<?xml version="1.0" encoding="UTF-8"?><xml><records><record><source-app name="Biblio" version="7.x">Drupal-Biblio</source-app><ref-type>17</ref-type><contributors><authors><author><style face="normal" font="default" size="100%">Chunxiang Ye</style></author></authors></contributors><titles><title><style face="normal" font="default" size="100%">Tropospheric HONO distribution and chemistry in the southeastern US</style></title><secondary-title><style face="normal" font="default" size="100%">Atmos. Chem. Phys.</style></secondary-title></titles><dates><year><style  face="normal" font="default" size="100%">2018</style></year></dates><urls><web-urls><url><style face="normal" font="default" size="100%">https://doi.org/10.5194/acp-18-9107-2018</style></url></web-urls></urls><volume><style face="normal" font="default" size="100%">18</style></volume><pages><style face="normal" font="default" size="100%">9107-9120</style></pages><language><style face="normal" font="default" size="100%">eng</style></language><abstract><style face="normal" font="default" size="100%">&lt;p&gt;&lt;span&gt;Here we report the measurement results of nitrous acid (HONO) and a suite of relevant parameters on the NCAR C-130 research aircraft in the southeastern US during the NOMADSS 2013 summer field study. The daytime HONO concentration ranged from low parts per trillion by volume (pptv) in the free troposphere (FT) to mostly within 5–15&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;pptv in the background planetary boundary layer (PBL). There was no discernible vertical HONO gradient above the lower flight altitude of 300&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;m in the PBL, and the transport of ground surface HONO was not found to be a significant contributor to the tropospheric HONO budget. The total in situ HONO source mean (±1&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;SD) was calculated as 53 (±21)&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;pptv&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;h&lt;/span&gt;&lt;span&gt;−1&lt;/span&gt;&lt;span&gt;&amp;nbsp;during the day. The upper-limit contribution from NO&lt;/span&gt;&lt;span&gt;&lt;em&gt;x&lt;/em&gt;&lt;/span&gt;&lt;span&gt;-related reactions was 10 (±5)&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;pptv&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;h&lt;/span&gt;&lt;span&gt;−1&lt;/span&gt;&lt;span&gt;, and the contribution from photolysis of particulate nitrate (&lt;/span&gt;&lt;em&gt;p&lt;/em&gt;&lt;span&gt;NO&lt;/span&gt;&lt;span&gt;3&lt;/span&gt;&lt;span&gt;) was 38 (±23)&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;pptv&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;h&lt;/span&gt;&lt;span&gt;−1&lt;/span&gt;&lt;span&gt;, based on the measured&amp;nbsp;&lt;/span&gt;&lt;em&gt;p&lt;/em&gt;&lt;span&gt;NO&lt;/span&gt;&lt;span&gt;3&lt;/span&gt;&lt;span&gt;&amp;nbsp;concentrations and the median&amp;nbsp;&lt;/span&gt;&lt;em&gt;p&lt;/em&gt;&lt;span&gt;NO&lt;/span&gt;&lt;span&gt;3&lt;/span&gt;&lt;span&gt;&amp;nbsp;photolysis rate constant of 2.0&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt; × &lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;10&lt;/span&gt;&lt;span&gt;−4&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;−1&lt;/span&gt;&lt;span&gt;&amp;nbsp;determined in the laboratory using ambient aerosol samples. The photolysis of HONO contributed to less than 10&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;% of the primary OH source. However, a recycling NO&lt;/span&gt;&lt;span&gt;&lt;em&gt;x&lt;/em&gt;&lt;/span&gt;&lt;span&gt;&amp;nbsp;source via&amp;nbsp;&lt;/span&gt;&lt;em&gt;p&lt;/em&gt;&lt;span&gt;NO&lt;/span&gt;&lt;span&gt;3&lt;/span&gt;&lt;span&gt;&amp;nbsp;photolysis was equivalent to  ∼ &lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;2.3&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt; × &lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;10&lt;/span&gt;&lt;span&gt;−6&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;mol&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;m&lt;/span&gt;&lt;span&gt;−2&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;h&lt;/span&gt;&lt;span&gt;−1&lt;/span&gt;&lt;span&gt;&amp;nbsp;in the air column within the PBL, a considerable supplementary NO&lt;/span&gt;&lt;span&gt;&lt;em&gt;x&lt;/em&gt;&lt;/span&gt;&lt;span&gt;&amp;nbsp;source in the low-NO&lt;/span&gt;&lt;span&gt;&lt;em&gt;x&lt;/em&gt;&lt;/span&gt;&lt;span&gt;&amp;nbsp;background area. Up to several tens of parts per trillion by volume of HONO were observed in power plant and urban plumes during the day, mostly produced in situ from precursors including NO&lt;/span&gt;&lt;span&gt;&lt;em&gt;x&lt;/em&gt;&lt;/span&gt;&lt;span&gt;&amp;nbsp;and&amp;nbsp;&lt;/span&gt;&lt;em&gt;p&lt;/em&gt;&lt;span&gt;NO&lt;/span&gt;&lt;span&gt;3&lt;/span&gt;&lt;span&gt;. Finally, there was no observable accumulation of HONO in the nocturnal residual layer and the nocturnal FT in the background southeastern US, with an increase in the HONO&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;∕&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;NO&lt;/span&gt;&lt;span&gt;&lt;em&gt;x&lt;/em&gt;&lt;/span&gt;&lt;span&gt;&amp;nbsp;ratio of  ≤ &lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;3&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt; × &lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;10&lt;/span&gt;&lt;span&gt;−4&lt;/span&gt;&lt;span class=&quot;thinspace&quot;&gt;&lt;/span&gt;&lt;span&gt;h&lt;/span&gt;&lt;span&gt;−1&lt;/span&gt;&lt;span&gt;&amp;nbsp;after sunset.&lt;/span&gt;&lt;/p&gt;</style></abstract></record></records></xml>