A sweeping 34-year investigation into India’s rainwater chemistry has revealed an unsettling trend — precipitation in cities like Visakhapatnam (Andhra Pradesh), Prayagraj (Uttar Pradesh), and Mohanbari (Assam) is becoming increasingly acidic. Although the situation hasn’t escalated to true “acid rain” yet, experts from the India Meteorological Department (IMD) and the Indian Institute of Tropical Meteorology (IITM) are raising alarms over consistent drops in rainwater pH across most sites studied.

The study, conducted between 1987 and 2021 at 10 Global Atmosphere Watch (GAW) stations, noted a steady reduction in rainwater pH — a key indicator of acidity. With pH below 5.65 classified as acidic, several locations are approaching or crossing this threshold. Urbanisation and industrial activity are the key culprits, with Visakhapatnam’s emissions from refineries, fertiliser units, and ports accelerating the trend.

In contrast, cities like Jodhpur and Srinagar benefit from desert dust, which helps counteract acid-forming elements. However, this natural balancing act is faltering elsewhere. Areas like Prayagraj and Nagpur are losing calcium particles, which historically neutralised acidity. Meanwhile, nitrates — stemming from traffic, factories, and stubble burning — are on the rise.

In Pune, pH is plummeting by 0.15 units per decade during the monsoon. Prayagraj sees even sharper declines — 0.4 in dry months and 0.74 in wet seasons. With pH being logarithmic, even slight drops imply exponential increases in acidity.

Experts caution that persistent acidification could lead to structural decay and toxic metal leaching, threatening heritage sites and ecosystems alike.