Air Quality Categories

Air quality was exceptionally good across the Namoi/North West Slopes region in autumn 2025, remaining below national benchmarks 99% of the season (90 days).

The Namoi/North West Slopes recorded the following air quality categories (AQCs) for autumn 2025:

• Below benchmarks:
  • Good AQC: 86 days (93.5% of autumn days)
  • Fair AQC: 5 days (5.4%)
• Above benchmarks:
  • Very Poor AQC: 1 day (1.1%)

Exceedances

PM10 was the only exceeding pollutant in autumn 2025, exceeding once on 27 May due to a dust storm originating in South Australia and Victoria. Across the network, 60% of air quality stations exceeded the national benchmark due to this dust storm. The Maules Creek industry site was the only Namoi/North West Slopes station not to exceed on this day

There were no national benchmark exceedances for PM2.5 particles, nitrogen dioxide, or ozone.

Trends

Season

Despite the single exceedance in autumn (none in summer 2024-25), regional air quality improved compared to summer 2024-25, with the region recording 17 more Good AQC days during autumn than summer. This is largely driven by a seasonal fall in Fair AQC days from ozone as day-time temperatures cool in the lead-up to winter. Very much above average rainfall during autumn likely contributed to the improvement in air quality relative to summer.

For comparison to previous years, there were no days over national benchmarks in autumn 2024, and 2 days over national benchmarks in autumn 2023. Both days in 2023 exceeded the PM2.5 benchmark at Maules Creek.

12-month review

PM10 and PM2.5 particles 12-month rolling averages from 1 June 2024 to 31 May 2025 in the Namoi/North West Slopes region were below the annual benchmark levels at all stations, except for PM2.5 at Werris Creek (8.6 µg/m3) and Wil-gai (8.5 µg/m3). 12-month averages fell at all stations except Werris Creek and Wil-gai, while Gunnedah recorded its lowest PM10 and PM2.5 averages of the past 5 years.

Air Quality Categories

Air quality was exceptionally good across the Namoi/North West Slopes region in winter 2025, remaining below national benchmarks on 87 days (95%).

The Namoi/North West Slopes region recorded the following air quality categories (AQCs) for winter 2025:

• Below benchmarks:
  • Good AQC: 76 days (83% of winter days)
  • Fair AQC: 11 days (12%)
• Above benchmarks:
  • Poor AQC: 5 days (5%)

Exceedances

National benchmarks were exceeded on 5 days during winter 2025, all due to PM2.5 particles from woodsmoke and all at Gunnedah.

PM10, ozone, and nitrogen dioxide all remained below their respective benchmarks for the season.

Trends

Season

In winter 2025, the Namoi/North West Slopes region experienced 5 days above national benchmarks compared to 1 day in autumn 2025. The 5 winter exceedances all being due to PM2.5 point to smoke from domestic wood heaters as a likely source. This also likely explains the increase in Fair AQC days during winter (11 days) compared to autumn (5 days).

Days above the PM2.5 benchmark in winter due to woodsmoke are a regular occurrence at Gunnedah in particular, with one exceedance day each occurring during winter 2024 and 2023. Days in the Fair AQC were similar between winter 2025 and 2024, with 11 days compared to 13 days, respectively, with 18 days in 2023.

Regional rainfall was average to very-much-above average during winter.

12-month review

The PM10 and PM2.5 particles 12-month rolling averages from 1 September 2024 to 31 August 2025 were below the annual benchmark levels at all stations. Levels at Gunnedah, Tamworth, Narrabri and Maules Creek were similar to previous 12-month periods, and were slightly lower than the 1 September 2023 to 31 August 2024 period. Werris Creek and Wil-gai recorded their second-highest levels since the network was established. However, these were much lower than the 1 September 2019 – 31 August 2020 period, during which air quality was significantly impacted by bushfires and dust storms.

Air Quality Categories

Air quality was exceptionally good across the Namoi/North West Slopes region in spring 2025, remaining below national benchmarks 100% of the season (91 days).

The Namoi/North West Slopes recorded the following air quality categories (AQCs) for spring 2025:

• Below benchmarks:
  • Good AQC: 70 days (77% of spring days)
  • Fair AQC: 21 days (23%)

Exceedances

All pollutants in the region remained below their respective benchmarks in spring 2025.

Trends

Season

The Namoi/North West Slopes region experienced no days above national benchmarks in spring 2025 compared to 5 days in winter 2025. Average spring rainfall and very much above average temperatures may have reduced woodsmoke and opportunities for hazard reduction burning following more mild conditions in winter.

The 21 Fair AQC days during spring were mostly due to ozone at Tamworth and Gunnedah. In comparison, winter had 11 days in the Fair AQC, which were all due to PM2.5 particles. There was one day in spring (9 October) where all sites across the region recorded either Fair PM10 or PM2.5. This was likely caused by bushfire smoke originating from South East Queensland.

No exceedances were recorded in spring 2025, while 2 exceedances were recorded in spring 2024 and 1 in spring 2023. The number of days in the Fair AQC in spring 2025 were similar to spring 2024 and 2023. Ozone accounted for most Fair days in spring 2025 and 2023, however, approximately half the Fair days in spring 2023 were due to particulate matter, primarily from Wil-gai.

12-month review

The PM10 and PM2.5 particles 12-month rolling averages from 1 December 2024 to 31 November 2025 were below the annual benchmark levels at all stations. Levels at Tamworth, Gunnedah, Narrabri and Maules Creek were similar to previous 12-month periods. Werris Creek and Wil-gai recorded lower levels than the 1 December 2023 to 30 November 2024 period, where benchmarks were exceeded. The 1 December 2018 to 30 November 2019 period remains the highest recorded pollutant levels, where bushfires and dust storms significantly impacted air quality.

Ozone in the region from 1 December 2024 to 30 November 2025 followed similar trends to previous 12-month periods, with high levels in spring and summer and little to none in autumn and winter.