The National Environment Protection (Ambient Air Quality) Measure (NEPM) air pollutant concentration standards for nitrogen dioxide (NO2), sulfur dioxide (SO2) and ozone (O3) were amended on 18 May 2021. Details can be found in the focus area – Standards.
NSW annual air quality statement 2021: Gases
Ozone levels met the new eight-hour national standard in New South Wales on 99% of days in 2021, compared with 98% of days in 2020. Sulfur dioxide met the national standards on all but 1 day in 2021. Levels of carbon monoxide and nitrogen dioxide met the national standards in 2021.
National standard carbon monoxide (CO)
- Eight-hour average – 9 parts per million (9 ppm).
Eight-hour carbon monoxide averages
There were no days over the 8-hour CO standard in 2021. The maximum 8-hour CO average was 5.1 ppm, recorded at Macquarie Park in East Sydney on 10 October 2021. These levels coincided with smoke impacts from hazard reduction burns which took place nearby (less than 100m from the monitoring location).
The Bradfield Highway roadside monitoring station (north of the Sydney Harbour Bridge, adjacent to one of the State's busiest roads) recorded a maximum 8-hour CO average of 1.1 ppm on 10 May 2021.
National standards nitrogen dioxide (NO2)
- One-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
There were no days over the 1-hour NO2 standard in 2021.The maximum 1-hour NO2 average was 7.3 pphm, recorded at Macquarie Park in East Sydney on 9 October 2021. These levels coincided with smoke impacts from hazard reduction burns nearby (less than 100m from the monitoring station).
The Bradfield Highway roadside monitoring station (north of the Sydney Harbour Bridge, adjacent to one of the State's busiest roads) recorded a maximum 1-hour NO2 average of 6.5 pphm on 28 October 2021. Several other stations in the Greater Metropolitan Region recorded their annual maximum 1-hour NO2 average on this day, such as Chullora which recorded 5.6 pphm. Weather conditions on this day were still and warm, contributing to small build-up of pollutants closer to the coast.
Annual nitrogen dioxide averages
Annual average NO2 levels remained below the national standard in 2021. For non-roadside monitoring stations, the maximum annual NO2 average was 1.2 pphm, recorded at the Cook and Phillip monitoring stations in East Sydney. Levels were typically higher at stations more impacted by traffic emissions, such as Liverpool (1.0 pphm), Lidcombe and Earlwood (0.9 pphm). The lowest annual average was recorded at Oakdale (0.1 pphm) on the urban fringes of Sydney.
At the Bradfield Highway roadside monitoring station, annual NO2 average was 1.9 pphm. As this is a roadside monitoring station it is not assessed against Australian standards.
National standard for ozone (O3)
- Eight-hour average – 6.5 parts per hundred million (6.5 pphm)
Eight-hour ozone averages
The State met the standard on 99% of days in 2021, and there were 5 days with ozone levels recorded over the 8-hour ozone standard at one or more stations in New South Wales. This compared with 9 exceedance days in 2020, and the State meeting the standard on 98% of days (when 8-hour ozone standards are applied to the 2020 data).
The maximum 8-hourly ozone average was 7.7 pphm, recorded at Penrith in North West Sydney on 21 December 2021.
All days with ozone levels above the standard in 2021, except 9 October 2021, were recorded in Sydney in summer, during hot conditions which are typical of ozone formation events. The largest impact typically occurs in Western Sydney in the early to late afternoon.
The fourth day above the standard was at Macquarie Park in East Sydney on 9 October 2021, with ozone level of 6.6 pphm. This exceptional event was caused by smoke from hazard reduction burns nearby (less than 100m from the monitoring station).
Days above the 8-hour ozone standard – 2021
| Date | Station exceeding the 8-hour average ozone standard (6.5 pphm) | Exceptional event?* |
|---|---|---|
| 23/01/2021 | Bringelly (7.6), Camden (7.2), Campbelltown West (7.2), Oakdale (6.6) | No |
| 24/01/2021 | Chullora (6.8), Lidcombe (7.1), Liverpool (7), Parramatta North (7.2), Prospect (6.7), Rouse Hill (6.6) | No |
| 25/01/2021 | Bargo (7.4), Bringelly (7.4), Camden (7.6), Campbelltown West (7.4), Liverpool (7), Oakdale (6.8), Parramatta North (6.7), Prospect (6.6) | No |
| 09/10/2021 | Macquarie Park (6.6) | Yes |
| 21/12/2021 | Penrith (7.7), Richmond (7.6) | No |
Note: Values in brackets are the maximum 8-hour ozone levels at each station on the day.
pphm = parts per hundred million in volume.
* An exceedance day determined to be impacted by bushfires or planned burns is deemed exceptional.
National standards sulfur dioxide (SO2)
- One-hour average – 10 parts per hundred million (10 pphm)
- Daily average – 2 parts per hundred million (2 pphm).
One-hour sulfur dioxide averages
There was one day over the 1-hour SO2 standard, at Muswellbrook in the Upper Hunter which recorded 12.3 pphm on 4 February 2021. Outside of Muswellbrook, the station which recorded the next highest was 7.1 pphm at the Morisset station in Lake Macquarie, on 15 December 2021.
Daily sulfur dioxide averages
There were no days over the daily SO2 standard in 2021. The maximum daily SO2 average was 1.6 pphm, recorded at 2 stations: Muswellbrook in the Upper Hunter on 29 January 2021; and Morisset in Lake Macquarie on 23 August 2021.