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How the global restrictions of the COVID-19 pandemic shed light on the link between transport and air pollution

by Kerry Nice, Jason Thompson, Sachith Seneviratne and Mark Stevenson, University of Melbourne

Wie globale COVID-19-Pandemiebeschränkungen die Beziehung zwischen Verkehr und Luftverschmutzung beleuchten

Unexplained NO2 (ppb) (top row) and PM10 (μg/mL3) (bottom row) in cities in China, the United States, and Italy. Photo credit: Wijnands et al., air pollution research (2022). DOI: 10.1016/j.apr.2022.101438

As around 4 billion people around the world shut their doors and cut their trips by more than half during the COVID-19 pandemic, the once pollution-covered skies over cities began to clear.

For governments around the world, public health measures at the start of the COVID-19 pandemic included restricting movement to reduce the rate of disease transmission. While these restrictions effectively impacted case numbers, they also resulted in significantly reduced air pollution.

For a short time the world enjoyed a blue sky.

Much like the global financial crisis, however, the clean air miracle was short-lived as the world headed back towards recovery.

In the case of COVID-19, air pollution rose sharply after these lockdowns were lifted. In many cases it got even worse, depending on the dominant mode of transport in different countries.

For example, many people keen to social distance in cities around the world have avoided using public transport, instead swapping their train and tram journeys for more polluting private car journeys.

Even the trips avoided by employees who were able to switch to working from home were often offset by increased home deliveries or non-working leisure trips.

In an effort to return to normal business as soon as possible after the pandemic, governments like the US have issued stimulus payments to their citizens and encouraged workplaces to reopen to “get back to normal”.

But this return to normal missed a significant opportunity to record the pollution reduction achieved and to increase the associated community and public health benefits.

Every year, an estimated 4.2 million people die prematurely from exposure to pollutants such as particulate matter (PM2.5). These are respirable particles, so small that they cannot be seen by the naked eye, that are released when fossil fuels are burned.

Animated map of global NO2 anomalies throughout 2020. Blue indicates reductions above normal expected levels (i.e. if the pandemic had not occurred), while red indicates elevated pollution levels above this baseline. Photo credit: Dr. Kerry Nice

Another estimated 250,000 people die prematurely from ozone exposure (O3), formed when pollutants emitted by cars and power plants react in the presence of sunlight.

Given the urgency of environmental health issues, our new study, published in air pollution research highlights the impact of pandemic restrictions – and reduced human mobility more broadly – on air pollution.

While previous studies presented case studies on pandemic air quality in a range of countries or a selection of cities, this study analyzed air pollution data from a collection of over 700 cities (all cities for which this data was available) around the world.

Using data on past weather patterns and pollution levels, we’ve taught machine learning models – which are programs that can find patterns or make decisions from previously invisible data – to predict what pollution levels would be in each individual city if it weren’t for the pandemic would have occurred.

Using this comprehensive sample of cities, our machine learning-based analysis highlights what could be achieved in each city – and globally – by changing traffic patterns during the lockdown.

Our study showed that cities in China, Europe, and India experience sharp declines in nitrogen dioxide (NO2) and PM2.5— two pollutants highly associated with fossil fuel burning and car use — that conform to severe pandemic levels, including mobility restrictions.

As the graphics show, NO2 levels (and to a lesser extent PM2.5 levels) fell around February/March 2020. In comparison, NO2 Values ​​in Italy only changed in March or April of this year.

ozone (or3) increased in the first half of 2020, with atmospheric chemical reactions that produce ozone being driven by the reduction of NO2. However, levels dipped below normal levels during the northern hemisphere summer months when O3 Levels usually peak.

Countries like China and India enjoyed the greatest reductions in ambient particulate matter. This is especially important as these two countries face some of the most serious health consequences of air pollution – together they are responsible for more than half of the world’s fine particulate matter2.5 Exposure-related deaths.

The pandemic has provided a natural experiment in understanding the relationship between modes of transport and air pollution. To fulfill some of the promises we’ve seen during the pandemic’s rapid decline in pollution, cities could aim to transform mobility through active and pollution-free transport.

Mobility changes in 2020 have given us an opportunity to examine how our use of transport systems contributes to pollution.

For example, New York City and Tokyo saw a corresponding drop in pollution when mobility ground to a halt in all modes of transport during the first wave of COVID.

However, upon opening up after the first lockdown, New York City’s mobility returned largely through travel by private motor vehicles — well beyond previous baselines, with public transit levels never returning to normal levels. Meanwhile, in Tokyo, both public transit use and car travel recovered at a more even rate.

Cities like Brussels, Rome and Paris have created a total of 250 kilometers of new bike lanes as part of post-pandemic transport plans. Australian cities have yet to do the same – there is certainly no shortage of demand for cycling infrastructure.

Post-pandemic, weekly cycle traffic on cycle lanes increased 140 percent on South Perth Foreshore, 165 percent on Adelaide’s Outer Harbor Greenway and a whopping 169 percent on Brighton’s Bay Trail in Victoria.

Creating bike lanes and providing other modes of transportation, such as ride-sharing, gives cities the opportunity to reduce emissions. People who can work from home should do so, which completely eliminates the need for the daily commute to work.

If governments are to protect their populations from pollution-related disease and death, they must create alternative transportation systems that do not focus on private car travel.

Only then will our “new normal” allow us to enjoy clear skies and longer lives.

Avoid the traffic jam left behind by the pandemic

More information:
Jasper S. Wijnands et al, The Impact of the COVID-19 Pandemic on Air Pollution: A Global Assessment Using Machine Learning Techniques, air pollution research (2022). DOI: 10.1016/j.apr.2022.101438

Provided by the University of Melbourne

Citation: How global COVID-19 pandemic restrictions shed light on the relationship between transport and air pollution (2022, August 10), retrieved August 10, 2022 from https://phys.org/news/2022-08-global-covid- pandemic-restrictions -relationship.html

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