The hydrogen-fuelled vehicle from the Ballymena bus builder was unveiled by London Mayor Sadiq Khan at the Zero Emission Bus Conference and Summit in London yesterday.
Messages have been displayed at 2,500 bus countdown signs, at the entrance of all 270 tube stations and on 140 roadside signs, where motorists have been warned to switch off engines when stationary to cut emissions.
People with asthma may need to use their reliever inhaler more often and older people should reduce physical exertion.
"This is particularly crucial for Londoners who are vulnerable, such as asthma sufferers", Mr Kahn added.
King's College London says that pollution in the capital is so high because pollutants are not easily dispersed as a result of calm, settled and cold conditions. Khan also stated that no more diesel double-decker buses will be added to the city's fleet starting in 2018.
"Zero emission buses are the future, and my staff are working hard with manufacturers and bus companies to make them a reality in the Capital as quickly as possible".
The Labour mayor announced he will host a business summit in the new year which will consider proposals, floated by the London Chamber of Commerce and City of London Corporation, for special work permits to allow European Union nationals to take up jobs in the city.
"London's businesses must retain access to the skilled workforce they need in order to grow - it's absolutely essential to protecting jobs, growth and tax revenues across Britain over the next decade", the mayor will say.
"Transforming London's bus fleet by accelerating the introduction of zero-emission buses is important and I plan to work with bus manufacturers, other cities, the European Commission and the C40 Climate Change Leadership Group of Cities to move this agenda forward", he said in a statement.
"So air quality should improve later on Friday and over the weekend as the breeze picks up".
The Environment Department's (Defra) air quality monitoring system UK-Air has notifications for high air pollution in two regions.
Responding to the news, Friends of the Earth air pollution campaigner Jenny Bates said: "This bold move to get rid of diesels, which are the most polluting vehicles, is exactly what is needed in the United Kingdom to help clean up the illegal and risky levels of air pollution now suffered by many of our cities, and which leads to 40,000 premature deaths a year".