Change in pollution

levels from 2019-2020

Cleaner air

More polluted

-50

-10

10

50

100

329%

-85%

Portland

San

Francisco

Akron

Salt Lake City

Washington

Los Angeles

Change in pollution

levels from 2019-2020

Cleaner air

More polluted

-50

-10

10

50

100

329%

-85%

Portland

San

Francisco

Akron

Salt Lake City

Washington

Los Angeles

Change in pollution

levels from 2019-2020

Cleaner air

More polluted

-50

-10

10

50

100

329%

-85%

Seattle

Portland

Boston

Minneapolis

Salt Lake City

Chicago

Akron

San Francisco

Denver

Washington

Yosemite Lakes

Los Angeles

Charlotte

Phoenix

Houston

Honolulu

Miami

Anchorage

Change in pollution

levels from 2019-2020

Cleaner air

More polluted

-50

-10

10

50

100

329%

-85%

Seattle

Portland

Boston

Minneapolis

Salt Lake City

Chicago

Akron

San Francisco

Denver

Washington

Yosemite Lakes

Los Angeles

Charlotte

Phoenix

Houston

Honolulu

Anchorage

Miami

Change in pollution

levels from 2019-2020

Cleaner air

More polluted

-50

-10

10

50

100

329%

-85%

Seattle

Portland

Boston

Minneapolis

Salt Lake City

Chicago

Akron

San Francisco

Denver

Washington

Yosemite Lakes

Los Angeles

Charlotte

Phoenix

Houston

Honolulu

Anchorage

Miami

Wildfires that charred millions of acres in the West wiped out the country’s pandemic-related clean air gains in 2020, according to a report released this week.

Because pandemic restrictions limited travel and other activities, fine-particle pollution from the burning of fossil fuels dropped 13 percent between March and July compared to the previous year and dipped again in November and December, said Lauri Myllyvirta, lead analyst at the Centre for Research on Energy and Clean Air, who collaborated on IQAir’s annual World Air Quality Report.

But the 2020 historic wildfire season more than made up the difference. Overall, the U.S. average for the deadliest type of air pollution rose nearly 7 percent over 2019 because of smoke from fall fires, primarily those in California, Oregon and Washington.

Fine-particle pollution refers to bits that are 2.5 microns in diameter or smaller, or less than one-20th the diameter of a human hair. These particles are tiny enough to penetrate deep into lungs and enter the bloodstream, where they can trigger asthma attacks and other lung and heart problems and may cause cancer.

While no fine-particle pollution is considered to be safe, the World Health Organization’s about target is 10 parts per cubic meter or less. In 2020, the U.S. average was 9.6, and thirty-eight percent of U.S. cities exceeded the target level compared to 21 percent in 2019.

The country’s worst annual average was in Yosemite Lakes, Calif., 37.8 micrograms per cubic meter. The highest U.S. reading was 4,709.3 during heavy smoke in Weed, Calif., on Sept. 13.

In September, 24 of the world’s top 25 most polluted cities were in California and Oregon, the report said. Leading the list was Happy Camp, Calif., with a monthly average of 154.4 micrograms per cubic meter. The city with the lowest fine pollution levels recorded was Waimea, Hawaii, with 2.2.

On Sept. 13, Portland saw PM2.5 levels 10 times higher than the limit recommended by the World Health Organization

Portland, Ore:.

15 days above WHO guidelines

for fine particulate matter

200 μg/m3

fine particulate matter

(PM2.5),

daily average

100

30-day rolling average

Daily guidelines for

fine particulate exposure

25

0

Jan.

2021

Jan.

2020

July

Los Angeles: 48 days

100 μg/m3

50

25

0

Jan.

2021

Jan.

2020

July

San Francisco: 24 days

100 μg/m3

50

25

0

July

Jan.

2021

Jan.

2020

Seattle: 12 days

100 μg/m3

50

25

0

Jan.

2021

July

Jan.

2020

Washington, D.C.: 4 days

100 μg/m3

50

25

0

Jan.

2021

Jan.

2020

July

Boston: 2 days

100 μg/m3

50

25

0

Jan.

2021

Jan.

2020

July

Phoenix: 2 days

100 μg/m3

50

25

0

July

Jan.

2021

Jan.

2020

On Sept. 13, Portland saw PM2.5 levels 10 times higher than the limit recommended by the World Health Organization

Portland, Ore:.

15 days above WHO guidelines

for fine particulate matter

200 μg/m3

fine particulate matter

(PM2.5),

daily average

100

30-day rolling average

Daily guidelines for

fine particulate exposure

25

0

July

Jan.

2021

Jan.

2020

Los Angeles: 48 days

100 μg/m3

50

25

0

Jan.

2021

Jan.

2020

July

San Francisco: 24 days

100 μg/m3

50

25

0

Jan.

2021

July

Jan.

2020

Seattle: 12 days

100 μg/m3

50

25

0

Jan.

2021

July

Jan.

2020

Washington, D.C.: 4 days

100 μg/m3

50

25

0

Jan.

2021

Jan.

2020

July

Boston: 2 days

100 μg/m3

50

25

0

Jan.

2020

July

Jan.

2021

Phoenix: 2 days

100 μg/m3

50

25

0

Jan.

2021

July

Jan.

2020

Portland, Ore:.

15 days above WHO guidelines

for fine particulate matter

On Sept. 13, Portland

saw PM2.5 levels 10 times higher than the limit recommended by the World Health

Organization

200 μg/m3 fine particulate matter

(PM2.5), daily average

100

30-day rolling average

Daily guidelines for fine particulate exposure

25

0

Feb.

March

May

June

July

Aug.

Sept.

Oct.

Nov.

Dec.

Jan.

2021

April

Jan.

2020

Los Angeles: 48 days

San Francisco: 24 days

100 μg/m3

50

25

0

Jan.

2021

Jan.

2021

Jan.

2020

July

July

Jan.

2020

Seattle: 12 days

Washington, D.C.: 4 days

100 μg/m3

50

25

0

Jan.

2020

July

Jan.

2021

Jan.

2021

July

Jan.

2020

Boston: 2 days

Phoenix: 2 days

100 μg/m3

50

25

0

July

Jan.

2021

July

Jan.

2021

Jan.

2020

Jan.

2020

Portland, Ore:.

15 days above WHO guidelines

for fine particulate matter

On Sept. 13, Portland

saw PM2.5 levels 10 times higher than the limit recommended by the World Health Organization

200 μg/m3 fine particulate matter

(PM2.5), daily average

100

30-day rolling average

Daily guidelines for fine particulate exposure

25

0

Feb.

March

May

June

July

Aug.

Sept.

Oct.

Nov.

Dec.

Jan.

April

Jan. 2020

Los Angeles: 48 days

San Francisco: 24 days

100 μg/m3

50

25

0

Jan. 2021

Jan. 2021

July

July

Jan. 2020

Jan. 2020

Seattle: 12 days

Washington, D.C.: 4 days

100 μg/m3

50

25

0

Jan. 2021

Jan. 2021

July

July

Jan. 2020

Jan. 2020

Boston: 2 days

Phoenix: 2 days

100 μg/m3

50

25

0

Jan. 2021

Jan. 2021

July

July

Jan. 2020

Jan. 2020

Portland, Ore:.

15 days above WHO guidelines

for fine particulate matter

On Sept. 13, Portland saw PM2.5 levels 10 times higher than the limit recommended by the World Health Organization

200 μg/m3 fine particulate matter (PM2.5), daily average

100

30-day rolling average

Daily guidelines for fine particulate exposure

25

0

Jan. 2020

Feb.

March

April

May

June

July

Aug.

Sept.

Oct.

Nov.

Dec.

Jan. 2021

Los Angeles: 48 days

San Francisco: 24 days

Seattle: 12 days

100 μg/m3

50

25

0

July

Jan. 2021

Jan. 2020

July

Jan. 2021

July

Jan. 2021

Jan. 2020

Jan. 2020

Washington, D.C.: 4 days

Boston: 2 days

Phoenix: 2 days

100 μg/m3

50

25

0

Jan. 2021

Jan. 2021

Jan. 2021

Jan. 2020

July

Jan. 2020

July

Jan. 2020

July

Worldwide, fine-particle pollution dropped in 84 percent of countries and 65 percent of cities included in the analysis. The company measured air quality at ground-based monitoring stations in 106 countries. About half of all European cities still missed the WHO target.

The country with the worst air quality was Bangladesh, with an annual average of 77.1 micrograms per cubic meter. All but one of the world’s 50 most polluted cities are in Bangladesh, China, India and Pakistan.

WHO annual air quality guideline

120 μg/m3

Cities with more air pollution in 2020 than 2019

Higher PM2.5

in 2020

80

Delhi, India

Yosemite

Lakes

40

Cities with cleaner air in 2020

Beijing

Los Angeles

10

U.S. cities

Higher PM2.5 in 2019

0

0

10

40

80

120 μg/m3

WHO annual air quality guideline

120 μg/m3

Cities with more air pollution in 2020 than 2019

Higher PM2.5

in 2020

Delhi, India

80

Dhaka, Bangladesh

Karachi, Pakistan

Yosemite

Lakes

40

Beijing

Cities with cleaner air in 2020

Los Angeles

10

U.S. cities

Higher PM2.5 in 2019

0

0

10

40

80

120 μg/m3

WHO annual air quality guideline

120 μg/m3

Higher PM2.5

in

2020

Cities with more air pollution in 2020 than 2019

Delhi, India

80

Dhaka, Bangladesh

Karachi, Pakistan

40

Yosemite Lakes

Beijing

Cities with cleaner air in 2020

Los Angeles

10

U.S. cities

Higher PM2.5 in 2019

0

0

10

40

80

120 μg/m3

WHO annual air quality guideline

120 μg/m3

Moradabad, India

Hotan, China

Higher PM2.5 in 2020

Cities with more air pollution in 2020 than 2019

Kanpur, India

Delhi, India

80

Dhaka, Bangladesh

Gujranwala, Pakistan

Karachi, Pakistan

40

Yosemite Lakes

Beijing

Peshawar, Pakistan

Cities with cleaner air in 2020

Los Angeles

10

U.S. cities

Higher PM2.5 in 2019

0

0

10

40

80

120 μg/m3

WHO annual air quality guideline

120 μg/m3

Moradabad, India

Hotan, China

Higher PM2.5 in 2020

Cities with more air pollution in 2020 than 2019

Kanpur, India

Delhi, India

80

Dhaka, Bangladesh

Gujranwala, Pakistan

Karachi, Pakistan

40

Yosemite Lakes

Beijing

Peshawar, Pakistan

Cities with cleaner air in 2020

Los Angeles

10

U.S. cities

Higher PM2.5 in 2019

0

0

10

40

80

120 μg/m3

Fire was not just a U.S. problem. Wildfires and agricultural fires significantly contributed to air pollution in Australia, Siberia, South America, Indonesia and Africa.

During a fire, the concentration of tiny pollution particles soars and increases the risk of acute respiratory problems such as asthma attacks.

“You might get up to a thousand [parts per million] in some of these places that are just downwind of a really bad fire in California,” said Jeffrey Pierce, an associate professor at Colorado State University who studies the health effects of wildfire smoke. “But generally those only last for a few days or few weeks at most. What we don’t know is, if you get hit by really high concentrations, is it the same as if you just took that and averaged it over a long period of time?”

For example, perhaps one large fire raises the annual average in an area from 10 to 20 micrograms per cubic meter. Epidemiologists are trying to figure out whether that is more — or less — harmful to a person’s long-term health than year-round exposure to 20.

The working hypothesis is that they are the same, Pierce said.

Now that wildfires are becoming larger and more common while fossil-fuel emissions have trended downward in the United States for decades, a better question may be which type of pollution is more toxic. Unfortunately, new research from the Scripps Institution of Oceanography suggests that wildfire smoke may be significantly worse.