A landmark 34-year study by the
Meteorological Department (IMD) and Indian Institute of Tropical Meteorology (IITM) has revealed a gradual but concerning rise in acid rain across Indian cities, especially Visakhapatnam, Prayagraj, and Mohanbari. Though not yet an immediate threat, the declining pH levels in rainwater highlight emerging environmental stress in urban and industrial regions.
The study, conducted between 1987 and 2021 at 10 Global Atmosphere Watch (GAW) stations, shows that rainwater is becoming more acidic, particularly during monsoons. A pH below 5.65 signals acidity, and a significant decline per decade has been observed — for instance, Prayagraj’s pH dropped by -0.74 per decade during wet months, and Pune’s by -0.15.
Air pollutants like nitrate (NO₃⁻) from vehicles, factories, and burning crop residue are the main contributors, especially in urban growth zones. In cities like Visakhapatnam, industrial activities — oil refineries, shipping yards, and power plants — have worsened the trend.
On the flip side, Jodhpur and Srinagar benefit from natural dust that helps neutralize acids. But even neutralizers like calcium and ammonium are declining, weakening nature’s balancing act.
Experts warn that continued acidification could corrode infrastructure, damage heritage, and leach heavy metals into water bodies — posing a public health risk over time.
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