AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Elucidating Emission Sources and Atmospheric Processes of Aerosols in Fresno, CA: Results from 2013 Winter NASA DISCOVER-AQ Study
CAROLINE PARWORTH, Hwajin Kim, Shan Zhou, Sonya Collier, Xiaolu Zhang, Christopher Cappa, Qi Zhang, University of California, Davis
Abstract Number: 407 Working Group: Urban Aerosols
Abstract From January – February 2013 an intensive field study sponsored by NASA called Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality (DISCOVER-AQ) took place throughout central California. This work focuses on elucidating sources and processes of aerosols in Fresno, CA. Ionic PM$_(2.5) and gases were characterized with a particle-into-liquid sampler coupled with ion chromatography (PILS-IC) and gas denuders. The mass concentration and size-resolved composition of non-refractory PM$_1 (NR-PM$_1) were measured with an Aerodyne high resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS).
From the PILS-IC the total mass concentration of ionic PM$_(2.5) was determined to be 17.5 micro-grams per cubic meter, where NH$_4NO$_3 dominated mass concentration. From gaseous measurements of HNO$_3 and NH$_3 it was determined that formation of NH$_4NO$_3 in the particle phase is limited by gaseous HNO$_3 concentrations. Instrument intercomparisons show that ~90% of PM$_(2.5) mass is made up of NR-PM$_1 species, and highlights the importance of measuring NR-PM$_1 composition.
From the HR-ToF-AMS the average mass concentration of NR-PM$_1 was determined to be 32.13 micro-grams per cubic meter, and was dominated by organics (56% of total mass concentration), followed by nitrate (28%), ammonium (10%), sulfate (4%) and chloride (1%). Positive matrix factorization (PMF) was performed on the HR-ToF-AMS mass spectra and several types of primary organic aerosols (POA) and oxygenated organic aerosols (OOA) were obtained. The elemental compositions, temporal and diurnal variations, correlations with tracer compounds, and size distributions of these components have been investigated to characterize the sources and processes of PM$_1 in Fresno during winter time. Diurnal variations of mass concentrations for secondary aerosols (i.e., nitrate, sulfate, OOAs) show evidence of daytime enhancements associated with boundary layer breakage and mixing down of particles that were formed the previous night.