Outdoor air quality

Most of Australia’s air quality monitoring is for outdoor air quality. Trends for the 10 main air pollutants affecting Australia are covered in this chapter, with specific assessments for key pollutants (ozone and coarse and fine particulate matter – PM₁₀ and PM_2.5) from 2015 to 2019 (see Approach).

Across Australia, most pollutants are at levels below the National Environment Protection Measure (NEPM) standards. Peak ozone and PM_2.5 levels are increasing in our cities. Lead and sulfur dioxide are a concern at some locations because of local industry sources.

Carbon monoxide

Carbon monoxide (CO) is produced by burning fuels. CO can reduce the amount of oxygen reaching the body’s tissues and organs. To protect human health and wellbeing, the NEPM limit for CO in the atmosphere is 9.0 parts per million (ppm).

Although CO can persist in the atmosphere for 1–2 months and is therefore always present, levels of CO have not breached the NEPM standards for many years at most air quality stations in Australia. Measured by the Measurements of Pollution in the Troposphere satellite sensor, the concentration of CO in Australia’s background atmosphere has been declining by 0.22 parts per billion (ppb) per year since 2002 (Figure 9; dark blue) (Buchholz et al. 2021). However, surface measurements at the Kennaook/Cape Grim atmospheric monitoring station in north-west Tasmania show weaker evolution in CO concentration, and lower minimums of around 38 ppb (Figure 9; light blue) than the Australian average. These minimums occur in February–March.

In 2020, the minimum CO level at Kennaook/Cape Grim was higher than usual (50 ppb) due to the large amount of fuel burned in the summer 2019–20 bushfires. The amount of land burned in south-east Australia was around 5.6 million hectares (Table 1).

Lead

Lead is a naturally occurring heavy metal that is mined and used in manufacturing. Lead from the atmosphere deposits onto soils and waterways, and is taken up by vegetation. Lead can enter the body via ingestion and is toxic to health, damaging the brain, nervous system and kidneys. The NEPM standard for lead is 0.5 micrograms per cubic metre (μg/m³), measured as an annual average, and allows no exceedances of this limit.

Levels of lead are not generally a concern in Australia, but specific locations with local sources of lead have high levels with potential health impacts. These are Port Pirie in South Australia and Mount Isa in Queensland.

The 2018–19 National Pollutant Inventory lists the 2 largest sources of lead in Australia as:

• air emissions from paved and unpaved roads (520,000 kg/yr), coming from tyre and brake dust in motor vehicles
• mining and metal processing (240,000 kg/yr); Port Pirie and Mount Isa are the 2 largest such facilities in Australia.

Although the emissions from tyre and brake dust are more than double those from mining and metal processing, the sources are spread out, and so the concentrations at any one place from this source are of less concern.

The lead levels surrounding the industrial facilities at Port Pirie and Mount Isa are monitored by the states to ensure compliance with the NEPM standards, and to inform the local communities about their exposure (Figure 10). The annual lead concentrations at 2 locations in Port Pirie (Frank Green Park and Oliver Street) increased from 2015 to a peak in 2018, and exceeded the NEPM standard at Oliver Street (0.54 μg/m³). Although the measurements for 2019 show lead concentrations beneath the NEPM standard at both locations, a new limit of 0.4 μg/m³ was set for Port Pirie on 1 July 2020 by the South Australian Environment Protection Authority. The limit was decreased to encourage industry commitment to reducing ongoing lead emissions. However, measurements in 2020 confirmed that the new limit had been exceeded (ABC News 2020).

In Queensland, lead and lead compounds are transported from the Mount Isa site to Townsville, where they are loaded onto ships for export. This activity is quite visible to residents nearby, with clouds of black dust seen above the port. Queensland has implemented dust monitoring at 3 locations around the port to measure the airborne particle concentrations. Since 2009, annual lead concentrations have averaged 0.1 μg/m³ at Mount Isa and 0.15 μg/m³ at the Townsville port.

The Australian health guideline for lead levels measured in blood is for no more than 5 micrograms per decilitre (µg/dL) (NHMRC 2015). Children are considered more at risk as they tend to ingest more deposited lead while playing on floors and play equipment.

A study of 30 children living in Mount Isa by Green et al. (2017) found:

• 40% with lead levels above 5 µg/dL
• 10% with levels above 10 µg/dL
• 1 child with lead levels measured at 17.3 µg/dL
• where the blood level was above 5 µg/dL, higher blood levels occurred in 3 times as many Indigenous children (64%) as non-Indigenous children (19%).

Potentially, lead levels in children living near the Port Pirie facility are increasing because ongoing droughts in the region are causing more dust uplift (Radford & Marchant 2020). One study suggested that lead emissions needed to be restricted to 0.11 μg/m³ annually (20% of the current NEPM level) to ensure that blood levels in children remain below 5 µg/dL (Taylor et al. 2019). Some companies are using water or chemical sprays to minimise dust emissions caused by lead loading and unloading operations.

Mercury

Mercury is a naturally occurring metal. It is used in gold mining and metal processing, and is emitted by power stations (mercury is a small component of brown coal). It was traditionally used for a range of applications such as batteries and fluorescent lighting, but many uses are being phased out because of its toxicity. Mercury poisoning results in neurological problems and is the origin of the phrase ‘mad as a hatter’: historically, mercury was used to cure felt, and hat makers who used felt often became mentally ill.

Emissions of naturally occurring elemental mercury to the atmosphere from soils and vegetation (72%) and fires (21%) outweigh any emissions from human sources (7%) such as power stations and goldmining (Nelson et al. 2012). Australia currently has relatively low levels of atmospheric mercury, and measurements at 2 background sites show levels of less than 1 nanogram per cubic metre (ng/m³) (Fisher & Nelson 2020). A recent paper measured slightly elevated mercury (1–2 ng/m³) in the region close to a power station in Victoria (Schofield et al. 2021).

The significant health risks from mercury mean that management is essential. Australia became a signatory to the international Minamata Convention on Mercury in 2013. The convention aims to reduce all anthropogenic (human) emissions of mercury to air and water. Modelling studies suggest that much of the mercury currently deposited from the atmosphere in Australia originates from other countries (Shah & Jaeglé 2017), which highlights the critical importance of all countries signing the Minamata Convention.

During the past 15 years, several of Australia’s largest mercury-emitting industries have upgraded their processing technologies, reducing emissions (Fisher & Nelson 2020). For example, the Kalgoorlie goldmine mercury emissions were more than 8,000 kg/yr in 2004, decreasing to 300 kg/yr by 2016. Reported in the 2019 year-end National Pollutant Inventory, 10,000 kg/yr of mercury and mercury-related compounds was emitted to the atmosphere by mining, metal processing and power station industries in Australia (Figure 11). This is an increase compared with the preceding 3 years, due to Mount Isa Mines reporting that its emissions had increased by around 2.8 tonnes in the 2019 reporting year. However, the company’s production data do not mean a real increase in production (Macfarlane 2021).

Nitrogen dioxide

Nitrogen dioxide (NO₂) is a highly reactive gas emitted from motor vehicles, industry, and gas heaters and stove tops. NO₂ can irritate airways, and trigger or aggravate respiratory diseases. The NEPM standard for NO₂ is 0.120 ppm as a 1-hour average. Recent studies have suggested that health impacts from NO₂ exposure can occur at levels 3–5 times lower than the NEPM limit (Hanigan et al. 2019b).

Concentrations of NO₂ from 2015 to 2019 remained below the NEPM standard in all Australian capital cities. This limit is allowed to be exceeded only once per year. Maximum hourly averaged NO₂ levels in Sydney (0.064 ppm at Paramatta North) and Melbourne (0.050 ppm at Alphington) during 2018 were around half of the NEPM standard. The 99th percentiles for NO₂ in Sydney, Melbourne, Brisbane and Perth have not changed much in the past 10 years (Figure 12), centring on 0.036 ppm – around one-third of the NEPM standard. Australia’s major cities will continue to remain compliant with the 2021 decision to lower the 1-hour NO₂ NEPM standard to 0.09 ppm.

Ozone

Ozone is a secondary pollutant formed from chemical interactions between volatile organic compounds and nitrogen oxides. Ozone has a naturally occurring background concentration of around 0.015 ppm. Long-term measurements at Cape Grim, Tasmania, show an increase in ozone background levels of around 10% (0.0016 ppm) since 1982 (Cooper et al. 2020).

Cities are hotspots for ozone because of greater emissions of the precursor pollutants, and generally have much higher concentrations than regional areas (Figure 13). Australia’s air quality for ozone is assessed on the maximum 4-hour average measurement made at a station on any day, and this maximum measurement must be below the NEPM limit of 0.08 ppm. Maximum ozone levels in Australia’s major cities increased between 2015 and 2019. On most days, the 95th percentiles were below the NEPM limit (Figure 13a); however, the overall levels exceeded the NEPM limit (Figure 13b) because of higher measurements on a small number of days.

We can assess where the 4-hour average ozone measurements lie on all days in the year compared with the air quality categories (see Approach) (Figure 14). These ‘box and whisker’ plots show the range in ozone measurements across each year, and how much of the data are in the ‘very good’ and ‘good’ air quality categories. The trends in ozone for this report are assessed on all days in the past 5 years. Ozone levels in all capital cities except Brisbane have increased since the 2016 state of the environment report. Brisbane increased the percentages of ozone days in the ‘very good’ air quality category from 31% to 55%. Overall, the city is experiencing decreased ozone levels throughout most of the year, with fewer days experiencing high maximum 4-hour ozone levels between 2016 and 2019.

Ozone concentrations for Brisbane, Melbourne, Perth and Sydney from 2009 to 2019 show different trends (Figure 14), but all are in the ‘good’ or ‘very good’ air quality assessment category. Of the 4 cities, Brisbane experienced the most years in the ‘very good’ category.

In the 2016 state of the environment assessments, Darwin, Melbourne, Perth and Sydney were classed as ‘very good’ for ozone, but have degraded to ‘good’ in this 2021 assessment. All 4 capital cities lost an average of 46 percentage points from the ‘very good’ classification. Melbourne is at the top of this range, losing 62 percentage points. Sydney and Melbourne continue to exceed the 4-hour NEPM standard of 0.08 ppm on some days each year.

Although a ‘good’ assessment is still well within the air quality limits, a new lower NEPM standard of 0.065 ppm (as 8-hour averages) with no exceedances was approved in April 2021 (NEPC 2019a). Analysis of 2019 ozone data in Melbourne (Melton) and Sydney (Oakdale), calculated with 8-hour averages, suggests that Melbourne would have only just met the new limit (0.061 ppm as the maximum 8-hour average) and Sydney would have exceeded it (0.106 ppm as the maximum 8-hour average). If sources of nitrogen oxides were reduced in these cities, this would limit the availability for ozone production and may be a solution to the problems of rising ozone levels (Ryan et al. 2020a).

Ozone trends were also assessed in 2 regional cities: Kembla Grange in New South Wales and Traralgon in Victoria. Similar to Australia’s capital cities, ozone levels increased in Kembla Grange and Traralgon between 2015 and 2019. Kembla Grange lost 59 percentage points and moved from an assessment of ‘very good’ to ‘good’. Traralgon lost 32 percentage points but is still within the ‘very good’ assessment category.

Assessment Ozone levels in main Australian cities, 2015–19

2021

Adequate confidence

Ozone levels are generally good in Australian cities; however, levels in many cities have increased since the 2016 assessment, and thus the overall situation is deteriorating. In addition, the National Environment Protection Measures standard was lowered in 2021, and many cities are likely to exceed the new standard. Reduction of the main sources of nitrogen oxides, especially vehicles, is needed to reduce ozone levels.
Related to United Nations Sustainable Development Goal targets 3.9, 11.6,12.4

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Assessment Adelaide ozone (4-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 38; good 61; fair <1; poor 0; very poor 0; extremely poor 0

Assessment Brisbane ozone (4-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 53; good 46; fair 1; poor 0; very poor 0; extremely poor 0

Assessment Canberra ozone (4-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 25; good 72; fair 2; poor <1; very poor <1; extremely poor 0

Assessment Darwin ozone (4-hour average)

2021

Adequate confidence

2016

Average percentage frequency distribution: very good 49; good 50; fair 1; poor <1; very poor 0; extremely poor 0

Assessment Melbourne ozone (4-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 32; good 65; fair 3; poor 0; very poor 0; extremely poor 0

Assessment Perth ozone (4-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 18; good 79; fair 3; poor <1; very poor 0; extremely poor 0

Assessment Sydney ozone (4-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 15; good 77; fair 7; poor <1; very poor <1; extremely poor 0

Assessment NSW (Kembla Grange) ozone (4-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 30; good 69; fair 2; poor <1; very poor 0; extremely poor 0

Assessment Vic (Traralgon) ozone (4-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 62; good 37; fair <1; poor 0; very poor 0; extremely poor 0

Persistent organic pollutants and polycyclic aromatic hydrocarbons

Persistent organic pollutants (POPs) include synthetically made insecticides, polychlorinated biphenyls, dioxins and furans. They are typically used in manufacturing pesticides, fire retardants and industrial lubricants. POPs have long chemical half-lives, which means they can persist in the atmosphere for a long time and travel long distances. Some POPs can exist for decades or hundreds of years in the environment. Because of this, POPs accumulate in the food chain and may become concentrated in plants and animals grown for food. This poses health risks because POPs are extremely harmful to humans.

POPs are controlled substances under the Stockholm Convention. Signed in 2001 and effective from 2004, the convention aims to eliminate or restrict the production and use of POPs. POPs are not easy to measure, so are not routinely monitored throughout Australia.

However, a study of trends in global atmospheric levels of POPs from 2009 to 2015 concluded that we are yet to see any significant declines in POPs (Rauert et al. 2018). The study examined data from more than 20 sites around the world (including Australia’s Cape Grim baseline atmospheric pollution monitoring site). It found that there was no significant decline in POPs, although certain types had decreased. Concentrations of perfluorosulfonic acids and perfluorocarboxylic acids increased between 2009 and 2015, while poly- and per-fluoroalkyl substances and hexamethylcyclotrisiloxane decreased.

Polycyclic aromatic hydrocarbons (PAHs) are not strictly classed as POPs, but they are carcinogenic to humans and hazardous to the environment. The National Pollutant Inventory lists emissions to air for PAHs and a combined set of POPs – polychlorinated dioxins and furans (Figure 15). PAH emissions in Australia have been declining since 2014, and in 2019 totalled 15,000 kg/yr. The emissions of polychlorinated dioxins and furans are comparatively much less than the PAHs. Emissions decreased to a low of 0.03 kg/yr in 2015, but have been rising slowly since then and were 0.04 kg/yr in 2019.

Sulfur dioxide

Sulfur dioxide (SO₂) is produced by burning fossil fuels and smelting mineral ores. Atmospheric SO₂ affects the respiratory system, can form fine particles and is the main source of acid rain.

The NEPM air quality limit for SO₂ is 0.2 ppm as a 1-hour average (there are also 24-hour and annual NEPM limits). SO₂ concentrations are well below these NEPM standards at most locations in Australia. Exceedances at Port Pirie (South Australia) and Mount Isa (Queensland) have occurred because of local ore smelting activities. At the Oliver Street monitoring station in Port Pirie, hourly SO₂ concentrations have exceeded the 0.2 ppm NEPM limit 1,001 times since 2003 (Taylor et al. 2019). The 2016 state of the environment report highlighted new technologies that were being installed at the Port Pirie facility to reduce SO₂ levels by a factor of 5. The proposed reductions have not been realised, mainly because of delays in implementing the new facilities. Submissions to the National Pollutant Inventory show SO₂ emissions from Port Pirie to be around 60 million kilograms per year (Figure 16). The Mount Isa facility emits nearly 4 times the amount of SO₂ as Port Pirie, and its emissions increased in 2018 and 2019.

The SO₂ NEPMs were reduced in 2021 (see National air quality standards) to 0.1 ppm as a 1-hour average, with an expectation that a further reduction to 0.075 ppm will occur in 2025.

Particulate matter

Particulate matter (PM) is small particles and liquid droplets in the air. It is produced mainly by motor vehicles, industry, wood-burning heaters, dust storms and bushfires. Particles are assessed at 2 sizes: PM₁₀ (coarse particles with a diameter of 10 μm or less) and PM_2.5 (fine particles with a diameter of 2.5 μm or less). For human health, the smaller the particles, the easier they are to inhale into the lungs, and the greater the impact on health. Whereas PM₁₀ is generally a primary pollutant, PM_2.5 is more likely to have formed from secondary processes (chemical reactions acting on volatile gas-phase substances). However, PM_2.5 also makes up the significant proportion of particles emitted with bushfire smoke.

In the summer of 2019–20, Australia experienced some of the country’s worst-ever bushfires (see Prescribed burning and bushfires). Fires burned across 6 states for 6 months. More than 80% of the population was affected by smoke, and the main effects were caused by PM. This section examines existing PM levels, outside extreme events such as these fires.

Levels of PM₁₀ and PM_2.5 are increasing in our cities, and in 2019 no cities met the NEPM standard for PM_2.5. The potential health impacts mean that more will need to be done to reduce PM levels.

Coarse particulate matter

The 24-hour NEPM standard for PM₁₀ is 50 μg/m³. To meet this standard, PM₁₀ levels on every day of the year must be below 50 μg/m³. If PM₁₀ levels exceed the standard on a single day, it is classed as a ‘miss’, even if all other days of the year had much lower levels of PM₁₀. In the past 5 years, PM₁₀ levels in all capital cities continued to be below the NEPM standard, but many cities (e.g. Canberra, Brisbane, Sydney) exceeded the standard in 2019 (Figure 17).

We can assess where the 24-hour average PM₁₀ measurements on all days in the year lie compared with the air quality categories (see Approach) (Figure 18). These ‘box and whisker’ plots show the range in PM₁₀ measurements across each year, and how much of these data are in the ‘very good’ and ‘good’ air quality categories. The trends in PM₁₀ for this report are assessed on all days in the past 5 years. If all days in the year are taken into account (Figure 17), at least 50% of days measure PM₁₀ concentrations less than one-third of the standard (blue line in Figure 18), and 75–100% of days at less than two-thirds of the standard (green line).

In the 2016 state of the environment report, all capital cities were graded as ‘very good’ for PM₁₀, meaning that at least 50% of all days reported measurements at one-third or less of the NEPM limit. In this 2021 report, most capital cities maintain their ‘very good’ assessment grade; PM₁₀ concentrations in Adelaide and Darwin only just missed out on the ‘very good’ assessment. Mean PM₁₀ concentrations have decreased on average, and the 5-year trend in the PM₁₀ assessments is improving in Hobart, Melbourne and Perth. PM₁₀ levels in Canberra and Darwin are stable compared with the 2016 report. In Adelaide, Brisbane and Sydney PM₁₀ levels are increasing, and the assessment trend is degrading: between ‘very good’ and ‘good’ for Sydney in this 2021 assessment.

The PM₁₀ assessments in Australia’s regional cities have stabilised compared with the 2016 assessments. There has been little change in the percentage distributions among the air quality categories, with most regional centres retaining a ‘very good’ or ‘good’ assessment grade. Geelong in Victoria and Bunbury in Western Australia have falling PM₁₀ concentrations and slight improvements in their assessment grades; Wagga Wagga in New South Wales and Mackay in Queensland have increasing PM₁₀ concentrations and a slight downward trend in assessments.

Assessment PM10 levels in main Australian cities, 2015–19

2021

Adequate confidence

Coarse particulate matter (PM10) levels are generally good or very good in Australian cities, and this assessment has remained generally stable since the 2016 assessment. Only Adelaide and Sydney have deteriorating levels of PM10. Related to United Nations Sustainable Development Goal targets 3.9, 11.6, 12.4

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Assessment Adelaide PM10 (24-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 44; good 51; fair 4; poor <1; very poor <1; extremely poor <1

Assessment Brisbane PM10 (24-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 62; good 34 fair 3; poor 1; very poor 0; extremely poor 0

Assessment Canberra PM10 (24-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 85; good 13; fair <1; poor <1; very poor <1; extremely poor <1

Assessment Darwin PM10 (24-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 49; good 41; fair 8; poor 1; very poor <1; extremely poor <1

Assessment Hobart PM10 (24-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 85; good 14; fair <1; poor 0; very poor 0; extremely poor 0

Assessment Melbourne PM10 (24-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 71; good 27; fair 2; poor <1; very poor 0; extremely poor <1

Assessment Perth PM10 (24-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 58; good 39; fair 3; poor <1; very poor <1; extremely poor 0

Assessment Sydney PM10 (24-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 50; good 43; fair 5; poor 1; very poor <1; extremely poor <1

Assessment NSW (Wagga Wagga) PM10 (24-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 42; good 38; fair 13; poor 5; very poor 1; extremely poor 1

Assessment Qld (Mackay) PM10 (24-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 26; good 69; fair 4; poor <1; very poor <1; extremely poor <1

Assessment SA (Port Pirie) PM10 (24-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 59; good 36; fair 4; poor 1; very poor <1; extremely poor <1

Assessment Tas (Launceston) PM10 (24-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 71; good 26; fair 2; poor <1; very poor <1; extremely poor <1

Assessment Vic (Geelong) PM10 (24-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 57; good 35; fair 5; poor 2; very poor <1; extremely poor <1

Assessment WA (Bunbury) PM10 (24-hour average)

2021

Adequate confidence

2016

2011

Average percentage frequency distribution: very good 61; good 36; fair 2; poor <1; very poor <1; extremely poor <1

Fine particulate matter

The 24-hour NEPM standard for PM_2.5 is 25 μg/m³. To meet this standard, PM_2.5 levels on every day of the year must be below 25 μg/m³. If PM_2.5 levels exceed the standard on a single day, it is classed as a ‘miss’, even if all other days of the year had much lower levels of PM_2.5. Maximum measured PM_2.5 concentrations in all capital cities remain above the standard (Figure 19). Hanigan et al. (2019a) estimated that, in 2006–16, 2,616 deaths in Australia each year were attributable to PM_2.5 exposure, which is around 2% of all deaths.

In recognition of the impacts of PM_2.5 on human health, in 2025 the 24-hour NEPM standard for PM_2.5 will be reduced to 20 μg/m³. As none of our capital cities achieve the current NEPM standard, there is much work to do in reducing PM_2.5 concentrations.

Because the NEPM limit for the year can be exceeded with just 1 daily maximum, we can assess where the 24-hour average PM_2.5 measurements on all days in the year lie compared with the air quality categories (see Approach) (Figure 20). These ‘box and whisker’ plots show the range in PM_2.5 measurements across each year, and how much of these data are in the ‘very good’ and ‘good’ air quality categories. The trends in PM_2.5 for this report are assessed on all days in the past 5 years. In the past 10 years, more than half of the days have had ‘very good’ PM_2.5 levels (Figure 20).

On average, 7 percentage points have been lost from the ‘very good’ assessment category across all capital cities between the 2016 and 2021 state of the environment reports, with Sydney losing the most at 14%. However, all capital cities retain their ‘very good’ assessments for PM_2.5, with more than 50% of the frequency distribution falling in the ‘very good’ category. However, the trend in all cities is either stable (in Darwin, Hobart and Melbourne) or degrading, meaning that PM_2.5 concentrations in 2015–19 are increasing. The assessment grade for PM_2.5 in Sydney is between the ‘very good’ and ‘good’ categories, which is similar to the result for PM₁₀.

Assessment PM2.5 levels in Australian capital cities, 2015–19

2021

Adequate confidence

Fine particulate matter (PM2.5) levels are generally good in Australian cities; however, this situation is deteriorating, with increasing levels in 5 out of 8 capital cities. This is particularly of concern because these smaller particles can have more severe health effects.
Related to United Nations Sustainable Development Goal targets 3.9, 11.6, 12.4

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Assessment Adelaide PM2.5 (24-hour average)

2021

Adequate confidence

2016

Average percentage frequency distribution: very good 60; good 39; fair 1; poor 0; very poor 0; extremely poor 0

Assessment Brisbane PM2.5 (24-hour average)

2021

Adequate confidence

2016

Average percentage frequency distribution: very good 83; good 16; fair 1; poor <1; very poor <1; extremely poor <1

Assessment Canberra PM2.5 (24-hour average)

2021

Adequate confidence

2016

Average percentage frequency distribution: very good 69; good 20; fair 6; poor 3; very poor <1; extremely poor <1

Assessment Darwin PM2.5 (24-hour average)

2021

Adequate confidence

2016

Average percentage frequency distribution: very good 56; good 31; fair 9; poor 3; very poor <1; extremely poor <1

Assessment Hobart PM2.5 (24-hour average)

2021

Adequate confidence

2016

Average percentage frequency distribution: very good 80; good 17; fair 2; poor <1; very poor <1; extremely poor <1

Assessment Melbourne PM2.5 (24-hour average)

2021

Adequate confidence

2016

Average percentage frequency distribution: very good 65; good 30; fair 4; poor 1; very poor <1; extremely poor 0

Assessment Perth PM2.5 (24-hour average)

2021

Adequate confidence

2016

Average percentage frequency distribution: very good 56; good 41; fair 2; poor <1; very poor <1; extremely poor 0

Assessment Sydney PM2.5 (24-hour average)

2021

Adequate confidence

2016

Average percentage frequency distribution: very good 50; good 44; fair 5; poor 2; very poor <1; extremely poor <1

Volatile organic compounds

Volatile organic compounds (VOCs) are a group of carbon-based chemicals that easily evaporate at room temperature. VOCs can cause irritation to eyes and airways, and can also damage the liver, kidneys and nervous system. In addition, VOCs in the atmosphere react with nitrogen oxides to form ozone.

Emissions of VOCs from industry, motor vehicles and natural sources in Australia increased from 2016 to 2019, to 3.18 billion kilograms per year (Figure 21).

In Australia, around three-quarters of all emitted VOCs are natural in origin (Figure 22). These biogenic VOCs are emitted by vegetation (see Biogenic emissions).

Of the anthropogenic VOC emissions in Australia, motor vehicles contribute just under 30%, and burning, industry and diffuse area sources provide 15–20% each. The diffuse sources are typically nonindustrial activities such as other transport (e.g. trucks and buses), commercial activities using solvents, and domestic activities such as lawnmowing and barbecuing. VOCs that were originally natural in origin are often synthesised and used to make household cleaning sprays, candles and air fresheners, which can affect indoor air quality (Fisher & Emmerson 2018).

When VOCs take part in chemical reactions in the atmosphere, one of their secondary formation products is formaldehyde. Lieschke et al. (2019) analysed the 20-year record of formaldehyde observations from the University of Wollongong and found a decreasing trend of 1.9% per year from 1996 to 2015. The study suggested that this decrease was very localised, as formaldehyde derived from biomass burning was increasing regionally. Industrial emissions in the Wollongong area have been in decline recently, and this is thought to be responsible for the localised decrease. Formaldehyde measurements in Melbourne showed a clear seasonal cycle, with a peak in summer due to biogenic VOC emissions (Ryan et al. 2020b).