New figures from the Environmental Protection Agency show that emissions of a key air pollutant in Ireland in 2012 continued to breach the EU ceiling.
The data shows also that emissions of nitrogen oxides (NOx) were up on the previous year.
According to the EPA, the increase mirrors the increase in greenhouse gas emissions in 2012.
Emissions of other pollutants sulphur dioxide, volatile organic compounds and ammonia were well within EU limits.
The pollutants can cause respiratory problems, acidify the soil and surface water and damage vegetation.
The research shows road transport was one of the main contributing factors to the nitrogen oxide increase, contributing 47% of all emissions in the period.
Industry and power generation are also key contributors and the EPA points the finger at the coal fired electricity sector.
The agency says the figures underline the need to decouple emissions from economic activity.
Dr Eimear Cotter of the EPA said: "An increase in NOx (nitrogen oxides) emissions and greenhouse gas emissions in 2012 underlines the need to decouple emissions from economic activity through, for example, promoting energy efficiency, alternative fuels and energy.
"Travelling less by car as well as influencing consumer choice in terms of buying cleaner vehicles with improved emission control technologies will also help to reduce NOx and greenhouse gas emissions", she said.
Dr Cotter said while ammonia emissions have stayed reasonably constant since 1990, that "ambitious targets under Food Harvest 2020 could put pressure on ammonia emissions into the future".