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Ammonia Emissions from Roads for Assessing Impacts on Nitrogen-Sensitive Habitats


AQC has examined evidence relating to ammonia emissions from road traffic, its contribution to roadside nitrogen deposition and how this might change in the future. AQC has also created a new emissions tool for traffic-related ammonia, which can be downloaded for use by others.

Emissions of nitrogen oxides (NOx) from road traffic are known to make a significant contribution to nitrogen deposition in sensitive habitats. Recent studies reviewed by AQC show that ammonia emissions from road traffic can be at least as important as NOx. Thus, assessments that exclude traffic-related ammonia emissions are likely to significantly under-predict nitrogen deposition at the roadside. AQC has produced an emissions tool, Calculator for Road Emissions of Ammonia (CREAM), to allow ammonia emissions from road traffic to be included in future assessments. 

Ammonia is produced by controls systems designed to reduce emissions of NOx from both petrol and diesel vehicles. These systems have been implemented in response to a tightening of the European type approval standards (Euro Standards). It is also the case that ammonia emission from petrol cars are greater than from diesel cars, thus future emissions will be affected by the current move away from diesel cars. While emissions of NOx are now clearly downward due to Euro Standards, future trends for ammonia emissions are less clear, but may be upward.  

The new CREAM emission factors developed by AQC have been applied to a number of scenarios to show the likely effects of future ammonia and NOx emissions on nitrogen deposition alongside roads. These reveal that while trends in NOx emissions in the near future are likely to be shaped by the current Euro standards, the same cannot be said for total nitrogen deposition at the roadside, due to the role of future ammonia emissions. It is clear from these scenarios that trends in roadside nitrogen deposition are much more likely to be driven by how rapidly the vehicle fleet electrifies and the future role and behaviour in use of hybrid vehicles. 

The full report is available to download here. The ammonia emissions factors used in the study are contained in an emissions factors tool (Calculator for Road Emissions of Ammonia (CREAM) V1A), which is available to download here.


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