Volatility and oxidative reactivity properties of diesel exhaust particles: role of fuel, engine load, and emissions control
Date
2018
Authors
Sharma, Naman, author
Jathar, Shantanu H., advisor
Volckens, John, committee member
Henry, Charles S., committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Diesel exhaust particles (DEP) are air pollutants that adversely affect air quality and human health. DEPs have been shown to be semi-volatile and hence they partition between the gas and particle phase. DEP's additionally are also very reactive and can directly or indirectly lead to the formation of reactive oxygen species inside the human body. The volatility and oxidative reactivity of DEP are not well understood and particularly uncertain when it comes to alternative fuels, engine load and modern emissions control devices. In this study, we measured DEPs from a modern-day non-road diesel engine for two different fuels (conventional diesel and soy-based biodiesel), two different engine loads (idle and 50% load), and with and without emissions control devices. The DEPs were collected on a combination of bare quartz (BQ), Teflon® and quartz behind Teflon® (QBT) filters for approximately 8 different dilution ratios. We also measure gaseous pollutants like CO, CO2, NOX, O2 and THC from diesel engine over the fuel-load-emissions control combinations. These collected filters were later used offline to determine volatility, composition and oxidative reactivity of DEPs. The Teflon® filters were used to determine gravimetric mass, inorganic ions, water soluble organic carbon, black carbon and oxidative reactivity. The quartz filters were used to determine trace metals, organic carbon, elemental carbon, volatility and oxidative reactivity. Differences between the bare quartz and quartz behind Teflon® filter were used to infer the volatility. A dithiothreitol chemical assay was used to measure the oxidative reactivity of DEP's. This study is an effort to determine the link between PM composition, volatility and oxidative reactivity for two different fuel combination, two different engine load and influence on emission control systems. The use of biodiesel fuel tends to decrease NOX, THC and CO2 emissions factors when compared against diesel fuel. However, we see an increase in CO emissions factor for biodiesel fuel. The NOX and CO emission factor increased as we go from idle to 50% load conditions but remain almost same for CO2 and decreases significantly for THC. The emissions control system decreases THC and NOX emissions for both ideal and load conditions. The estimated volatility distribution did not change with fuel, engine load, or emissions control system and only one distribution could be used in atmospheric models. In contrast, the oxidative reactivity of DEPs from the use of biodiesel fuel seemed to be lower (~83 and 97%) than that for diesel fuel on an emission factor basis. The oxidative reactivity for different engine loads does not seem to show any trend on a per PM basis unlike some other previous studies. However, the oxidative reactivity was lower for 50% load condition (~67%) as compared to idle conditions on an emissions factor basis. The use of a diesel particulate filter (DPF), which is an emissions control device, significantly reduced (~93%) the oxidative reactivity of DEPs. This study also observed the influence of semi-volatile vapors (QBT), which contributed nearly 25% of the oxidative reactivity of particles and vapors (BQ). Finally, the oxidative reactivity of DEPs was compared for filter and solvent membrane effects. The oxidative reactivity of DEPs extracted from Teflon® was found out to be higher by a factor of ~2 when compared with the reactivity associated with quartz membrane filter. The oxidative reactivity for organic solvent is higher and show very strong response than water-based solvent especially for biodiesel exhaust particles.