Measurement of ambient NO<sub>3</sub> reactivity: design, characterization and first deployment of a new instrument
We describe the first instrument for measurement of the rate constant (s<sup>−1</sup>) for reactive loss (i.e., the total reactivity) of NO<sub>3</sub> in ambient air. Cavity-ring-down spectroscopy is used to monitor the mixing ratio of synthetically generated NO<sub>3&...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-03-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | http://www.atmos-meas-tech.net/10/1241/2017/amt-10-1241-2017.pdf |
| Summary: | We describe the first instrument for measurement of the
rate constant (s<sup>−1</sup>) for reactive loss (i.e., the total reactivity) of
NO<sub>3</sub> in ambient air. Cavity-ring-down spectroscopy is used to monitor
the mixing ratio of synthetically generated NO<sub>3</sub> ( ≈ 30–50 pptv)
after passing through a flow-tube reactor with variable residence time
(generally 10.5 s). The change in concentration of NO<sub>3</sub> upon modulation
of the bath gas between zero air and ambient air is used to derive its loss
rate constant, which is then corrected for formation and decomposition of
N<sub>2</sub>O<sub>5</sub> via numerical simulation. The instrument is calibrated and
characterized using known amounts of NO and NO<sub>2</sub> and tested in the
laboratory with an isoprene standard. The lowest reactivity that can be
detected (defined by the stability of the NO<sub>3</sub> source, instrumental
parameters and NO<sub>2</sub> mixing ratios) is 0.005 s<sup>−1</sup>. An automated
dilution procedure enables measurement of NO<sub>3</sub> reactivities up to 45 s<sup>−1</sup>, this upper limit being defined mainly by the dilution accuracy.
The typical total uncertainty associated with the reactivity measurement at
the center of its dynamic range is 16 %, though this is dependent on
ambient NO<sub>2</sub> levels. Results from the first successful deployment of the
instrument at a forested mountain site with urban influence are shown and
future developments outlined. |
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| ISSN: | 1867-1381 1867-8548 |