Population

The population of Australia increased from 24 million in 2016 to 25.6 million in 2020 (ABS 2020a). Net migration to Australia has been increasing each year, except for 2020 when the COVID-19 pandemic forced Australia’s international borders to close and migration to all but cease. Population growth creates an increasing need for housing, amenities and employment, which in turn can cause pressures on air quality.

The following sections detail emissions to the atmosphere under a ‘business as usual’ scenario. The 2020 lockdowns associated with COVID-19 caused many normal activities to cease and thus affected air quality (see case study: COVID-19 lockdown action temporarily reduces emissions).

The main sources of pollution vary depending on location.

More than 90% of Australia’s residents live in cities, most of which are located on the coast. People create emissions that contribute to poor air quality, and emissions inventories are used to investigate the sources and levels of emissions created by Australians living in cities.

The Sydney emissions inventory is the most recently developed inventory (released in 2018 for activities in 2013). In the Sydney region (Figure 33), domestic and commercial sources contribute the largest proportion of the fine particulate matter (PM2.5) and volatile organic compound (VOC) emissions, largely from domestic wood heaters and solvent emissions. Off-road mobile sources contribute the biggest proportion of sulfur dioxide (SO2), largely from use of fuels with high sulfur content (see Shipping). Onroad mobile sources emit the largest proportion of carbon monoxide (CO) and nitrogen oxides (NOx), from the burning of petrol and diesel in cars.

Figure 33 Sources of pollutants in emissions inventory for the Sydney region, 2013

The latest New South Wales emissions inventory (2013) shows reductions in all the pollutants compared with the previous emissions inventory in 2008 (Figure 34). The largest reductions are a 42% reduction in lead emissions, a 25% reduction in NOx emissions and a 15% reduction in CO emissions.

Figure 34 Reduction in emissions of the most common pollutants between the 2008 and 2013 emissions inventory for the Sydney region

The National Pollutant Inventory (NPI) takes into account all Australia, and therefore a higher percentage of pollutants come from industry (Figure 35) – many large heavy industries and mining operations take place outside cities, and their emissions are not counted in city inventories. The NPI also shows on-road mobile sources contributing a larger proportion of pollutants such as lead and CO than the Sydney inventory. The proportion of PM2.5 from industrial processes in the NPI far outweighs the proportion from other sources.

Figure 35 Breakdown of pollutants by anthropogenic source category, 2018–19

Motor vehicles

In Australia, the number of vehicles and the distances we are driving are increasing, and our fleet is ageing.

Motor vehicles make a significant contribution to air pollution, especially in cities. For example, motor vehicles emit most of the nitrogen oxides (NOx) and carbon monoxide (CO) in the Sydney emissions inventory (Figure 34). Bowatte et al. (2017) found that people living within 200 m of a major road were more likely to suffer asthma and reduced lung function due to NOx exposure.

At the beginning of January 2020, the Australian Bureau of Statistics estimated that there were just under 20 million registered vehicles in Australia, an increase of 1.5% over the previous year. By the end of December 2020, Australian vehicles were estimated to travel 238 billion kilometres per year, a decrease of 2.5% since the 2016 state of the environment report (Keywood et al. 2017). The reduction is due to travel disruptions in 2020 because of bushfires and coronavirus restrictions. Trends in vehicle types and kilometres travelled is in the Urban chapter) (see the Urban chapter).

The average age of Australian vehicles has increased to 10.4 years (ABS 2020b) from 10 years in 2016. This means that newer technologies aimed at decreasing vehicle emissions will take longer to have an impact on air quality. Modelling has also suggested that a 10% increase in electric vehicle uptake in Melbourne would prevent 500,000 litres of petrol being burned per day (Li & Dodson 2020).

Impact

The percentage of diesel vehicles on our roads has increased by 6% since 2015. If the total vehicular emissions are summed and split according to engine type, diesel vehicles produce more lead, NOx and PM emissions than petrol vehicles (Figure 36), while petrol vehicles contribute more CO, SO2 and VOCs. Lead emissions overall have decreased since 2008 in Sydney, but the proportion of lead emissions coming from motor vehicles increased from 24% in 2008 to 34% in 2013, because other sources of the pollutant also decreased. In Australia, the latest 2021 motor vehicle census (all passenger and commercial vehicles) showed 14.4 million petrol engines and 5.3 million diesel engines. Of the petrol engines, 308,000 still rely on leaded petrol (ABS 2020b).

Figure 36 Percentage of emissions from all on-road diesel (light-duty diesel and heavy-duty commercial diesel) and petrol (passenger vehicle petrol and light-duty commercial petrol) vehicles in the Sydney region, 2013

Emissions from both petrol and diesel cars vary with driving activities, from large initial emissions at ignition to lower emissions if the vehicle is driven smoothly along freeways. Emissions also vary with time. Congestion and vehicle idling restrict the emissions from many vehicles to localised areas and cause increases in air pollution. This tends to occur on weekdays during peak-hour morning and afternoon traffic (Figure 37). Peak traffic emissions on a Saturday are around 60% of the peak weekday emissions, whereas a late afternoon peak exists on Sunday as people return home from weekend activities.

Figure 37 Modelled timeseries of a typical week of NOx (NO + NO2) emissions from petrol vehicles, normalised to the maximum NOx emission

Mitigation

Low-cost sensors were used to measure PM2.5 levels around busy roads in Liverpool, New South Wales. The levels of PM2.5 at the roadside were 10 times higher than the levels measured at the nearest air quality monitoring station (Forehead et al. 2020). Discouraging drivers from leaving their engines on when parked, creating low-emission zones around schools and residential areas, upgrading to electric cars and encouraging public transport use would reduce vehicle emissions at the source. There are also simple ways for residents to reduce their exposure to vehicle emissions, such as walking one street back from the main road and not exercising during the morning commute (Wadlow et al. 2019). These options could reduce their exposure to vehicle emissions by half.

To reduce the level of roadside pollution, researchers have found that moss is particularly good for absorbing pollution and was better at removing particulate matter than native trees (Haynes et al. 2019). Other plants with evergreen leaves were also good at trapping particles because of the waxy surface coating on their leaves (Popek et al. 2019).

Other engines

Emissions from nonroad spark-ignition engines are produced by recreational boat engines and domestic outdoor power tools such as lawnmowers. There is no separate category for ‘outdoor power tools’ in emissions inventories, so emission levels from that source are unknown. In the past 5 years, emissions from lawnmowers and recreational boats have not changed in the NPI. However, the 3 most recent New South Wales emissions inventories show a general upward trend in the emissions from domestic lawnmowing and recreational boating (Figure 38). The latest 2013 New South Wales emissions inventory was released in 2018. Legislation to tighten the quality of new imported nonroad spark-ignition engines was introduced in 2018 (see Commercial and domestic), and the impacts of this will be further assessed when New South Wales releases subsequent inventories.

In the 2013 inventory, combining lawnmowers and recreational boat emissions produced an estimated 61 million kilograms of CO and 16 million kilograms of VOCs. Other emissions include PM and NOx, but these levels are much lower than CO and VOCs.

Figure 38 Emissions from (a) domestic lawnmowing and (b) recreational boating in the greater metropolitan region of New South Wales (includes Newcastle, Wollongong and non-urban regions), 2003, 2008 and 2013

Urban development

Australia’s cities are growing (see the Urban chapter). In the years leading up to 2020, demand for housing and amenities continued to place pressures on urban emissions. These emissions can have a large influence on urban air quality and contribute to summer smogs. And because a high proportion of Australia’s population lives in cities, this affects the health of many Australians.

Sources of domestic emissions include vehicle use, cooking, heating and cooling systems, emissions from new furnishings, and household aerosols and solvents.

Other emissions from the home stem from outdoor activities. These include barbecues, pizza ovens, meat smokers and firepits, which emit PM, and outdoor heaters, lawnmowing and other small petrol-fuelled gardening tools such as leaf blowers and hedge trimmers, which emit VOCs. Emissions from small power generators and recreational marine engines such as outboard motors and jet skis, which emit CO, NOx and VOCs, are also considered domestic emissions. The emission levels from generators and small marine engines on a per-engine basis are higher than those from motor vehicles because clean-emissions technology is not as advanced in the recreational sector.

Outward expansion of cities encroaches on green space on the urban fringes, with construction of new facilities and housing estates (see the Urban chapter). As cities are concentrated areas of high anthropogenic emissions, increasing their spatial extent increases the spatial extent of emissions, leading to an increased risk of summertime smogs and winter pollution. New suburbs require transport connections, which increase the road network and emissions from vehicles. Larger cities create more emissions and more people exposed to those emissions, meaning that the populated-weighted exposure metric (see Approach) is likely to increase.

Following COVID-19 lockdowns, as working from home became less appealing from small city apartments with no outside space, there has been a short-term trend in people moving from cities to regional areas to gain more space. However, it is too early to make any conclusions on the trends of people moving permanently away from cities.

Solid fuel heaters

Heating the home in winter with a solid fuel burner, such as a wood heater, is a popular choice for many Australian homes, particularly in cooler southern states and in regional areas. However, wood heaters are the main source of air emissions from the home, contributing more than 80% of total domestic emissions of formaldehyde, PM, and air toxics such as furans and dioxins (Figure 39). Robinson et al. (2021) estimated that 14 deaths per year were attributable to wood heater smoke in the regional New South Wales town of Armidale alone (population 30,000). Banning wood heaters is one of the major recommendations of the Clean Air Plan for Sydney (Paton-Walsh et al. 2019).

Depending on the stability of the atmosphere, wood heater smoke either is transported away in moderate to high wind conditions, remains in the area and pools overnight if conditions are very calm, or can even return rapidly to the ground near the emission sources. On a winter’s evening, the atmospheric boundary layer decreases in height at dusk, causing emissions to become trapped closer to the ground. Calm conditions then result in smoke levels building up overnight in the local area. In other circumstances, local microclimatic and topological effects can mean that individual smoke plumes affect neighbouring properties. This can result in very degraded air quality on very small spatial scales, and often leads to complaints to the local authorities (Innis & Cox 2017). (See case study: Exposure to wood heater smoke.)

Figure 39 Contribution of solid fuel–burning emissions to total domestic emissions in the Sydney region, 2013
Case Study Exposure to wood heater smoke

Tasmania is a state with a small population, relatively low traffic volumes and relatively little heavy industry. It is also influenced by very clean air from the Southern Ocean during westerly or south-westerly winds. However, in winter, the smoke from wood heater use is very noticeable, and forms a large proportion of Tasmania’s annual fine particulate matter (PM2.5) pollution.

Exposure to smoke is a known public health issue for Tasmania. Borchers Arriagada et al. (2020) estimated that, from 2010 to 2019, smoke in Tasmania contributed on average to 69 deaths per year, with 74% attributed to wood heater smoke and 26% to prescribed burning smoke. The estimated annual health cost of wood heater smoke in Tasmania was more than $250 million.

Over the past decade, the Environment Protection Authority Tasmania (EPA) has increased the statewide air monitoring network to better understand and plan for reducing population exposure to smoke.

Using data on wood heater density within a 1 km radius of Tasmania’s air stations, together with wind data, a population exposure relationship was determined that could be applied to regions with no smoke monitoring (Innis 2021). This work is subject to further analysis but may provide a means of estimating the mean wintertime PM2.5 across the state.

Launceston

Launceston, in the north of Tasmania, is located in a valley where wood smoke is easily trapped in the nocturnal boundary layer. In the winters of 2015 and 2017, the EPA conducted a series of extensive smoke measurement surveys to map the spatial distribution of smoke across the city (Figure 40). These surveys used vehicle-mounted PM2.5 monitors, which provided geolocated measurements every 5 seconds. Consistent patterns in the smoke distribution across the city were seen in both winters, with suburbs such as Ravenswood (north-east), Newnham (north) and Summerhill (south-west) regularly exhibiting some of the highest PM2.5 concentrations.

High levels of PM2.5 were correlated with the number of wood heaters in the area (Innis et al. 2017). These spatial surveys demonstrate how localised the high concentrations of PM2.5 can be, at times even localised to 1 or 2 streets (Figure 40). For example, short-term concentrations of PM2.5 above 150 micrograms per cubic metre (μg/m3) occurred in Summerhill during winter 2017, but 400–500 metres away in an area of lower housing density the concentrations were mostly as low as 20 μg/m3.

High ambient smoke levels typically peak in the later evening. At these times, it is not expected that many people would be outdoors in Tasmania, and hence few people are directly exposed to ambient wood smoke, but leaky buildings allow wood smoke indoors.

Figure 40 Evening smoke surveys of Launceston in 2015 (left) and 2017 (right)

μg/m3 = microgram per cubic metre; PM2.5 = fine particulate matter

Note: Peak instantaneous PM2.5 measurements are represented by symbol colour.

Source: Redrawn from Innis et al. (2017)

Poor wood heater operation occurs when the appliance is kept smouldering overnight, when new fuel is loaded, and when oxygen levels to the burn are damped to a minimum. Modern wood heaters are manufactured to burn more cleanly, but there is currently no requirement in Tasmania to replace older heaters.

A wood heater buy-back scheme was implemented in Launceston in 2001 and removed around 2,000 appliances, possibly more in the central area of the city than in the outer suburbs (J Innis, EPA Tasmania, pers. comm.). This helped to reduce the measured wintertime smoke levels (ABC News 2007).