A new study funded by the Environmental Protection Agency finds that while EU limits were not breached, significant air pollution was detected in Letterkenny and three other towns between 2010 and 2011.
According to the Irish Independent, the report, 'Assessing the Impact of Domestic Solid Fuel Burning on Ambient Air Quality in Ireland', found that particulate pollution levels in Letterkenny were "higher than might have been anticipated".
The report found that Letterkenny had the highest annual Particulate Matter average, more than double that of the other towns, Navan, Killarney and Tralee.
This was due to almost 11pc of homes using solid fuels including coal, peat and wood to heat their homes, and 77pc using oil.
Patticulate Matter, which is produced by burning fossil fuels, has been linked with cardiovascular and lung diseases, heart attacks and cancer.
The report found while no legal limits were breached, levels Letterkenny and Tralee were above World Health Organisation guidelines.
In May 2013, a ban on smoky coal came into effect in Letterkenny, with the ban being extended into other towns over the next three years.