The impacts of the COVID-19’s mobility restriction measures on the Australian Air Quality

Written by Simon Welchman, Manning Young, Michael Burchill and Plistina Almeida

 

The COVID-19 global pandemic has brought significant changes to our personal and professional lives as well as to the natural environment in which we live. During March 2020, a range of restrictions was put in place by the Australian Federal and State governments to fight the spread of COVID-19. For example, gatherings and other activities have been banned or suspended and most employees around Australia were directed to work from home from around 16 March 2020.

This is evident in Google Maps data for public transport station hubs such as bus and train stations, which show a drop of more than 60% in foot traffic in Queensland since March 2020 according to Google Map’s Community Mobility Report.

Similar restrictions have been instituted around the world. NASA satellite images show significant improvement in China’s and Italy’s air quality since those counties introduced lockdowns and the sudden cleanliness of the Venice Canal. An important question for us is how are the lockdown measures affecting air quality in Australia?

In this article, we look at the factors that affect air quality in Australian cities, some recent air quality data from Brisbane, Melbourne and Sydney, a cross-evaluation with road traffic data for March and early April, and examine how Katestone will help you keep up with the air quality changes in the next months.

 

Air Quality and Air Pollutants

Air pollution occurs when gases, liquids or solid particles exist in the air in sufficient quantities to adversely affect human comfort or health or cause environmental damage. Air pollutants are generated by natural causes such as bushfires, wind-blown dust and salt spray and man-made activities such as exhausts of fossil-fuelled vehicles and industrial activities.

Nitrogen dioxide (NO₂) and PM_2.5 are two air pollutants that are commonly found in cities around the world. These air pollutants are mainly generated by human activities in cities. For example, in Sydney, nearly 96% of oxides of nitrogen (NOx) and 72% of PM_2.5 are due to human activities (NSW EPA, 2019).

                         

Figure 1 – The graphs show percentage contributions from natural and human-made sources to total emissions of oxides of nitrogen and PM_2.5 in Sydney (NSW EPA, 2019)

 

More than 55% of NOx and 12.9% of PM_2.5 emissions that are caused by human activities are due to motor vehicle traffic. Domestic solid fuel burning (e.g. wood heaters) make up the majority (more than 50%) of human-induced emissions of PM_2.5.

The effect of motor vehicle traffic on air quality is easy to see in daily plots of monitoring data because our working hours are commonly arranged between mornings and evenings. We, therefore, tend to see a clear pattern with higher levels occurring in the morning and evening with peak traffic volumes.

The number of motor vehicles on the roads has also changed significantly during the lockdown. “The lockdown effect” article (ABC News, 202o) presents data from Google maps, which contrasts traffic speed at 9 am on Friday, April 3, 2020, with typical traffic speed at 9 am on Fridays before lockdown. These maps displayed below, show freely flowing traffic during lockdown where there used to be considerable gridlock. This data indicates a two-fold benefit for air quality. Firstly, fewer cars mean lower emissions and secondly, there is less congestion, which means that the motor vehicles that are operating are working more efficiently with lower emissions per kilometre travelled.

 

Sydney

Typical traffic	April 3, 2020
Figure 2 – Comparison maps of traffic speed in Sydney from the ABC News “The lockdown effect” article (ABC, 2020).

Melbourne

Typical traffic	April 3, 2020
Figure 3 – Comparison maps of traffic speed in Melbourne from the ABC News “The lockdown effect” article (ABC, 2020).

 

Brisbane

Typical traffic	April 3, 2020
Figure 4 – Comparison maps of traffic speed in Brisbane from the ABC News “The lockdown effect” article (ABC, 2020).

Air Quality Analyses

Australian State and Territory governments have responsibility for monitoring air quality in our cities. Katestone’s preliminary review of this air quality data since lockdown began suggests that there has been a reduction in traffic-related air pollutants such as NO₂ and PM_2.5. The reduction is most likely because of fewer vehicles on the road and less traffic congestion. This will likely continue whilst the current restrictions are in place.

The table below shows the change in urban NO₂ and PM_2.5 concentrations for the beginning of 2020 compared with the same period last year. Common to all locations is the consistent reduction in the PM_2.5 emissions during March 2020. The average reduction was 31%. However, the same cannot be said about the NO₂ emission rates: the reductions do not follow a consistent pattern across the main capitals despite some minor reductions being observed in Brisbane.

 

Table 1- NO₂ and PM_2.5 Emissions for the main receptors in Queensland, New South Wales and Victoria for January, February, and March 2020 in relation to the same period in 2019

 

The graphs below show the average NO₂ and PM_2.5 concentrations and 95% confidence intervals, by hour of day for March 2020 compared with the same period last year. Data is sourced from the Department of Environment and Science (QLD); Department of Planning, Industry and Environment (NSW); and Environment Protection Authority Victoria (VIC).

 

Nitrogen dioxide

Figure 5 – NO₂ Concentrations for New South Wales in March – Randwick and Rozelle

 

Figure 6 – NO₂ Concentrations for Victoria in March – Alphington and Footscray

 

 

Figure 7 – NO₂ Concentrations for Queensland in March – South Brisbane and Woolloongabba

 

Once again, some reductions can be observed in Brisbane. However, the data from Sydney does not convey a clear pattern for NO₂ concentrations: morning peak concentrations for March 2020 are lower in Randwick but higher for Rozelle.

NO₂ concentrations are also significantly lower in the weekends in Melbourne. While Woolloongabba, Rozelle and Alphington have the concentration peaks shifted from the mornings to other hours of the day.

 

Particulate matter (PM_2.5)

Figure 8 – PM_2.5 Concentrations for New South Wales in March – Randwick and Rozelle

 

Figure 9 – PM_2.5 Concentrations for Victoria in March – Alphington and Footscray

 

Significant reductions can be observed for PM_2.5 concentrations in Sydney. Smaller reductions can be detected in Melbourne, however, emissions next to Alphington have shifted away from road traffic peak hours. Melbourne also shows consistent reductions observed during the weekends.

Overall air quality in Australia more generally, is very good. We do not have the very high levels of air pollutants that we see in China and other parts of the world. Consequently, improvement is less dramatic. April will probably provide an even clearer picture as to the degree of improvement in air pollutants that have resulted by the current restrictions.

Katestone is watching these numbers closely and will have updates on the effects of the social distancing on the Australian Air Quality within a fortnight. Make sure you follow us on LinkedIn for updates.

 

Find more recent updates below:

• 24/05/2020 – CO, PM_2.5 and NO₂: which air pollutant best illustrates the effect of COVID-19 mobility restrictions on air quality
• 14/05/2020 – Update on the Australian Air Quality after the implementation of the COVID-19 mobility restrictions

 

Notes about this article

• The graphs show diurnal profiles of nitrogen concentrations (an air pollutant associated with petrol and diesel motor vehicles and other combustion activities) at two sites in Brisbane (South Brisbane and Woolloongabba), 2 sites in Melbourne (Alphington and Footscray) and two sites in Sydney (Rozelle and Randwick). The graphs compare measurements for March 2019 and March 2020. These stations are managed by the Department of Environmental Sciences in QLD and by the Department of Environmental, Energy and Science in NSW.
• Data on movement from Google Maps’ COVID-19 Community Mobility Report for Australia, April 11, 2020. The baseline is the median value, for the corresponding day of the week, during the 5-week period Jan 3–Feb 6, 2020.
• Google LLC “Google COVID-19 Community Mobility Reports.”
  https://www.google.com/covid19/mobility/ Accessed: 22 April 21 April 2020.
• Information on the road traffic speed for the main capitals is from the very insightful ABC News article “The lockdown effect” by Inga Ting, Alex Palmer and Stephen Hutcheon published on 5 April 2020.
• Additional inspiration on road traffic numbers was pulled from available public data from the QLD TMR, the Brisbane City Council, and insights from the TMM Group. We are very grateful for the direction provided by the professionals within these 3 organisations.
• NSW EPA, 2019, Air Emissions Inventory for the Greater Metropolitan Region in New South Wales, NSW Environment Protection Authority, viewed 22 April 2020, < https://www.epa.nsw.gov.au/-/media/epa/corporate-site/resources/air/19p1918-air-emissions-inventory-2013-summary.pdf?la=en&hash=59CF67ACA719CD8E06B34356C35A7C172B43640F>.