SHANGHAI--Chinese air pollution rose in April for the first time since December, official data showed on Monday, with analysts attributing the rebound to the resumption of economic activity following the coronavirus outbreak.

The Ministry of Ecology and Environment (MEE) said concentrations of hazardous airborne particles known as PM2.5 rose 3.1 percent in April to an average of 33 micrograms per cubic meter in 337 cities across the country, the first year-on-year increase since December when PM2.5 rose by 10 percent.

Concentrations of ground-level ozone, sulfur dioxide and nitrogen dioxide also rose over the month, the official data showed.

The worst performing cities in April were Changchun, Harbin and Shenyang, the capitals of the three northeastern provinces, the data showed.

In contrast, in the smog-prone region of Beijing-Tianjin-Hebei PM2.5 fell by a quarter to 39 micrograms in April, even though factories had reopened. PM2.5 dropped by 35.4 percent in that region the first four months of the year, the data showed.

Liu Bingjiang, an official in charge of air pollution at the MEE, said last week that the resumption of industrial activity could cause pollution to rise by a certain amount but it wasn’t the primary cause of a spike in April.

He said straw burning in the three northeastern provinces of Jilin, Heilongjiang and Liaoning had increased by eight times compared with the same period of last year, and sandstorms had also caused air quality to deteriorate in some regions.

Average PM2.5 fell 12.5 percent in the 337 cities over the first four months, with lockdowns, factory closures and transport restrictions leading to a steep decline in emissions, mostly in February and March.

“Air pollutant levels plummeted during the national lockdown in February, bottomed out in early March and have now overshot their pre-crisis levels,” the Helsinki-based Center for Research on Energy and Clean Air (CREA) said in a report published on Monday.

“Rebounding air pollutant levels are a demonstration of the importance of prioritizing green economy and clean energy in the recovery from the COVID-19 crisis,” it added.

Now that the economy has reopened there is a risk that China, by aiming for a fast economic rebound, will further damage the environment, CREA said.

“Due to emphasis on GDP targets and on construction and manufacturing projects to hit those targets, China’s recoveries have tended to be ‘dirty,’ with negative economic shocks followed by surges in fossil fuel consumption, air pollution and CO2 emissions,” it said.

The most obvious recent example was a 2008 stimulus package that ushered in an unprecedented wave of construction projects and record levels of coal, cement and steel consumption, CREA said.