influx of smog has reinforced the need for cooperation between neighboring countries.