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The primary aim of this research was to improve the understanding of how vehicle emissions are trending over time in New Zealand and how this relates to observed trends in local air quality.

Two sites (Auckland and Christchurch) were used to assess the roadside trends in CO and NOx concentrations from 2006 to 2014. To assess trends in the on-road vehicle fleet profile and vehicle emissions, 10 days of roadside vehicle emission monitoring were undertaken using the remote sensor device (RSD) in Auckland in February and March 2015.

The information collected for this study suggests the underlying causes for the observed trends in roadside air quality at the case study sites from 2006 to 2014 were most likely (in no particular order):

• reduced average emissions from the LDV petrol fleet (downward pressure)
• increased average NO emissions from the LDV diesel fleet (upward pressure)
• increasing proportion of diesel vehicles within the LDV fleet (upward pressure)
• increasing effect of older and gross emitting LDV petrol vehicles (upward pressure)
• steady traffic numbers, LDV/HDV fleet composition and driving conditions (neutral pressure)
• steady average emissions from the HDV fleet (neutral pressure)

The report recommends continuing RSD monitoring of vehicle emission trends in New Zealand.

Keywords: roadside air quality, vehicle emissions trends