Tropospheric ozone measurements at a rural town in New South Wales, Australia

In Australia, tropospheric ozone measurements in rural locations are scarce with measurements mostly made in cities. This limits the ability to estimate background ozone levels that inform policy development. The few studies that have assessed rural ozone in Australia have been associated with short campaign monitoring or specific, short-term research programs. Recognising this deficit of information, the New South Wales Government has established long-term ozone monitoring at two rural locations. This paper presents results from the first three years of monitoring at Gunnedah. We assess seasonal, diurnal and sectoral patterns of ozone. Several events are analysed, including high ozone associated with the 2019/20 Australian Bushfire Emergency and an extreme heatwave event. We find that ozone levels at Gunnedah exceed the screening standards set by Australia's National Environmental Protection (Ambient Air Quality) Measure, emphasising the need for additional ozone monitoring in rural and regional Australia. Our early results indicate that in NSW, background ozone mixing ratios for airmasses of continental origin is likely in the range of 36–39 ppb, higher than the 14–30 ppb associated with air masses of marine origin and greater than the 30 ppb background mixing ratio used for monitoring design and standard setting in Australia. Maximum 8-hourly ozone in non-bushfire impacted events is as high as 64 ppb, demonstrating the challenges that rural/regional communities may face in always meeting the new Australian 8-h ozone standard of 65 ppb. These results add to our understanding of rural background ozone within Australia and in the southern hemisphere.