Urban flask measurements of CO2ff and CO to identify emission sources at different site types in Auckland, New Zealand

Abstract

As part of the CarbonWatch-NZ research programme, air samples were collected at 28 sites around Auckland, New Zealand, to determine the atmospheric ratio (RCO) of excess (local enhancement over background) carbon monoxide to fossil CO2(CO2ff). Sites were categorized into seven types (background, forest, industrial, suburban, urban, downwind and motorway) to observeRCOaround Auckland. Motorway flasks observedRCOof 14 ± 1 ppb ppm−1and were used to evaluate trafficRCO. The similarity between suburban (14 ± 1 ppb ppm−1) and trafficRCOsuggests that traffic dominates suburban CO2ff emissions during daytime hours, the period of flask collection. The lower urbanRCO(11 ± 1 ppb ppm−1) suggests that urban CO2ff emissions are comprised of more than just traffic, with contributions from residential, commercial and industrial sources, all with a lowerRCOthan traffic. Finally, the downwind sites were believed to best representRCOfor Auckland City overall (11 ± 1 ppb ppm−1). We demonstrate that the initial discrepancy between the downwindRCOand Auckland's estimated daytime inventoryRCO(15 ppb ppm−1) can be attributed to an overestimation in inventory traffic CO emissions. After revision based on our observed motorwayRCO, the revised inventoryRCO(12 ppb ppm−1) is consistent with our observations.This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.