Ozone Precursor Sources and Box Modeling of Ozone in Mexico City Under Altered Emission Conditions

This dissertation investigated ozone (O3) precursor sources and their impact on O3 formation in Mexico City Metropolitan Area (MCMA) under altered emission condition for March-May, 2016. Since the O3 formation regime in the MCMA has transitioned to VOC-limitation, the identification of key VOCs with highest O3 formation potential (OFP) and their precise source identification is essential. In the first task, initial VOC concentrations (IC-VOCs) were calculated for both day and night from measured VOCs (MC-VOCs). The fraction reacting before reaching the receptor site, contributing to O₃ formation, is termed consumed VOCs (C-VOCs). During rush hour times, the top C-VOCs were trans-2-butene (1.12 ppb), cis-2-butene (0.60 ppb), trans-2-pentene (0.43 ppb), propylene (0.33 ppb), ethylene (0.24 ppb), and isoprene (0.16 ppb). Despite trans-2-butene’s highest consumption rate, m,p-xylene was the top VOC for O3 formation due to its high atmospheric abundance, linked to industrial and vehicular emissions. In the second task, a modified positive matrix factorization (PMF) with Fpeak rotation (0.3 for MC-PMF and 0.5 for IC-PMF) was utilized to identify VOC emission sources. Similar eight main sources were found, albeit with differing contributions from MC-PMF and IC-PMF. While vehicular emissions (29.28%) remain the dominant source, biogenic emissions, initially ranked 6th, emerged as the 2nd largest C-VOC contributor, increasing by 0.41% in IC-PMF. Therefore, traditional PMF underestimates biogenic sources, highlighting the need for refined methods for source apportionment. Our approach distinguishes primary emissions from the reactive portion of VOCs driving secondary pollution. In the third task, the O3 production P(O3) was studied using a zero-dimensional box model for a severe O3 episode (12-15 March, 2016) to determine whether O3 formation in this region is VOC or NOx limited and implemented an updated strategy for VOC emission reduction. A combination of P(O₃) isopleths, VOC/NOx throughout the day, a satellite-retrieved HCHO/NO2 during the O3 episode at midday confirmed MCMA as VOC-limited regime for O3 formation. Unlike previous studies suggesting reduction of liquefied petroleum gas emissions, reductions of traffic emissions prior to 14:00 might be an essential step in lowering in-situ O3 production, as this time is in particular sensitive for VOC induced O3 formation.

Name thesis:degree_name

Doctor of Philosophy

Discipline thesis:degree_discipline

Atmospheric Sciences

Grantor

University of Houston

Year dc:date.issued

2025

Author dc:creator

• Akther, Tanzina 1993-

Advisor dc:contributor.advisor

• Rappenglueck, Bernhard

Committee members dc:contributor.committeemember

• Jiang, Xun
• Czader, Arkadiusz
• Choi, Yunsoo

• Atmospheric science

Language dc:language.iso

English

Handle dc:identifier.uri

https://hdl.handle.net/10657/19547

OAI identifier oai:identifier

oai:uh-ir.tdl.org:10657/19547