AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Volatility Profile, Low Volatile Core and Mixing State of Ultra-fine Particles in the Midwestern United States
ASHISH SINGH, Robert Bullard, Matthew Johnson, Charles Stanier, University of Iowa
Abstract Number: 589 Working Group: Urban Aerosols
Abstract Volatility measurement of ultrafine particles (10-100 nm) provides important information about particle growth pathways and thermodynamic properties, and can assist in constraining chemical composition. Bondville, Illinois is a Midwestern United States site where particle nucleation and extensive secondary sulfate and organic aerosol formation has been reported. Furthermore, the volatility of UFPs using V-TDMA has not been reported for many sites in the Midwestern U.S. Consequently, the relative contributions of organic and inorganic constituents to particle growth in the UFP size ranges, and the presence or absence of low-volatile particle cores in 10-100 nm particles, has not been determined.
This study will present size-resolved volatility analysis of ultrafine particles from a yearlong field campaign in Bondville, IL. Analysis of volatility profiles is performed using K-means cluster analysis. The cluster analysis reveals three types of profiles for 15, 30, 50 and 80 nm particles. These profiles vary in the low volatile core, and in their resemblance to a pure ammonium sulfate volatility profile.
Aerosol mass resistant to evaporation (i.e. residue) is consistently observed at 200°C in all sizes from 15 to 80 nm. The amount of residue increases with particle size and ranges from 10-15% in 15 nm to 30-40% of the volume in 80 nm particles. V-TDMA at high temperature also reveals 20-30% of samples are external mixed, especially at the larger sizes of 30, 50 and 80nm. The timing and characterization of the external mixture with respect to different mode is analyzed.
Significant correlation between residue and ozone (O3), sulfur dioxide (SO2) and solar radiation is observed. The association of residue is further explored at different atmospheric conditions such as particle burst and growth events, local combustion and regional background, as well as across different sampling months, and also during consecutive particle formation and growth events.