Beat the Smog by understanding Smog vs Fog
Countless discussions with family and friends have ended with them trying to convince me that the burn rubber smelling haze I see around me is not Smog but Fog. Well, you know what they say about ducks. Walks like a duck, smells like a duck…
So what is the relationship between fog and smog? In the first post for Beat the Smog I will try to lay out this relationship.
What is Fog?
Straight from National Geographic – “Fog is a cloud that touches the ground. Fog can be thin or thick, meaning people have difficulty seeing through it. In some conditions, fog can be so thick that it makes passing cars. Even monuments like London Bridge, in London, England, or the Golden Gate Bridge, in San Francisco, California, are almost impossible to see in thick fog.”
“Fog shows up when water vapor, or water in its gaseous form, condenses. During condensation, molecules of water vapor combine to make tiny liquid water droplets that hang in the air. You can see fog because of these tiny water droplets. Water vapor, a gas, is invisible.
Fog happens when it’s very, very humid. There has to be a lot of water vapor in the air for fog to form. In order for fog to form, dust or some kind of air pollution needs to be in the air. Water vapor condenses around these microscopic solid particles.”
So what does this mean for those of us living in Northern India waking up to a sea of fog in the winter. There are a few ingredients that are needed for this fog recipe:
- Water bodies and irrigation – North India is full of riverways and irrigation canals. Specially in Punjab, Delhi, Uttarakhand. This provides ample of water sources for the fog to form.
- Cool Himalayan Air – elevation is the lowest in the north Indian plains. With the result, cold air from Himalayan plateaus results in the accumulation of cold dense air in the trough region. This enhances the relative humidity.
- Low pressure / High pressure cycles – We get cycles of low and high pressure zones. The low pressure zones make it cloudy and rainy but follow it with high pressure zones that bring calm winds. The cooling of the earth’s surface during the winter condenses these cycles.
- Westerly disturbances – Rain clouds come from the Arabian sea adding more moisture to our humidity soup
So this is how we get the lovely and romantic North Indian fog. Note that the fog still needs something to coalesce around and without modern day inventions it would likely be dust particles.
See this video if you want to learn the mechanics of fog:
Enter the Smog
Smog = Smoke + Fog and this is how it was defined when intense smog first came around in 1950s London when it killed over 4000 people in London.
Today the definition of Smog is a little further refined to be as a mix of ground-level ozone and other pollutants. Smog forms when organic compounds and nitrogen oxides chemically react with sunlight to create ozone. These pollutant compounds often come from automotive exhaust, factories, power plants and even your hairspray. Smog when mixed with water vapor can form a weak acid that can irritate the respiratory tracts of those inhaling the smog.
So how does this impact the North Indian fog.
With the booming economies of 90s and the two decades hence we have no shortage of the following:
- Paddy burning
- Industrial pollution
- Coal power plants
- Road traffic
All of this adds to the particulate matter in the air – the PM2.5, PM10 you hear so much about. Water vapor that is present in significant volume in the winter now combines with these particles and these particles are light enough to hang in the air. To add a poison cherry to this smog cake these particles then react with sunlight to create ground level ozone that is further damaging to our health. So much so that where the ozone content of the smog rises to 30 ppm it becomes toxic to humans, plants, and animals; even higher levels cause death after two hours (~65 ppm).
So beware my friends, if you are in Delhi – ye fog nahin smog hai.
Not scared yet, watch this harrowing video from Wall Street Journal:
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