Rainwater turning acidic in several Indian cities: Study
What's the story
A 34-year study (1987-2021) by the India Meteorological Department (IMD) and Indian Institute of Tropical Meteorology (IITM) has found that rainwater is becoming acidic in several Indian cities. The research tracked rain chemistry at 10 Global Atmosphere Watch stations, including Srinagar, Jodhpur, Prayagraj, Mohanbari, Visakhapatnam, Kodaikanal, Pune, Nagpur, Minicoy, and Port Blair. The study found a general decrease in pH value, indicating higher acidity, over time in these cities.
Environmental impact
What causes acid rain?
Rain with a pH below 5.65 is considered acidic, and cities like Visakhapatnam, Prayagraj, and Mohanbari have often crossed this limit. Visakhapatnam, Prayagraj, and Mohanbari have frequently exceeded this threshold, according to a TOI report. The main contributors to this acidity are nitrate and sulfate ions from pollutants such as vehicle emissions, factory releases, power plants, and crop residue burning. These pollutants react with water to form sulfuric and nitric acids, which mix with rainwater before falling to the ground.
Toxic effects
Acid rain does not pose major immediate threat: Author
The study also found that both acidic and alkaline rain can have toxic effects on the environment, impacting aquatic and plant life. However, the author noted that "acid rain does not currently pose a major and immediate threat to our region." The research team observed that rainfall in dry seasons is slightly more acidic than in wet seasons due to the washing out of acidic particles during initial rainfall events.
Pollution impact
Acid rain in Delhi
In Delhi, high levels of nitrogen dioxide and sulfur dioxide from vehicle emissions, coal combustion, and stubble burning contribute to the formation of nitric and sulfuric acids in rain droplets. This is a major factor behind the city's consistently poor Air Quality Index (AQI), especially during winter months. As early as 1995, Delhi's rain had a pH over 5.6 in the monsoon but went below that later, indicating acidity due to lack of neutralizing alkaline particles like calcium and magnesium.