Last year, the U.S. West suffered wildfires that charred millions of acres, left dozens of people dead and ravaged air quality from Los Angeles to Seattle.

The devastating wildfires that torched a record 4.3 million acres in the U.S. in 2020 made North America the only region in the world where air quality was worse than during the previous year. 

Most of the world’s major cities had better air last year than in 2019, mainly thanks to coronavirus lockdowns that cleared skies for weeks or months, according to the annual report by air quality platform IQAir. Though Indias New Delhi was the most-polluted capital city, its pollution levels nevertheless fell 16% from the previous year. 

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Los Angeles, Melbourne and Sao Paulo, all of which were close to major wildfires in 2020, were among the few where pollution was worse than in 2019.

In the U.S., 38% of cities had levels of fine particulate matter, known as PM2.5, that exceeded World Health Organization quality standards in 2020, up from 21% the previous year. Skies in the western coast were so choked with wildfire smoke during September that 77 of the worlds 100 most polluted cities that month were in the U.S. 

Clean Air

Air pollution fell in most major cities in 2020 due to lockdowns

Source: 2020 World Air Quality Report

Note: De-weathered changes in annual PM2.5 calculated by the Centre for Research on Energy and Clean Air (CREA) by isolating pollution from weather factors

High exposure to PM2.5, which is emitted by fossil-fuel powered vehicles, industrial activity and biomass burning, can cause asthma, lung cancer, heart disease, and has been associated with low birth weight, acute respiratory infections and strokes, IQAir said.

An increasing amount of studies are also linking worsening air pollution to increased vulnerability to Covid-19, which attacks respiratory and cardiovascular systems. Coronavirus deaths attributable to long-term air pollution exposure could represent between 7% and 33% of all fatalities due to the virus, according to an

early study published in Cardiovascular Research and cited by IQAir.

The same fumes also contain greenhouse gases that are warming the planet and in turn are making wildfires more frequent and intense.  

Satellite data show the monthly average nitrogen dioxide concentrations over China in February 2019, February 2020 and February 2021.

IQAirs analysis suggests that as cities tightened lockdowns last year, pollution tended to improve, and these gains were lost when movement restrictions eased. This indicates 2020s improvements will prove fleeting without significant changes to the energy mix and to human behavior.

Chinese cities regularly rank as some of the most polluted, but last year 86% of them had cleaner air. Pollution levels are returning to pre-pandemic levels, according to satellite data published Monday by the European Space Agency.

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