Beijing’s environmental watchdog has vowed to further improve air quality in the capital this year.

The city will strive to decrease its annual PM2.5 concentration, as well as its average three-year density of airborne particles, by focusing efforts on three major pollution culprits — diesel-powered trucks, kicked-up dust and volatile organic compounds — the Beijing Ecological Environment Bureau said on Feb 19.

It said greater efforts will be made to improve air quality through better, more detailed management of pollution sources in what it’s calling the 1 Microgram Campaign, which underscores the increasing difficulty of reducing PM2.5 density by even a single microgram.

The three-year average metric was introduced to help reduce the skewing of data due to meteorological conditions and show how the public’s efforts contribute to overall improvements, the bureau said.

The plan was announced as Beijing saw its PM2.5 density drop by about 12 percent year-on-year to 51 micrograms per cubic meter last year－5 mcg/cu m lower than the target set in the 13th Five-Year Plan (2016-20). In January, however, the density increased almost 53 percent year-on-year to 52 mcg/cu m. The authorities have yet to explain the increase.

To move the 1 Microgram Campaign forward, Beijing authorities will speed up restrictions on diesel-powered trucks and eventually phase out obsolete ones. An online monitoring system for heavy-duty trucks will be accelerated, under the plan, which also said that all construction sites will be equipped with video monitoring systems to help the city control airborne dust.

Mobile sources contributed 45 percent of locally generated PM2.5 in Beijing, with diesel trucks the top culprit. Kicked-up dust came in second at 16 percent, according to the bureau’s analysis of pollution sources in 2018.

Officials have stressed that it will be increasingly difficult for Beijing to further improve its air quality, especially since the capital has already rolled out all major measures capable of achieving quick results. This includes, for example, the shift from coal to clean energy for heating.

Liu Bingjiang, head of air quality management at the Ministry of Ecology and Environment, told a news conference last month that “it will be the biggest victory for Beijing if it could safeguard the PM2.5 density of 51 mcg/cu m” this year.

He also warned of the possibility that the density will increase if unfavorable meteorological conditions are in play.

The ministry said average PM2.5 density from October to January in the 28 major cities in the Beijing-Tianjin-Hebei province cluster increased by 6.7 percent year-on-year to 80 mcg/cu m. Despite the increase in January, the PM2.5 concentration in Beijing during the period was still the lowest in the cluster.

It added that, compared with last year, meteorological conditions in the cluster will be less favorable for pollutant dispersal this month and in March, though conditions are close to the 10-year average.

Moderate to heavy air pollution will settle into the cluster and the Fenhe and Weihe plains, mostly in Shanxi and Shaanxi provinces, from Feb 20 to Feb 24 because of unfavorable meteorological conditions, the setting off fireworks for Lantern Festival on Feb 19, and resumption of industrial activities after the Spring Festival holiday break, it said.