Volatile organic compounds in urban environments: composition, source apportionment, and chemical transformation

Embargoed until 2023-03-17
Author
Date
2020Type
- Doctoral Thesis
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Abstract
Volatile organic compounds (VOCs) contribute significantly to the formation of ozone
(O3) and secondary organic aerosol (SOA) in the troposphere. Besides their influence on
tropospheric chemistry, VOCs also affect air quality and climate both directly and indirectly.
Biogenic VOC (BVOCs) emissions are the predominant source on a global scale, while in
the urban areas anthropogenic VOCs are more important. Among them, traffic and solid fuel
combustion are important emission sources. After emission, they react with various oxidants,
yielding oxygenated VOCs (OVOCs). Due to the high variabilities of VOC sources and
reactivity, the determination of VOC sources remains challenging. Due to limitations in the
measurement techniques, a large fraction of OVOCs in the urban areas is still poorly
understood.
In this dissertation, we used a proton-transfer-reaction time-of-flight mass
spectrometer (PTR-ToF-MS) in different urban environments to investigate the VOC
emission sources and to obtain a deeper understanding of their chemical evolution with
support from the positive matrix factorization (PMF) receptor model. Intensive campaigns
were carried out at two sites in Delhi, India, as well as an urban site in Beijing, China, and
an urban site in Zurich, Switzerland.
The measurement campaigns in Delhi aimed at characterizing for the first time a wide
range of VOCs in this severely polluted environment. At both the urban and suburban site,
high nocturnal concentrations of VOCs were observed with strong day-night variations.
Primary emissions were predominant at both sites, mostly from traffic and solid fuel
combustion. Large amount of aromatics, furans and phenols were emitted and were
significantly elevated at night. The secondary factors, which were dominated by oxygenated
VOCs were substantially higher during daytime. A comparison between the two sites
showed that primary sources were significant at both sites, however, OVOC concentrations
were higher at the suburban site. While the urban OVOCs were tightly associated with aging
of local primary emissions, the suburban OVOCs represented both local oxidation and
regional aging.
The measurement campaign in Beijing was performed to investigate VOC evolution
during winter and the potential roles of VOCs to SOA formation under haze conditions. Ten VOC families were classified, which showed clear variation of the relative composition as a
function of the VOC concentration. The haze periods were driven by very high
concentrations of aromatics originating from traffic and solid fuel combustion. Trajectory
analysis indicated that both accumulation and regional influences were important for high
VOC concentrations during haze periods. The OVOC factor was predominant during the
clean periods, but decreased significantly during the haze periods. Meanwhile, oxygenated
organic aerosol (OOA) concentration were enhanced during high VOC concentration
periods, indicating the importance of OVOCs to secondary organic aerosol formation.
The Zurich campaign focused on the chemical evolution of VOCs and their oxidation
products in a relatively clean urban environment in summer. Traffic was the major
anthropogenic source, with an additional local source related to activities such as cigarette
smoke. Three OVOC factors were identified representing oxidation processes of different
oxidants and precursors. Two OVOC factors featured strong contributions from aromatic
oxidation and were separated by day-night chemistry. The third OVOC factor was
characterized by strong biogenic influences and exhibited similar temporal variation as
biogenic SOA. A comparison with the biogenic SOA composition showed similarities in
important organic family time series in both the gas and aerosol phase. Show more
Permanent link
https://doi.org/10.3929/ethz-b-000475028Publication status
publishedExternal links
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Contributors
Examiner: Baltensperger, Urs
Examiner: McNeill, Kristopher

Examiner: Prévôt, André Stephan Henry
Examiner: Holzinger, Rupert
Examiner: Slowik, Jay Gates
Publisher
ETH ZurichOrganisational unit
03850 - McNeill, Kristopher / McNeill, Kristopher
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