NSW annual air quality statement 2019: gases

One-hour and four-hour ozone averages

There were 33 days in 2019 when ozone levels were over the national standards at one or more sites in NSW, meeting the national standard on 91% of days.

Within the Greater Metropolitan Region (GMR, comprising Sydney, Lower Hunter, Central Coast and Illawarra regions), ozone levels were over the national standards on 29 days (meeting the standards 92% of the time). This was 22 more days than 2018 when the ozone standards were exceeded on 7 days.

Ozone levels peaked in the warmer months during January to February and October to December. Within the GMR, ozone events occurred on:

• 28 days at one or more sites in the Sydney region
• 5 days in the Lower Hunter region
• 3 days each in the Central Coast and Illawarra regions.

In comparison, within the GMR, there were no ozone exceedances in the Central Coast and Illawarra regions in 2018.

The most extensive ozone events in 2019 are outlined below:

• On 16 January 2019, ozone levels above the national standards were recorded at 9 sites in Sydney North-west and South-west regions due to a heatwave across New South Wales. The maximum hourly ozone was 13.8 pphm, recorded at Camden in Sydney South-west. The heatwave was caused by the persistence of a slow-moving high-pressure system over the Tasman sea. The maximum temperature on this day in Sydney was 39.4°C at Richmond in Sydney North-west.
• On 26 January 2019, ozone levels above the national standards were recorded at 9 sites throughout Sydney due to heatwave conditions across New South Wales. The maximum hourly ozone was 11.4 pphm, recorded at Liverpool in Sydney South-west. The meteorological conditions were similar to the event day on 16 January 2019. The maximum temperature on this day in Sydney was 41.6°C at St Marys in Sydney North-west.
• On 31 October 2019, ozone levels above the national standards were recorded at 10 sites in central and western Sydney due to smoke transported from bushfires in northern New South Wales. The maximum hourly ozone was 10.6 pphm, recorded at St Marys in Sydney North-west. A slow-moving high-pressure system over the Tasman sea created calm conditions along with northerly and north-easterly wind, which transported smoke from the fires in northern parts of the State. A strong temperature inversion in the morning trapped smoke in the Sydney basin which acted as an ozone precursor. The maximum temperature on this day was 32.5°C at St Marys in Sydney North-west.
• On 10 December, 16 sites in the Sydney and Lower Hunter regions recorded ozone levels over the national standards. On this day, the hourly ozone concentration of 17.9 pphm at Earlwood was the third-highest recorded in NSW since 1994. North-easterly and north-westerly wind transported smoke from the bushfires to the Sydney basin. This was coupled with a strong temperature inversion in the morning, with smoke trapped in the Sydney basin and acting as an effective ozone precursor. The maximum temperature on this day was 41.1°C at Richmond in Sydney North-west.
• On 19 December, the most extensive ozone event for 2019 occurred. On this day, 18 of the 21 available sites in the Sydney, Illawarra and Lower Hunter regions recorded ozone levels over the national standards. The maximum hourly ozone concentration of 17.9 pphm was observed at Rozelle, in the Sydney East, equalling the annual maximum recorded on 10 December 2019 at Earlwood. Westerly to north-westerly winds transported smoke from bushfires at Warragamba and the Blue Mountains into the Sydney basin. The Illawarra region was impacted by smoke from bushfires at Warragamba. The Lower Hunter region was affected by the bushfire smoke from Wollemi National Park and fires in the NSW North Coast. The large quantities of smoke in these regions on this day acted as an ozone precursor. The maximum temperature on this day was 41.8°C at St Marys in Sydney North-west.

In NSW regional centres, monitoring stations were established at Gunnedah (North-west Slopes) in March 2018 and Goulburn (Southern Tablelands) in November 2019:

• At Gunnedah, ozone levels exceeded the national standards on 2 days in December 2019. These events were associated with extensive bushfire smoke and high temperatures during the bushfire emergency period. There were no days recorded over the standards in 2018.
• At Goulburn, ozone levels exceeded the national standards on 4 days in December 2019. These events were associated with bushfire smoke transported from Warragamba, Wollemi National Park and the New South Wales South Coast.

Days above the 1-hour and 4-hour ozone standards – 2019

Note: Values in brackets are the actual maximum ozone levels at each station on the day. pphm = parts per hundred million in volume.  Ozone data from the new Goulburn air quality monitoring station are available from 6 November 2019. 

One-hour nitrogen dioxide averages

The 1-hour standard for NO₂ was met on 99.7% of days in 2019, with 1 day above the standard on 31 December 2019 at the new Goulburn monitoring station in the Southern Tablelands (monitoring commenced on 6 November 2019). This was the first exceedance of the NO₂ standard since an early exceedance on 26 February 1998, which occurred at Lidcombe in Sydney East.

On 31 December, at 7pm, hourly average NO₂ levels at Goulburn reached 16.1 pphm, the highest recorded value since 1994. This event was caused by a southerly change, which concentrated smoke from the large Currowan and Palerang fires on the south coast and moved it through the Southern Tablelands and towards Canberra. This event occurred at the same hour when the second highest nephelometer (visibility) reading recorded in the NSW network (with the highest being an atypical high reading at Earlwood in 2011 that was caused by a car fire adjacent to the monitoring station).

A similar southerly change on 21 December 2019 resulted in NO₂ levels close to the hourly standard, reaching 11.8 pphm at Goulburn. This occurred at the same hour when the third highest nephelometer (visibility) reading recorded across the NSW network, associated with the impact of smoke and strong southerly winds on air quality in Southern Tablelands during December 2019.

The Bradfield Highway roadside monitoring station, which measures air quality adjacent to one of the busiest roads in NSW (located to the north of the Sydney Harbour Bridge), recorded a maximum hourly NO₂ level of 15.3 pphm on 19 December at 1pm. While there was some traffic influence present, Sydney air quality on this day was significantly impacted by smoke. Elevated concentrations (below the national standard) were recorded at other Sydney East stations around the same time, with a value of 9.0 pphm recorded at Rozelle at 3pm on the day.

One-hour sulfur dioxide averages

There were no days over the one-hour SO2 standard in 2019. The maximum hourly SO₂ average was 13.0 pphm, recorded at Muswellbrook in the Upper Hunter on 15 October 2019.

Daily sulfur dioxide averages

There were no days over the daily SO₂ standard in 2019. The maximum daily SO₂ average was 2.4 pphm, recorded at Muswellbrook in the Upper Hunter on 21 April 2019.

Annual sulfur dioxide averages

Annual average SO₂ levels remained well below the national standard in 2019. The maximum annual average was 0.3 pphm, recorded at Muswellbrook in the Upper Hunter and Stockton in the Port of Newcastle.

Eight-hour carbon monoxide averages

In 2019, long-term (non-roadside) monitoring stations had no days over the 8-hour CO standard. The maximum 8-hourly CO average was 3.6 ppm, recorded at Rouse Hill in Sydney North-west on 19 November 2019. Since 1994, the record high value of 9.1 ppm was measured at Campbelltown West in Sydney South-west on 21 October 2013 due to the impact of the 2013 bushfires in the Blue Mountains. However, it should be noted that a higher values were recorded at temporary stations in 2019 due to the bushfire emergency, on 6 days at Port Macquarie during November, and on 2 days at Katoomba during December. Two exceedances were measured at the temporary Port Macquarie bushfire emergency monitoring station, with a new record of 9.6 ppm recorded on 15 November 2019.