Outlook The 5-year period since the 2016 state of the environment report has shown us the potential extremes of air quality. On the one hand, major events have challenged the usually good quality of Australia’s air (Table 1). Melbourne experienced the world’s most severe thunderstorm asthma episode in 2016, causing acute breathing difficulties in thousands of people and killing 10 people. Smoke and dust have always played a part in Australia’s air quality history, but 2019 and 2020 saw unprecedented dust and smoke events. The summer 2019–20 bushfires were some of the worst on record, burning across several states and blanketing towns in dense smoke for weeks. On the other hand, air pollution from motor vehicle and industrial sources was significantly reduced after Australia logged its first case of coronavirus infection in January 2020, sending the country into lockdown in March 2020. In many parts of the world, this appeared to lead to visibly improved air quality, offering a lens into a world using cleaner vehicles and industrial technologies (see case study: COVID-19 lockdown action temporarily reduces emissions). These extremes show the highs and lows of air quality. But air quality during ‘business as usual’ periods is also important. Research into the health effects of air pollution is pointing strongly towards there being no ‘safe’ level of pollution, particularly with regard to levels of ozone and particulate matter experienced by sensitive populations. Thus the pressures on air quality continue to be of concern. An increasing population with increasing needs for motor vehicles and housing in urban areas means that emissions will continue to increase. Population-based pressures on air quality can only be improved by a move to cleaner technologies such as electric vehicles and solar panels. Climate change is expected to exacerbate natural emissions from dust and biogenic sources, through increased prevalence of widespread droughts and rising temperatures. Temperature-driven chemical reactions in the atmosphere are likely to cause more summertime smogs in urban areas. The predicted increase in extreme heatwave events will lead to increased summer bushfire activity, meaning that extremely poor air quality due to smoke may be a recurrent feature of future Australian summers. Reducing long-term exposure to all air pollution remains the best method of preserving health. Government policy around air pollution regulation could be improved with an exposure minimisation approach (Zosky et al. 2021). However, such an approach relies on increasing air quality monitoring infrastructure, and active participation by industry and residents to drive down emissions. It is not enough to set new National Environmental Protection Measures targets for air pollution levels if behavioural change is not encouraged in legislation. A range of pollution sources could be tackled with such an approach, such as motor vehicles and wood heaters. When people are not subject to an extreme event, most complaints about poor air quality are from the nearby use of domestic wood heaters. Tackling wood heater use via behavioural change would seem to offer the best pathway to better air quality. Legislation forcing appliance manufacturers to improve burn efficiencies is underway in New South Wales, meaning that new appliances must be 60% efficient and emit no more than 1.5 grams of particles per kilogram of fuel burned. However, given that urban areas are well served by gas and electrical infrastructure, use of wood heaters in cities is an outdated and dirty practice. Banning their use in cities would go a long way to improving air quality in winter. The National Pollutant Inventory shows that industrial emissions of many pollutants, such as coarse particulate matter (PM10), sulfur dioxide, volatile organic compounds and mercury, decreased after 2009 but then increased again in 2019, despite attempts to control them. Large industrial facilities are usually located away from urban centres, which restricts the impact their emissions have on most of the population. However, some people, usually from lower economic backgrounds, live close by. Protecting the health of these residents, and particularly their children, should be a priority via targeted emissions reductions. Motor vehicles continue to be a major source of pollution in urban areas, and the number of motor vehicles continues to increase. There were just over 20 million registered vehicles in Australia at the beginning of 2021, with an average fleet age of 10.4 years. The proportion of diesel vehicles has increased by 6% since 2015. Diesel vehicles emit more particulate matter than petrol vehicles, but petrol vehicles emit more volatile organic compounds and carbon monoxide. Although there are ongoing consultations about improving fuel standards to reduce the sulfur content of petrol to less than 15 parts per million, these standards will not come into force until 2027. This has implications for the ability of new cars to deliver emissions reductions, as Australia will not import the higher standard Euro 6 vehicles because their catalytic emission control devices cannot work with petrol with high sulfur content. Encouraging the oldest and dirtiest vehicles off the road would rapidly improve air quality. Encouraging people out of their vehicles and onto public transport would also improve air quality in cities. There should be a focus on improving access to reliable public transport, which is still severely lacking in many urban areas in Australia. Along with legislative change to reduce air pollution, real-time information can help people to avoid air pollution exposure. Health information advises residents to self-assess how sensitive they are to air pollution and take action, either by staying indoors with the windows shut, which might help keep out the worst of the pollution, or by seeking ‘clean rooms’ within large public buildings operating high-efficiency particulate air (HEPA) filtration systems. But, in order to take action, residents need to know what to expect. Air pollution can vary rapidly over short distances, even from street to street. In addition, air quality can change rapidly, depending on meteorological conditions and topography. In Canberra during the summer 2019–20 bushfires, there were days with very good air quality sandwiched between days with extremely poor air quality. Australian health researchers argue that relying on relatively few fixed air quality monitoring stations to assess the air pollution exposure of residents is unsatisfactory. The use of low-cost sensors is rising, particularly by the general public. Despite some concerns about the accuracy of individual sensors, these can help fill in the spatial gaps between the fixed air quality monitoring stations. Increasing the number of networked air quality monitors would pick up real spikes in air pollution very quickly, and track these plumes as they travel across residential areas. However, although pollution avoidance tactics help improve the health outcomes of the population, they should not be a substitute for action on reducing air pollution sources. Regulation of most air pollution sources relies on the availability of long-term measurements to continually assess the impacts of reduction strategies. The importance of good-quality measurements cannot be overestimated. In conjunction with meteorological measurements, the strength and location of pollution sources should be ascertained. Independent measurements (e.g. by the states and territories) keep industry operators honest. The National Pollutant Inventory (NPI) relies on self-reporting of emissions, which can lead to errors. Increases in the type and accuracy of information in the NPI will help to improve Australia’s air quality and health impacts. Table 1 Timeline of major air quality events in Australia, 2016–20 Year Month Jurisdiction Air quality event Pollutant involved 2016 January Tas Bushfires in north-west Tasmania burn 91,983 haa,b Smoke 2016 January WA Bushfire at Yarloop burns 67,871 haa,b Smoke 2016 November Vic Thunderstorm asthma kills 10 peoplec Pollen 2018 August Vic 20,000 m2 factory fire occurs on site storing waste at West Footscrayd Smoke 2019 Summer Tas Bushfires west of Huon Valley burn 170,988 haa,b Smoke 2019 April Vic Large factory fire occurs on site storing waste at Campbellfielde Smoke 2019 November NSW Dustiest month since records began in 2005f Dust 2019–20 Summer South-east Australia Bushfires burn 5,567,402 haa,b, contributing to 417 excess deathsg Smoke, accompanied by smog 2020 March–April Australia COVID-19 pandemic Varies by jurisdiction 2020 May WA Cyclone Mangga produces 100 km/h winds and very high levels of PM10 in Geraldton Dust ha = hectare; km/h = kilometre per hour; m2 = square metre; NSW = New South Wales; PM10 = coarse particulate matter; Tas = Tasmania; Vic = Victoria; WA = Western Australia Sources: a MODIS MCD64A1 Collection 6 Burned Area product; b Giglio et al. (2018); c DHHS (2017); d IGEM (2020); e Personal communication, EPA Victoria; f Community DustWatch (2019); g Borchers Arriagada et al. (2020) Share on Twitter Share on Facebook Share on Linkedin Share this link Case Study COVID-19 lockdown action temporarily reduces emissions Pushan Shah, South Australian Environment Protection Authority Jason Choi, Environment Protection Authority Victoria The beginning of 2020 brought COVID-19, an unexpected global pandemic that caused normal activities to cease with government directives to stay at home. These directives were termed ‘lockdowns’, with many businesses forced to close and everyday movements restricted. The restrictions manifested themselves in different ways in Australia’s capital cities, but all impacted airborne emissions. Here, the evidence of emissions reductions is examined through ambient pollutant concentrations measured in Adelaide, Brisbane, Melbourne and Sydney during these lockdown periods. Adelaide On 12 March 2020, the South Australian Government implemented lockdown measures, lasting until the end of April. The measures were expected to reduce air pollution due to a decrease in noncommercial vehicle traffic, and in industrial and commercial activity. The average reduction in traffic volume was 40% during the peak of the restrictions, before returning to near-normal levels at the end of July (Figure 1). Figure 1 (a) Traffic volume and (b) CO concentration across metropolitan Adelaide, March–July 2020 CO =carbon monoxide; ppm = parts per million Source: Traffic data, South Australian Department of Infrastructure and Transport Download Go to data.gov There are no roadside monitoring stations in Adelaide to observe the impacts of these reductions directly, but the reduction in people travelling to Adelaide central business district (CBD) is observed from the centrally positioned station in the CBD. In Adelaide CBD, levels of carbon monoxide (CO) decreased by 40% in accordance with the traffic volumes, compared with measurements taken during the same period (March–April) in the 5 years before the COVID-19 lockdowns (Figure 2). Evidence of decreases in nitrogen oxides (NOx) and fine particulate matter (PM2.5) is harder to observe. Five years of data were used for the pre-pandemic period to reduce the influence that large-scale events, such as bushfires and land burns, can have on estimates of ambient pollutant concentrations. Although there was a small reduction in NOx levels, PM2.5 levels continued to be influenced by bushfire smoke in the early part of 2020 and remained very similar to past averages. Overall, an improvement in air quality was recorded, with 20–40% reduction in all pollutants during March and April 2020. Figure 2 CO, NOx and PM2.5 levels during the initial peak COVID-19 restrictions in Adelaide compared with the previous 2015–19 average and the rest of 2020 CO = carbon monoxide; µg/m3 = microgram per cubic metre; NOx = nitrogen oxides; PM2.5 = fine particulate matter; ppm = parts per million Source: South Australian Environment Protection Authority Download Go to data.gov Brisbane Numbers of coronavirus cases in Brisbane were much lower than elsewhere in Australia in early 2020, so restrictions were less strict. Still, many people chose to work from home, and this is reflected in a 13% decrease in nitrogen dioxide (NO2) levels in Brisbane compared with the 10-year average (Welchman et al. 2020). However, the Katestone report notes that the impact of meteorology (e.g. stagnant, pollutant-trapping conditions) may have masked the level of reductions that might otherwise have occurred in Brisbane. Melbourne Lockdown measures in Melbourne were introduced on 17 March 2020. Traffic flows began decreasing immediately, to a minimum of 30% in the week of 12 April 2020, compared with pre-lockdown flows. Traffic began resuming steadily and by the beginning of June had reached 80% of normal levels. This was curbed again in August when very strict lockdown measures were in place for more than 100 days. The impact of the traffic reductions is most easily seen in the NO2 columns (Figure 3). Comparing the 2020 profile on 10 April with the profiles calculated from the preceding 5 years shows a 24% reduction in NO2 in the area surrounding the city of Melbourne. Figure 3 (a) Fifteen-day running mean total column NO2 on 10 April 2020, (b) as an average of the same time across 2015–19 and (c) as the difference between the 2 plots cm2 = square centimetre; NO2 = nitrogen dioxide Source: NASA Aura OMI satellite, originally published in Air Quality and Climate Change, publication of the Clean Air Society of Australia and New Zealand Air quality data collected at all Environment Protection Authority Victoria monitoring stations in Melbourne between 17 March and 12 May for 6 years (2015–20) were examined, separating out 2020 to assess the impacts of the lockdowns. The average diurnal columns over these periods also show a 25% decrease in NO2 during the lockdowns (Figure 4), similar to the NO2 reduction calculated by Ryan et al. (2021). At the same time, there was a 3% increase in ozone. This increasing ozone effect has been observed all over the world and tends to be greater in cities where the lockdown measures were strictest (Gkatzelis et al. 2021). Although NOx compounds are involved in the chemical production and removal of ozone, a direct link between decreasing NO2 and increased ozone cannot be made without considering other ozone-forming chemicals such as volatile organic compounds (VOCs), and the impact of temperature. Reductions in other pollutants such as carbon monoxide (CO) and PM2.5 during the lockdown period in Melbourne were more difficult to observe, as reductions were also observed in February and early March. This might be caused by reduced tourism to the area following the severe summer 2019–20 bushfires. Post-lockdown, there were increases in CO levels during 2020 beyond those from the previous 5 years. This was caused by smoke from wood heaters being used more prolifically when evening temperatures decreased well below 10 °C. Figure 4 NO2 and ozone levels during the peak COVID-19 restrictions across all Melbourne air quality stations compared with the previous 2015–19 average for the same period NO2 = nitrogen dioxide; ppb = parts per billion Note: Solid line represents the mean; shaded area represents the data range. Source: Environment Protection Authority Victoria, originally published in Air Quality and Climate Change, publication of the Clean Air Society of Australia and New Zealand Sydney Traffic volumes decreased by 19–44% across Sydney as the lockdowns started to take effect from 16 March 2020 (Duc et al. 2021). Duc et al. (2021) examined the raw air quality data and observed decreases in concentrations of NO2 (–18%), CO (–13%) and PM2.5 (–13%), while ozone levels increased (+1.5%). However, by detrending the air quality data for meteorological effects, Ryan et al. (2021) estimated that NO2 levels decreased by 8% as a result of lockdowns, but concentrations of ozone and PM2.5 increased by 20% and 24%, respectively. Conclusions Chemical reactions in the atmosphere are highly nonlinear, and unexpected changes in secondary pollutants (e.g. ozone increases) can occur when primary pollutants such as NO2 are reduced. However, reducing NOx emissions in Australia will almost always lead to better overall air quality in our urban areas. Although there is some nonlinearity in the chemistry, and there are occasions when ozone levels may be more related to VOCs than NOx, policies that reduce primary emissions of NOx and other air pollutants and their precursors will almost always succeed in improving air quality. Share on Twitter Share on Facebook Share on Linkedin Share this link Impacts The most significant impact of poor air quality is on human health. Strong associations have been found between outdoor air pollution and cardiorespiratory mortality and morbidity, all-cause mortality and morbidity, birth outcomes, asthma, reduced lung function, and atopy (Walter et al. 2021). In December 2020, a landmark ruling in the United Kingdom declared that air pollution should be recognised as a contributing factor in a 9-year-old girl’s death (BBC News 2020a). She was continually exposed to high levels of pollution, which exacerbated her asthma symptoms. She had lived near a busy main road in London, which regularly exceeded World Health Organization air quality limits for nitrogen dioxide. The inquest reignited the social equity debate, where the poorest in society tend to be exposed to higher levels of air pollution than people with higher incomes. The costs to health from the 2019–20 bushfire smoke in Australia have been estimated at 417 excess deaths across Australia, 1,124 hospital admissions for related cardiovascular problems, 2,027 hospital admissions for respiratory problems and 1,305 asthma presentations at emergency departments (Borchers Arriagada et al. 2020). In turn, health effects cause economic effects. In economic terms, the health costs from the 2019–20 bushfire smoke translate to $1.95 billion, far outweighing costs of previous catastrophic fire seasons – for example, $566 million was estimated for the 2002–03 season (Johnston et al. 2020). Poor air quality can also have other economic effects. For example, poor air quality in a region can impact the perception of that region, reducing overall visitor numbers. High smoke levels will reduce visibility and cause unpleasant conditions for those enjoying the outdoors. Burden of disease Measurable health impacts are found even at low levels of air pollution (Barnett et al. 2006). Average annual levels of fine particulate matter (PM2.5) in Sydney and Perth are lower than those in European cities, but studies have shown morbidity increases of 5% in Australian cohorts for each unit increase in PM2.5, and an increase of 3% morbidity per 5 micrograms per cubic metre (μg/m3) increase in nitrogen dioxide (NO2) (Hanigan et al. 2019b). The latest Australian Institute of Health and Welfare burden of disease assessment estimates that 2,566 deaths were caused by air pollution in 2015, or 1.6 % of all deaths in Australia (AIHW 2019). Air pollution reduces the life expectancy of Australians. The total number of years lost to air pollution is estimated to be more than 29,000 each year, mainly due to coronary heart disease (Figure 5). The total number of years of life lost due to air pollution has increased by 1,000 since the previous burden of disease report (AIHW 2016). This suggests that the mortality rate attributed to ambient air pollution is increasing in Australia. Indicator 3.9.1 of the United Nations Sustainable Development Goals (SDGs) aims to monitor and reduce this rate. Figure 5 Years of life lost attributed to poor air quality in Australia Source: AIHW (2019) Download Go to data.gov Share on Twitter Share on Facebook Share on Linkedin Share this link Air quality levels per person The aim of the United Nations SDG 11 is to make cities and human settlements inclusive, safe, resilient and sustainable. Relevant to air quality, SDG 11 has a target to reduce the adverse per-person environmental impact of cities by 2030. The key indicator for this target is the annual PM2.5 concentration, weighted by the population (see Approach). The upper limit for the annual average concentration of PM2.5 as prescribed by the National Environmental Protection Measures (NEPMs) is 8 μg/m3. The wellbeing assessment has been completed for the first time in this 2021 report (Figure 6), so will provide the baseline metric for assessing the direction of trends in future reports. The highest population-weighted PM2.5 concentrations occur in locations where there are high levels of dust (e.g. the north-eastern region of South Australia; Figure 6), which matches the locations of the largest dust emissions (Figure 33). These regions of high dust tend to be less densely populated than the city locations; each individual block of colour represents around 10,000 people at the scale of Statistical Area Level 2 (SA2). The calculations show that: the central business districts of Sydney and Melbourne have population-weighted PM2.5 concentrations in the region of 7 and 8.5 μg/m3, respectively, which are at, or just exceed, the annual NEPM limit there are 285 SA2 blocks exposed to >8.01 μg/m3 (i.e. just above the annual NEPM limit), representing nearly 3 million people; the highest population-weighted concentration is at Coober Pedy in South Australia (11.7 μg/m3) regional centres in New South Wales and northern Victoria have a higher population-weighted exposure than regional centres in Queensland the lowest population-weighted exposures tend to be found in areas of wilderness, such as western Tasmania (1 μg/m3), Wilsons Promontory in Victoria (1 μg/m3) and the northern Blue Mountains region of New South Wales (1.1 μg/m3). Figure 6 Population-weighted PM2.5 levels in SA2 regions across Australia µg/m3 = microgram per cubic metre; PM2.5 = fine particulate matter; SA2 = Statistical Area Level 2 Note: The maps are constructed from annual averaged 2015–18 PM2.5 data (Knibbs 2020) and do not include the summer 2019–20 bushfire period. SA2 data are from ABS (2015). Source: Christy Geromboux, Centre for Air pollution, Energy and Health Research data platform Share on Twitter Share on Facebook Share on Linkedin Share this link
Year Month Jurisdiction Air quality event Pollutant involved 2016 January Tas Bushfires in north-west Tasmania burn 91,983 haa,b Smoke 2016 January WA Bushfire at Yarloop burns 67,871 haa,b Smoke 2016 November Vic Thunderstorm asthma kills 10 peoplec Pollen 2018 August Vic 20,000 m2 factory fire occurs on site storing waste at West Footscrayd Smoke 2019 Summer Tas Bushfires west of Huon Valley burn 170,988 haa,b Smoke 2019 April Vic Large factory fire occurs on site storing waste at Campbellfielde Smoke 2019 November NSW Dustiest month since records began in 2005f Dust 2019–20 Summer South-east Australia Bushfires burn 5,567,402 haa,b, contributing to 417 excess deathsg Smoke, accompanied by smog 2020 March–April Australia COVID-19 pandemic Varies by jurisdiction 2020 May WA Cyclone Mangga produces 100 km/h winds and very high levels of PM10 in Geraldton Dust ha = hectare; km/h = kilometre per hour; m2 = square metre; NSW = New South Wales; PM10 = coarse particulate matter; Tas = Tasmania; Vic = Victoria; WA = Western Australia Sources: a MODIS MCD64A1 Collection 6 Burned Area product; b Giglio et al. (2018); c DHHS (2017); d IGEM (2020); e Personal communication, EPA Victoria; f Community DustWatch (2019); g Borchers Arriagada et al. (2020) Share on Twitter Share on Facebook Share on Linkedin Share this link
Pushan Shah, South Australian Environment Protection Authority Jason Choi, Environment Protection Authority Victoria The beginning of 2020 brought COVID-19, an unexpected global pandemic that caused normal activities to cease with government directives to stay at home. These directives were termed ‘lockdowns’, with many businesses forced to close and everyday movements restricted. The restrictions manifested themselves in different ways in Australia’s capital cities, but all impacted airborne emissions. Here, the evidence of emissions reductions is examined through ambient pollutant concentrations measured in Adelaide, Brisbane, Melbourne and Sydney during these lockdown periods. Adelaide On 12 March 2020, the South Australian Government implemented lockdown measures, lasting until the end of April. The measures were expected to reduce air pollution due to a decrease in noncommercial vehicle traffic, and in industrial and commercial activity. The average reduction in traffic volume was 40% during the peak of the restrictions, before returning to near-normal levels at the end of July (Figure 1). Figure 1 (a) Traffic volume and (b) CO concentration across metropolitan Adelaide, March–July 2020 CO =carbon monoxide; ppm = parts per million Source: Traffic data, South Australian Department of Infrastructure and Transport Download Go to data.gov There are no roadside monitoring stations in Adelaide to observe the impacts of these reductions directly, but the reduction in people travelling to Adelaide central business district (CBD) is observed from the centrally positioned station in the CBD. In Adelaide CBD, levels of carbon monoxide (CO) decreased by 40% in accordance with the traffic volumes, compared with measurements taken during the same period (March–April) in the 5 years before the COVID-19 lockdowns (Figure 2). Evidence of decreases in nitrogen oxides (NOx) and fine particulate matter (PM2.5) is harder to observe. Five years of data were used for the pre-pandemic period to reduce the influence that large-scale events, such as bushfires and land burns, can have on estimates of ambient pollutant concentrations. Although there was a small reduction in NOx levels, PM2.5 levels continued to be influenced by bushfire smoke in the early part of 2020 and remained very similar to past averages. Overall, an improvement in air quality was recorded, with 20–40% reduction in all pollutants during March and April 2020. Figure 2 CO, NOx and PM2.5 levels during the initial peak COVID-19 restrictions in Adelaide compared with the previous 2015–19 average and the rest of 2020 CO = carbon monoxide; µg/m3 = microgram per cubic metre; NOx = nitrogen oxides; PM2.5 = fine particulate matter; ppm = parts per million Source: South Australian Environment Protection Authority Download Go to data.gov Brisbane Numbers of coronavirus cases in Brisbane were much lower than elsewhere in Australia in early 2020, so restrictions were less strict. Still, many people chose to work from home, and this is reflected in a 13% decrease in nitrogen dioxide (NO2) levels in Brisbane compared with the 10-year average (Welchman et al. 2020). However, the Katestone report notes that the impact of meteorology (e.g. stagnant, pollutant-trapping conditions) may have masked the level of reductions that might otherwise have occurred in Brisbane. Melbourne Lockdown measures in Melbourne were introduced on 17 March 2020. Traffic flows began decreasing immediately, to a minimum of 30% in the week of 12 April 2020, compared with pre-lockdown flows. Traffic began resuming steadily and by the beginning of June had reached 80% of normal levels. This was curbed again in August when very strict lockdown measures were in place for more than 100 days. The impact of the traffic reductions is most easily seen in the NO2 columns (Figure 3). Comparing the 2020 profile on 10 April with the profiles calculated from the preceding 5 years shows a 24% reduction in NO2 in the area surrounding the city of Melbourne. Figure 3 (a) Fifteen-day running mean total column NO2 on 10 April 2020, (b) as an average of the same time across 2015–19 and (c) as the difference between the 2 plots cm2 = square centimetre; NO2 = nitrogen dioxide Source: NASA Aura OMI satellite, originally published in Air Quality and Climate Change, publication of the Clean Air Society of Australia and New Zealand Air quality data collected at all Environment Protection Authority Victoria monitoring stations in Melbourne between 17 March and 12 May for 6 years (2015–20) were examined, separating out 2020 to assess the impacts of the lockdowns. The average diurnal columns over these periods also show a 25% decrease in NO2 during the lockdowns (Figure 4), similar to the NO2 reduction calculated by Ryan et al. (2021). At the same time, there was a 3% increase in ozone. This increasing ozone effect has been observed all over the world and tends to be greater in cities where the lockdown measures were strictest (Gkatzelis et al. 2021). Although NOx compounds are involved in the chemical production and removal of ozone, a direct link between decreasing NO2 and increased ozone cannot be made without considering other ozone-forming chemicals such as volatile organic compounds (VOCs), and the impact of temperature. Reductions in other pollutants such as carbon monoxide (CO) and PM2.5 during the lockdown period in Melbourne were more difficult to observe, as reductions were also observed in February and early March. This might be caused by reduced tourism to the area following the severe summer 2019–20 bushfires. Post-lockdown, there were increases in CO levels during 2020 beyond those from the previous 5 years. This was caused by smoke from wood heaters being used more prolifically when evening temperatures decreased well below 10 °C. Figure 4 NO2 and ozone levels during the peak COVID-19 restrictions across all Melbourne air quality stations compared with the previous 2015–19 average for the same period NO2 = nitrogen dioxide; ppb = parts per billion Note: Solid line represents the mean; shaded area represents the data range. Source: Environment Protection Authority Victoria, originally published in Air Quality and Climate Change, publication of the Clean Air Society of Australia and New Zealand Sydney Traffic volumes decreased by 19–44% across Sydney as the lockdowns started to take effect from 16 March 2020 (Duc et al. 2021). Duc et al. (2021) examined the raw air quality data and observed decreases in concentrations of NO2 (–18%), CO (–13%) and PM2.5 (–13%), while ozone levels increased (+1.5%). However, by detrending the air quality data for meteorological effects, Ryan et al. (2021) estimated that NO2 levels decreased by 8% as a result of lockdowns, but concentrations of ozone and PM2.5 increased by 20% and 24%, respectively. Conclusions Chemical reactions in the atmosphere are highly nonlinear, and unexpected changes in secondary pollutants (e.g. ozone increases) can occur when primary pollutants such as NO2 are reduced. However, reducing NOx emissions in Australia will almost always lead to better overall air quality in our urban areas. Although there is some nonlinearity in the chemistry, and there are occasions when ozone levels may be more related to VOCs than NOx, policies that reduce primary emissions of NOx and other air pollutants and their precursors will almost always succeed in improving air quality. Share on Twitter Share on Facebook Share on Linkedin Share this link
CO =carbon monoxide; ppm = parts per million Source: Traffic data, South Australian Department of Infrastructure and Transport Download Go to data.gov
CO = carbon monoxide; µg/m3 = microgram per cubic metre; NOx = nitrogen oxides; PM2.5 = fine particulate matter; ppm = parts per million Source: South Australian Environment Protection Authority Download Go to data.gov
cm2 = square centimetre; NO2 = nitrogen dioxide Source: NASA Aura OMI satellite, originally published in Air Quality and Climate Change, publication of the Clean Air Society of Australia and New Zealand
NO2 = nitrogen dioxide; ppb = parts per billion Note: Solid line represents the mean; shaded area represents the data range. Source: Environment Protection Authority Victoria, originally published in Air Quality and Climate Change, publication of the Clean Air Society of Australia and New Zealand
Source: AIHW (2019) Download Go to data.gov Share on Twitter Share on Facebook Share on Linkedin Share this link
µg/m3 = microgram per cubic metre; PM2.5 = fine particulate matter; SA2 = Statistical Area Level 2 Note: The maps are constructed from annual averaged 2015–18 PM2.5 data (Knibbs 2020) and do not include the summer 2019–20 bushfire period. SA2 data are from ABS (2015). Source: Christy Geromboux, Centre for Air pollution, Energy and Health Research data platform Share on Twitter Share on Facebook Share on Linkedin Share this link