Urban flask measurements of CO 2 ff and CO to identify emission sources at different site types in Auckland, New Zealand.

As part of the CarbonWatch-NZ research programme, air samples were collected at 28 sites around Auckland, New Zealand, to determine the atmospheric ratio ( R CO ) of excess (local enhancement over background) carbon monoxide to fossil CO 2 (CO 2 ff). Sites were categorized into seven types (background, forest, industrial, suburban, urban, downwind and motorway) to observe R CO around Auckland. Motorway flasks observed R CO of 14 ± 1 ppb ppm -1 and were used to evaluate traffic R CO . The similarity between suburban (14 ± 1 ppb ppm -1 ) and traffic R CO suggests that traffic dominates suburban CO 2 ff emissions during daytime hours, the period of flask collection. The lower urban R CO (11 ± 1 ppb ppm -1 ) suggests that urban CO 2 ff emissions are comprised of more than just traffic, with contributions from residential, commercial and industrial sources, all with a lower R CO than traffic. Finally, the downwind sites were believed to best represent R CO for Auckland City overall (11 ± 1 ppb ppm -1 ). We demonstrate that the initial discrepancy between the downwind R CO and Auckland's estimated daytime inventory R CO (15 ppb ppm -1 ) can be attributed to an overestimation in inventory traffic CO emissions. After revision based on our observed motorway R CO , the revised inventory R CO (12 ppb ppm -1 ) is consistent with our observations. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.