Deteriorating air quality
9. METEOROLOGICAL OR ENVIRONMENTAL FACTORS
The winters play a fundamental role in impacting the overall air pollution in Delhi, characterised by dry, cold air and ground-based inversion with low wind conditions, which are responsible for increasing the concentration of pollutants. Due to atmospheric pressure, a high concentration of pollutants is trapped close to the earth’s surface, under a layer of warm air, which acts as a lid on top. These conditions, exacerbated by other sources of pollution, mean Delhi is subject to dense fog during the winter months. Similarly, wind has a direct bearing on air pollution. During autumn and winter, approximately 500m tons of crop residue is burnt in the Indo-Gangetic Plains. The particulate matter from crop burning is aided by the north/north-east wind, resulting in a combination of pollution and fog, leading to heavy smog formation in Delhi. In summers, although there is no inversion phenomenon, there is still deterioration in the air quality because of dust coming in from the Thar Desert, although in the monsoon season, pollution level goes down due to dust suspension. Consequently, air pollution in Delhi is also a trans-boundary and climate induced phenomenon.
In addition to man-made factors, geographic, local climatic and seasonal factors also affect the air quality in Delhi. Geographically, Delhi is a land- locked territory, with limited dispersal of pollutants, unlike costal metropolitan cities, such as Mumbai, Kolkata and Chennai which enjoy favourable wind conditions. The seasonal pattern of Delhi is greatly variable and plays a pivotal role in diffusing pollutants into the atmosphere. It is surrounded by regions of varied climate: at its west, there is Thar Desert of Rajasthan, while in the north and east directions there are cool hilly regions,andfinally to its south, there are central hot Indo-Gangetic Plains. Delhi is located in the subtropical belt with extremely hot summers, moderate rainfall and cold winters.
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