BEIJING: Environmental authorities in Beijing say the Chinese capital's air quality in 2015 was better than the year before despite the city's first two red alerts for air pollution late in the year.

China has been setting national and local targets to reduce its notorious air pollution as citizens have become increasingly aware of the health dangers. Beijing's municipal government has been replacing coal-fired boilers with natural gas-powered facilities, forcing older, more polluting vehicles off the road, and closing or moving factories that are heavy polluters.

The city's average concentration of PM2.5 — small, inhalable particles that can penetrate deep into the lungs and are considered a reliable gauge of air quality — was 81 microgrammes per cubic metre in 2015. That was a drop of 6 percent from 2014, and 10 percent lower than 2013, when Beijing started publishing data on PM2.5.

The "number of days of most serious PM2.5 pollution is falling each year," Beijing's municipal environmental protection bureau said Monday.

It was, however, still more than twice China's own standard of 35 microgrammes per cubic metre, and seven times higher than an annual mean of 10 that the World Health Organisation gives as its guideline for safe air.

Other pollutants also fell, including sulfur dioxide by 38 percent and nitrogen dioxide by 12 percent. The environmental protection bureau attributed the lowering of sulfur dioxide to the phasing out of coal-fired heating systems.

Beijing's air gets especially bad in the winter, when the burning of coal in northern China increases and weather patterns add to the smog.

Beijing issued its first two red alerts in December under a four-tier warning system that has been in place for two years. The city had earlier experienced more hazardous levels of pollution and come in for criticism for not issuing a red alert sooner, but authorities said at least three consecutive days of smog at particular levels on the city's air quality index must be forecast before issuing the highest alert.

The red alerts meant half the city's vehicles were ordered off the roads on a given day, factory production was restricted and schools were closed.

Beijing sits in one of China's most heavily polluted regions. Its main sources of pollution are vehicles, coal-burning, industry and dust from construction sites.

The capital aims to eliminate coal use in its six downtown districts and close all coal-fired boilers throughout the city by 2020.