AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Summer-time Volatility Measurement of Ultrafine Particles in the Midwestern United States: Field Measurement from Bondville, IL and Iowa City, IA
ASHISH SINGH, Robert Bullard, Charles Stanier, University of Iowa
Abstract Number: 578 Working Group: Aerosol Physics
Abstract Volatility measurement of ultrafine particles (10-100 nm) provides important information about particle formation pathways and thermodynamic properties, and can assist in constraining chemical composition. Bondville, IL and Iowa City, IA are two Midwestern U.S. sites where particle nucleation and extensive secondary sulfate and organic aerosol formation have been reported. Furthermore, the volatility of UFPs using V-TDMA has not been reported for many sites in the Midwest. Consequently, the relative contributions of organic and inorganic constituents to particle growth in the UFP size ranges, and the presence or absence of non-volatile particle cores in 10-100 nm particles, has not been determined. Summer volatility measurement in Iowa City showed 20% residual volume at 260 0C for the total particle population. In contrast, size resolved volatility at nuclei mode detected less than 2% residual volume. Preliminary data also shows diurnal patterns and little residence time sensitivity.
This study will present results for UFP volatility from preliminary measurements (Iowa City, 2012) and a 2013 sampling campaign (summer, Bondville, IL). Temporal variability of size resolved volatility; including diurnal, weekday-weekend, and month-to-month variability will be investigated. The mixing state of UFPs will be investigated using size resolved volatility at 80-260 0 C and its variability will be explained. The contribution of non-volatile core to volatility profiles will also be determined. VTDMA results will be interpreted with respect to pollutant trace gases and particulate times series (e.g. CO, SO$_2 and NO$_x, NH$_3 and BC). The non-volatile core will be investigated to identify the possible anthropogenic sources.
In addition to field measurements, a computational model (size resolved, fully dynamic aerosol model with volatility basis set) will be used to explain observations and to infer possible chemical compositions of the aerosol, as well as fractions of volatile, semi-volatile to non-volatile species.