National standards for gaseous pollutants were met on all but 14 days in 2025:

  • Ozone exceeded the national standard on 12 days, at 17 stations across 9 regions.
  • One-hour sulfur dioxide exceeded on 2 days at Morisset.
  • Bradfield Highway exceeded the nitrogen dioxide annual standard.

Carbon monoxide

The national standard for carbon monoxide (CO) is an 8-hour rolling average of 9.0 parts per million (9.0 ppm). 

Eight-hour carbon monoxide averages

No CO exceedances occurred in 2025.

The maximum 8-hour CO level of 1.9 ppm (21% of the national standard) was recorded at Cook and Phillip (East Sydney), on 19 May.

Nitrogen dioxide

The national standards for nitrogen dioxide (NO2) are:

  • one-hour average – 8 pphm
  • annual average – 1.5 pphm.

One-hour nitrogen dioxide averages

There were no one-hour NO2 exceedances in 2025.

The highest one-hour NO2 level of 7.2 pphm (90% of the national standard) was recorded at Bradfield Highway on 28 February. Hazard reduction burning was occurring in Sydney on this day.

Annual nitrogen dioxide averages

Annual average NO2 exceeded the national standard at Bradfield Highway (1.6 pphm). Commissioned in September 2018, Bradfield Highway has exceeded the NO2 annual standard every year since 2019.

Ozone

The national standard for ozone (O3) is an 8-hour average of 6.5 parts per hundred million (6.5 pphm).

Eight-hour ozone averages

There were 12 days above the ozone standard in 2025, occurring at 17 stations across 9 regions. Exceedances occurred on 6 days in Sydney, 2 days at Wollongong and one each at Wagga Wagga North, Morisset and Wallsend.

The maximum 8-hour O3 level of 8.0 pphm was recorded at Macquarie Park on 28 February. Hazard reduction burning was occurring in Sydney on this day.

In 2024, the ozone standard was exceeded on 3 days, at 10 stations in 4 regions.

Sulfur dioxide

The national standards for sulfur dioxide (SO2) are:

  • one-hour average – 7.5 pphm
  • daily average – 2.0 pphm.

From 1 January 2025, the one-hour average standard for sulfur dioxide was lowered from 10 pphm to 7.5 pphm. The daily average standard was left unchanged at 2.0 pphm.

One-hour sulfur dioxide averages

There were 2 days above the new one-hour SO2 standard in 2025, both at Morisset. The highest level was 8.4 pphm on 16 September.

There were no days over the previous 10 pphm standard in 2024. If the new standard had been applied retrospectively to 2024 data, a sulfur dioxide exceedance would have been recorded at Morisset on 25 July 2024.

Daily sulfur dioxide averages

No daily SO2 exceedances occurred in 2025.

The maximum daily SO2 level was 1.1 pphm (55% of the standard), recorded at Muswellbrook on 20 May.