Wei, Nana;
(2025)
Characterizing Reactive Nitrogen Sources and Abundances in Under-Sampled Regions of the World using Aircraft, Satellite Observations, and 3D Global Modelling.
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
Oxidized reactive nitrogen (NOy) influences global climate, air quality, and atmospheric chemistry. But the understanding of its sources and abundances is limited and outdated in under-sampled areas of Sub-Saharan Africa and the global upper troposphere (UT; ~8-15km). This thesis utilizes sporadic NASA DC-8 aircraft campaign observations, screened for plumes and stratospheric influence, to characterize UT NOy composition and evaluate current knowledge of UT NOy as represented by a state-of-science model (GEOSChem). The use of DC-8 data is supported by its ability to reproduce NOy seasonality from routine commercial aircraft measurements. I find that peroxyacetyl nitrate (PAN) dominates UT NOy (30-64% of NOy), followed by nitrogen oxides (NOx º NO + NO2) (6-18%), peroxynitric acid (HNO4) (6-13%), and nitric acid (HNO3) (7-11%). The model consistently overestimates peroxypropionyl nitrate (PPN) and underestimates NO2, as the model is missing PPN photolysis. An ~80 pptv (20-fold) underestimate in modelled methyl peroxy nitrate (MPN) over the Southeast US results from uncertainties in chemical aging of air masses. I derive top-down estimates of hotspot NOx emissions in Sub-Saharan Africa using satellite observations from TROPOMI to address data gaps for a rapidly growing region. I estimate annual (2019) top-down NOx emissions of 20 isolated hotspots totalling 322.8 Gg NOx that range from 0.95 Gg for Ibadan (Nigeria) and Hwange (Zimbabwe) to 101 Gg for the industrial Highveld in South Africa. The agreement between modelled and TROPOMI NO2 is significantly improved for large hotspots in South Africa when scaling down a widely used bottom-up emission inventory to match my top-down NOx than the default. Both local and regional inventories overestimate hotspot NOx emissions in South Africa by up to 65%. Further advancement of knowledge should focus on UT NOy sources, advection, chemical processing, and NOx emissions in data-deficit regions like Sub- Saharan Africa.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Characterizing Reactive Nitrogen Sources and Abundances in Under-Sampled Regions of the World using Aircraft, Satellite Observations, and 3D Global Modelling |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2025. Original content in this thesis is licensed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International (CC BY-NC 4.0) Licence (https://creativecommons.org/licenses/by-nc/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL SLASH UCL > Provost and Vice Provost Offices > UCL SLASH > Faculty of S&HS |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10216240 |
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