Recently, the summertime’s extremely high temperature phenomenon, caused by climate change, and urban heat islands have become a serious social problem. Urban areas have low albedo and huge thermal capacity, creating high temperatures and long-lasting characteristics. According to many studies, temperature increases in large cities is due to urban heat islands rather than global warming. We studied the distribution of air temperature using the high density urban climate observation network data of Daegu (2016-2018). From the distribution of monthly averaged air temperatures, we concluded that air temperatures at the center of Daegu were higher than in the suburbs. At the elementary school near the center of Daegu, the daily minimum air temperature is more than or equal to 25°C, and the daily maximum air temperature is more than or equal to 35°C. We also investigated the effects of urban heat islands on the deterioration of the city̓s air quality. It was concluded that the air pollution level in the city center increased because the suburban wind blew into the city overnight when the urban heat island’s intensity was strong, causing air pollution to be transported and stagnant.