Goals
The objective of this project is to gain a better fundamental understanding of the atmospheric oxidation of volatile organic compounds (VOCs) important to urban and regional air quality. Specific aim is to elucidate the mechanisms of formation of organic aerosols from the atmospheric oxidation of VOCs.
Background
Gas-to-particle conversion is a ubiquitous process in the atmosphere, determining the size and composition of particles from the polluted urban atmosphere to the remote marine boundary layer. Understanding the detailed chemistry and physics of atmospheric gas-to-particle conversion will allow us to predict the effects of primary gaseous and particulate emissions changes on airborne particulate matter, in the urban and regional setting, and the effects of sulfur and other species on the generation of cloud condensation nuclei in the remote atmosphere. A principal goal of the research program is the development of comprehensive air quality models based on the most complete description of atmospheric chemistry and physics. These models are forerunners of those that will eventually be used in the regulatory process. This research is aimed at developing the organic portion of advanced gas-aerosol models, and to advance the current state of understanding of molecular processes. The component of the proposed research on gas-phase photooxidation chemistry has the goals of adding to the body of kinetic and mechanistic data for atmospheric organics, with particular emphasis on those VOCs that are potential aerosol precursors.
Method of Approach
The integrated research program to determine the mechanisms of photooxidation and secondary organic aerosol formation in the atmosphere for a number of important anthropogenic and biogenic hydrocarbons was carried out in the Caltech outdoor reactor and via ab initio molecular simulation. The smog chamber is employed to study integrated gas-phase and gas-to-particle conversion dynamics.
Summary of Progress and Accomplishments
Experiments were performed with _-pinene as the parent hydrocarbon in dark ozonolysis experiments that took a first look at the effect of relative humidity on SOA partitioning. Experiments were performed comparing the SOA yield of _-pinene onto initially dry and humid particles, and it was found that the SOA partitioning to the aerosol phase decreased when the initial seed aerosol was wet. A tandem differential mobility analyzer (TDMA) was developed and used to continuously monitor the hygroscopic nature of Pasadena fine particulate matter over a one-month period. A thorough investigation of cyclohexene-ozone dark reaction was completed with the identification of 15 compounds in the aerosol and gas phase, the determination of its SOA yield, as well as a first order attempt at modeling the gas-particle chemistry occurring in the system.
Finally, a new environmental smog chamber was designed and completed in the latter half of 1999 which allows for temperature control of the environmental test chamber. The new system provides temperature control of +/- 0.5º C for dark reactions and +/- 1.5º C for photolysis reactions and allows for the all aerosol-phase and gas-phase instrumentation to be equilibrated to the same temperature and conditions as that occurring inside the test chamber. The indoor facility sports two 28,000L Teflon chambers lit by nearly 300 4 foot, 40 watt blacklight lamps with an attainable equivalent NO2 photolysis rate twice that of Pasadena summer conditions. The facility has the capability of simulating dark experiments from 10 to 50º C and light experiments from 20 to 50º C. The temperature control also creates an stable environment for the study of relative humidity effects on the chamber aerosol.
Future Plans
Handling of QA/QC
All work is carried out in accordance with the CAO QA/QC Control Plan.
Key Personnel
Graduate Students:
Robert Griffin and David Cocker
Postdoctoral Fellow:
Jian Yu
CAO Collaborators:
Joe Bozzelli (NJIT)
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