Direct visibility between the two cities, some 80 km away across the Gulf of Finland, has not been possible for decades, reports Xinhua news agency.
Researchers in Finland said that the phenomenon is likely due to less transport exhaust gases in the air as a result of reduced passenger transport on the Gulf during the coronavirus
pandemic.
Under the Finnish emergency legislation which was activated to prevent the further spread of COVID-19, the country has prohibited passenger transport between Finland, Estonia and Sweden.
This has reduced departures of large ferries from Helsinki by half.
Ninety-seven scheduled weekly departures were down to 51, as some of the ferries continue carrying freight, local media reported.
Jukka-Pekka Jalkanen, a researcher on air quality at the
--IANS
ksk/