China has experienced vast declines in the density of some major air pollutants in the first half of this year as its overall environment continues to improve, an environmental official said.

"As monitoring of air and surface water shows, the country saw its environmental and ecological quality continue to improve from January to June," Liu Youbin, spokesman of the Ministry of Ecology and Environment, said at a news conference on Tuesday.

During that time, the average density of PM2.5 particulate matter in the 337 major cities across the country decreased by 10 percent year-on-year to 36 micrograms per cubic meter. Following a year-on-year decrease of 16.7 percent, the average density of sulfur dioxide in the first six months of the year stood at 10 mcg per cubic m, he said.

However, he said ozone has been the top air pollutant in some cities, especially in summer. With a drop of 1.4 percent, the average density of the pollutant in the first half was 141 mcg per cubic m.

While the ozone layer helps shield the Earth from harmful ultraviolet radiation, the gas is harmful to people's health and could damage the lungs and result in shortness of breath even if people breathe in a relatively low amount.

In June, the ministry rolled out a campaign on control of volatile organic compounds, a major contributor to ozone pollution. While 168 work teams have arrived in 58 key cities to facilitate local governments in zone pollution control, the ministry is preparing to send another 227 teams to 78 cities, he said.

Ma Jun, director of the Institute of Public and Environmental Affairs, an NGO, said air quality across the country in the first half of the year improved because of both the impact of COVID-19 on production activity and favorable meteorological conditions.

As the country's economy recovers from the impact of COVID-19, more precipitation than average, especially in southern parts of the country, has helped disperse air pollutants, he said.

Marked progress has also been made in water pollution control in the first six months, according to the ministry.

Nationwide, the share of surface water with a good quality rating－Grade III or above in the country's five-tier water quality system－reached 80.1 percent, up by 5.6 percentage points year-on-year, while 1.1 percent was rated below Grade V, the poorest quality, down by 3.2 percentage points.