Concurrent increases of PM2.5 and Ozone observed in Seoul, May 2019
Authors: Son Jeewon , Kang Sunggu , Kim Joo-ae , Gil Junsu , Lee Meehye , Lee Taehyung , Park Moon-soo , Heo Gookyoung 
Published: March 2020

&lt;p&gt;&amp;#160;In Seoul, PM&lt;sub&gt;2.5&lt;/sub&gt; concentrations were frequently elevated with O&lt;sub&gt;3&lt;/sub&gt; in May 2019. The most abundant constituent of PM&lt;sub&gt;2.5&lt;/sub&gt; was nitrate, which was the best correlated with OC (organic carbon) as well as NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;. An intensive experiment was conducted in the eastern part of Seoul from March 29 to June 19, 2019. Measurement was made for PM&lt;sub&gt;2.5 &lt;/sub&gt;and its chemical composition including NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;, SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2-&lt;/sup&gt;, NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+ &lt;/sup&gt;, OC, EC (elemental carbon), and reactive gases including O&lt;sub&gt;3&lt;/sub&gt;, NO, NO&lt;sub&gt;2&lt;/sub&gt;, CO, HONO, HNO&lt;sub&gt;3&lt;/sub&gt;, NH&lt;sub&gt;3&lt;/sub&gt;, and SO&lt;sub&gt;2&lt;/sub&gt;, and meteorological variables including vertical winds and mixed layer height (MLH). The particle number concentration was measured using SMPS (Scanning Mobility Particle Sizer). All measurements were averaged for 1 hour according to the resolution of PM&lt;sub&gt;2.5&lt;/sub&gt; chemical composition. For the entire experiment, the mean mass concentrations of PM&lt;sub&gt;2.5&lt;/sub&gt;, NO&lt;sub&gt;3&lt;/sub&gt;&lt;sup&gt;-&lt;/sup&gt;, SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2-&lt;/sup&gt;, NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt;, OC, and EC were 20.40 &amp;#956;g/m&lt;sup&gt;3&lt;/sup&gt;, 4.07 &amp;#956;g/m&lt;sup&gt;3&lt;/sup&gt;, 2.62 &amp;#956;g/m&lt;sup&gt;3&lt;/sup&gt;, 2.01 &amp;#956;g/m&lt;sup&gt;3&lt;/sup&gt;, 4.01 &amp;#956;g/m&lt;sup&gt;3&lt;/sup&gt;, and 1.04 &amp;#956;g/m&lt;sup&gt;3&lt;/sup&gt;, respectively. For reactive gases, the mean concentration was 1.03 ppbv for HONO, 0.70 ppbv for HNO&lt;sub&gt;3&lt;/sub&gt;, 14.87 ppbv for NH&lt;sub&gt;3&lt;/sub&gt;, 2.77 ppbv for SO&lt;sub&gt;2&lt;/sub&gt;, and 48.79 ppbv for O&lt;sub&gt;3&lt;/sub&gt;.&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;The maximum PM&lt;sub&gt;2.5&lt;/sub&gt; concentration of 72.81 &amp;#956;g/m&lt;sup&gt;3 &lt;/sup&gt;was observed under the influence of weak Asian dust event in the end of April. In May, there were three distinct episodes with highly enhanced PM&lt;sub&gt;2.5&lt;/sub&gt;. In the early May, the maximum nitrate concentration (36.11 &amp;#956;g/m&lt;sup&gt;3&lt;/sup&gt;) was observed with high HONO (2.41 ppbv) on 4 May. In the middle of May, PM&lt;sub&gt;2.5&lt;/sub&gt; was raised with SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2-&lt;/sup&gt; under stagnant condition. On 25 May, PM&lt;sub&gt;2.5&lt;/sub&gt; was raised up to 92 &amp;#956;g/m&lt;sup&gt;3 &lt;/sup&gt;with high nitrate concentration (18.56 &amp;#956;g/m&lt;sup&gt;3&lt;/sup&gt;) , when O&lt;sub&gt;3&lt;/sub&gt; reached 205 ppbv. In this episode, O&lt;sub&gt;3&lt;/sub&gt; concentration remained around 90 ppbv at night and OC and EC were well correlated with highly enhanced K&lt;sup&gt;+&lt;/sup&gt;. Thus, the concurrent enhancement of PM&lt;sub&gt;2.5&lt;/sub&gt; and O&lt;sub&gt;3&lt;/sub&gt; was likely due to the influence of aged biomass combustion plume laden air transported from southeast China. At the same time, HNO&lt;sub&gt;3&lt;/sub&gt; and HONO concentration was highly elevated, indicating that heterogeneous reactions played a role.&lt;/p&gt;