Characterization of ultrafine and fine particles at a site near the Great Smoky Mountains National Park

Abstract

Continuous measurements were taken during a 22-day campaign held in the summer of 2000 at a site close to the Great Smoky Mountains National Park in eastern Tennessee. The campaign was conducted to investigate the relationships between ultrafine/fine particles and gaseous species observed. A varimax-rotation factor analysis was performed to explore the relationship of the fine and ultrafine particle number concentrations, the gaseous species concentration, the mean wind speed, and the solar radiation. A 6-factor model was found to best resolve 79.7% of the variability embedded in the data. The model suggests that 31.4% of the data variability could be explained by ultrafine particles (the diameters smaller than or equal to 100 nm). It was difficult to label this factor without chemistry information of the ultrafine particles. However, no gas species were loaded on Factor 1 indicating the ultrafine particles observed in this study were not associated with primary source emissions. The decoupling of the ultrafine particles from the fine particles also implies that the former ones might have been produced and transported to the site by separated mechanisms from those of fine particles. The second factor included the PM 2.5 mass concentration and the number concentrations of particles in the diameter range of 101–400 nm. The loading pattern on Factor 2 led to the conclusion that this factor was contributed by regional transport. The third factor includes CO, NO 2, reactive odd nitrogen (NO y ), and SO 2 that were contributed by primary source emissions. The mean wind speed and ozone were loaded in Factor 4 that was labeled as ozone transport. Identification of this factor led to an observation that ozone transport to the site was essentially decoupled from the regional transport factor of fine particles (i.e., Factor 2). Solar radiation was singly included in the fifth factor indicating this is a unique factor. The quality of NO data was marginal and the variable was distilled by the model into Factor 6. A multiple regression analysis further indicated that PM 2.5 mass concentration was best explained by CO, O 3, and number concentrations of particles in the diameter range between 0.1 and 0.4 μm. We also identified two unique events during the campaign in which the number concentrations of 31–51 nm particles dramatically increased by a factor of 10 in 30 min, reaching 40,000 cm −3 and lasting for a couple of hours. Particles in the size range just below and above those in the 31–51 nm diameter range also exhibited increases during these events, but the changes were much less dramatic.