Physical Chemical and Toxicological Characteristics of Ultrafine Particulate Matter (PM).....

Physical, Chemical and Toxicological Characteristics of Ultrafine Particulate Matter (PM): Summary of 6 years Research by the US EPA Southern California Particle Center Speaker:
Prof. Costas Sioutas,
USC- Department of Civil and Environmental EngineeringIncreasing epidemiological and toxicological evidence links cardio-respiratory health effects with exposures to ultrafine particles (diameter < 0.1 µm). Emission inventories suggest that motor vehicles may be primary direct emission sources of ultrafine particles to urban atmospheres. Given the amount of traffic in the Los Angeles Basin, it is important to understand how ultrafine particles behave after emission as they are transported away from busy roadways. Understanding the characteristics of ultrafine particle volatility and how these traffic-emitted ultrafine particles penetrate indoor environments is also vitalThe goals of our research undertaken by the Southern California Particle Center and Supersite were to create an extensive inventory on what is known about the physical and chemical characteristics of atmospheric ultrafine particles. Utilizing a mobile particle concentrator, researchers set about characterizing the physical and chemical PM characteristics and volatility on/near freeways, in source and receptor areas of the Los Angeles Basin, the impact of mobile sources on indoor environments as well as ultrafine PM characteristics and emission factors in roadway tunnels with light-duty or heavy-duty vehicles.The data provided an increased understanding of how physical and chemical characteristics of ultrafine particles change on/near heavily trafficked areas; this information is necessary to better understand exposure outcomes. Relative concentrations of CO, black carbon and particle number decreased exponentially and tracked each other well as one moves away from the freeway. Our studies also showed that particles emitted from vehicles are externally mixed; different particles of the same size can have different chemical compositions. Depending on ambient conditions, between 70-90% of the particles by number, and 10-30% by mass consisted of semi-volatile material originating from condensation of organic vapors from fuel and lube oil. The non-volatile portion is known to primarily consist of elemental carbon, which is often coated with more volatile organic species. The volatility of these particles explains the more rapid decay in their concentration with respect to distance from a roadway, compared to that of non-labile PM species (such as EC) or gaseous co-pollutants such as CO and NOx, the concentration decrease of which would be affected mostly my atmospheric dilution. Our studies also showed that the volatile component of these particles may likely be present in its gaseous phase in indoor environments, causing particle shrinkage and-or compete evaporation as they infiltrate indoors. In future research, given that the majority of people's exposure during commute will be dominated (at least based on particle numbers) to these particles, it would be useful to know whether the non-volatile or semi-volatile material is more toxic.A better understanding of ultrafine particle characteristics and their volatility allows for the narrowing of the search for the most toxic PM components, and would also suggest new emissions control technologies that better protect the public health. Current particle traps remove non-volatile soot particles but not the precursors of the smaller semi-volatile particles. An unintended result of this reduction of the larger, non-volatile particles from the exhaust is the potential increase in the formation/emission of the smaller, semi-volatile PM as seen in our experiments performed at the Caldecott tunnel in which we determined size fractionated emission factors for heavy and light duty vehicles and compared them to those of previous studies in the same location.

Location: Kaprielian Hall (KAP) - rielian Hall, 203

Audiences: Everyone Is Invited

Contact: Evangeline Reyes