A relaxed eddy accumulation (REA) LOPAP system for flux measurements of nitrous acid (HONO)
<p>In the present study a relaxed eddy accumulation (REA) system for the quantification of vertical fluxes of nitrous acid (HONO) was developed and tested. The system is based on a three-channel long-path absorption photometer (LOPAP) instrument, for which two channels are used for the updraft...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2022-03-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/15/1983/2022/amt-15-1983-2022.pdf |
| Summary: | <p>In the present study a relaxed eddy accumulation (REA) system for the quantification of vertical fluxes of nitrous acid (HONO) was developed and tested. The system is based on a three-channel long-path absorption photometer (LOPAP) instrument, for which two channels are used for the updrafts and downdrafts, respectively, and a third one for the correction of chemical interferences. The instrument is coupled to a REA gas inlet, for which an ultrasonic anemometer controls two fast magnetic valves to probe the two channels of the LOPAP instrument depending on the vertical wind direction. A software (PyREA) was developed, which controls the valves and measurement cycles, which regularly alternates between REA, zero and parallel ambient measurements. In addition, the assignment of the updrafts and downdrafts to the physical LOPAP channels is periodically alternated, to correct for
differences in the interferences of the different air masses. During the
study, only small differences of the interferences were identified for the
updrafts and downdrafts excluding significant errors when using only one
interference channel. In laboratory experiments, high precision of the two
channels and the independence of the dilution-corrected HONO concentrations
on the length of the valve switching periods were demonstrated.</p>
<p>A field campaign was performed in order to test the new REA-LOPAP system at
the TROPOS monitoring station in Melpitz, Germany. HONO fluxes in the range
of <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M1" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><mn mathvariant="normal">4</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">13</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="48pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="b026503226488e6628a56f2e8e230b2a"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-1983-2022-ie00001.svg" width="48pt" height="14pt" src="amt-15-1983-2022-ie00001.png"/></svg:svg></span></span> molecules m<span class="inline-formula"><sup>−2</sup></span> s<span class="inline-formula"><sup>−1</sup></span> (deposition) to
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>+</mo><mn mathvariant="normal">1.0</mn><mo>×</mo><msup><mn mathvariant="normal">10</mn><mn mathvariant="normal">14</mn></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="57pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="abdafd5694fac859a007439b63b29673"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-1983-2022-ie00002.svg" width="57pt" height="14pt" src="amt-15-1983-2022-ie00002.png"/></svg:svg></span></span> molecules m<span class="inline-formula"><sup>−2</sup></span> s<span class="inline-formula"><sup>−1</sup></span> (emission) were
obtained. A typical diurnal variation of the HONO fluxes was observed with
low, partly negative fluxes during night-time and higher positive fluxes
around noon. After an intensive rain period the positive HONO emissions
during daytime were continuously increasing, which was explained by the
drying of the uppermost ground surfaces. Similar to other campaigns, the
highest correlation of the HONO flux was observed with the product of the
NO<span class="inline-formula"><sub>2</sub></span> photolysis frequency and the NO<span class="inline-formula"><sub>2</sub></span> concentration
<span class="inline-formula">(<i>J</i>(NO<sub>2</sub>)⋅[NO<sub>2</sub>])</span>, which implies a HONO formation by photosensitized conversion of NO<span class="inline-formula"><sub>2</sub></span> on organic surfaces, such as humic
acids. Other postulated HONO formation mechanisms are also discussed but
are tentatively ranked being of minor importance for the present field
campaign.</p> |
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| ISSN: | 1867-1381 1867-8548 |