NO<sub>2</sub> vertical profiles and column densities from MAX-DOAS measurements in Mexico City
<p>We present a new numerical code, Mexican MAX-DOAS Fit (MMF), developed to retrieve profiles of different trace gases from the network of MAX-DOAS instruments operated in Mexico City. MMF uses differential slant column densities (dSCDs) retrieved with the QDOAS <span class="cit"...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-05-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/12/2545/2019/amt-12-2545-2019.pdf |
| Summary: | <p>We present a new numerical code, Mexican MAX-DOAS Fit (MMF),
developed to retrieve profiles of different trace gases from the network of
MAX-DOAS instruments operated in Mexico City. MMF uses differential slant
column densities (dSCDs) retrieved with the QDOAS <span class="cit" id="xref_paren.1">(<a href="#bib1.bibx9">Danckaert et al.</a>, <a href="#bib1.bibx9">2013</a>)</span> software. The
retrieval is comprised of two steps, an aerosol retrieval and a trace gas
retrieval that uses the retrieved aerosol profile in the forward model for
the trace gas. For forward model simulations, VLIDORT is used
<span class="cit" id="xref_paren.2">(e.g., <a href="#bib1.bibx44">Spurr et al.</a>, <a href="#bib1.bibx44">2001</a>; <a href="#bib1.bibx42">Spurr</a>, <a href="#bib1.bibx42">2006</a>, <a href="#bib1.bibx43">2013</a>)</span>. Both steps use
constrained least-square fitting, but the aerosol retrieval uses Tikhonov
regularization and the trace gas retrieval optimal estimation. Aerosol
optical depth and scattering properties from the AERONET database, averaged
ceilometer data, WRF-Chem model data, and temperature and pressure
sounding data are used for different steps in the retrieval chain.</p>
<p>The MMF code was applied to retrieve <span class="inline-formula">NO<sub>2</sub></span> profiles with 2 degrees of
freedom (DOF <span class="inline-formula">=</span> 2) from spectra of the MAX-DOAS instrument located at the Universidad Nacional Autónoma de
México (UNAM)
campus. We describe the full error analysis of the retrievals and include a
sensitivity exercise to quantify the contribution of the uncertainties in the
aerosol extinction profiles to the total error. A data set comprised of
measurements from January 2015 to July 2016 was processed and the results
compared to independent surface measurements. We concentrate on the analysis
of four single days and additionally present diurnal and annual variabilities
from averaging the 1.5 years of data. The total error, depending on the exact
counting, is 14 %–20 % and this work provides new and relevant information
about <span class="inline-formula">NO<sub>2</sub></span> in the boundary layer of Mexico City.</p> |
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| ISSN: | 1867-1381 1867-8548 |