Scientists are testing the power of trees and plants to clean the air and absorb greenhouse gases in cities in a drive to make new developments carbon neutral.
Experts in Dublin, New York and Tokyo are carrying out similar tests to find out how urban landscapes cope with emissions and heavy traffic.
The aim is to plan more sustainable developments as the fight against climate change widens in the coming decades.
Gerald Mills, geographer at University College Dublin, said cities make up about 80% of the CO2 emissions attributed to man.
"In many urban areas, the absence of trees means that CO2 that might otherwise be captured in the city drifts into the wider atmosphere and contributes to global climate change."
Instruments have been fixed on masts above Marrowbone Lane in the Liberties, where there is virtually no vegetation, and above St Pius X Girl's National School in Terenure, south Dublin, which is surrounded by trees.
A third mobile measuring device will be moved around the city.
The research, carried out by scientists from UCD and NUI Maynooth, will run for up to five years.
Dr Mills said: "By measuring the flow of CO2 into and out of urban areas with different land use, our findings will help to inform city planners about the role of urban developments in moderating greenhouse gas emissions.
"This will contribute to broader discussions on carbon-neutral and sustainable cities."