According to the Shenyang Environmental Protection Bureau, winter usage of coal by boiler stations for hydronic district heating is the source of 30 percent of the air pollution in Shenyang. Half of the 16 million metric tons of coal consumed by the city during the winter of 2013–2014 were used for heating. Other major factors include dust from construction sites (20 percent), vehicle exhaust (20 percent), industrial emissions (10 percent) and extraterritorial dust (20 percent, mostly yellow dust from Gobi Desert).