Paulot, Fabien Georges Andre (2011) Insights into the isoprene photochemical cascade. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:04292011-155605494
Isoprene emissions are the single largest source of non-methane reduced carbon to the atmosphere. Proper simulation of the effect of its photooxidation on regional air quality and secondary organic aerosol formation requires detailed multi-generation and multi-phase photochemical mechanisms. In this work, I first demonstrate that CF3O- chemical ionization mass spectrometry (CIMS) is a powerful method to probe isoprene photochemical oxidation. Under high NOx, isoprene nitrates and their photochemical products are directly observed and quantified. As isoprene nitrates are critical to the impact of isoprene photochemistry on ozone, these observations provide an important constraint on the effect of isoprene emissions on air quality in polluted and biogenic rich regions (e.g., Southeastern United States). The use of tandem CIMS in association with isotopically labelled hydroxy radicals is used to identify dihydroxyepoxides as major products of isoprene photooxidation in low NOx conditions. This class of compounds may provide an important precursor for secondary organic aerosols under acidic conditions. The chemical mechanism derived from these laboratory observations is then incorporated in a chemical transport model to assess the impact of isoprene photooxidation on atmospheric chemistry. I examine how the photooxidation of isoprene impacts the budget of formic and acetic acids, two ubiquitous trace gases whose sources are poorly constrained. Comparison with observations from satellite, ground and aircraft platforms, reveal a major missing source that may originate from the aging of secondary organic aerosols. Finally, the consequences of the multi-scale interplay between NOx and isoprene photochemistry on the tropical budget of ozone are examined using forward and adjoint sensitivity simulations.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Subject Keywords:||Atmospheric chemistry; biogenics; isoprene; chemical transport model|
|Degree Grantor:||California Institute of Technology|
|Division:||Engineering and Applied Science|
|Major Option:||Environmental Science and Engineering|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||23 May 2011|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Fabien Paulot|
|Deposited On:||06 Sep 2012 16:22|
|Last Modified:||26 Dec 2012 04:34|
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