Context:
Conducted over 34 years (1987–2021) by IMD and Indian Institute of Tropical Meteorology (IITM). Tracked rainwater chemistry at 10 Global Atmosphere Watch stations across India.
Notable locations: Visakhapatnam, Prayagraj, Mohanbari, Srinagar, Jodhpur, Pune, Nagpur, Kodaikanal, Minicoy, Port Blair.
Key Findings:
- Consistent Decrease in Rainwater pH:
- Indicates increasing acidity, especially in urban-industrial regions.
- pH values below 5.65 classify rainfall as acidic.
- Cities with Rising Acidic Rainfall:
- Visakhapatnam: Attributed to emissions from oil refineries, power plants, fertilizer units, and shipping yards.
- Prayagraj and Mohanbari: Similarly show marked decline in rainwater pH levels.
- Natural Neutralisers in Decline:
- Calcium particles, which help counteract acidity, are decreasing in Prayagraj, Jodhpur, and Nagpur.
- Although ammonium levels are rising in some areas, they aren’t sufficient to offset the acidic trend.
- Pollutant Sources:
- Nitrate compounds—main contributor to acidic rain—are increasing.
- Emission sources include:
- Vehicle exhaust
- Industrial activities
- Burning of crop residue
- Household pollutants
- Regional Contrasts:
- Jodhpur and Srinagar see less acidity due to natural dust (e.g., from Thar Desert) which helps neutralize acid content.
- Conclusion:
- Urbanisation and industrial expansion are altering rainwater composition.
- The natural buffering capacity of rain is weakening, raising long-term concerns for ecosystems, agriculture, and public health.
