Measurement of NO<sub><i>x</i></sub> and NO<sub><i>y</i></sub> with a thermal dissociation cavity ring-down spectrometer (TD-CRDS): instrument characterisation and first deployment
<p>We present a newly constructed, two-channel thermal dissociation cavity ring-down spectrometer (TD-CRDS) for the measurement of <span class="inline-formula">NO<sub><i>x</i></sub></span> (<span class="inline-formula">NO+NO<sub&...
| Main Authors: | , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-10-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/13/5739/2020/amt-13-5739-2020.pdf |
| Summary: | <p>We present a newly constructed, two-channel thermal
dissociation cavity ring-down spectrometer (TD-CRDS) for the measurement of
<span class="inline-formula">NO<sub><i>x</i></sub></span> (<span class="inline-formula">NO+NO<sub>2</sub></span>), <span class="inline-formula">NO<sub><i>y</i></sub></span> (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi mathvariant="normal">NO</mi><mi>x</mi></msub><mo>+</mo><msub><mi mathvariant="normal">HNO</mi><mn mathvariant="normal">3</mn></msub><mo>+</mo><msub><mi mathvariant="normal">RO</mi><mn mathvariant="normal">2</mn></msub><msub><mi mathvariant="normal">NO</mi><mn mathvariant="normal">2</mn></msub><mo>+</mo><mn mathvariant="normal">2</mn><msub><mi mathvariant="normal">N</mi><mn mathvariant="normal">2</mn></msub><msub><mi mathvariant="normal">O</mi><mn mathvariant="normal">5</mn></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="161pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="11678d3d4ff61e4be37d70b8eec0e724"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-13-5739-2020-ie00001.svg" width="161pt" height="13pt" src="amt-13-5739-2020-ie00001.png"/></svg:svg></span></span> etc.), <span class="inline-formula">NO<sub><i>z</i></sub></span> (<span class="inline-formula">NO<sub><i>y</i></sub>−NO<sub><i>x</i></sub></span>)
and particulate nitrate (pNit). <span class="inline-formula">NO<sub><i>y</i></sub></span>-containing trace gases are detected
as <span class="inline-formula">NO<sub>2</sub></span> by the CRDS at 405 nm following sampling through inlets at ambient
temperature (<span class="inline-formula">NO<sub><i>x</i></sub></span>) or at 850 <span class="inline-formula"><sup>∘</sup></span>C (<span class="inline-formula">NO<sub><i>y</i></sub></span>). In both cases,
<span class="inline-formula">O<sub>3</sub></span> was added to the air sample directly upstream of the cavities to
convert NO (either ambient or formed in the 850 <span class="inline-formula"><sup>∘</sup></span>C oven) to
<span class="inline-formula">NO<sub>2</sub></span>. An activated carbon denuder was used to remove gas-phase
components of <span class="inline-formula">NO<sub><i>y</i></sub></span> when sampling pNit. Detection limits, defined as the
2<span class="inline-formula"><i>σ</i></span> precision for 1 min averaging, are 40 pptv for both <span class="inline-formula">NO<sub><i>x</i></sub></span>
and <span class="inline-formula">NO<sub><i>y</i></sub></span>. The total measurement uncertainties (at 50 % relative humidity, RH) in the
<span class="inline-formula">NO<sub><i>x</i></sub></span> and <span class="inline-formula">NO<sub><i>y</i></sub></span> channels are <span class="inline-formula">11 <i>%</i>+10</span> pptv and <span class="inline-formula">16 <i>%</i>+14</span> pptv
for <span class="inline-formula">NO<sub><i>z</i></sub></span> respectively. Thermograms of various trace gases of the
<span class="inline-formula">NO<sub><i>z</i></sub></span> family confirm stoichiometric conversion to <span class="inline-formula">NO<sub>2</sub></span> (and/or NO)
at the oven temperature and rule out significant interferences from <span class="inline-formula">NH<sub>3</sub></span>
detection (<span class="inline-formula"><2</span> %) or radical recombination reactions under
ambient conditions. While fulfilling the requirement of high particle
transmission (<span class="inline-formula">>80</span> % between 30 and 400 nm) and essentially
complete removal of reactive nitrogen under dry conditions (<span class="inline-formula">>99</span> %), the denuder suffered from <span class="inline-formula">NO<sub><i>x</i></sub></span> breakthrough and memory effects
(i.e. release of stored <span class="inline-formula">NO<sub><i>y</i></sub></span>) under humid conditions, which may
potentially bias measurements of particle nitrate.</p>
<p>Summertime <span class="inline-formula">NO<sub><i>x</i></sub></span> measurements obtained from a ship sailing through the
Red Sea, Indian Ocean and Arabian Gulf (<span class="inline-formula">NO<sub><i>x</i></sub></span> levels from <span class="inline-formula"><20</span> pptv to 25 ppbv) were in excellent agreement with those taken by a
chemiluminescence detector of NO and <span class="inline-formula">NO<sub>2</sub></span>. A data set obtained locally
under vastly different conditions (urban location in winter) revealed large
diel variations in the <span class="inline-formula">NO<sub><i>z</i></sub></span> to <span class="inline-formula">NO<sub><i>y</i></sub></span> ratio which could be
attributed to the impact of local emissions by road traffic.</p> |
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| ISSN: | 1867-1381 1867-8548 |