Full metadata record
| DC Field | Value | Language |
|---|---|---|
| dc.contributor | Department of Civil and Environmental Engineering | en_US |
| dc.contributor.advisor | Guo, Hai (CEE) | en_US |
| dc.creator | Huo, Yunxi | - |
| dc.identifier.uri | https://theses.lib.polyu.edu.hk/handle/200/13920 | - |
| dc.language | English | en_US |
| dc.publisher | Hong Kong Polytechnic University | en_US |
| dc.rights | All rights reserved | en_US |
| dc.title | New insights into the characteristics and chemistry of organic aerosols in Hong Kong : transition from outdoor to indoor environments | en_US |
| dcterms.abstract | Fine particulate matter (PM2.5, define as particulate matter with an aerodynamic diameter of 2.5 micrometers or less) pollution has become a significant environmental and public health issue in densely populated megacities like Hong Kong. Recent studies indicate that secondary organic aerosols (SOA) are increasingly contributing to PM2.5 levels, yet their sources and formation mechanisms remain insufficiently understood. Hong Kong, situated adjacent to the Pearl River Delta (PRD) region and the South China Sea, is influenced by both continental and marine air masses. This unique land-sea transitional zone may have an enhanced atmospheric oxidative capacity compared to typical urban areas, potentially facilitating SOA formation and the chemical evolution of organic aerosols (OA). Additionally, Hong Kong’s urban environment is characterized by dense, tall buildings and limited living space per-capita, where numerous chemicals, predominantly organics, are present in indoor air. However, there is a lack of understanding regarding the composition and evolution of indoor organic compounds. In this study, we collected OA samples from both indoor and outdoor environments using advanced chemical analysis techniques. This approach allowed us to obtain a high time-resolution dataset of OA markers, providing new insights into the characteristics and chemical processes of SOA in outdoor air. Building on this knowledge, I further investigated the indoor environment, thereby addressing a critical knowledge gap in Hong Kong’s indoor air quality research. The findings from this study enhance our understanding of the abundance and evolution of organic aerosols in both indoor and outdoor settings, and offer valuable guidance for developing effective air quality management strategies. | en_US |
| dcterms.abstract | To explore the formation and evolution processes of SOA in the outdoor environment, a comprehensive sampling campaign was conducted at a regional background site in Hong Kong. A central question in atmospheric chemistry is the extent to which anthropogenic emissions influence the formation of natural OA. To address this, a suite of state-of-the-art instruments was deployed to measure both bulk and speciated organic compounds in submicron particles. The study revealed that average carbon oxidation states (OSC) were higher at night in coastal air, contrasting with afternoon peaks in continental air. This suggests that aqueous reactions dominated in coastal air, as indicated by correlations between OS C, ozone and sulfate, while photochemical processes were more prevalent in continental air passing through the PRD region. The concentrations of ten speciated SOA markers were highest in continental air from the PRD, with high concentrations of anthropogenic SOA (ASOA) markers linked to precursor levels and intense photochemical reactions. A significant correlation (R² > 0.30) between these markers and total organics highlights the influence of anthropogenic emissions. In contrast, biogenic SOA (BSOA) markers derived from isoprene and monoterpenes were not directly explained by precursor levels. Detailed analysis showed that isoprene-derived SOA (iSOA) formation was influenced by aqueous reactions and potential aerosol seed formation. Elevated nighttime levels of 2-methyltetrols, differing from other SOA markers, were potentially linked to variations in relative humidity and/or gas-to-particle partitioning. Monoterpene-derived SOA (mSOA) formation was facilitated by in-situ photochemical processes in continental air, transforming fresh products into aged ones. Integrating bulk and molecular-level OA data, this study found that BSOA suppressed ASOA levels in coastal air, with SO₂ levels promoting BSOA formation. In two continental clusters, comparable levels of BSOA and ASOA were observed, but continental air traveling through the PRD region experienced higher atmospheric oxidation, favoring ASOA production. Hydroxyl dicarboxylic acids (OHDCA), important constituents of SOA, were observed at notable levels, with malic acid (a typical OHDCA species) concentrations reaching up to 533 ng m⁻³. In coastal air, OHDCA correlated well with sulfate (R²=0.48) during periods of higher relative humidity (RH) and droplet-mode sulfate size distribution, suggesting aqueous formation. In short-range continental air, OHDCA levels rose significantly from morning to early afternoon (406 ng m⁻³), correlating with corrected ozone levels considering titration loss (O3_corr, sum of ozone and nitrogen dioxide). underscoring the role of gas-phase photochemistry in regulating OHDCA formation. The elevated OHDCA was likely attributed to aqueous photooxidation, with dominant factors varying under different atmospheric conditions. The precursors of OHDCA may include biogenic emissions, as indicated by correlations of OHDCA with 2-methylglyceric acid (bihourly data) and isoprene and monoterpenes (daily average data). However, anthropogenic aromatics might also contribute, especially in short-range continental air. These findings provide valuable observational evidence for refining simulations of OHDCA formation and its impact on air quality and climate. | en_US |
| dcterms.abstract | To understand the emission characteristics and evolution processes of indoor OA, a detailed sampling campaign was carried out in a typical apartment in Hong Kong. While numerous studies have highlighted the adverse health effects of indoor particulate matters (PM), the molecular compositions and emission characteristics of PM-bound organic matter (OM) indoors remain poorly understood. This group of species is particularly critical due to its high concentration and complexity in indoor PM. In the Hong Kong residence where typical activities were performed at normal frequency and intensity, it was observed that these activities significantly elevated both the total concentration and the fraction of OM in indoor PM. However, during undisturbed periods-when no high-emission activities were occurring, though residual effects from previous activities might persist-the concentration of total PM-bound OM outdoors (10.3 ± 0.7 µg m⁻³) exceeded that indoors (8.2 ± 0.1 µg m⁻³). Indoor activities involving combustion or high-temperature processes significantly increased the indoor-to-outdoor (I/O) ratios for many organic species. In addition, factors such as gas-to-particle partitioning, secondary formation, carry-over (residues of pollutants in the air), and re-emission modulated the I/O ratios of certain compounds. We obtained detailed emission profiles of speciated organics for five indoor activities within a residence. During undisturbed periods, the indoor contribution to PM-bound OM was estimated to be no higher than 13.1%. However, carry-over and/or re-emission were evident for certain compounds emitted from cigarette smoking and incense burning. Clear evidence of the aging of indoor cooking emissions was observed, suggesting the presence of indoor heterogeneous chemistry. Kinetic analysis indicated that the effective rate constants for oleic acid indoors are higher than those outdoors, likely due to elevated indoor temperatures accelerating reaction rates. Despite lower ozone levels indoors, the lifetime of oleic acid is comparable to that outdoors, implying the presence of undiscovered oxidants in indoor air. These findings enhance our understanding of the emissions and airborne fate of speciated organics in indoor PM. | en_US |
| dcterms.abstract | Overall, this study comprehensively explored the characteristics and formation chemistry of OA in both indoor and outdoor environments in Hong Kong. Through online measurements, we identified key factors driving SOA formation in this land-sea transitional zone and examined the behavior of indoor OA in compact living spaces. The findings of this PhD thesis highlight the significant roles of aqueous and photochemical reactions in outdoor SOA formation. In addition, the study reveals the emission characteristics and evolution processes of indoor OA influenced by human activities. These results not only deepen our understanding of SOA formation in densely populated urban settings but also provide valuable insights for improving air quality management and mitigating health risks associated with particulate matter pollution. | en_US |
| dcterms.extent | 177 pages : color illustrations | en_US |
| dcterms.isPartOf | PolyU Electronic Theses | en_US |
| dcterms.issued | 2025 | en_US |
| dcterms.educationalLevel | Ph.D. | en_US |
| dcterms.educationalLevel | All Doctorate | en_US |
| dcterms.accessRights | open access | en_US |
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