Mongolia is a landlocked country with a total land area of 1,564,116 square kilometers. The ambient annual average particulate matter (PM) concentration in Ulaanbaatar is 10-25 times greater than the Mongolian air quality standards (AQS). More than 40 percent of the nation's total population lives in Ulaanbaatar. The study aims at defining the relationship between the ambient air PM2.5 level and hospital admissions in Ulaanbaatar in 2011-2014. The pollution data included a 24-hour average PM2.5. The air was sampled daily and recorded by the national air monitoring stations located in Ulaanbaatar. The sampling frame of hospital admissions for cardiovascular disease (CVD) were the records of all outpatient hospitals of Ulaanbaatar. The data covered the period from January 2011 to January 2014. To test the differences of the results, appropriate statistical tests were employed. During 2011-2014, the highest concentration of PM2.5 was in the coldest period and the particulate matter level recorded was 3.7 times higher in the cold period than the warm period. The number of admissions for CVD were the highest during cold periods. Four days after exposure, the PM2.5 impact on hospital admissions weakened but there remained a positive correlation. For PM2.5, 100 μg/m 3 growth of the pollutant led to 0.65 % increase in the hospitalization for CVD on the exposure day. On the second day of exposure, 10 μg/m 3 growth of the pollutant led to 0.66 % increase; on the third day of exposure, 10 μg/m 3 growth of the pollutant led to 0.08 % increase of hospital admissions for CVD, and at the fourth day, such growth led to 0.6 % increase of CVD cases in 2011-2014 in Ulaanbaatar. In conclusion we may state that most incidences of CVD registered during the cold months in Ulaanbaatar in the last four years were a result of PM2.5 exposure. This shows that the PM2.5 exposure and hospital admissions for cardiovascular system chronic diseases are positively correlated. CVD in Ulaanbaatar residents was affected greater on the same and the third day of exposure.

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