AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
The Effect of Hydrophobic Gas-phase Organics on Formation and Properties of Biogenic Secondary Organic Aerosol
Alla Zelenyuk, David Bell, Jacqueline Wilson, Dan Imre, KAITLYN J. SUSKI, Josef Beranek, ManishKumar Shrivastava, Pacific Northwest National Laboratory
Abstract Number: 711 Working Group: Aerosol Chemistry
Abstract A number of field measurements indicate that significant fraction of atmospheric secondary organic aerosol (SOA) mass forms from biogenic precursors through pathways that are either driven by or enhanced by anthropogenic pollution, in a phenomenon that has been termed anthropogenic-biogenic interactions. Thus far, the laboratory studies attempting to reproduce this phenomenon were predominantly focused on the effect of acidic sulfate seeds, NOx, and SO2 on SOA formation mechanisms and yields.
We have previously shown that when SOA particles are formed from biogenic precursors in the presence of the vapors of polycyclic aromatic hydrocarbons (PAHs), which are common atmospheric anthropogenic pollutants, these PAHs become incorporated and trapped inside the formed SOA particles. While PAHs comprise only a small fraction of the total particle mass, their presence during particle formation, drastically changes the SOA particle properties. Compared with pure SOA particles, particles formed in the presence of PAHs have higher viscosity and oligomer content, and exhibit significantly lower evaporation rates.
Our recent studies demonstrate that the presence of PAHs during SOA formation significantly increases particles number concentrations and mass loadings, providing direct evidence related to field data indicating that biogenic-anthropogenic interactions could be responsible for an increase in SOA loadings. For example, ozonolysis of alpha-pinene in the presence of pyrene yields significantly higher loadings and particle number concentrations compared to pure alpha-pinene SOA, especially at low precursor concentrations. For 20 ppb alpha–pinene, the presence of pyrene increases mass loading by a factor of 1.7 and particle number concentration by a factor of 1.2, while for 5 ppb alpha–pinene, the presence of pyrene increases mass loading by a factor of 5 and particles number concentration by a factor of 200. Most recently we extended these studies to other biogenic precursors (isoprene and beta-caryophyllene) and hydrophobic organics, including benzo(a)pyrene, phenanthrene, and dibenzothiophene