A small, silver lining on the COVID-19 cloud has been reductions in emissions of air pollutants as a result of nationwide lockdowns and the closure of international borders. In early March, NASA reported dramatic reductions in concentrations of nitrogen dioxide over China. Nitrogen dioxide is formed from the combustion of fossil fuels and is a useful indicator of emissions from transport and industry. Available ambient air quality monitoring data in New Zealand suggests similar reductions are occurring here.
Figure 1 below presents daily nitrogen dioxide concentrations measured in Takapuna in the first 20 days of lockdown which began on 26 March, with the previous (three-year average of) daily nitrogen dioxide concentrations for this period.1 The data show an average reduction of 58% in daily concentrations of nitrogen dioxide at Takapuna.
Figure 1: Daily nitrogen dioxide concentrations at Takapuna during the first 20 days of lockdown (beginning 26 March 2020). [Source: Auckland Council]
The same analysis carried out for particulate matter less than 10 micrometres in diameter (PM10) shows a 42% reduction in daily PM10 concentrations in Takapuna.
Of interest, the average reduction in daily concentrations of nitrogen dioxide and PM10 has been significantly smaller at the Penrose monitoring station in Auckland (average reductions of 43% in daily nitrogen dioxide and 29% in daily PM10). This is most likely due to the presence of industry near the Penrose monitoring station which has continued to operate during the lockdown period.
A more simplistic comparison of daily concentrations 20 days before with 20 days after lockdown suggests similar reductions have also occurred in other cities in New Zealand. For example, available data2 show an average reduction of 41% in Wellington (Figure 2), and 56% in Christchurch (Figure 3), in daily nitrogen dioxide concentrations for the 20 days of lockdown compared with the 20 days prior.
Figure 2. Daily nitrogen dioxide concentrations at Willis Street, Wellington 20 days before and the first 20 days of lockdown (beginning 26 March 2020) [Source: Greater Wellington]
Figure 3. Daily nitrogen dioxide concentrations at St Albans, Christchurch 20 days before and the first 20 days of lockdown (beginning 26 March. 2020) [Source: Environment Canterbury]
We know that significant reduction in ambient levels of PM10 will reduce adverse health effects in mortality and morbidity. It is tempting to estimate the health benefits likely to be realised from lockdown as offsets to the impacts of COVID-19. However, other unforeseen adverse effects of the extreme measures taken to address covid-19 will also be realised. As noted by Anna Hansell, Professor in Environmental Epidemiology at the University of Leicester, there will also be impacts from “financial hardship and stress (we know that poverty increases risk and severity of chronic diseases and also death rates), adverse impacts of isolation of the elderly (impacting on their health in various ways) and impact of restrictions on access to healthcare for non-COVID-19 diseases. The latter are likely to have knock-on effects on mortality for several years after the pandemic”.3
In other words, it’s complicated.
Postscript 1 May 2020: The (European) Centre for Research on Energy and Clean Air estimated 11,000 air pollution-related deaths have been avoided in Europe as a result of lockdowns, but also noted:
“Air pollution levels are plummeting as an unintended result of measures against the virus; this should not be seen as a ‘silver lining’, but it does show how normalised the massive death toll from air pollution has become, and points to what can be achieved if we shift to clean energy. When restrictions are fully lifted, European decision-makers can continue to implement policies to green electricity grids and transport systems in order to clear up our skies so we don’t return to heavy pollution.
As we are all anxious for life and business to return to normal, no one is looking forward to the return of fossil fuel pollution. It is vital for European decision-makers to prioritise clean air, clean energy and clean transport as a part of the plans for recovering from the crisis.
- Data have been annualised to compare the same days of the week (to account for known changes in traffic patterns at weekends). NB: Data have not been quality assured and should be treated with caution.
- Greater Wellington Regional Council and lawa.org.nz. NB: Data have not been quality assured and should be treated with caution.
- Science Media Centre, (2020). Expert reaction to drop in air pollution because of COVID-19. [Online: https://www.sciencemediacentre.org/expert-reaction-to-drop-in-air-pollution-because-of-covid-19/] 24 March.