Characterization of Non-Traditional Urban Emission Sources Utilizing a Mobile Laboratory

Exposure to ambient fine particulate matter (PM2.5) (fine particulate matter with diameter < 2.5 μm) has hazardous health impacts worldwide. A major challenge in reducing PM2.5 concentrations is that it comes from a variety of sources. This is especially true in urban areas, where there is a mixture of primary and secondary sources. The motivation for this study stems from the need to understand how anthropogenic emissions from multiple source sectors vary spatially and temporally in urban areas. As the trend of urbanization persists and cities undergo population expansion, the necessity to comprehend and mitigate air pollution in urban environments becomes increasingly vital. In addition, there are large spatial variations in PM2.5 concentration and composition in urban areas, and this variability is driven by differences in the spatial distribution of sources. This thesis aims to enhance our understanding of intra-city source contribution of both traditional (e.g. traffic) and non-traditional (e.g. asphalt and cooking) emission sources across space and time by investigating separate field campaigns in 2019 and 2021 to analyze the characteristics of organic aerosol (OA) from these sources.

While Cooking Organic Aerosol (COA) forms a significant proportion of ambient PM2.5 in urban areas, several knowledge gaps still exist. One important knowledge gap is the variability of the composition of COA emissions from real urban cooking sources. The majority of previous works have relied on a relatively small number of laboratory studies; less is known about how emissions from real cooking sources (e.g., restaurants) vary across urban areas. In addition, prior papers found that a massive amount of Volatile Organic Chemicals (VOCs) can be emitted from hot asphalt mixtures. Recent research has identified Volatile Chemical Products (VCPs), including personal care products like deodorant, printing inks, and asphalt paving, as an important source for subsequent SOAs in the atmosphere. Emissions from these source categories scale with population and are only lightly regulated. This is unlike other conventional forms of air pollution, such as traffic, which has been routinely identified and incorporated into substantial environmental policies. The initial field campaign in summer 2019 was conducted to explore characteristics of the PM compositions emitted by real-world restaurant cooking sources and asphalt paving fumes using Aerosol Mass Spectrometer (AMS). Findings from the field campaign in 2019 suggest that these plumes as significant sources of urban UltraFine Particles (UFPs) and reduced nitrogen. Variations were observed across different restaurants in terms of OA composition and reduced nitrogen species emissions, which are likely due to the different cooking method and ingredients at each restaurant sites. In our observations, PM mass emitted from restaurants was almost entirely Organic Aerosol (OA). Aerosol mass spectra show that while emissions from most restaurants were similar, there were key mass spectral differences. All restaurants emit OA at m/z 41, 43, and 55, though the composition (e.g., the ratio of oxygenated to reduced ions at specific m/z) varied across locations. All restaurant emissions included reduced nitrogen species detected as CxHyN+ fragments, making up ~15% of OA mass measured in plumes, with reduced molecular functionalities (e.g., amines, imides) that were often accompanied by oxygen-containing functional groups. The largest reduced nitrogen emissions were observed from a commercial bread bakery (i.e., 30-50% of OA mass), highlighting the marked differences between restaurants and their importance for emissions of both urban UFPs and reduced nitrogen. This study also focuses on Polycyclic Aromatic Hydrocarbons (PAHs) with the aim of isolating factors specifically related to PAHs, and hence improving the understanding of asphalt-related factors and their impact on urban air quality.

Incorporating PAH-related fragments derived from the previous chamber study in our group, this thesis examined that including higher m/z ranges of PAHs for the PMF analysis could potentially increase the accuracy of identifying asphalt-related factors, serving as an indicator of the subtle improvement in separation power.

To further understand the complexity of Cooking Organic Aerosol (COA), this study also identifies cooking markers detected by adopting the Offline Filter Inlet for Gases and AEROsols (FIGAERO)-Chemical Ionization Mass Spectrometer (CIMS) measurement. During the summer of 2021, we investigated OA concentration and composition across urban locations characterized by diverse levels of nearby anthropogenic emissions using the same mobile lab. Real-time measurements of NR-PM1 were obtained via AMS using a mobile laboratory, while PM2.5 samples were gathered on filters for subsequent analysis with iodide-based CIMS utilizing a FIGAERO inlet. The main findings from this campaign explain the discrepancies of CHN family contribution measured by the AMS and the CIMS. The 2021 campaign revealed an average CHN contribution of less than 1 % to the COA identified through the PMF analysis while the FIGAERO-CIMS revealed approximately 16 % of nitrogen containing compounds to the total. the online AMS measurement did not detect a high level of oxidized nitrogen compounds. This study also found that targeted analysis captures a small fraction (3.8 %) of the total compounds detected across the samples in this study.

This thesis demonstrated the variable characteristics of non-traditionally identified emission sources and potential to contain significant amount nitrogen in the COA emission formula in the real-world cooking environments. This integrated approach in our work will not only enhance our understanding of COA complexities but also demonstrate how CIMS can complement molecular information detected by AMS. Moreover, while targeted analysis provides useful insights, this comprehensive study highlights the critical need to adopt a broader analytical scope in environmental research on cooking emissions. This comprehensive analysis sheds light on the importance of understanding and mitigating often overlooked sources of urban air pollution, essential for developing effective air quality management strategies that protect public health.