China’s major cities should reach their targets in reducing major air pollutants by 2017 as planned, experts said, though ozone poses a more stubborn problem.

Among the six major air pollutants listed in the Action Plan on Air Pollution Control and Prevention, the concentrations of five saw significant decreases in 2014 in 74 major cities, according to the Ministry of Environmental Protection.

For example, PM2.5, a fine particle that poses health hazards, saw a reduction of 11.1 percent per cubic meter in 2014, while the concentration of sulfur dioxide was reduced by 20 percent year-on-year.

Levels of nitrogen dioxide, carbon monoxide and PM10 also decreased.

However, a rising level of ozone may require the country to take more comprehensive measures, experts warned.

“It has become harder for governments to cut the emissions of airborne pollutants as more complicated problems pop up,” He Kebin, head of School of Environment at Tsinghua University, said on Nov 16.

Excessive ozone concentrations at ground level are generated mainly through complicated photochemical reactions. They have a close relationship with many other air pollutants, such as volatile organic compounds and nitrogen oxides, said He.

Average ground-level ozone levels－which can be harmful to health, unlike the protective layer of ozone in the upper atmosphere－increased by 4.3 percent in 2014, reaching 145 micrograms per cubic meter, Fu Lu, the China office director of Clean Air Asia, an international nongovernmental organization, said on Nov 16.

China plans to reduce the concentration of PM2.5 in Beijing to 60 micrograms per cubic meter by 2017, according to the municipal environmental watchdog, down from 89 micrograms per cubic meter in 2014.

The country has seen a great improvement in major air pollutant levels since the release of the action plan in June 2013, which marked the start of the national campaign against smog.

Governments will face tougher challenges in improving air quality, like the thorny problem of curbing ozone, and some cities will not see a large reduction in pollutants in 2015, He said.

Survey says tougher for northeast to clean its air

Northeastern China, where heavy haze lingered for days, faces a tougher situation in curbing air pollution due to greater pressure on economic growth and a lack of scientific guidance, a survey said on Nov 16.

Officials from the environmental protection bureaus in northeastern provinces have expressed their urgent need to receive support on air pollution control technology, said Wan Wei, a researcher from Clean Air Asia, a global NGO, which released a survey on air pollution control in China on Nov 16.

The survey found that many cities in eastern regions such as Shanghai had a clear picture on sources of pollution and drafted targeted control efforts. But provinces in the northeastern region have lagged behind in this respect.

Besides, the region, with heavy industry as its economic pillar, has faced slowing economic growth recently, giving policymakers greater pressure to maintain the pace of development and reluctant to restrict industrial output, which is a major way to reduce air pollution.

In the past week, cities in the region have seen heavy smog. Shenyang, for example, had PM2.5 readings surpassing 1,400 micrograms per cubic meter.