The quantification of NO<sub><i>x</i></sub> and SO<sub>2</sub> point source emission flux errors of mobile differential optical absorption spectroscopy on the basis of the Gaussian dispersion model: a simulation study
<p>Mobile differential optical absorption spectroscopy (mobile DOAS) has become an important tool for the quantification of emission sources, including point sources (e.g., individual power plants) and area emitters (e.g., entire cities). In this study, we focused on the error budget of mobile...
| Main Authors: | , , , , , , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-11-01
|
| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://amt.copernicus.org/articles/13/6025/2020/amt-13-6025-2020.pdf |
| Summary: | <p>Mobile differential optical absorption spectroscopy (mobile DOAS)
has become an important tool for the quantification of emission sources,
including point sources (e.g., individual power plants) and area emitters
(e.g., entire cities). In this study, we focused on the error budget of
mobile DOAS measurements from point sources, and we also offered
recommendations for the optimum settings of such measurements via a
simulation with a modified Gaussian plume model. Following the analysis, we
conclude that (1) the proper sampling resolution should be between 5 and
50 m. (2) When measuring far from the source, undetectable flux (measured
slant column densities (SCDs) are under the detection limit) resulting from wind dispersion is the main
error source. The threshold for the undetectable flux can be lowered by
larger integration time. When measuring close to the source, low sampling
frequency results in large errors, and wind field uncertainty becomes the
main error source of SO<span class="inline-formula"><sub>2</sub></span> flux (for NO<span class="inline-formula"><sub><i>x</i></sub></span> this error also increases, but
other error sources dominate). More measurement times can lower the flux
error that results from wind field uncertainty. The proper wind speed for
mobile DOAS measurements is between 1 and 4 m s<span class="inline-formula"><sup>−1</sup></span>. (3) The remaining
errors by [NO<span class="inline-formula"><sub><i>x</i></sub></span>] <span class="inline-formula">∕</span> [NO<span class="inline-formula"><sub>2</sub></span>] ratio correction can be significant when
measuring very close. To minimize the [NO<span class="inline-formula"><sub><i>x</i></sub></span>] <span class="inline-formula">∕</span> [NO<span class="inline-formula"><sub>2</sub></span>] ratio correction error, we recommend minimum distances from the source, at which 5 % of the NO<span class="inline-formula"><sub>2</sub></span> maximum reaction rate is reached and thus NO<span class="inline-formula"><sub><i>x</i></sub></span> steady state can be assumed. (4) Our study suggests that emission rates <span class="inline-formula"><</span> 30 g s<span class="inline-formula"><sup>−1</sup></span> for NO<span class="inline-formula"><sub><i>x</i></sub></span> and <span class="inline-formula"><</span> 50 g s<span class="inline-formula"><sup>−1</sup></span> for SO<span class="inline-formula"><sub>2</sub></span> are not recommended for mobile DOAS
measurements.</p>
<p>Based on the model simulations, our study indicates that mobile DOAS
measurements are a very well-suited tool to quantify point source emissions.
The results of our sensitivity studies are important to make optimum use of
such measurements.</p> |
|---|---|
| ISSN: | 1867-1381 1867-8548 |