Airborne observations of peroxy radicals during the EMeRGe campaign in Europe
<p>In this study, airborne measurements of the sum of hydroperoxyl (<span class="inline-formula">HO<sub>2</sub></span>) and organic peroxy (<span class="inline-formula">RO<sub>2</sub></span>) radicals that react with nitrogen...
| Main Authors: | , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-07-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/23/7799/2023/acp-23-7799-2023.pdf |
| Summary: | <p>In this study, airborne measurements of the sum of hydroperoxyl
(<span class="inline-formula">HO<sub>2</sub></span>) and organic peroxy (<span class="inline-formula">RO<sub>2</sub></span>) radicals that react with nitrogen
monoxide (NO) to produce nitrogen dioxide (<span class="inline-formula">NO<sub>2</sub></span>), coupled with
actinometry and other key trace gases measurements, have been used to test
the current understanding of the fast photochemistry in the outflow of major
population centres. The measurements were made during the airborne campaign
of the EMeRGe (Effect of Megacities on the transport and transformation of
pollutants on the Regional to Global scales) project in Europe on board the
High Altitude and Long Range Research Aircraft (HALO). The measurements of
RO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="7pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="fd4a150ed7fc0e56f6ccb122f99fad19"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00001.svg" width="7pt" height="14pt" src="acp-23-7799-2023-ie00001.png"/></svg:svg></span></span> on HALO were made using the in situ instrument Peroxy
Radical Chemical Enhancement and Absorption Spectrometer (PeRCEAS).
RO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M5" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="7pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="dc715b30bb4b2971849cf622a92fb972"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00002.svg" width="7pt" height="14pt" src="acp-23-7799-2023-ie00002.png"/></svg:svg></span></span> is to a good approximation the sum of peroxy radicals
reacting with NO to produce <span class="inline-formula">NO<sub>2</sub></span>. RO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="7pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="935d4c0fecd64115e8392d3800193226"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00003.svg" width="7pt" height="14pt" src="acp-23-7799-2023-ie00003.png"/></svg:svg></span></span> mixing ratios up to
120 pptv were observed in air masses of different origins and composition
under different local actinometric conditions during seven HALO research
flights in July 2017 over Europe.</p>
<p>Radical production rates were estimated using knowledge of the photolysis
frequencies and the <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="90f0d3a735c442370932468183b20a0c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00004.svg" width="23pt" height="14pt" src="acp-23-7799-2023-ie00004.png"/></svg:svg></span></span> precursor concentrations measured
on board, as well as the relevant rate coefficients. Generally, high
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M9" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="5ad9b05d81fe95b177981272e8e72d4f"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00005.svg" width="23pt" height="14pt" src="acp-23-7799-2023-ie00005.png"/></svg:svg></span></span> concentrations were measured in air masses with high
production rates. In the air masses investigated, <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="29774666fa07d0130d6c3e173b51d104"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00006.svg" width="23pt" height="14pt" src="acp-23-7799-2023-ie00006.png"/></svg:svg></span></span> is
primarily produced by the reaction of O<span class="inline-formula"><sup>1</sup></span>D with water vapour and the
photolysis of nitrous acid (HONO) and of the oxygenated volatile organic
compounds (OVOCs, e.g. formaldehyde (HCHO) and glyoxal (CHOCHO)). Due to
their short lifetime in most environments, the RO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="7pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="f69ba1e67fd7490011f8dc70772617c8"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00007.svg" width="7pt" height="14pt" src="acp-23-7799-2023-ie00007.png"/></svg:svg></span></span> concentrations are expected to be in a photostationary steady state (PSS), i.e. a balance between production and loss rates is assumed. The
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="3c652b72f8bc010245d5be5a33c051f5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00008.svg" width="23pt" height="14pt" src="acp-23-7799-2023-ie00008.png"/></svg:svg></span></span> production and loss rates and the suitability of PSS
assumptions to estimate the <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="534989f86575c5fc292ccd2f645e4276"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00009.svg" width="23pt" height="14pt" src="acp-23-7799-2023-ie00009.png"/></svg:svg></span></span> mixing ratios and variability
during the airborne observations are discussed. The PSS assumption for
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M15" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="3f5f98d409b58bbdca81231a9925f388"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00010.svg" width="23pt" height="14pt" src="acp-23-7799-2023-ie00010.png"/></svg:svg></span></span> is considered robust enough to calculate <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="a51f955c63512163fd7e6ba00146b54c"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00011.svg" width="23pt" height="14pt" src="acp-23-7799-2023-ie00011.png"/></svg:svg></span></span> mixing ratios for most conditions encountered in the air masses measured.
The similarities and discrepancies between measured and PSS calculated
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M17" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="f486b3871ba3e547a77b15c8ecc5e6ed"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00012.svg" width="23pt" height="14pt" src="acp-23-7799-2023-ie00012.png"/></svg:svg></span></span> mixing ratios are discussed. The dominant terminating
processes for <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M18" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="f1272cb2e619b08efea0c17bb672e7bd"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00013.svg" width="23pt" height="14pt" src="acp-23-7799-2023-ie00013.png"/></svg:svg></span></span> in the pollution plumes measured up to 2000
m are the formation of nitrous acid, nitric acid, and organic nitrates. Above
2000 m, <span class="inline-formula">HO<sub>2</sub></span>–<span class="inline-formula">HO<sub>2</sub></span> and <span class="inline-formula">HO<sub>2</sub></span>–<span class="inline-formula">RO<sub>2</sub></span> reactions dominate the
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M23" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="4b21409fb721dd8d6083a08cb5969439"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00014.svg" width="23pt" height="14pt" src="acp-23-7799-2023-ie00014.png"/></svg:svg></span></span> removal. <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M24" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="d40a64dc053d84b0d57e7a1ac43c7d75"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00015.svg" width="23pt" height="14pt" src="acp-23-7799-2023-ie00015.png"/></svg:svg></span></span> calculations by the PSS
analytical<span id="page7800"/> expression inside the pollution plumes probed often
underestimated the measurements. The underestimation is attributed to the
limitations of the PSS equation used for the analysis. In particular, this
expression does not account for the yields of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M25" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="75b17a135f9c377d1630bf5a1c20ce98"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00016.svg" width="23pt" height="14pt" src="acp-23-7799-2023-ie00016.png"/></svg:svg></span></span> from the
oxidation and photolysis of volatile organic compounds, VOCs, and OVOCs
other than those measured during the EMeRGe research flights in Europe. In
air masses with NO mixing ratios <span class="inline-formula">≤50</span> pptv and low <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M27" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><mi mathvariant="normal">VOC</mi><mo>/</mo><mi mathvariant="normal">NO</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="48pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="9e5dd82552b18a5be00b4afd1355323b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00017.svg" width="48pt" height="14pt" src="acp-23-7799-2023-ie00017.png"/></svg:svg></span></span> ratios, the
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M28" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn><mo>∗</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="23pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="13fb75362b4a332622a92b075d869218"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="acp-23-7799-2023-ie00018.svg" width="23pt" height="14pt" src="acp-23-7799-2023-ie00018.png"/></svg:svg></span></span> measured is overestimated by the analytical expression.
This may be caused by the formation of H<span class="inline-formula"><sub>2</sub></span>O and O<span class="inline-formula"><sub>2</sub></span> from OH and
<span class="inline-formula">HO<sub>2</sub></span>, being about 4 times faster than the rate of the OH oxidation
reaction of the dominant OVOCs considered.</p> |
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| ISSN: | 1680-7316 1680-7324 |