How a warming Arabian Sea is contributing to Mumbai’s smog through airborne sea salt

Mumbai’s civic administration has identified sodium chloride (NaCl), commonly known as sea salt, as one of the compounds contributing to the thick haze shrouding the city’s skyline. The Thursday announcement marks the first time the administration has cited sea salt as a factor behind the haze, amid growing concerns over air pollution since 2022.

How does sea salt contribute to haze?

Mumbai is experiencing the effects of El Niño, a climate pattern associated with warmer temperatures and changing rainfall. Warmer Arabian Sea waters can increase evaporation, while waves release sea spray and aerosols into the atmosphere.

As seawater evaporates, salt particles remain suspended in the air, contributing to haze and reducing visibility.

“Salt or NaCl is an opaque element, therefore, it directly affects the visibility of people, leading to formation of a thick haze-like envelope around the skyline,” Tuhin Banerjee, an air quality expert and former scientist at the National Environmental Engineering Research Institute (NEERI), told The Indian Express.

These airborne particles can also interact with pollutants from vehicles and industries, including nitrogen oxides and sulphur oxides, potentially contributing to the formation of secondary pollutants. Low wind speeds may worsen the situation by allowing aerosols and other suspended particles to linger in the atmosphere.

Is sea salt harmful?

Scientists say there is no established evidence that inhaling sea salt aerosols at typical ambient concentrations poses a significant direct health risk. The Central Pollution Control Board (CPCB) does not list sodium chloride as a separate pollutant among its conventional air quality indicators, which include particulate matter, ozone, sulphur dioxide and carbon monoxide.

However, Banerjee said sea salt could react with other atmospheric compounds to contribute to secondary pollution. Prolonged exposure to salt particles can also corrode electrical equipment, including circuit boards and mobile phones.