Temperature Dependent High-Resolution UV- and IR-Absorption-Cross-Section Spectra of Low-Volatility SOA Precursor Hydrocarbons in the Gas-Phase
EMSL Project ID
25718
Abstract
This proposal is a continuation of research under EMSL User Proposal #10894. Aerosols pose and increasingly serious concern for public health, agriculture and global climate. Increasing amounts of volatile organic compounds of (VOCs), NOx and primary organic aerosol (POA) are emitted into the atmosphere. SOA forms from the condensation of VOC oxidation products as the result of atmospheric chemistry. Recent testing of our predictive capabilities of aerosols in urban air revealed large gaps in the current understanding of SOA formation [Volkamer et al., 2006]. Contrary to previous believe, SOA was found a major component of fine particulate mass, and missing SOA precursors were identified as one possible explanation to resolve the inability to predict the SOA amounts that were observed. Since then, POA evaporation upon exhaust dilution has been demonstrated a previously unrecognized source for additional SOA precursor hydrocarbons in form of SVOCs (defined by a vapor pressure range 10-8 < vp < 10-4 kPa), and IVOCs (defined by a vapor pressure range 10-4 < vp < 10-2 kPa) [Robinson et al., 2007]. Polycyclic aromatic hydrocarbons (PAHs)are a particular form of IVOCs. Naphthalene, the most volatile, has a vapor pressure at room-temperature of 5 x10-3 kPa. PAHs are currently not considered among the precursors represented in SOA models. Recent advances with the direct detection of naphthalene, 1-methyl-naphthalene, 2-methylnaphthalene has been demonstrated in Mexico City by Differential Optical Absorption Spectroscopy (DOAS). DOAS enables the direct detection of these IVOCs in the ultraviolet spectral range at high time-resolution, and breaks novel ground for the assessment of sources, health effects, and studies of the partitioning between the gas- and aerosol phases. While the capability to obtain isomer-specific quantitative information of these most volatile PAHs could be demonstrated (from using relative absorbance spectra as reference spectra), the DOAS calibration requires a-priori knowledge of high-resolution absorption cross-section spectra in digital form. Such spectra are currently not available in the literature, partly due to experimental challenges that are to be overcome with characterizing gas-phase absorption cross-sections of low-volatility hydrocarbons.
The aim of this proposal is to measure high-resolution absorption cross-section spectra of a series of substituted PAHs in the ultraviolet and infrared spectral ranges as a function of temperature, and improve the wavelength accuracy of absorption cross-section spectra of other known SOA precursor VOCs (monocyclic aromatic hydrocarbons).
Project Details
Project type
Large-Scale EMSL Research
Start Date
2007-06-01
End Date
2009-04-06
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members