Delhi Pollution : Geography of an Expanding City
From last few days the Air Quality Index of National Capital Region and surrounding region is showing hazardous level of pollution. Including PM 2.5 level which is the most dangerous component of pollution.
Various people are discussing the reason behind such a high pollution, some are asking why now and some why here ??
Lets look the issue from a right perspective. NCR is a big conglomerate with expanding area and population. The below two satellite image showing the expansion:
There are many reasons behind air pollution in NCR. Lets look everything from geographical point of view.
The Indo Gangetic plain, sandwiched between Himalayas & Vindhya, home to 600 million people. This region also houses a number of big cities which are expanding rapidly. The domestic pollution of these cities lets say Delhi is also remarkable given the total household numbers & recent expansion. Just look at the above map. (Source Epicmaps Twitter)
The rainfall is less with alluvial soil. Historically also the Ganga plain is used for wheat cultivation. This is true now also but intensity has increased. Surrounding region Haryana, Western UP, Punjab etc grows both Rice & Wheat. They are alternate crops. Stubble burning takes place in both the crops, but more prevalent in Rice.
Stubble burning has increased due to many factors including increase in rice cultivation, electricity subsidy etc. One of the major reason for this in recent years is mechanisation of harvesting process. Earlier the rice harvesting was done manually by cutting the crop from below & then separating grains manually. Then the residue was used as cattle feed.
Now combined harvesters cut the crop from very above leaving a large part of stubble on field. Then farmers use another machine to cut it and then it is burned because they need to make ready the farm in short time. There can be many reason attributed to it including non availability of labour and saving time.
The paddy growing season has also been delayed in last few years due to water crisis as a result very less time is available to make the field available for next crop.
But it is not only the stubble burning which is an issue here. The expanding city creates a lot of pollution by vehicles, construction debris and industries. One extra is occasional Sand storms from Thar due to loss of Aravali.
Here in winter winds blow from north-west to east which carry pollutants from other regions to NCR. Same winds carry western disturbances later which provides winter rains in North West India. The season coincides with temperature inversion, longer the inversion lasts, higher the levels of pollution trapped under it.
Since the big cities like NCR region are in valley the pollution has less space to expand. Addition is urban heat island with local vehicular pollution & construction debris. All smoke with fog and local vehicular volatile compounds get trapped into this island.
Due to continental location no mixture of air like in Chennai or Bombay by sea breeze. Sea breeze in some cities help in reduction of pollution in the city as it expands.
Adding all factors we have a peak of pollution & PM2.5 in this season and in this region.
AQI due to expanding city which is normal for this region = 200–300
After effect of Diwali = 100–150
Stubble burning = 200–300
When all above factors are added with winter & geographical factors = AQI of 500–800 (even crosses 1000) with high level of PM2.5.
Below graph shows how the PM2.5 is increased in last 60 days in the region.
The below graph clearly shows how PM2.5 spike is there in this season and then reduces by January.
So there are many causative factors and above all geography is like a multiplication factor which increases the pollution exposure in the region. Geography can not be changed but on other factors we can work. The only thing is that our actions should consider the geography as well as its impact on the pollution level in NCR.
To solve also we need multiple solutions. All for solving individual issues.
