Date of Degree
PhD (Doctor of Philosophy)
Chemical and Biochemical Engineering
Charles O. Stanier
Aerosols are ubiquitous throughout Earth's atmosphere and their size, chem- ical composition, and concentration cause varying degrees of impact on climate and human health. Atmospheric aerosols can affect climate by their varied interactions with incoming solar radiation and their role in cloud formation and microphysics. Nucleation of fresh particles plays a significant role in the number of boundary layer cloud condensation nuclei (CCN). Elevated sulfuric acid concentration from power production has long been shown to contribute to new particle formation, but is not present in all instances where nucleation is observed. A third component has long been hypothesized and different studies in different locations have shown evidence of either ammonia, amines, or organics acting in conjunction with sulfuric acid and water to initiate new particle formation under certain meteorological conditions. While atmospheric nucleation has been examined world-wide in many urban as well as remote forested locations, it has not been studied extensively in the non-forested Midwestern United States, where sulfuric acid from coal-fired power plants and ammonia from agricultural activity are prevalent. For this doctoral dissertation work, instruments were designed, built, and tested for the purpose of investigating the concentration, size distribution, and volatility of atmospheric aerosols in non-forested rural continental environments in the Midwestern United States. An impact assessment of the University of Iowa Power Plant on air quality in Johnson County, IA highlights the ability to field test the emission ratios of fine particulates emissions to other gaseous emissions. Analysis on 20 years of climatically relevant aerosol properties in the rural Midwestern location of Bondville, IL reveals enhancement of particle number in the Spring and Fall seasons. Bondville is also the location of a three-year aerosol vertical profiling field campaign, where ultra-fine particles were found to be enhanced in the planetary boundary layer. The long standing records are compared with current full aerosol size distribution particle measurements for a period of ∼ 10 months in Bondville, where the seasonality of high particle number concentrations are verified and attributed to nucleation. Nucleation is observed to varying degrees in all seasons at this location, but is most prevalent and intense in the Spring and Fall months under otherwise clean atmospheric conditions. This work paves the way for a more in depth examination of the volatility of fine particle matter during nucleation and the development of a Midwestern chemical nucleation model to investigate numerous nucleation conditions and mechanisms. This work will contribute important information to the atmospheric science community on the process controlling the particle number size distribution in the region.
An aerosol is defined as a liquid or solid particle suspended in a gas. Each cubic centimeter of air contains several thousand particles; and depending on how big they are, how many there are, and what they are made of – they can cause different impacts on climate and human health. An aerosol, for example can absorb or deflect incoming sunlight and can change the amount of solar energy that heats the atmosphere or reaches Earth's surface. Fine aerosols, also called fine particulate matter, smaller than 2.5 μm (PM2.5) have been shown to have negative effects on the human respiratory system. The sources, sizes, and types of particles from different natural and human activities are well characterized, but many particles in the atmosphere are not released directly into the atmosphere. Instead, they form within the atmosphere itself from gas molecules that cluster together (or nucleate) to form particles under certain atmospheric conditions. Sulfuric acid, which originates mainly from coal burnt in power plants, has long been known to cause formation of new particles in the atmosphere. Scientific studies have shown that the presence of ammonia, amines, and organic carbon may contribute to the formation and early growth of particles.
This thesis dissertation discusses evidence of new particle formation in the Midwestern United States, where sulfuric acid from coal-fired power plants and ammonia from agricultural activities are both prevalent. Instruments were designed, built, and tested for the purpose of investigating the amount, size, and composition of atmospheric aerosols in a rural environment in the Midwestern United States. An assessment of the impact of the University of Iowa Power Plant on the air quality in Johnson County, IA, determined that the power plant increases the concentration of NOx, NO, SO2 & PM, but that SO2 and PM2.5 are also influenced by other sources in the region. Analysis of 20 years of particle concentration data in the rural Midwestern location of Bondville, IL, reveals enhancement of the number of particles in the Spring and Fall. Bondville is also the location of a three-year aerosol aircraft data set, where ne particles were found to be enhanced at ground level. The longstanding data records are compared with additional particle sizing information for a period of ~ 10 months in Bondville, where the seasonality of high particle number concentrations are verified and attributed to the formation of new particles by nucleation. Nucleation is observed to varying degrees in all seasons at this location, but is most prevalent and intense in the Spring and Fall months under otherwise clean atmospheric conditions. This work contributes important information to the atmospheric science community in understanding the factors that control aerosol concentrations in the Midwest.
publicabstract, Aerosols, Nucleation, Particle Growth
Copyright 2015 Robert Lesley Bullard