The publicʼs concern on ambient PM10 has increased sharply since 2013. To check whether the concern is related the PM10 concentration, the trends of (1) the annual mean PM10 concentration, (2) the frequency by the PM10 concentration interval, and (3) the high concentration occurrence duration time are studied. It is found that all three indicators have decreased between 2001 and 2017. For example, the annual mean PM10 concentration decreased from 71 μg/m³ in 2001 to 44 μg/m³ in 2017 in Seoul. Generally, the frequency of the PM10 concentration over 50 μg/m³ has decreased while that less than 20 μg/m³ has changed little. Thus, the frequency between 20 and 50 μg/m³ has increased. However, different trends in the PM10 concentration, frequency by concentration level and frequency over 50 μg/m³ for duration are observed among the administrative districts. To reduce the annual average concentration of PM10, there should be more measures to reduce the frequency of PM10 concentration between 20 and 50 μg/m³ as well as over 50 μg/m³ for increasing the frequency of low PM10 below 20 μg/m³.