13 May 2022
13 May 2022

Estimation of OH in urban plume using TROPOMI inferred NO2 / CO

Srijana Lama1, Sander Houweling1,2, K. Folkert Boersma3,4, Ilse Aben2,1, Hugo A. C. Denier van der Gon5, and Maarten C. Krol3,6 Srijana Lama et al.
  • 1Vrije Universiteit, Department of Earth Sciences, Amsterdam, the Netherlands
  • 2SRON Netherlands Institute for Space Research, Leiden, the Netherlands
  • 3Wageningen University, Meteorology and Air Quality Group, Wageningen, the Netherlands
  • 4Royal Netherlands Meteorological Institute, R&D Satellite Observations, de Bilt, the Netherlands
  • 5TNO, Department of Climate, Air and Sustainability, Princetonlaan, the Netherlands
  • 6Institute for Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, the Netherlands

Abstract. A new method is presented to estimate urban hydroxyl radical (OH) concentrations using the downwind decay of the Tropospheric Monitoring Instrument (TROPOMI) derived nitrogen dioxide (NO2) / carbon monoxide (CO) ratio combined with Weather Research Forecast (WRF) simulations. Seasonal OH concentrations, nitrogen oxides (NOx) and CO emissions for summer (June to October, 2018) and winter (November, 2018 to March, 2019) are derived for Riyadh. WRF is able to spatially simulate NO2 and CO urban plumes over Riyadh as observed by TROPOMI. However, WRF-simulated NO2 plumes close to center of the city are overestimated by 25 % in summer and 40 to 50 % in winter compared to TROPOMI observations. WRF simulated CO plumes differ by 10 % with TROPOMI in both seasons. The differences between model and TROPOMI are used to optimize the OH concentration, NOx and CO emissions iteratively using a least squares method. For summer, both the NO2 / CO ratio optimization and the XNO2 optimization imply that the OH prior from the Copernicus Atmospheric Monitoring Service (CAMS) has to be increased by 32.03±4.0 % . The OH estimations from the NO2 / CO ratio and the XNO2 optimization differ by 10 %. Summer Emission Database for Global Atmospheric Research v4.3.2 (EDGAR) NOx and CO emissions over Riyadh need to be increased by 42.1±8.7 % and 100.8±9.5 %. For winter, the optimization method increases OH by ~52.0±5.3 %, while reducing NOx emission by 15.45± 3.4 % and doubling the CO emission. TROPOMI derived OH concentrations and pre-existing Exponentially Modified Gaussian function fit (EMG) method differ by 18 % in summer and 7.5 % in winter, confirming that urban OH concentrations can be reliably estimated using the TROPOMI-observed NO2 / CO ratio.

Srijana Lama et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-278', Anonymous Referee #1, 04 Jun 2022
  • RC2: 'Comment on egusphere-2022-278', Anonymous Referee #2, 10 Jun 2022

Srijana Lama et al.

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Estimation of OH in urban plume using TROPOMI inferred NO2/CO Srijana Lama; Sander Houweling; Ilse Aben; K. Folkert Boersma; Maarten C. Krol; Hugo A. C. Denier van der Gon

Srijana Lama et al.


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Short summary
Hydroxyl radical (OH) is the important chemical species that determines the life time of some greenhouse gases and trace gases. OH plays vital role in the air pollution chemistry. OH has short lifetime and extremely difficult to measure directly. OH concentrations derived from the chemistry transport model (CTM) has uncertainties >50 %. Therefore in this study, OH is derived indirectly using satellite date in urban plume.