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.