Air Pollution Has Fallen Significantly in Nine Major Global Cities, Report Finds

As the COVID-19 pandemic rages, with ongoing lockdown measures affecting millions of people around the globe, levels of air pollution are falling dramatically in many parts of the world. This trend has been highlighted by a new report published by Swiss company IQAir looking at ten key global cities that normally suffer from high levels of pollution: Los Angeles, New York City, London, Madrid, New Delhi, Mumbai, São Paulo, Wuhan, Seoul and Rome. The report compared measurements from ground-based monitoring stations regarding a type of pollutant known as PM2.5—tiny inhalable particles measuring 2.5 micrometers or smaller that are emitted by various sources such as vehicles and power plants. It found significant falls in nearly all the locations listed.

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This is, perhaps, not surprising given the large decreases in vehicle traffic and industrial activity that have occurred with lockdown measures imposed on these cities. The report examined data collected over a three-week period for each city while they were under lockdown conditions. IQAir then compared these measurements to the same time period for the years between 2016 and 2019. The time period was kept the same for every city across the years so that an accurate comparison could be made, given that air pollution levels often vary with seasonal changes in weather, as well as other factors. IQAir found that nine out of the ten cities in the report experienced significant reductions in PM2.5 compared to the same period for 2019. Those with historically higher levels of PM2.5 pollution saw the most substantial drops including New Delhi (-60 percent,) Seoul (-54 percent) and Wuhan (-44 percent.) Nevertheless, seven of the cities saw reductions in PM2.5 of 25 to 60 percent compared to the same period last year. The number of days rated as "unhealthy" in Delhi—the world's most polluted city according to IQAir's 2019 annual report—during the three-week lockdown period fell from 68 percent in 2019 to 17 percent during the study period. The Indian government introduced a national lockdown—the world's largest, affecting 1.3 billion people—on March 25. In normal times, the country is one of the most polluted in the world, with an average resident exposed to levels of PM2.5 that exceeds the World Health Organization's (WHO) annual target by more than 500 percent, according to the report. But this year, both New Delhi and Mumbai experienced their best March on record with regards to PM2.5 levels, the authors say. The situation is similar in Wuhan—where the COVID-19 pandemic was first identified—which experienced is cleanest air on record for February and March. The city was placed under one of the strictest lockdowns in the world on January 24, which was only lifted after 10 weeks. And in the United States, Los Angeles—a city reliant on cars for transport and notorious for its air pollution—experienced its longest amount of time in meeting WHO air quality targets during the three-week lockdown study period (March 7-28,) with PM2.5 levels down 31 percent from last year, and 51 percent from the average of the previous four years, according to the report. In this period, 90 percent of hours were below the WHO PM2.5 target. A similar pattern can be seen with European cities, with both London and Madrid experiencing reductions of PM2.5 of 9 and 11 percent respectively in their three-week lockdown periods. However, Rome was an outlier in the study, witnessing a 30 percent increase in particle pollution compared to 2019. While it is not clear why this is the case, the authors of the report speculate that domestic heating systems could be a factor.

"Domestic heating is a significant source of air pollution in Rome from November 1 to April 15," the authors wrote. "Increased reliance on residential heating systems, coupled with cool air inversions that trap particulate pollution in the atmosphere, may explain PM2.5 gains in the city as compared to 2019." Because weather conditions and geographical location can play a big role in air quality measurements, the report notes that the collection of more data during these lockdown periods will help provide a clearer picture of how PM2.5 levels compare to previous years. Nevertheless, the picture emerging across the globe during the coronavirus pandemic is that many areas are experiencing dramatic falls in air pollution. Unfortunately though, these drastic improvements in air quality have coincided with significant economic disruption, suffering and loss of life across the globe. Furthermore, experts warn that without sustained action to curb pollution once the crisis subsides, levels will likely rebound, as has been witnessed following previous economic downturns.