Annual Air Pollution Fingerprint

Abhilasha Purwar
Oct 29, 2019 · 5 min read
Air Quality in Kolkata over the last one year. To see the air quality in your city, visit

Much like the annual seasonal cycle, air pollution too has its yearly patterns of ups and downs. Some months of the year you will be able to go outside and play, whereas others will leave you gasping for breath.

This air quality is contingent on some factors, mainly the location of the city in question as well as other meteorological conditions such as wind speed and humidity. For example, the likelihood of Mumbai having better air quality than Delhi is higher due to the fact that Mumbai has a coastline which allows polluted air to travel out of the city (like how a sink functions in your bathroom). Delhi on the other hand, due to being completely landlocked, has no outlet for the polluted air to escape, leading to the polluted air getting recirculated in the city itself, eventually settling down to create the “haze” that Delhi has become (in)famous for. Lack of proximity to the coast also means that Delhi (unlike Mumbai or Bangalore) does not enjoy high wind speeds which help push out polluted air from the city.

The above list of graphs is a comparison of the air quality between one coastal cities (Mumbai) and two landlocked cities (Delhi and Lucknow). As you can see, the difference between the two terms of air quality is quite stark. In the landlocked cities of Lucknow and Delhi, the average air quality is significantly worse than in Mumbai, where the average AQI generally falls into the “good” category (i.e <50)

With that short background, let us now take a closer look at the annual pollution fingerprint in India:

July to September

From July to September, we have (what we like to call) “good air days”. July to September is generally when heavy rainfall occurs across the country which means that most of pollutants get washed away (due to high humidity levels and rainfall) or get swept away by higher wind speeds than usual. This can especially be observed in cities like Delhi where there is a lot of dust which is generally conducive to air pollution. However, during the monsoon when the ground gets damp, there is inevitably a lack of dust in the air as it cannot be tossed up in the air as compared to a bright sunny day. Most of India generally enjoy good air days between July and September largely due to the monsoon season, which makes rainfall scarcity across the country a much more serious problem (than it already is).

October to January

This is time of year when most of India starts getting colder. The air starts getting heavier because of colder temperatures, allowing pollutants in the air to settle. When the pollutants in the air mix with the mist released by clouds and trees, it becomes even more heavier, leading to the emergence of the modern and very urban phenomenon of “smog”. Smog (essentially Smoke + Fog) is the single largest deterrent to air quality and visibility across large chunks of India. Where do these pollutants come from? Vehicles, industries and construction are major contributors towards air pollution anyway, but the main contributor is more to do with the time of the year than anything else. And the reason for that is…..

The Diwali Peak

The festival of Diwali is one that is associated with lights, new clothes, good food as well as a promise to improve oneself and turn over a new leaf. This is the time when farmers plant new crops for the winter season, besides lighting diyas and creating rangolis around the house. But, this is also the time when thousands of Indians step out onto the road and burst millions of firecrackers, leading to an enormous buildup of smoke and heavy particulate matter in the air. This is further aggravated by farmers who burn off the remainders of the previous harvest so that they can prepare themselves for the upcoming harvest season. This combination of firecrackers and farm fires contribute towards towns and cities all across north India to be enveloped with a deadly haze. In 2017, Delhi’s AQI levels were so high that AQI monitors around the city just showed the figure of “999” as it just could not calculate air quality worse than 999 AQI. In a nutshell, the air was so toxic that most of the machines in place could not deal with how bad it was!

February to April

As the winter subsides, so does the haze surrounding the cities. Sunlight, while being generally conducive to the rise of pollutants, cuts through the foggy air, and by extension, the pollutants that have mixed with the fog and mist to limit the number of pollutants in the air. This is the first round of good air days that one experiences in the year, before India’s sweltering summer season begins.

May to June

Summertime in India is arguably one of the worst months to spend in India, as the heat and humidity combine to create a deadly cocktail, where all you can experience is the feeling of melting slowly into a puddle of your blood, sweat, and tears. Either that or you will make a beeline for the nearest hill station only to get have your mood spoiled by the number of people there, who (unsurprisingly) had the same idea as you. As bad as the summer is for your mood, it is far worse for the environment. The dust, which vehicles on the road had already kicked up into the air, is further compounded by the humidity present, making the air sticky and heavy. Sunlight (especially harsh sunlight) is also conducive to the formation of nitrogen and sulphuric oxides in the air, which contributes to the number of pollutants floating in the air. And just as you thought it could not get any worse, we are joined by frequent dust-storms which exacerbate lack of visibility as well as breathing troubles.

Check the annual pollution fingerprints of your city at BreeZo, you can also download the BreeZo App and chat with our BreeZo Air Quality bot on Facebook Messenger to get all air quality details on your finger-tips

Blue Sky Thinking

Abhilasha Purwar

Written by

Founder & CEO, Blue Sky Analytics

Blue Sky Thinking

Using Technology & Data to save the Planet

Welcome to a place where words matter. On Medium, smart voices and original ideas take center stage - with no ads in sight. Watch
Follow all the topics you care about, and we’ll deliver the best stories for you to your homepage and inbox. Explore
Get unlimited access to the best stories on Medium — and support writers while you’re at it. Just $5/month. Upgrade