Since the lockdowns in response to the COVID-19 pandemic began, the level of two major air pollutants has decreased dramatically, but new research has shown that secondary ground level ozone pollutants have increased in China.

Two new studies in AGU’s Geophysical Research Letters show that nitrogen pollution in northern China, Western Europe and the United States fell by almost 60 percent in early 2020 compared to the same period last year.

Nitrogen dioxide is a very reactive gas that is produced during combustion and has many harmful effects on the lungs.

Gas usually enters the atmosphere through emissions from vehicles, power plants and industrial activities.

In addition to nitrogen dioxide, a new study found that particle pollution (particles smaller than 2.5 microns) in northern China was reduced by 35 percent. Particles consist of solid particles and liquid droplets that are small enough to penetrate deep into the lungs and cause damage.

The only other comparable event is the reduction of short-term emissions in China due to strict regulations at events such as the 2008 Beijing Olympics.

Improved air quality tends to be temporary, but the results give scientists an idea of ​​what future air quality would be like if emissions regulations were tightened, the researchers said.

“Maybe this unexpected experiment can be used to better understand emissions regulations,” Stavrakou said. “This is positive news in a very tragic situation.”

However, according to a new study, the reduction in nitrogen pollution has caused an increase in surface ozone in China.

Ozone is a secondary pollutant that appears when sunlight and high temperatures catalyze chemical reactions in the lower atmosphere.

Ozone is dangerous to humans on earth and causes lung and heart disease.

In highly polluted areas, especially in winter, surface ozone can be broken down by nitrogen oxides, so ozone levels can rise if nitrogen pollution is reduced.

“This means that only reducing [nitrogen dioxide] and particles does not solve the ozone problem,” Brasseur said.

They found that nitrogen pollution during the blockade in 2020 decreased by an average of 40 percent compared to Chinese cities and 20 to 38 percent in Western Europe and the United States compared with the same time in 2019.

However, this study found that nitrogen pollution was not reduced compared to Iran, one of the earliest and most affected countries. The authors suspect that this is due to the fact that there was no complete blockade at the end of March and that orders to stay at home were largely ignored.