Browsing by Subject "Particulate Matter"

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    New particle formation: sulfuric acid and amine Chemical nucleation photochemical reaction chamber studies and the laboratory cluster-CIMS.
    (2012-02) Titcombe, Mari E.
    The formation of new particles from gas phase condensation has been shown to significantly enhance concentrations of cloud condensation nuclei (CCN) in the Earth's atmosphere. Particles that have grown to CCN size contribute significantly to Earth's radiation balance. And particle nucleation has been observed throughout the atmosphere in varying meteorological conditions. Yet the chemical processes involved in particle nucleation are not well understood. Sulfuric acid has long been recognized as a contributor to new particle formation. However, sulfuric acid condensation alone cannot account for high particle production and growth rates observed in many regions of the atmosphere. Scientific understanding of these processes has been limited by available instrumentation and the chemical complexity of the atmosphere. A novel Chemical Ionization Mass Spectrometer (cluster-CIMS) has been developed, in collaboration with colleagues at the National Center for Atmospheric Research, to characterize homogeneously nucleated molecular clusters produced in a controlled laboratory environment. The cluster-CIMS gently ionizes neutral molecular clusters for quadrupole mass filtration with a minimum of disturbance to cluster composition. It is capable of characterizing particles from molecular sizes up to 1.5 nm in diameter with a resolution of +/- 1 amu. A climate controlled photochemical reaction chamber, designed as a 1000 L batch reactor, was built to produce nucleated molecular clusters at atmospherically relevant conditions. Laboratory experiments were conducted to elucidate potential molecular candidates for particle nucleation. The role of amines in particle formation was experimentally examined after atmospheric observations revealed enhanced sulfuric acid nucleation rates in the presence of amine compounds. Experimental results obtained with the cluster-CIMS, as well as other aerosol instrumentation, support the hypothesis that amines enhance sulfuric acid nucleation rates.
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    Predicting Influence of Relative Humidity (RH) on Low-Cost Particulate Matter Sensors (LCPMSs) with Empirically Derived Single-Parameter for Hygroscopicity based on K-Kohler Theory
    (2022-12) Tejada, Rayan
    Low-cost particulate matter sensors (LCPMSs) could provide significant insight into air quality data with their ability to be placed virtually anywhere, short sampling time, and cost to build. However, LCPMSs are also known to significantly overestimate particle counts when the relative humidity (RH) is above 65%. It is widely considered that the hygroscopic growth of aerosols is the cause. Hygroscopicity of PM can be described by a single parameter, symbolized as K, and was used in a previous study (Di Antonio et al., 2018) to correct LCPMS data with promising results. However, the study assumed ambient PM to be a pure substance, however, it is often found to be a complex mixture of organic and inorganic chemical species. This study tested if a statistically derived empirical value of K, referred to as “ambient K”, could improve representing the RH influence on LCPMSs. Ambient K is defined as the statistically best-fitting value for several experimental observations of hygroscopy and makes no assumptions on the number of species in ambient PM. Ambient K was graphically demonstrated to be more representative of the experimentally observed RH error compared to assuming K, while having the same statistical performance as conventionally assuming K. Varying observations of hygroscopic behavior among multiple sensors provided strong evidence of multiple chemical species in the observed ambient PM.