A new TROPOMI product for tropospheric NO<sub>2</sub> columns over East Asia with explicit aerosol corrections

Abstract

Abstract. We present a new product with explicit aerosol corrections, POMINO-TROPOMI, for tropospheric nitrogen dioxide (NO2) vertical column densities (VCDs) over East Asia, based on the newly launched TROPOspheric Monitoring Instrument with an unprecedented high horizontal resolution. Compared to the official TM5-MP-DOMINO (OFFLINE) product, POMINO-TROPOMI shows stronger concentration gradients near emission source locations and better agrees with MAX-DOAS measurements (R2=0.75; NMB=0.8 % versus R2=0.68, NMB=-41.9 %). Sensitivity tests suggest that implicit aerosol corrections, as in TM5-MP-DOMINO, lead to underestimations of NO2 columns by about 25 % over the polluted northern East China region. Reducing the horizontal resolution of a priori NO2 profiles would underestimate the retrieved NO2 columns over isolated city clusters in western China by 35 % but with overestimates of more than 50 % over many offshore coastal areas. The effect of a priori NO2 profiles is more important under calm conditions.

Evaluating Sentinel-5P TROPOMI tropospheric NO<sub>2</sub> column densities with airborne and Pandora spectrometers near New York City and Long Island Sound

“…A component not explicitly explored in this work, which could be in the fu-ture, is the potential impact of aerosols on the TROPOMI retrieval and whether their indirect accounting through the cloud retrieval accurately reflects the impacts within the radiative transfer calculations for the air mass factor calculation (e.g., Leitão et al, 2010;Ma et al, 2013;Jin et al, 2016). Some differences between TROPOMI and airborne TrVCs can be related to differences in a priori assumptions between the TROPOMI and airborne retrievals; Lorente et al (2017) discussed that the structural uncertainty in tropospheric air mass factors is up to 42 % in polluted regions due to different retrieval methodologies. Future comparisons should consider using common methodologies for AMF calculation for both airborne and TROPOMI TrVCs to better quantify the sensitivity of specific a priori assumptions in AMF calculations.…”

“…Relative uncertainties are largest for relatively clean sites (up to and over 100 % in individual cases); however, they decrease as pollution increases. Lorente et al (2017) found that different methodologies applied to the same datasets can lead to structural uncertainty of 31 %-42 %, which is mostly due to sensitivity to selection of a priori vertical profile shapes in the AMF calculation. In this work, airborne TrVCs are evaluated by comparing to Pandora NO 2 columns (Sect.…”

Satellite-based estimates of decline and rebound in China’s CO 2 emissions during COVID-19 pandemic

“…The averaging approach also helps reduce part of the systematic errors in the air mass factor, i.e., those originating from a priori NO 2 profiles and surface albedo assumptions. Meanwhile, TROPOMI NO 2 is found to be systematically underestimated over China ( 40 ), especially over polluted regions. However, relative differences between 2019 and 2020 are used to derive NO x emission changes, which is expected to cancel out a major part of the systematic errors.…”

Ground-based validation of the Copernicus Sentinel-5P TROPOMI NO<sub>2</sub> measurements with the NDACC ZSL-DOAS, MAX-DOAS and Pandonia global networks

“…Second, vertical sensitivity (and thus averaging kernels) and a priori vertical profiles are known to be different for MAX-DOAS and nadir UV-visible satellite retrievals (Wang et al, 2017;Liu et al, 2019b;Compernolle et al, 2020b), with MAX-DOAS measurements sensitive to layers close to the surface and satellite retrievals sensitive mostly to the free troposphere. The effect of the a priori vertical profile on the comparison was estimated for TROPOMI by Dimitropoulou et al (2020) for Uccle, showing an increase by about 55 % when recalculating the TROPOMI column with MAX-DOAS daily mean tropospheric profile.…”

“…Follow-on missions combining limb and occultation measurements are in development, like ALTIUS planned for the coming years. Pioneered in 1995 with ERS-2 GOME (Burrows et al, 1999), which for the first time brought NO 2 column measurements into space by Differential Optical Absorption Spectroscopy (DOAS;Noxon et al, 1979;Platt and Perner, 1983), the global monitoring of tropospheric NO 2 has continued uninterruptedly with a suite of UV-visible DOAS instruments with improving sensitivity and horizontal resolution: Envisat SCIAMACHY (Bovensmann et al, 1999), EOS-Aura OMI (Levelt et al, 2018), and the series of MetOp-A/B/C GOME-2 (Valks et al, 2011;Liu et al, 2019b).…”