G01_03

Investigating the variability in the CO:CO₂ff emission ratio at different site types and times of day in Auckland, New Zealand

Young H¹, Turnbull J^1,2, Keller E^1,3, Domingues L¹, Parry-Thompson J¹, Hilton T¹

¹GNS Science, Wellington, New Zealand, ²University of Colorado, Boulder,, USA, ³Antarctic Research Centre, Wellington, New Zealand

Cities occupy just 3% of Earth’s surface area yet contribute ~70% of the world’s fossil fuel CO₂ (CO₂ff) emissions resulting in them becoming focal points for observing emissions. While it is difficult to determine CO₂ff emissions from CO₂ measurements alone, radiocarbon in CO₂ (¹⁴CO₂) is an excellent tracer for CO₂ff. Carbon monoxide (CO) is produced as a by-product of combustion, with each emission source producing a varying amount of CO and CO₂ff, reported as the CO:CO₂ff emission ratio. By combining CO and ¹⁴CO₂ measurements, it is possible to evaluate local source types as each has its own unique signature.

As part of the CarbonWatch-NZ research programme, air samples were collected in flasks around Auckland and measured to determine CO:CO₂ff at 28 sites over four years. Samples were grouped by location to provide overall emission ratios for each site type (motorway, urban, suburban, and industrial). The emission ratios were then used to identify and compare local CO₂ff sources at each site type. Since vehicles are major contributors to city emissions, CO:CO₂ff for traffic is especially useful. Flasks collected at motorway sites showed emission ratios consistent with expectations for traffic.  Suburban and light industrial locations showed ratios consistent with traffic as the dominant CO₂ff source. Urban areas showed a smaller ratio, reflecting a larger CO₂ff contribution from other sources. This observed distribution of sources provides an independent validation of the expected CO₂ff emission sources determined from the Mahuika high-resolution CO₂ff inventory for Auckland.