Unfavorable meteorological conditions and a surge in emissions led to a decline in air quality in China in the first half of this year, said Huang Runqiu, minister of ecology and environment.

China experienced upticks in the concentration of most major air pollutants from January to June, compared with the same period last year.

The average density of PM2.5 particulate matter was 34 micrograms per cubic meter, up by 6.2 percent.

The concentration of ozone and nitrogen dioxide rose by 1.4 percent and 4.8 percent, respectively.

The increases have brought down the proportion of days with fairly good air quality — below 100 on a 0-500 air quality index scale — by 3.2 percentage points year-on-year.

Due to COVID-19 preventative measures and restrictions, China saw marked decreases in emissions of air pollutants over the past three years. The average concentration of PM2.5 dropped to 32 micrograms per cubic meter in 2022, an eight-year low, Huang said on Thursday.

As economic activities gradually recover, however, emissions have gone up as the outputs from high energy-consuming industries have increased from last year's levels, he said.

The minister also noted frequent sandy and dusty weather events and scorching heat waves as major contributors to the rise of air pollutants.

The country experienced 37 sandy and dusty weather events in the first half of this year, he said. Of them, 15 were classified as large-scale ones, outpacing similar periods in the past 15 years.

Air pollutants brought by all of the events resulted in a loss of 5.4 percentage points in the proportion of days with fairly good air quality, he said.

In June, North China experienced 5.2 more days with temperatures at or above 35 C, leading to a surge in the number of days with excessive ozone density, he said.

Sunlight and high temperatures can trigger chemical reactions between volatile organic compounds and nitrogen oxides that lead to the formation of ozone. Vehicle exhaust, for example, is one of the major contributors to the substances.

"Generally, the country's air quality tends to show a trend of significant improvement," Huang said.

Compared with the same period before the outbreak of the COVID-19 pandemic in 2019, the country's average density of PM2.5 in the first half of this year dropped by 15 percent, and the proportion of days with fairly good air quality increased by 1.3 percentage points, he noted.

The minister vowed a series of measures to beef up air pollution control.

The country will unswervingly crack down on the development of smokestack industries with high energy consumption and emissions, he said, as it makes all-out efforts to promote the development of new and renewable energies.

Intensified efforts will also be made to develop a green and low-carbon transportation system, and more bulk cargo will be transported by railway and waterway, he said.