HR: 0800h
AN: A41A-0007    [Abstracts]
TI: Temperature and Composition Dependence of Secondary Organic Aerosol Formation From Terpenes
AU: * Donahue, N M
EM: nmd@andrew.cmu.edu
AF: Carnegie Mellon University, Doherty Hall, 5000 Forbes Avenue, Pittsburgh, PA 15213 United States
AU: Huff-Hartz, K
EM: karah@andrew.cmu.edu
AF: Carnegie Mellon University, Doherty Hall, 5000 Forbes Avenue, Pittsburgh, PA 15213 United States
AU: Presto, A
EM: apresto@andrew.cmu.edu
AF: Carnegie Mellon University, Doherty Hall, 5000 Forbes Avenue, Pittsburgh, PA 15213 United States
AU: Marquis, B
EM: styles@cmu.edu
AF: Carnegie Mellon University, Doherty Hall, 5000 Forbes Avenue, Pittsburgh, PA 15213 United States
AU: Lane, T
EM: tlane@andrew.cmu.edu
AF: Carnegie Mellon University, Doherty Hall, 5000 Forbes Avenue, Pittsburgh, PA 15213 United States
AU: Robinson, A L
EM: alr@andrew.cmu.edu
AF: Carnegie Mellon University, Doherty Hall, 5000 Forbes Avenue, Pittsburgh, PA 15213 United States
AB: Secondary Organic Aerosols (SOA) are formed in the atmosphere after oxidation of a volatile precursor. SOA comprise approximately 1/3 of the organic aerosol mass, and organic aerosol in turn is often the single most important fraction of total aerosol mass. SOA are also often semi volatile, with substantial mass fractions in both the condensed and vapor phases. The most important source of SOA appears to be ozonolysis of terpenes, including monoterpenes (C$_{10}$H$_{16}$) and sesquiterpenes (C$_{15}$H$_{24}$). Our knowledge of SOA mass yields from terpene ozonolysis is limited in two major ways. First, there are few data constraining the temperature dependence of SOA yields, and second, ozonolysis yields are typically only well constrained under low NO$_x$ conditions. We shall address both of these limitations here. First, to constrain the temperature dependence of SOA production we must separate the effect of temperature on the chemistry itself from the effect of temperature on the vapor pressure. Our solution is to carry out ozonolysis in a temperature-controlled smog chamber at a fixed temperature ranging from 15 to 40 $^o$C and then to vary the chamber temperature through its full range after the chemistry has run to completion. Bulk SOA mass yields are determined through SMPS measurement, while composition is determined via periodic filter sampling followed by solvent extraction derivatization GC/MS. In this way we are able to observe partitioning (vapor pressure) effects in the ozonolysis of d-limonene, culminating in large yields of SOA near 20 $^o$C, followed by a shift in chemistry at lower temperature causing lower SOA yields. Second, to constrain the VOC/NO$_x$ dependence of SOA production, we also carry out experiments in the presence of NO$_x$, under near UV illumination to maintain a stable NO/NO$_2$ ratio. Basic functional group levels (e.g.\ carbonyls vs nitrates) are monitored via FTIR analysis of teflon filter samples. Consistent with expectations, SOA yields decrease with increasing NO$_x$, as progressively more nitrates are observed on collected aerosols.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0317 Chemical kinetic and photochemical properties
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting