Measurement of tropospheric HO2 radical using fluorescence assay by gas expansion with low interferences

Yihui Wang,Renzhi Hu,Wenqing Liu,Jianguo Liu,Pinhua Xie,Fengyang Wang

doi:10.5194/egusphere-egu2020-12969

Abstract

&lt;p&gt;&amp;#160; &amp;#160; An instrument to detect atmospheric HO&lt;sub&gt;2&lt;/sub&gt; radicals using fluorescence assay by gas expansion (FAGE) technique has been developed. HO&lt;sub&gt;2&lt;/sub&gt; is measured by reaction with NO to form OH and subsequent detection of OH by laser-induced fluorescence at low pressure. The system performance has been improved by optimizing the expansion distance and pressure, and the influence factors of HO&lt;sub&gt;2 &lt;/sub&gt;conversion efficiency are also studied. The interferences of RO&lt;sub&gt;2&lt;/sub&gt; radicals produced from OH plus some typical organic compounds were investigated by determining the conversion efficiency of RO&lt;sub&gt;2&lt;/sub&gt; to OH during the measurement of HO&lt;sub&gt;2&lt;/sub&gt;. The dependence of the conversion of HO&lt;sub&gt;2&lt;/sub&gt; on NO concentration was investigated, and low HO&lt;sub&gt;2&lt;/sub&gt; conversion efficiency was selected to realize the ambient HO&lt;sub&gt;2&lt;/sub&gt; measurement, where the conversion efficiency of RO&lt;sub&gt;2&lt;/sub&gt; derived by propane, ethene, isoprene and methanol to OH has been reduced to no more than 6%. Furthermore, no significant interferences from PM&lt;sub&gt;2.5&lt;/sub&gt; and NO were found in the ambient HO&lt;sub&gt;2&lt;/sub&gt; measurement. The detection limits for HO&lt;sub&gt;2&lt;/sub&gt; (S/N=2) are estimated to 4.8&amp;#215;10&lt;sup&gt;5&lt;/sup&gt; cm&lt;sup&gt;-3&lt;/sup&gt; and 1.1&amp;#215;10&lt;sup&gt;6&lt;/sup&gt; cm&lt;sup&gt;-3 &lt;/sup&gt;(the conversion efficiency of HO&lt;sub&gt;2&lt;/sub&gt; to OH, =20%) under night and noon conditions, with 60s signal integration time. The instrument was successfully deployed during STORM-2018 field campaign at Shenzhen graduate school of Peking University. The diurnal variation of HOx concentration shows that the OH maximum concentration of those days is about 5.5&amp;#215;10&lt;sup&gt;6 &lt;/sup&gt;cm&lt;sup&gt;-3 &lt;/sup&gt;appearing around 12:00, while the HO&lt;sub&gt;2&lt;/sub&gt; maximum concentration is about 5.0&amp;#215;10&lt;sup&gt;8 &lt;/sup&gt;cm&lt;sup&gt;-3 &lt;/sup&gt;appearing around 13:30.&lt;/p&gt;

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