Spatiotemporal variability patterns of PM2.5 in severe pollution events based on a large dataset from air quality monitoring stations over South Korea
Authors: Han Subin , Park Yongmi , Choi Wonsik 
Published: March 2020

&lt;p&gt;East Asia has suffered from severe air pollution, particularly concerning particulate matter less than 2.5 &amp;#181;m in diameter (PM&lt;sub&gt;2.5&lt;/sub&gt;). Although air quality in Korea has been gradually improved with respect to annual mean PM&lt;sub&gt;2.5&lt;/sub&gt; and PM&lt;sub&gt;10&lt;/sub&gt; concentrations, high PM pollution events have been worse in their peak concentrations and durations.&lt;/p&gt;&lt;p&gt;In this study, we attempted to find statistically how the characteristics of PM&lt;sub&gt;2.5&lt;/sub&gt; pollution over Korea have changed with a focus on temporal and spatial variations. Hourly PM&lt;sub&gt;2.5&lt;/sub&gt; concentration data were obtained from 374 air quality monitoring stations (AQMS) throughout the country from January 2015 to June 2019. With obtained air quality data, we selected high PM pollution periods based on the national air pollution standard, and examined how the magnitudes and durations of high PM pollution events, as well as the background concentrations, have changed since 2015 over Korea. Additionally, we applied the time-lag correlation method to see how the onsets of PM&lt;sub&gt;2.5&lt;/sub&gt; pollution events differ in space and how high PM&lt;sub&gt;2.5&lt;/sub&gt; spread out in time. We also applied the coefficient of divergence (COD) to countrywide datasets of PM&lt;sub&gt;2.5&lt;/sub&gt; as a measure of spatial heterogeneity of PM&lt;sub&gt;2.5&lt;/sub&gt; distributions.&lt;/p&gt;&lt;p&gt;Although annual mean concentrations of PM&lt;sub&gt;2.5&lt;/sub&gt; tend to decline from 2015 to 2018, the peak concentrations and durations for severe PM&lt;sub&gt;2.5&lt;/sub&gt; pollution events tend to increase in most regions of Korea for the periods of January to April. We also categorized the characteristic distribution patterns in severe PM events combining the time-lag correlation and COD results. In most pollution events, the time-lag distributions showed clear delay patterns of pollution events from the reference area (Seoul). Additionally, COD results showed a clear heterogeneity of PM&lt;sub&gt;2.5&lt;/sub&gt; distributions as the distance from the reference area increases along the time-lag. Although spatial correlations and COD results of PM&lt;sub&gt;2.5&lt;/sub&gt; concentrations between the reference area and other regions indicated heterogeneous distributions, time-lag corrected COD values imply that PM&lt;sub&gt;2.5&lt;/sub&gt; over much wider regions of Korea are homogeneously distributed in both magnitudes and temporal variations. The R&lt;sup&gt;2&lt;/sup&gt; values were significantly improved after time-lag correction. These results imply that high PM&lt;sub&gt;2.5&lt;/sub&gt; events are significantly affected by synoptic weather conditions over most regions of Korea; thus, potential modification of synoptic weather patterns in East Asia caused by climate change can be an important factor for variations in high PM&lt;sub&gt;2.5&lt;/sub&gt; pollution events.&lt;/p&gt;&lt;p&gt;Keywords: coefficient of divergence (COD), PM&lt;sub&gt;2.5&lt;/sub&gt; pollution events, spatial heterogeneity of PM distributions, pattern analysis.&lt;/p&gt;