These 5 images show how air pollution changed over Australia’s major cities before and after lockdown
- Written by Elena Sánchez-García, Postdoctoral researcher at LARS group, Universitat Politècnica de València
Have you recently come across photos of cities around the world with clear skies and more visibility?
In an unexpected silver lining to this tragic crisis, urban centres, such as around Wuhan in China, northern Italy and Spain, have recorded a vastly lower concentration of air pollution since confinement measures began to fight the spread of COVID-19.
Read more: Coronavirus: lockdown's effect on air pollution provides rare glimpse of low-carbon future
Likewise, the Himalayas have been visible from northern India for the first time in 30 years.
But what about Australia?
Researchers from the Land and Atmosphere Remote Sensing group at the Physical Technology Center in the Polytechnic University of Valencia – Elena Sánchez García, Itziar Irakulis Loitxate and Luis Guanter – have analysed satellite data from the new Sentinel-5P satellite mission of the Copernicus program of the European Space Agency.
The data shows a big improvement to pollution levels over some of our major cities – but in others, pollution has, perhaps surprisingly, increased.
These images measure level of nitrogen dioxide in the atmosphere, an important indicator of air quality. They show changes in nitrogen dioxide concentrations between March 11 to March 25 (before lockdown effectively began) and March 26 to April 11 (after lockdown).
Why nitrogen dioxide?
Nitrogen dioxide in urban air originates from combustion reactions at high temperatures. It’s mainly produced from coal in power plants and from vehicles.
High concentrations of this gas can affect the respiratory system and aggravate certain medical conditions, such as asthma. At extreme levels, this gas helps form acid rain.
Declining nitrogen dioxide concentrations across Europe in the northern hemisphere are normally expected around this time – between the end of winter and beginning of spring – due to increased air motion.
But the observed decreases in many metropolises across Europe, India and China since partial and full lockdowns began seem to be unprecedented.
Nitrogen dioxide levels across Australia
Preliminary results of the satellite data analysis are a mixed bag. Some urban centres such as Brisbane and Sydney are indeed showing an expected decrease in nitrogen dioxide concentrations that correlates with the containment measures to fight COVID-19.
On average, pollution in both cities fell by 30% after the containment measures.
Like a heat map, the red in the images shows a higher concentration of nitrogen dioxide, while the green and yellow show less.
Authors: Elena Sánchez-García, Postdoctoral researcher at LARS group, Universitat Politècnica de València