NO<sub>2</sub> vertical profiles and column densities from MAX-DOAS measurements in Mexico City

Abstract

Abstract. 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 (Danckaert et al., 2013) 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 (e.g., Spurr et al., 2001; Spurr, 2006, 2013). 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. The MMF code was applied to retrieve NO2 profiles with 2 degrees of freedom (DOF = 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 NO2 in the boundary layer of Mexico City.

Inter-comparison of MAX-DOAS measurements of tropospheric HONO slant column densities and vertical profiles during the CINDI-2 campaign

“…Five inversion algorithms based on the optimal estimation (OE) method are used in this study: PriAM (Y. Wang et al, 2013aWang et al, , b, 2017b, BePro (Clémer et al, 2010), MMF (Friedrich et al, 2019), HEIPRO (Frieß et al, 2006(Frieß et al, , 2011, and M 3 (Chan et al, 2018). Different from the other algorithms, MAPA (Beirle et al, 2019) implemented by the "MPIC" participants is based on a profile parameterization.…”

“…wavelength ranges, cross sections, polynomials, and intensity offset corrections. Inversion algorithms of vertical profiles of trace gases and aerosols have been developed in previous studies based on the optimal estimation (OE) method (Rodgers, 2000;Frieß et al, 2006Frieß et al, , 2011Wittrock, 2006;Irie et al, 2008Irie et al, , 2011Clémer et al, 2010;Yilmaz, 2012;Hartl and Wenig, 2013;Y. Wang et al, 2013aY.…”

Validation of tropospheric NO<sub>2</sub> column measurements of GOME-2A and OMI using MAX-DOAS and direct sun network observations

“… Vertical profile algorithms using an Optimal Estimation Method (OEM, Rodgers, 2000): these make use of a-priori vertical profiles and associated uncertainties (Friess et al, 2006;Clémer et al 2010;Hendrick et al, 2014;Wang et al, 2017b;Friedrich et al, 2019;Bösch et al, 2018), https://doi.org/10.5194/amt-2020-76 Preprint. Discussion started: 30 March 2020 c Author(s) 2020.…”

Formaldehyde total column densities over Mexico City: comparison between MAX-DOAS and solar absorption FTIR measurements

“…Approaching the zenith direction, the scan is continued in reverse order for the elevation angles towards the opposite azimuthal direction, from large elevation angles towards small elevation angles. The measurement sequence, as specified in Friedrich et al (2019) is: 90 • zenith, 0, 2, 6, 13, 23, 36, 50, 65, 82 • W, 82, 65, 50, 36, 23, 13, 6, 2, 0 • E. At the end of each scan, a dark spectrum is taken (closed shutter). The dark spectrum is subtracted from all other spectra measured during the sequence (including the zenith spectrum).…”

“…The dark spectrum is subtracted from all other spectra measured during the sequence (including the zenith spectrum). A detailed instrument description and measurement strategy can be found in Arellano et al (2016) and Friedrich et al (2019).…”