Long-Term Variations and Relationships between Urban Heat Island and Air Pollutants in Seoul over the Past 20 Years

In this study, the long-term variations of urban heat island (UHI) and air pollutants were analyzed using air temperature and air quality data observed in urban and suburban areas of Seoul over the past 20 years (2001 similar to 2020). In addition, we investigated the relationships between UHI intensities and air pollutant concentrations during the study period. The UHI intensities, which were estimated using the mean and maximum temperature, showed a weak increasing trend (+0.006 and +0.067 degrees C yr(-1), respectively) during the study period. In contrast, the UHI intensity estimated using the minimum temperature showed a decreasing trend (-0.124 degrees C yr(-1)) because the increase in minimum temperature was larger in suburban areas than in urban areas. The UHI intensity showed a continuously decreasing pattern when wind speed increased from 0 m s(-1) to 4 m s(-1), but little change was observed when wind speed exceeded 4 m s(-1). Moreover, the long-term decreasing trend in primary air pollutants (e.g., CO, NO2, SO2, and PM10) was observed for 2001 similar to 2020, whereas the increasing trend in O-3 concentrations. In correlation analysis, we found that most air pollutants (except for O3) showed positive correlations with UHI intensity during the study period (CO: +0.354, NO2: +0.415, SO2: +0.088, PM10: +0.118). At the same time, O-3 was negatively correlated with UHI intensity (r=-0.450). For most air pollutants (except for O-3), we also found stronger correlations at night than during the day. In addition, the concentrations of primary air pollutants tended to increase with increasing UHI intensities (i.e., increasing UHI levels), while O-3 concentrations tended to decrease with increasing UHI levels, suggesting a potential interaction between UHI and air pollution.