Rainfall in Visakhapatnam turning increasingly acidic, warns new study

A new long-term study has raised red flags about the increasing acidic levels of rainfall in several parts of India, with Visakhapatnam emerging as one of the most affected cities. Conducted over 34 years by the India Meteorological Department (IMD) and the Indian Institute of Tropical Meteorology (IITM), the study tracked rainwater chemistry at 10 locations across the country from 1987 to 2021.

Visakhapatnam, along with Prayagraj in Uttar Pradesh and Mohanbari in Assam, showed a marked decline in rainwater pH levels—indicating a gradual but consistent shift towards acidification. Researchers attribute this worrying trend of growing acidic rainfall in Visakhapatnam to emissions from its industrial zone. The city’s oil refinery, thermal power plant, fertiliser factories, and busy port are all major sources of pollutants that react with atmospheric moisture to form acidic compounds, which return to the ground in the form of acid rain.

In contrast, places like Jodhpur and Srinagar have fared better. These regions benefit from the natural presence of alkaline dust, particularly from the Thar Desert, which acts as a buffer, neutralising acidic particles in the atmosphere before they can impact rainwater pH.

However, even some of these relatively resilient areas are beginning to show signs of vulnerability. The study reports a decline in calcium-rich particles in places like Prayagraj, Jodhpur, and Nagpur, compounds that normally help balance out acidic elements in the air. While there has been a slight rise in other neutralisers, such as ammonium compounds, researchers warn this is not enough to offset the overall increase in acidity.

At the heart of this trend is a surge in nitrate levels in the atmosphere. Nitrates, which are formed primarily from emissions by vehicles, industrial activity, the burning of crop residues, and household combustion, convert into nitric acid upon contact with atmospheric moisture. This acid then dissolves into rainwater, reducing its pH and contributing to long-term environmental degradation.

Although rainwater in most areas has not yet reached levels considered dangerous under the definition of “acid rain” (pH below 5.65), the steady downward trend is clear—and concerning. The researchers urge a reevaluation of existing pollution control strategies, especially in rapidly industrialising urban areas, and advocate for a shift towards cleaner, more sustainable practices to protect India’s water sources and ecosystems from further harm.

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