Urban Methane Emissions in Auckland, New Zealand

Using a mobile survey sampling technique, my research investigates the spatial distribution of urban methane emissions in Auckland, New Zealand. The mobile survey technique uses a car equipped with a high precision methane measurement instrument. This is the first time this technique has been implemented in New Zealand. Methane is the second most important greenhouse gas. Methane emissions from urban areas make up about 10% of NZ’s methane emissions and are poorly constrained. Urban methane emissions are understood to come from landfills, wastewater treatment plants, and fugitive natural gas. Results of this research can help improve existing greenhouse gas inventories. The first component of this research, a city-wide survey, yielded many results. Wastewater treatment plant emissions were observed in detail, showing substantial emissions, with the most emissions around the H2S scrubber and odour bed components of the wastewater plant. Landfills showed variable emission rates, several landfills with methane capture technology appear to have substantial emissions to the atmosphere. Closed landfills were identified as an emission source that appeared to be excluded from current inventory estimates. We found methane emissions present near two thirds of natural gas infrastructure sampled, indicating natural gas is a significant methane source for Auckland. This has advanced the understanding of urban methane emissions in Auckland.

The second focus of this research is “behind-the-meter emissions”. These are emissions from private dwellings and household gas appliances either leaking or emitting un- combusted natural gas. This research has observed evidence of behind the meter emissions happening at an appliance level consistent with previous international research. Then, an experiment was performed to observe temporal variations of emission profiles at a suburb level. The number of “spikes” indicative of methane leaks were observed at least three times more frequently during the early evening than other parts of the day, suggesting the temporal variation was caused by the on/off cycle of natural gas appliances which are used more in the evening. This source could be a significant contribution to urban methane emissions in Auckland. This is the first-time temporal variations in behind the meter emissions have been observed, advancing the wider field of urban greenhouse gas emission research.