The move, expected to be approved on Tuesday, would see prices on all of Barcelona's ATM transport network halved when heavy smog descends on the coastal city.
It is part of a wide-ranging plan to reduce atmospheric levels of toxic nitrogen oxide gas in an area of some 725 square kilometres (280 square miles).
The plan — designed to bring particle levels in line with European Union standards — would also see costs for road tolls and places in municipal car parks rise by a quarter.
Companies which cut down their emissions would also receive tax breaks under the sweeping reforms, while Catalonia also hopes to boost the use of rail for the transport of goods.
Authorities plan to roll out the measures in 2015 and 2016, local daily La Vanguardia reported.
Barcelona periodically suffers from heavy smog with industry and traffic both playing a role.
The city's topography and geographic location are also contributing factors. When there is a lack of wind, the mountains behind Barcelona can service to trap toxic smog.
Spain saw its carbon dioxide emissions drop 12.6 percent in 2013, the third highest fall in the European Union, possibly a result of declining industrial output during the country's crisis.