Authorities in Beijing issued their highest-level smog warning in the city on Sunday. Authorities declared the orange level alert in the city, the second-highest possible category in the weather warning system.

When atmospheric particulate matter levels exceeded the safety level considered safe by the Word Health Organization (WHO), residents were advised to limit outdoor activities, while people with respiratory conditions and the elderly were told to stay indoors.

The US embassy in Beijing reported that PM2.5 (refers to particles with diameters of 2.5 microns or smaller) levels exceeded 400 microgrammes per cubic metre on Sunday. WHO asserts that only 25 microgrammes per cubic metre is considered safe.

The smog is caused by coal-powered industries, heating systems and the dust from building sites and worsened by humidity and a lack of wind, according to BBC. Authorities did not allow the transport of construction sites’ wastes or building materials, and heavy-duty trucks were banned from using the roads.

Cities in the northeast part of China have the worst air quality. Apparently, the Chinese government is attempting to reduce pollution, but the country's heavy reliance on coal has resulted in China becoming the world’s largest producer of greenhouse gases.

In other parts of the world, thousands have gathered in rallies to call for immediate action on climate change ahead of the climate conference in Paris. However, Channel NewsAsia reports that similar protests did not happen in the country where the Communist party does not tolerate organised political opposition.

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