Belfast bonfire air pollution was double advised level
The amount of dangerous air pollution over Belfast during bonfire night was more than double internationally accepted levels.
Over a period of more than six hours, monitors recorded the amount of potentially lethal fine particulates.
Data from across the city revealed pollutants known as PM2.5 - about one fortieth the width of a human hair - were four or five times the levels normally seen in the city.
The pollution began to rise after 10pm and peaked at midnight, before dropping and peaking again at 6am on Wednesday.
Air pollution expert Dr Liz Coleman, from NUI Galway's School of Physics, said PM2.5 was recorded at levels more than twice the limit recommended by the World Health Organisation (WHO).
"Some problems associated with PM2.5 are lung problems, cardiovascular problems and recent studies link exposure to fine particles to dementia," she added.