NSW annual air quality statement 2023: gases

Only one station, the Bradfield Highway roadside station, exceeded the annual nitrogen dioxide limit. Ozone exceeded the national standard on 3 days. Sulphur dioxide levels exceeded the standards on 2 days at Muswellbrook.

Carbon monoxide (CO)

The national standard for carbon monoxide is:

• 8-hour average – 9 parts per million (9 ppm).

Eight-hour carbon monoxide averages

No days exceeded the 8-hour CO standard in 2023. Seven Sydney region stations recorded their maximum CO levels in mid-September during a period of widespread hazard reduction burns. The maximum 8-hour CO average was 1.4 ppm, (16% of the national standard), recorded at Camden and Campbelltown West on 12 and 13 September 2023, respectively.

Nitrogen dioxide (NO₂)

The national standards for nitrogen dioxide are:

• 1-hour average – 8 parts per hundred million (8 pphm)
• annual average – 1.5 parts per hundred million (1.5 pphm).

One-hour nitrogen dioxide averages

No days exceeding the 1-hour NO₂ national standard were recorded in 2023, compared with one day in 2022.

The highest 1-hour NO₂ was recorded at the Bradfield Highway roadside monitoring station (6.8 pphm on 15 March 2023).

Annual nitrogen dioxide averages

Annual average NO₂ exceeded the national standard at the Bradfield Highway station. This roadside monitoring station recorded annual NO₂ level of 1.9 pphm, exceeding the standard by 27%. The station has exceeded the annual NO₂ standard every year since 2019.

The next highest NO₂ annual average was recorded at Cook and Phillip located in the Sydney CBD (1.2 pphm).

Ozone (O₃)

The national standard for ozone is:

• 8-hour average – 6.5 parts per hundred million (6.5 pphm).

Eight-hour ozone averages

The ozone standard was exceeded on 3 days in 2023, compared with no days in 2022, and 5 days in 2021.

Ozone levels exceeding the standard were recorded over 4 to 6 hours during 19 March 2023. The maximum 8-hour ozone level was 8.3 pphm, recorded at Liverpool in South West Sydney.

Of all 39 stations monitoring ozone across the state, 13 recorded their highest ozone levels for 2023 on this day when the Bureau of Meteorology reported a low-intensity heatwave across the state, an event that saw new autumn temperature records set.

Two ozone event days occurred in early summer, during heatwave conditions on 8 to 9 December. Three stations exceeded the national standard: at Oakdale and Bargo in South West Sydney, and Albion Park South in the Illawarra.

This ozone event saw a maximum 8-hour ozone level of 6.9 pphm at Albion Park South. While only 3 stations exceeded the national standard, 12 of 39 stations across the state recorded their highest ozone levels for the year during this event.

Sulphur dioxide (SO₂)

The national standards for sulphur dioxide are:

• 1-hour average – 10 parts per hundred million (10 pphm)
• daily average – 2 parts per hundred million (2 pphm).

One-hour sulphur dioxide averages

The 1-hour SO₂ standard was exceeded on 2 days at Muswellbrook in the Upper Hunter. Two consecutive hours over the standard were recorded on 2 January, and another one hour exceeded the standard on 24 March. On both days, light south-east winds transported emissions from nearby power stations over the monitoring station.

Daily sulphur dioxide averages

There was one day over the daily SO₂ standard in 2023, compared to no days in 2022.

This was at Muswellbrook in the Upper Hunter on 2 January 2023, where a daily average SO₂ level of 2.5 pphm was recorded.