| Current urban air pollution models do not adequately describe the concentrations of semivolatile aerosol components including nitrate, chloride, water, and organics. Our hypothesis has been that our lack of understanding of the thermodynamics of the aerosol system is inhibiting further progress. A state-of-the-art thermodynamic model predicting the partitioning of inorganic aerosol components is first developed. This model (GFEMN) accurately reproduces observed behavior of multicomponent inorganic aerosols over a broad range of temperature, relative humidity (rh), and composition.; GFEMN was used to evaluate the performance of several previous models which have been incorporated into large scale aerosol transport models. On average predictions of aerosol nitrate and total particulate matter (PM) agreed with those of GFEMN whereas for H+ and aerosol water predictions, significant differences were present. In reproducing ambient aerosol nitrate measurements taken in Southern California, a negative bias of approximately 30% in model predictions was present. However, the addition of crustal material into the modeling framework improved model performance implicating the importance of crustal material for atmospheric aerosol thermodynamics.; With GFEMN, the response of inorganic PM to precursor changes has been determined. A graphical methodology has been developed mapping these response regions for PM to total nitrate, ammonia, and sulfate.; To quantify the effect of metastable equilibrium states on the partitioning of total nitrate, aerosol behavior was simulated along the deliquescence and efflorescence branches. Comparing aerosol nitrate predictions from both cases, the effect of metastable solutions can be neglected for dealing with high pollutant concentrations (Southern California). However, in areas characterized by intermediate pollution levels (Eastern US), significant differences arise between the deliquescence and efflorescence branches for aerosol nitrate; efflorescence branch concentrations of aerosol nitrate are ∼ 50% greater. These findings implicate the importance of considering both branches of aerosol behavior in PM related studies for low to moderately polluted areas.; With regards to PM2.5 behavior in Mexico City, atmospheric equilibrium models predicted aerosol nitrate concentrations within 30% on average. However, the highest discrepancies existed for cases characterized by high temperatures and low rh. For these conditions, the dynamics of aerosol behavior may explain the high discrepancies.; In predicting the secondary organic aerosol (SOA) contribution to the total aerosol water, it appears that SOA accounts for approximately 7% of the total water on average. However, in areas of low inorganic mass fractions, this contribution can be as high as 20--30%. With regards to the effect on the partitioning of nitrate between the gas and aerosol phases, SOA are predicted to increase the concentration of nitrate in the aerosol phase by 10%. At low inorganic mass loadings, the predicted increase may be as high as 50%.; Ultimately, the findings of this research have increased our understanding of the behavior of inorganic and organic aerosols. If the role of crustal elements (i.e. dust), the efflorescence branch behavior, the SOA effect on nitrate partitioning, and the dynamics of aerosol behavior are all incorporated into existing air quality models, increased performance against measurements is expected. (Abstract shortened by UMI.)... |
