NOx source apportionment and oxidation in a coastal urban airshed using stable isotope techniques
| dc.contributor.advisor | Felix, J. David | |
| dc.contributor.author | Shealy, Kaiya | |
| dc.contributor.committeeMember | Coffin, Richard | |
| dc.contributor.committeeMember | Abdulla, Hussain | |
| dc.date.accessioned | 2024-08-09T21:53:20Z | |
| dc.date.available | 2024-08-09T21:53:20Z | |
| dc.date.issued | 2024-04-24 | |
| dc.description.abstract | NOx (NO + NO2) emissions decrease urban air quality, and its subsequent deposition can be a significant source of excess nitrogen loading to coastal waters. Photochemical reactions between volatile organic compounds and NOx in the atmosphere create ozone (O3). Previous studies suggest coastal urban airsheds tend to have a NOx limited ozone regime, so an increase in NOx would lead to an increase in O3. The first step to NOx emission mitigation and thus ozone reductions in these regions is to quantify the contributions of NOx sources. These sources have unique nitrogen isotopic compositions (δ15N-NOx) or “source signatures”, which allow the use of isotope mixing models to aid in determining emission source contribution. The corresponding oxygen isotopic composition (δ18O-NO2) of NO2 can be used to estimate the NO oxidation chemistry after emission from the sources. To investigate NOx dynamics in a representative coastal urban air shed, NOx and NO2 were passively sampled at four NOx and ozone monitoring stations of the City of Corpus Christi, Texas each month for one year and the nitrogen and oxygen isotopic composition (δ15N, δ18O) of each sample was measured. The δ15N-NOx and δ18O-NO2 values were applied to a Bayesian type mixing model to determine the apportionment of point (natural gas combustion) and nonpoint (biogenic soils, vehicles, marine shipping, biomass burning, and lightning) NOx sources in the air shed and determine NO oxidation chemistry (i.e. peroxy radical vs ozone pathway). Often, studies using this Bayesian mixing model include biomass burning and lightning as sources however, these are not continuous sources, and biomass burning and lightning events do not always produce enough NOx to be considered significant. We present an alternative to this “blanket” source approach by coupling HYSPLIT airmass back trajectories with lightning and fire remote sensing products to determine the significance of intermittent sources before including in a mixing model. This study also uses a more detailed approach to estimating the source signature of vehicular and industrial emissions. The average source signature for the combined diesel and gasoline vehicle fleet emissions was weighted according to proportion of diesel and gasoline emissions reported for the study region, and the industrial emission signature was expanded to also include marine shipping NOx emissions (weighted according to ship-type). This study determined NOx emissions are dominated by biomass burning emissions (41%) followed by vehicular (34%), lightning (12%), industrial (7%), and biogenic (6%) emissions and time periods of significant NOx emissions from biomass burning coincide with the burning season in Mexico. Emission apportionment results are within agreement of previous studies, but it is important to note the overlap in source signatures incorporated into the Bayesian mixing model. The most common isotopic endmembers for vehicular, biomass burning, and lightning overlap, and therefore introduce increased error into apportionment models. This highlights the future importance of having isotopic source signatures that are representative of specific regions of study. It was determined that the peroxy radical pathway (65%) is the dominant pathway for NO oxidation, with an increase in oxidation via the ozone pathway correlating with ambient ozone concentration. This study provided a first attempt at calculating the kinetic isotope effect (KIE) and subsequent enrichment factor of the radical pathway, estimated to be approximately -15‰. Results provide a greater understanding of NOx and ozone dynamics in coastal urban airsheds and can directly aid in the modification of coastal communities’ ozone action plans. Results enhance the understanding of atmospheric oxidative chemistry, information that is vital to constrain chemical transport models. Accurate source apportionments will be extremely useful for creating air quality regulations and ozone mitigation. | |
| dc.description.college | College of Science | |
| dc.description.department | Physical and Environmental Sciences | |
| dc.format.extent | 78 pages | |
| dc.identifier.uri | https://hdl.handle.net/1969.6/98127 | |
| dc.language.iso | en_US | |
| dc.rights | This material is made available for use in research, teaching, and private study, pursuant to U.S. Copyright law. The user assumes full responsibility for any use of the materials, including but not limited to, infringement of copyright and publication rights of reproduced materials. Any materials used should be fully credited with its source. All rights are reserved and retained regardless of current or future development or laws that may apply to fair use standards. Permission for publication of this material, in part or in full, must be secured with the author and/or publisher. | |
| dc.subject | environmental science | |
| dc.subject | ozone | |
| dc.subject | urban air quality | |
| dc.title | NOx source apportionment and oxidation in a coastal urban airshed using stable isotope techniques | |
| dc.type | Text | |
| dc.type.genre | Thesis | |
| thesis.degree.discipline | Environmental Science | |
| thesis.degree.grantor | Texas A & M University--Corpus Christi | |
| thesis.degree.level | Masters | |
| thesis.degree.name | Master of Science |