Air quality special statement spring-summer 2019-20: gases

Key points

During spring–summer 2019–20, gaseous air pollutants reached record levels across the NSW Air Quality Monitoring Network (the network).

• The highest one-hour average ozone (O₃) level reached 17.9 pphm (above the benchmark of 10 pphm) at Rozelle and Earlwood in Sydney East in December 2019. This ranked the highest one-hour ozone level since 2001 and the third highest since enhanced air quality monitoring began in 1994.
• The highest one-hour average nitrogen dioxide (NO₂) level reached 16.1 pphm (above the benchmark of 12 pphm) at Goulburn in the Southern Tablelands on 31 December 2019. This was the first day above the benchmark since 1998 and ranked as the highest one-hour NO₂ level since 1994.
• The highest eight-hour rolling average carbon monoxide (CO) level reached 9.6 ppm (above the benchmark of 9 ppm) at the bushfire monitoring station at Port Macquarie on 15 November 2019. This event was due to smoke from a peat fire in wetland and was the first day above the benchmark since the NSW bushfire emergency in spring 2013.

More detail

• Ozone levels across the Network were above either the one-hour or four-hour average benchmarks on 32 days, or 18% of days in spring-summer 2019-20, compared to 13 days (7% of days) in spring–summer 2018–19. The Network experienced 8 consecutive days above ozone benchmarks from 26 December 2019 to 2 January 2020.
• The number of days above ozone benchmarks across regions ranged from 2 days in the North-west Slopes to 16 days in Sydney North-west and Sydney South-west. Maximum 1-hour and 4-hour ozone levels were up to 1.8 and 1.9 times the benchmark, respectively. Sydney East recorded the third highest one-hour ozone level since 1994, with 17.9 pphm recorded at Earlwood on 10 December and at Rozelle on 19 December 2019. Rozelle recorded the third highest four-hour ozone level since 1994, with 14.9 pphm on 19 December 2019.
• Nitrogen dioxide was above the benchmark on 1 day across the network. Goulburn in the Southern Tablelands recorded the highest hourly NO₂ level (16.1 pphm, 1.3 times the benchmark) since 1994, at 7 pm on 31 December 2019. At the same hour, Goulburn recorded the highest nephelometer reading (visibility reduction) since 1994. A southerly change brought thick smoke to the region from the Currowan and Palerang fires to the south and east. Before spring–summer 2019–20, the previous NO₂ record was 13.3 pphm at Bringelly in Sydney South-west on 15 January 1996.
• The 8-hour rolling average CO levels were above the benchmark on 2 days (9.6 and 9.3 ppm on 11 and 15 November, respectively) at the Port Macquarie bushfire monitoring station. Before spring–summer 2019–20, the previous record for a non-roadside station was 9.1 ppm at Campbelltown West in Sydney South-west on 21 October 2013, during the NSW bushfire emergency in 2013.
• Sulfur dioxide levels were below benchmarks across the network, with the highest SO₂ level (13.0 pphm) recorded at Muswellbrook in the Upper Hunter on 15 October 2019. This record ranked as the highest since 2016.

Summary statistics

• Ozone
• Nitrogen dioxide
• Carbon monoxide
• Sulfur dioxide

Ozone pollution

One-hour and four-hour average ozone levels in spring–summer 2019–20

Days above ozone benchmarks, across the standard monitoring network by region

Ozone levels were over the one-hour and/or four-hourly benchmarks on 32 days, or 18% of spring-summer days.

• ranging from 9 to 16 days across the Sydney regions (Sydney East, Sydney North-west, Sydney South-west)
• 10 days in the Blue Mountains (at Katoomba)
• 8 days in the Southern Tablelands (at Goulburn)
• 4 and 5 days in the Illawarra, Central Coast and Lower Hunter
• 2 days at Gunnedah in the North-west Slopes

Days above ozone benchmarks, at bushfire air quality monitoring stations on the Mid-North Coast

• 2 days at Port Macquarie
• 1 day at Coffs Harbour

Note: Coffs Harbour may have experienced ozone levels above the benchmarks before monitoring began on 22 November 2019.

Maximum one-hour ozone levels, across the standard monitoring network by region

• 11.1 to 17.9 pphm, 1.1 to 1.8 times the benchmark, in the Illawarra and Sydney regions
• 14.7 pphm, 1.5 times the benchmark, in the Southern Tablelands
• 10.1 to 12.6 pphm, 1.01 to 1.3 times the benchmark, in the Central Coast and Lower Hunter
• 11.6 pphm, 1.2 times the benchmark in the Blue Mountains (at Katoomba)
• 9.4 pphm, below the benchmark, in the North-west Slopes

Maximum one-hour ozone levels, at bushfire air quality monitoring stations on Mid-North Coast

• 10.2 pphm, 1.02 times the benchmark at Coffs Harbour
• 9.4 pphm, below the benchmark at Port Macquarie

Maximum four-hour ozone levels, across the standard monitoring network by region

• 9.4 to 14.9 pphm, 1.2 to 1.9 times the Illawarra and Sydney regions
• 13.7 pphm, 1.7 times the in the Southern Tablelands
• 10.9 pphm, 1.4 times the benchmark in the Blue Mountains (at Katoomba)
• 9.0 to 10.7 pphm, 1.2 to 1.3 times the benchmark in the Central Coast and Lower Hunter

Maximum four-hour ozone levels, at bushfire air quality monitoring stations on the Mid-North Coast

• 9.8 pphm, 1.2 times the benchmark at Coffs Harbour
• 9.0 pphm, 1.1 times the benchmark at Port Macquarie

Nitrogen dioxide pollution

Hourly average nitrogen dioxide levels in spring–summer 2019–20

Days above the benchmark

• 1 day in the Southern Tablelands (measured at Goulburn)

Maximum one-hour nitrogen dioxide levels, across the standard monitoring network by region

• 16.1 pphm, 1.3 times the benchmark in the Southern Tablelands, highest since 1994 and the first day above the benchmark since 1996.
• 4.2 to 11.0 pphm, below the benchmark across the Illawarra and Sydney regions
• 8.6 pphm, below the benchmark in the Blue Mountains (at Katoomba)
• 3.6 to 5.7 pphm, below the benchmark in the Central Coast and Upper Hunter and Lower Hunter
• 2.9 pphm, below the benchmark in the North-west Slopes

Maximum one-hour nitrogen dioxide levels, at bushfire air quality monitoring stations on the Mid-North Coast

• 7.6 pphm, below the benchmark at Coffs Harbour
• 3.5 pphm, below the benchmark at Port Macquarie

Carbon monoxide pollution

Eight-hour rolling average carbon monoxide levels in spring–summer 2019–20

Days above the benchmark

• 2 days at Port Macquarie on the Mid-North Coast

Maximum eight-hour rolling average carbon monoxide levels, across the standard monitoring network by region

• 8.1 ppm, below the benchmark in the Blue Mountains (at Katoomba)
• 2.9 to 3.6 ppm, below the benchmark across the Illawarra and Sydney regions
• 2.4 to 2.6 ppm, below the benchmark across the Central Coast and Lower Hunter

Maximum eight-hour rolling average carbon monoxide levels, at bushfire air quality monitoring stations on the Mid-North Coast

• 9.6 ppm, 1.1 times the benchmark at Port Macquarie, the highest since 1994 and the first day above the benchmark since the NSW bushfire emergency in spring 2019
• 1.6 ppm, below the benchmark at Coffs Harbour

Note: Coffs Harbour may have experienced higher carbon monoxide levels before monitoring began on 22 November 2019.

Sulfur dioxide pollution

Hourly average sulfur dioxide levels in spring–summer 2019–20

Days above the benchmarks

• There were no days above the hourly and daily SO₂ benchmarks.

Maximum one-hour sulfur dioxide levels by region

• 13.0 pphm, below the benchmark at Muswellbrook in the Upper Hunter, the highest since 2016
• 7.7 pphm, below the benchmark at Stockton in the Newcastle local region
• 6.8 to 6.9 ppm, below the benchmark in the Lower Hunter and Central Coast
• 2.6 pphm, below the benchmark at Katoomba in the Blue Mountains
• 2.0 to 3.4 pphm, below the benchmark across Sydney regions and the Illawarra

Maximum one-hour sulfur dioxide levels, at bushfire air quality monitoring stations on the Mid-North Coast

• 3.9 pphm, below the benchmark at Port Macquarie. Levels reaching 8.1 pphm were observed in late July (before spring–summer 2019–20) due to smoke from a the peat fire in a dry wetland.