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Extending the physicochemical characterization of aerosol particles in California


Aerosols affect the radiative balance of earth, alter cloud formation, and adversely impact human health. Knowledge of the physicochemical properties of particles, which can rapidly change, is essential to predict and mitigate their negative impacts. Hence, in-situ measurements of single-particle composition and physical properties are needed. Aerosol time-of-flight mass spectrometry (ATOFMS), which measures the size-resolved chemical mixing state of individual particles, was used to study aerosols at different locations in California. Soot particles internally mixed with soluble ammonium, nitrate, and sulfate transported from the Central Valley were found to be a major source of cloud condensation nuclei in the Sierra Nevada during winter 2010, never identified before. These aged soot particles may be affecting regional cloud microphysics and potentially precipitation. Rapid aging of biomass burning aerosols during intense urban fires were analyzed for the first time via single-particle mass spectrometry throughout the 2007 San Diego Wildfires. Furthermore, estimated size-resolved mass concentrations of particulate matter during the wildfires showed for the first time that particles < 400 nm contributed significantly to mass, with maximum PM₀.₄=148 [mu]g/m³. These observations are essential for predicting climate and health impacts of biomass burning aerosols. Measurements during May, 2011 at the Port of Los Angeles coupled to air mass back-trajectories indicate that transport from the Central Valley brings amines to the Los Angeles air basin, which has not been documented previously. Unexpectedly, nearly 60% of all ambient particles sampled contained amines. These results are important because amines cause adverse health problems. In addition to these ambient studies, work was done to improve the ATOFMS technique. Due to concern over health and climate impacts, a novel method was developed to study ultrafine (<100 nm) particles by coupling condensational growth to the ATOFMS. In a separate study, ion peak areas were successfully scaled into mass concentrations for the first time by comparison with data obtained from the particle-into-liquid sampler coupled to ion chromatography (PILS-IC) allowing the quantification of chemical data from the ATOFMS. By being able to probe smaller particles and quantify ATOFMS data, further insights into the variability of aerosol chemistry and sources can be gained

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