The conditions (for forming ozone) are different across the country because different regions have different economic and industrial structures and pollution levels, so they need targeted measures.”

Zhao Yingmin, vice-minister of environmental protection

“We have noticed the climbing level of ozone in many regions and have taken strict control measures, but it will take time to reduce it effectively,” said Zhao Yingmin, vice-minister of environmental protection, at a February media briefing in Beijing.

Ground-level ozone only forms when its precursors — mainly nitrogen oxides and volatile organic compounds that are easily transformed intogasesorvapors—reactin the presence of strong sunlight, Zhao said, citing the ministry’s research data.

He pointed out that while many countries have solved the problem of PM2.5, they, like China, are also struggling to contain rising concentrations of ground-level ozone.

The ministry has issued regulations to reduce emissions of precursors by levying extra charges on 14 industries, such as petroleum-refining, that discharge volatile organic compounds in pilot regions such as Beijing.

Last year, the State Council, China’s cabinet, ordered governments at all levels to target nitrogen oxides, one of the main precursors, and ensure that by 2020 the level is 15 percent lower than in 2015. The move has already resulted in a reduction in emissions, according to Zhao.

Ministry data show that Contact the writer at zhengjinran@chinadaily.com.cn