Urban flask measurements of CO2ff 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 (RCO) of excess (local enhancement over background) carbon monoxide to fossil CO2 (CO2ff). Sites were categorised into seven types (background, forest, industrial, suburban, urban, downwind, and motorway) to observe RCO around Auckland. Flasks from motorway sites observed RCO of 14 ± 1 ppb/ppm and were used to evaluate traffic RCO. The similarity between suburban (14 ± 1 ppb/ppm) and traffic RCO suggests that traffic dominates suburban CO2ff emissions during daytime hours, the period of flask collection. The lower urban RCO (11 ± 1 ppb/ppm) suggests that urban CO2ff emissions are comprised of more than just traffic, with contributions from residential, commercial, and industrial sources, all with a lower RCO than traffic. Finally, the downwind sites were believed to best represent RCO for Auckland City overall (11 ± 1 ppb/ppm). We demonstrate that the initial discrepancy between the downwind RCO and Auckland’s estimated daytime inventory RCO (15 ppb/ppm) can be attributed to an overestimation in inventory traffic CO emissions. After revision based on our observed motorway RCO, the revised inventory RCO (12 ppb/ppm) is consistent with our observations.