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Browsing by Author "Tu, Jingyi"

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  • Tu, Jingyi (2023)
    Atmospheric aerosol particles play a significant role in urban air pollution, and understanding their size distribution is essential for assessing pollution sources and urban aerosol dynamics. In this study, we use a novel method developed by Kontkanen et al. (2020) to determine size-resolved particle number emissions in the particle size range of 3-800 nm at an urban background site and a street canyon site in Helsinki. Our results show overall higher particle number emissions in the street canyon compared to the urban background. On non-NPF event days, the particle number emissions of 3-6 nm particles in the urban background are highest in the noon. The emissions to the size range of 6-30 nm are highest during the morning or afternoon at both sites, indicating traffic is the main particle source in this size range. The emissions of larger particles are relatively low. Seasonal analysis suggests higher emissions during the summer in comparison to the winter which might be linked to higher product of mixing layer height (MLH) and particle number concentration in summer. Further investigations into particle emissions from different wind sectors suggest higher particle emissions from the urban sector than from the road sector in the urban background, contrary to the results for NOx concentrations. More research is needed to better understand the underlying factors. In addition, a comparison between particle number emissions estimated using FMI measurement MLH data and ERA5 model MLH data reveals that FMI data provides a more reliable representation of the MLH in the study area. Overall, the methods show limitations in accurately capturing particle dynamics in Helsinki. Future studies should address these limitations by employing more accurate NPF event classification and refining sector division methods.