Iron ore prices have fallen worldwide after Chinese steel mills were ordered to halt production while the Asia-Pacific Economic Cooperation (APEC) conference is held in Beijing.The steep descent in iron ore prices back below $80 per tonne were apparently due to China's desire to clear the smog from the Beijing air, according to Bloomberg, as global leaders including Barack Obama, Shinzo Abe and Vladimir Putin descend on the city.Chinese officials reportedly "asked" steel mills and other factories in the surrounding Hebei province, China's largest steel-producing region, to suspend production in the lead-up to the APEC meeting that will be held in Beijing from 7 November to 12 November."Demand remains weak as Chinese buyers sit on the sidelines, with many Beijing steel mills forced to halt production leading up to the APEC meeting," ANZ said in a report.The aim is to prevent from the city from being choked by smog during the event."Steel mills in Hebei have been asked to suspend production due to APEC, which affects iron ore demand temporarily," Bloomberg Intelligence analysts said. "The mills will resume producing after the conference."