The Upper Hunter air quality monitoring network comprises 14 stations. There are 3 stations in larger population centres, 6 stations in smaller communities, 3 diagnostic stations close to mining operations and 2 background stations – one each at the north-western and south-eastern ends of the valley.
Annual averages
All but one monitoring station in the Upper Hunter recorded annual average PM10 levels, which met the 25 µg/m3 benchmark in 2023 (see Upper Hunter PM10 summary graph). The exception was Warkworth, which is located near mining operations. PM10 annual averages in the Upper Hunter ranged from 14 µg/m3 at Merriwa to 33 µg/m3 at Warkworth. The annual PM10 averages for each station were 40% higher in 2023 than in 2022.
All 4 stations monitoring PM2.5 in the Upper Hunter (Muswellbrook, Singleton, Camberwell, and Merriwa) recorded annual average PM2.5 levels met the 8.0 µg/m3 benchmark in 2023 (see PM2.5 daily and annual summary graph).
The PM2.5 annual averages ranged from 4.7 µg/m3 at Merriwa to 7.5 µg/m3 at Muswellbrook. This is the third year in a row that Muswellbrook and Singleton met the standard. PM2.5 exceedances at both stations are predominantly driven by woodsmoke in cooler months and bushfire and hazard reduction burn smoke during the warmer months.
Daily averages
Particles as PM10
Across the 14 Upper Hunter stations, there were 49 days when daily average PM10 levels were over the benchmark in 2023. In 2022, there were 2 days at 2 stations.
Days exceeding the PM10 daily benchmark were more frequent in September (6 days), October (13), November (3) and December (11). Collectively, these 4 months accounted for 33 PM10 exceedance days out of 49 (67%) in the Upper Hunter for 2023. Drier-than-average conditions, including the second-driest September on record, combined with warmer-than-average temperatures during winter and spring, likely resulted in intensifying drought conditions during this period.
There were widespread particle events in the latter half of 2023. The highest daily average PM10 level of 94 µg/m3 was recorded at Warkworth on 19 September 2023, during a regional dust event when 3 stations exceeded the benchmark.
The most widespread dust event was on 25 October 2023, when 7 stations exceeded the benchmark, the highest number on any one day. This was likely due to a mix of dust from long-range transport, and smoke from a large grass fire. On 19 December 2023, 4 stations, including Warkworth recorded PM10 levels exceeding the benchmark because of smoke from the Duck Creek Pilliga Forest bushfire near Narrabri.
Special note on Warkworth and Mount Thorley
Warkworth recorded most days (42) over the PM10 daily benchmark in the region, a significant increase from one day during 2022 (see Upper Hunter PM10 summary graph). Mount Thorley recorded 18 days exceeding the benchmark in 2023, compared with zero days in 2022. The significant increases in PM10 at both Warkworth and Mount Thorley largely occurred during the final 4 months of the year.
Geographically, the 2 stations are relatively close. Warkworth sits between open cut coal mines and is situated on the southern side of the Hunter Valley, near the Wollemi State Conservation Area. Mount Thorley is located to the south-east of Warkworth, with an open cut coal mine to its west. That the increase in PM10 exceedances was largely restricted to these 2 stations reflects a combination of mining activity together with dryer conditions related to El Niño. Successive La Niña events from 2020 to 2022 significantly reduced dust in the recent past at these stations.
Particles as PM2.5
All stations in the Upper Hunter network met the annual average PM2.5 standard in 2023 (see PM2.5 daily and annual summary graph on the PM2.5 page).
The Upper Hunter did experience one day exceeding the daily average PM2.5 benchmark on 19 December 2023, as smoke dispersed south-east from the Duck Creek Pilliga Forest bushfire. This resulted in PM2.5 exceedances at Merriwa, with an average of 27 µg/m3, and Muswellbrook, with an average of 25.2 µg/m3. This compares relatively favourably with 2022 and 2021, when no days over the daily PM2.5 benchmark were recorded.
Upper Hunter PM10 summary
The bar chart shows the maximum daily average, annual average, and days exceeding the PM10 benchmark for each of the 14 stations in the Upper Hunter.
Note: Exceedance days have not been divided into exceptional and non-exceptional events, as the NEPM compliance goals are not applied to smaller community, diagnostic or background stations.