Diurnal variability of stratospheric column NO₂ measured using direct solar and lunar spectra over Table Mountain, California (34.38° N)

Creators: Li, King-Fai¹; Khoury, Ryan¹; Pongetti, Thomas J.²; Sander, Stanley P.²; Mills, Franklin P.³; Yung, Yuk L.^{2, 4}

1. University of California, Riverside
2. Jet Propulsion Lab
3. Australian National University
4. California Institute of Technology

Abstract

A full diurnal measurement of stratospheric column NO₂ has been made over the Jet Propulsion Laboratory's Table Mountain Facility (TMF) located in the mountains above Los Angeles, California, USA (2.286 km above mean sea level, 34.38^∘ N, 117.68^∘ W). During a representative week in October 2018, a grating spectrometer measured the telluric NO₂ absorptions in direct solar and lunar spectra. The stratospheric column NO₂ is retrieved using a modified minimum-amount Langley extrapolation, which enables us to accurately treat the non-constant NO₂ diurnal cycle abundance and the effects of tropospheric pollution near the measurement site. The measured 24 h cycle of stratospheric column NO₂ on clean days agrees with a 1-D photochemical model calculation, including the monotonic changes during daytime and nighttime due to the exchange with the N₂O₅ reservoir and the abrupt changes at sunrise and sunset due to the activation or deactivation of the NO₂ photodissociation. The observed daytime NO₂ increasing rate is (1.34 ± 0.24) x 10¹⁴cm⁻² h⁻¹. The observed NO₂ in one of the afternoons during the measurement period was much higher than the model simulation, implying the influence of urban pollution from nearby counties. A 24 h back-trajectory analysis shows that the wind first came from inland in the northeast and reached southern Los Angeles before it turned northeast and finally arrived at TMF, allowing it to pick up pollutants from Riverside County, Orange County, and downtown Los Angeles.

Copyright and License

Published by Copernicus Publications on behalf of the European Geosciences Union.

Acknowledgement

The assistance of George Mount (Washington State University) in Langley analysis is greatly appreciated. King-Fai Li thanks Sally Newman and Tracy Xia (Bay Area Air Quality Management District) for their assistance in setting up and executing the HYSPLIT model. Ryan Khoury was an undergraduate research assistant under the supervision of King-Fai Li. We thank Ralf Sussmann for handling our paper and providing useful comments.

Funding

Thomas J. Pongetti was supported in part by the NASA SAGE-III/ISS Validation, Upper Atmosphere Research and Tropospheric Composition Programs. Yuk L. Yung was supported in part by NASA grant P1847132 via UCLA. Ryan Khoury was supported by the AGU Student Travel Grant Award and the Marsh Environmental Sciences Travel Award by the University of California, Riverside.

Contributions

KFL and TJP prepared the manuscript, with significant conceptual input from SPS and YLY and critical feedback from all the co-authors. SPS and TJP designed and operated the instrument at Table Mountain. TJP retrieved the slant column NO₂ from the spectra and developed the Langley method. KFL and YLY performed the model simulations. RK analyzed some of the observational and model data.

Data Availability

The differential slant column NO₂ used in this paper can be obtained from the Supplement of this article. The QDOAS code used for spectral fitting can be accessed at http://uv-vis.aeronomie.be/software/QDOAS/index.php (Danckaert et al., 2017).

Supplemental Material

The supplement related to this article is available online at: https://doi.org/10.5194/amt-14-7495-2021-supplement.

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