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'.