Authors:	Tauer, Sebastian Manuel
Title:	The oxidative capacity of the atmosphere around the Arabian Peninsula: Ship-based atmospheric measurements of OH and HO2 radicals using laser induced fluorescence spectroscopy
Online publication date:	16-Feb-2023
Year of first publication:	2023
Language:	english
Abstract:	The oxidative capacity of the atmosphere is largely governed by the radicals OH and HO2 (HOx), which are the primary self-cleaning agents of the atmosphere. A measure for the strength of the self-cleaning is the recycling probability of HOx, that varies strongly with atmospheric composition and temperature. Due to climate change, global temperatures are expected to rise, which will lead to a change in atmospheric composition from increased emissions of biogenic VOC. Coupled with decreasing NOx emissions from combustion processes, it is important to understand the impact of these changes on the recycling probability and, thus, the oxidative capacity. To study the oxidative capacity under high temperatures and VOC loading, the Air Quality and Climate Change in the Arabian Basin (AQABA) ship-based field campaign was conducted in the summer of 2017, starting in Toulon, France travelling around the Arabian Peninsula and back. The Arabian Gulf is characterized by intense solar radiation and high ambient temperatures, combined with strong emissions from the exploitation of its rich oil and gas reserves. As a comparison with the cooler and less polluted Mediterranean Sea, the Arabian Gulf can give insight into the impact of rising global temperatures on the recycling probability under conditions of large anthropogenic VOC emissions. The radicals OH and HO2 were measured by the ground-based HydrOxyl Radical Measurement Unit based on fluorescence Spectroscopy (HORUS). Despite higher primary production in the Arabian Gulf (2.3±0.2 ∙107 molec cm-3 s-1, Mediterranean Sea: 1.3±0.2 ∙107 molec cm-3 s-1), radical concentrations were lower by a factor of >1.5 and the recycling probability (15±10 % (1σ) @ 0.1 pptv NO) showed values greatly decreased compared to the Mediterranean Sea (57±5 % (1σ) @ 0.1 pptv NO). Box-model calculations, investigating the reason for the reduced recycling probability compared to the Mediterranean Sea, show an increased importance of radical-radical reactions in the Arabian Gulf, due to high concentrations of RO2 radicals. These reactions can cause radical recycling or destruction. While radical destruction directly decreases the recycling probability through termination of the radical propagation, radical recycling from these reactions caused an indirect decrease, as they could not be included in the calculation. Throughout the recycling of HOx in the troposphere, tropospheric O3 is produced, which causes plant stress and is harmful for the respiratory system of humans and animals. Therefore, the radical recycling probability has a direct impact on the net ozone production rate (NOPR). The NOPR was calculated using, measured NO and HO2 and calculated RO2 concentrations. It is expected, that the NOPR has a maximum at the crossover point between its NOx-limited and VOC-limited regimes. However, no NO concentration was found throughout the AQABA campaign, where the NOPR peaked. Due to this finding, it was concluded that NOPR was NOx-limited in the marine boundary layer during the whole campaign.
DDC:	540 Chemie 540 Chemistry and allied sciences
Institution:	Johannes Gutenberg-Universität Mainz
Department:	FB 09 Chemie, Pharmazie u. Geowissensch.
Place:	Mainz
ROR:	https://ror.org/023b0x485
DOI:	http://doi.org/10.25358/openscience-8772
URN:	urn:nbn:de:hebis:77-openscience-08364545-937e-4f65-9716-d67497240b1d0
Version:	Original work
Publication type:	Dissertation
License:	CC BY
Information on rights of use:	https://creativecommons.org/licenses/by/4.0/
Extent:	xii, 181 Seiten ; Illustrationen, Diagramme, Karten
Appears in collections:	JGU-Publikationen