Why Mumbai is witnessing more poor air quality days

Subject: Geography

Section: Physical Geography

Context:

Like Delhi, Mumbai is also witnessing the longest spell of poor air quality since the past two years.

Details:

Mumbai is considered to be immune to air pollution due to its coastal location. Strong sea breezes would blow dust and other suspended particles away, keeping the city’s air relatively clean.
But, recently the air quality index (AQI) in some parts of Mumbai went beyond 300 (very poor).

Wind patterns:

Winds usually alternate between moving from the sea towards the land, and moving from the land towards the sea. This cycle repeats every three to four days during winter.
When the wind is directed towards the sea, the dust particles get swept away. This acts as a natural cleansing mechanism. Sometimes, when the cycle gets temporarily disrupted for some reason, it has an impact on the city’s air quality.
Climatic events like La-Nina disrupted these cycles last year.
- La Nina is a condition in which the sea surface temperatures in the eastern Pacific Ocean become cooler than normal. This large-scale phenomenon influences weather events across the world, and has a wide variety of impacts.
Cause of pollution this year:
- Winds in Mumbai were relatively calmer as the monsoon retreated from the city.
- The city’s temperature soared to a four-year high for October. That created a big temperature gradient between the city and the nearby hilly regions in the Sahyadri ranges. As a result, winds from these areas began moving towards Mumbai, picking up dust from the major construction projects being carried out in Navi Mumbai and surrounding areas.
- Unfavorable local weather conditions are certainly not the cause of bad air quality in Mumbai. The problem is the increasing number of sources of pollutants.

System of Air Quality and Weather Forecasting And Research (SAFAR):

Initiative of: Ministry of Earth Science, Govt. of India.
Operated by: Indian Institute of Tropical Meteorology, Pune
SAFAR envisages a research based management system where strategies of air pollution mitigation go hand in hand with a nation’s economic development to target a win-win scenario.
Air Quality Index of SAFAR:
- There are six AQI categories, namely Good + Satisfactory, Moderately polluted, Poor, Very Poor, and Severe.
- Each of these categories is decided based on ambient concentration values of air pollutants and their likely health impacts (known as health breakpoints).
- AQ sub-index and health breakpoints are evolved for eight pollutants (PM10, PM2.5, NO2, SO2, CO, O3, NH3, and Pb) for which short-term (upto 24-hours)
- National Ambient Air Quality Standards are prescribed.

Source: IE