Airborne particulate matter (PM) consists of solid and liquid particles suspended in air. PM causes many negative health effects when inhaled like exacerbations of asthma, chronic obstructive pulmonary disease (COPD), and premature death. The health impacts of PM depend on the physical size and chemical composition of the inhaled particles. Particles less than 2.5 micrometers can penetrate the deep lung and enter the bloodstream. Understanding the composition of PM helps study human exposures and evaluate PM sources to support control and mitigation strategies. This thesis examines PM in power plant emissions, in ambient air, and in homes, with an emphasis on characterizing hazardous metals.
PM emissions from the University of Iowa power plant were examined during a transition away from coal. Biomass is a renewable fuel and when used in place of or co-fired alongside coal it directly reduces emissions of fossil CO2 and PM to the atmosphere. PM emissions were examined under two scenarios: the first was a stoker boiler that fired 100% renewable energy pellets. PM and metal emissions reduced by 59 and 80% respectively despite increases to polycyclic aromatic hydrocarbons (PAHs) that was attributed to emission of unburned carbon fuel. The second test was done in a circulating fluidized bed boiler firing 78% oat hulls, 17% coal, and 5% energy pellets. Decreases in PM, PAHs, and metal emissions were 32, 33, and 50%, respectively. Reductions in PM, PAHs, and metals when firing renewable fuels provide environmental advantages to local air quality while trying to eliminate the use of coal.
Ambient air quality was examined downwind of the power plant. The levels of PM2.5 in Iowa City in 2016 ranged from 1.4-32.1 µg m-3 with an annual mean of 7.5 µg m-3. These levels are below the National Ambient Air Quality Standards (NAAQS) for 24-hours (35 µg m-3) and the annual average (12 µg m-3). On average, the analyzed metals accounted for 10.7 ± 5.3% of PM2.5. Potassium, calcium, and zinc were the most abundant metals (averaging 250 ± 10, 170 ± 40, and 11.2 ± 0.5 ng m-3, respectively) and are associated with geological sources and biomass burning. Metals associated with fossil fuel combustion such as arsenic, lead, or vanadium were observed at low levels (averaging 0.58 ± 0.01, 1.32 ± 0.03, and 0.19 ± 0.01 ng m 3, respectively). Harmful metals were at least an order of magnitude lower than the World Health Organization’s guideline concentrations in Iowa City PM2.5. Overall, the hazardous metals in ambient PM2.5 observed in Iowa City were not at concerning levels. The work in this chapter helps provide a metal speciation profile for future studies and these measurements can be used to assess future changes in PM2.5 metal concentrations.
Indoor PM collected in homes of Eastern Iowa COPD patients was characterized for its metal content. COPD patients are at higher risk of developing respiratory infections, which cause acute exacerbations of COPD—the leading cause of mortality in COPD patients—and airborne PM increases risk of infection. From the 21 homes studied 6-87 mg of indoor PM was collected over 30 days in winter. Crustal metals such as magnesium, iron, and aluminum were the most concentrated in indoor PM, having mass fractions from 3000-25,000 ng mg-1. Toxic metals like vanadium and arsenic were at lower levels from 3-65 ng mg-1. Between homes the relative abundance of metals was similar, but the absolute abundance was highly variable. Analyzing indoor PM is essential since Americans on average spend 80% of their day indoors making it a significant environment for PM exposure. This chapter provides a chemical profile for different homes when studying the impact PM has on respiratory health.
This thesis also provides new measurements of the chemical composition of PM at the point of emission, in ambient air, and within homes. Advancing knowledge of PM composition in different environments is vital in understanding its impacts on human health. Improvements to local air quality with reductions to PM and metal emissions were observed when firing alternative fuels. Ambient PM2.5 concentrations in Iowa City were lower than NAAQS levels and the composition of both ambient and indoor PM was evaluated. With greater understanding of PM composition, better control strategies can be studied and employed to improve local air quality.