Heterogeneous conversion of NO2 on secondary organic aerosol surfaces: A possible source of nitrous acid (HONO) in the atmosphere?

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Bröske, R. ; Kleffmann, J. ; Wiesen, P. (2003)

The heterogeneous conversion of NO<sub>2</sub> on different secondary organic aerosols (SOA) was investigated with the focus on a possible formation of nitrous acid (HONO). In one set of experiments different organic aerosols were produced in the reactions of O<sub>3</sub> with alpha-pinene, limonene or catechol and OH radicals with toluene or limonene, respectively. The aerosols were sampled on filters and exposed to humidified NO<sub>2</sub>&nbsp; mixtures under atmospheric conditions. The estimated upper limits for the uptake coefficients of NO<sub>2</sub>&nbsp; and the reactive uptake coefficients NO<sub>2&nbsp;</sub> -&gt; HONO are in the range of 10<sup>-6 </sup>and 10<sup>-7</sup>, respectively. The integrated HONO formation for 1 h reaction time was &lt;10<sup>13</sup> cm<sup>-2</sup> geometrical surface and &lt;10<sup>17</sup> g<sup>-1</sup> particle mass. In a second set of experiments the conversion of NO<sub>2</sub> into HONO in the presence of organic particles was carried out in an aerosol flow tube under atmospheric conditions. In this case the aerosols were produced in the reaction of O<sub>3</sub> with beta-pinene, limonene or catechol, respectively. The upper limits for the reactive uptake coefficients NO<sub>2 </sub>-&gt; HONO were in the range of 7 x 10<sup>-7 </sup>- 9 x 10<sup>-6</sup>. The results from the present study show that heterogeneous formation of nitrous acid on secondary organic aerosols (SOA) is unimportant for the atmosphere.
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