Nitrogen dioxide (NO2), a substance that causes fine dust that is emitted through car or factory smoke, is found to increase the possibility of miscarriage of pregnant women as much as smoking itself. 

A team led by Matthew Fuller, a professor of emergency medicine at the University of Utah, announced in the international journal "Embiotic" on Monday that the correlation between the quality of air and the records of 1,300 women who visited the emergency room on their own in major cities, including Salt Lake City, Utah, between 2007 and 2015.

The researchers analyzed that the highest correlation with miscarriage was due to the concentration of nitrogen dioxide in the seven days before the inheritance. According to the research team, the risk of miscarbonation increased by 16 percent every time the concentration of nitrogen dioxide increased by 20μg (microgram, 1μg, equals one millionth of a gram). "This is similar to the effects of smoking on abortion for the first three months of pregnancy," Fuller said. 

Nitrogen oxides, such as nitrogen dioxide, are produced when part of the nitrogen in the atmosphere reacts with oxygen during hot combustion. Automobile exhaust is the main source of emissions. 

The study focused on short-term exposure effects of air pollutants and found that the concentration of fine dust itself had little to do with miscarriage. However, researchers explain that fine dust can also have a significant impact on the health of pregnant women and infants if they are exposed over the long term.

Utah's nitrogen dioxide levels are similar to those of London and Paris and much lower than that of Korea. According to the Ministry of Environment, Seoul has the highest annual average level of nitrogen dioxide in the country. As of 2016, Incheon came in second and Ulsan and Sejong came in third.