A Second Wave? An update on the Australian Air Quality after COVID-19 mobility restriction measures

Written by Simon Welchman, Manning Young and Plistina Almeida


The COVID-19 pandemic is a global tragedy happening before our eyes. Its effects on human health and the economy are likely to be with us for years to come. We have seen through our analysis of air quality during the COVID-19 pandemic that the generally suppressed activity and the stricter lockdowns have reduced levels of air pollutants in our major cities. This, at least, provides a useful case study with which we can better understand our impact on air quality.


At the same time, researchers are also trying to identify links between certain air pollutants, weather conditions and the spread of COVID-19. However, it is too early to establish clear linkages.


Katestone has analysed the effect of the lockdown measures on air quality in Australia’s three largest cities since March 2020. Our most recent analysis covered the months of March, April and the start of May, which seems like a long time ago now. Australia’s early lockdown saw the virus effectively suppressed in the second half of April.  However, in July 2020, a second wave of infections resulted in further lockdowns, particularly in Melbourne (Stage 4 lockdown) and regional Victoria (Stage 3 lockdown) from 2 August 2020, which have extended into September.


Throughout Australia, there has been a sustained reduction in activity, which is most prominent in Victoria in the last six weeks.  This can be seen in the Google Mobility Report for Australia, which summarises mobility trends for places that are public transport hubs, such as underground, bus and train stations. The baseline for this analysis is the period from 3 January to 6 February 2020. Data from the City of Sydney, Melbourne City and Brisbane City LGAs are shown in the graphs below.


Figure 1 – Comparison of mobility changes (weekly averages) for Sydney, Melbourne and Brisbane for 2020 in comparison with established baseline from the Google Mobility Reports.



Figure 2 – Comparison of mobility changes (weekly averages) in Public Transport for Sydney, Melbourne and Brisbane in 2020 in comparison with established baseline from the Google Mobility Reports.



Katestone’s preliminary review of air quality data since the COVID-19 pandemic began, suggests that there has been a reduction in traffic-related air pollutants such as nitrogen dioxide (NO2) and particulate matter (PM2.5). In this article, we will focus on NO2 for the following reasons:

  • NO2 is a good marker for traffic emissions in urban areas.
  • NO2 data capture rates are high going back to 2010 at all sites, which makes for the most robust analysis.

The figures below show monthly average concentrations of NO2 in micrograms per cubic metre (µg/m3) and 95% confidence intervals for 2020 in comparison to the past 10 years.




The imposition of Stage 4 lockdown in Melbourne in early August is evident in the NO2 concentrations at Alphington and Footscray, which dropped in August by 38% and 31%, respectively, compared to July 2020.

The trend across the year shows a significant reduction in NO2 concentrations relative to the 10 year average during the first lockdown (March – April 2020), followed by a return to average levels in June 2020 and above average levels in July 2020. The second lockdown in Melbourne has resulted in concentrations of NO2 at Alphington and Footscray being lower by 28% and 17%, respectively.

It is important to note that this analysis has not taken account of the potential influence of meteorology on concentrations of NO2. Meteorology has an important influence on air quality from year to year and we are further analysing the data to investigate this further.

Figure 3 – NO2 Concentrations for Victoria in 2020 in comparison with the ten previous years – Alphington and Footscray




Relative to the 10 year average, Randwick and Rozelle have shown significant and sustained reductions in concentrations of NO2 after April 2020 of 26% and 22%, respectively.  The most significant monthly reduction compared to the 10-year average occurred in May 2020 at both monitoring sites.

Figure 4 – NO2 Concentrations for New South Wales in 2020 in comparison with the ten previous years – Randwick and Rozelle




Overall, Brisbane is the least affected city of the three comparing the monthly average concentrations of NO2 with the 10-year average. Since April, there has been a significant and sustained reduction in concentrations of NO2. Compared with the 10-year average, concentrations are, on average, lower by 13% and 14% at South Brisbane and Woolloongabba, respectively.

The relativities in air pollutant levels and mobility data across the three cities suggests that other factors such as meteorological conditions may also be playing a significant role, which may have suppressed the apparent reductions in Brisbane or enhanced reductions elsewhere.

Figure 5 – NO2 Concentrations for Queensland in 2020 in comparison with the ten previous years – South Brisbane and Woolloongabba



Next Steps

We will continue to analyse the air quality data over the coming months. We anticipate more interesting findings as we head into summer and as Victoria comes out of its second lockdown.

We intend to take a more detailed approach to the data analysis by considering the effect of meteorological conditions on air quality. We know that meteorology effects air quality in important ways, for example, strong winds will disperse air pollutants, whilst lighter winds and calm conditions lead to generally higher concentrations of traffic-related air pollutants.

Seasonal factors also play an important role.  This is evident in the data that is presented above, where we see higher average levels of air pollutants in the cooler months due to more stable atmospheric conditions that suppress dispersion.

The influence of industrial activities is also quite important in terms of air pollutants. In places where intensive industrial activities occur and those activities are not reduced due to COVID-19, emission levels and air pollutant concentrations may not be reduced.

In our next update on the COVID-19 effects on air quality, we hope to account for meteorological variation using a machine learning approach.


Find the previous updates below:


This article featured in the Katestone’s Clear Skies 2020 Spring edition. Click here to view other featured articles.



The graphs show diurnal profiles of nitrogen dioxide at two sites in Brisbane (South Brisbane and Woolloongabba), two sites in Melbourne (Alphington and Footscray) and two sites in Sydney (Randwick and Rozelle). The graphs compare measurements from 1 January to 10 September 2020 with the same period in the previous ten years. The monitoring stations are managed by the Department of Environmental Sciences in QLD, by the Department of Environmental, Energy and Science in NSW, and by the by the Department of Environmental, Energy and Science in Victoria.

Data on movement from Google Maps’ COVID-19 Community Mobility Report for Australia, September 8, 2020. Google LLC “Google COVID-19 Community Mobility Reports.” https://www.google.com/covid19/mobility/ Accessed: 14 September 2020.


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