Comparison of isoprene chemical mechanisms under atmospheric night-time conditions in chamber experiments : Evidence of hydroperoxy aldehydes and epoxy products from NO3 oxidation

The gas-phase reaction of isoprene with the nitrate radical (NO3) was investigated in experiments in the outdoor SAPHIR chamber under atmospherically relevant conditions specifically with respect to the chemical lifetime and fate of nitrato-organic peroxy radicals (RO2). Observations of organic products were compared to concentrations expected from different chemical mechanisms: (1) the Master Chemical Mechanism, which simplifies the NO3 isoprene chemistry by only considering one RO2 isomer; (2) the chemical mechanism derived from experiments in the Caltech chamber, which considers different RO2 isomers; and (3) the FZJ-NO3 isoprene mechanism derived from quantum chemical calculations, which in addition to the Caltech mechanism includes equilibrium reactions of RO2 isomers, unimolecular reactions of nitrate RO2 radicals and epoxidation reactions of nitrate alkoxy radicals. Measurements using mass spectrometer instruments give evidence that the new reactions pathways predicted by quantum chemical calculations play a role in the NO3 oxidation of isoprene. Hydroperoxy aldehyde (HPALD) species, which are specific to unimolecular reactions of nitrate RO2, were detected even in the presence of an OH scavenger, excluding the possibility that concurrent oxidation by hydroxyl radicals (OH) is responsible for their formation. In addition, ion signals at masses that can be attributed to epoxy compounds, which are specific to the epoxidation reaction of nitrate alkoxy radicals, were detected. Measurements of methyl vinyl ketone (MVK) and methacrolein (MACR) concentrations confirm that the decomposition of nitrate alkoxy radicals implemented in the Caltech mechanism cannot compete with the ring-closure reactions predicted by quantum chemical calculations. The validity of the FZJ-NO3 isoprene mechanism is further supported by a good agreement between measured and simulated hydroxyl radical (OH) reactivity. Nevertheless, the FZJ-NO3 isoprene mechanism needs further investigations with respect to the absolute importance of unimolecular reactions of nitrate RO2 and epoxidation reactions of nitrate alkoxy radicals. Absolute concentrations of specific organic nitrates such as nitrate hydroperoxides would be required to experimentally determine product yields and branching ratios of reactions but could not be measured in the chamber experiments due to the lack of calibration standards for these compounds. The temporal evolution of mass traces attributed to product species such as nitrate hydroperoxides, nitrate carbonyl and nitrate alcohols as well as hydroperoxy aldehydes observed by the mass spectrometer instruments demonstrates that further oxidation by the nitrate radical and ozone at atmospheric concentrations is small on the timescale of one night (12gh) for typical oxidant concentrations. However, oxidation by hydroxyl radicals present at night and potentially also produced from the decomposition of nitrate alkoxy radicals can contribute to their nocturnal chemical loss

A Four Carbon Organonitrate as a Significant Product of Secondary Isoprene Chemistry

Abstract Oxidation of isoprene by nitrate radicals (NO3) or by hydroxyl radicals (OH) under high NOx conditions forms a substantial amount of organonitrates (ONs). ONs impact NOx concentrations and consequently ozone formation while also contributing to secondary organic aerosol. Here we show that the ONs with the chemical formula C4H7NO5 are a significant fraction of isoprene-derived ONs, based on chamber experiments and ambient measurements from different sites around the globe. From chamber experiments we found that C4H7NO5 isomers contribute 5%?17% of all measured ONs formed during nighttime and constitute more than 40% of the measured ONs after further daytime oxidation. In ambient measurements C4H7NO5 isomers usually dominate both nighttime and daytime, implying a long residence time compared to C5 ONs which are removed more rapidly. We propose potential nighttime sources and secondary formation pathways, and test them using a box model with an updated isoprene oxidation scheme

Learning About Urbanism and Life in Brazil

In 2005 a total of six Cal Poly students participated in the CRP department´s exchange program with the School of Architecture and Urbanism at the Federal University of Rio de Janeiro. This was the largest contingent of Cal Poly students in Brazil over a single academic year and also included students from the Landscape Architecture Department, what proves the success of this exchange program. CRP students Aaron, Karlo and Leah, and LA student Aron Nussbaum share their thoughts about academic and life experiences in Brazil

Bulletin, Howard Payne College, Volume 39, Number 1, April 1950

Catalogue describes the history, governance, admission requirements, course offerings, and campus life of Howard Payne College in Brownwood, Texas

Bulletin, Howard Payne College, Daniel Baker College, Volume 49, Number 1

Catalog describes the history, governance, admission requirements, course offerings, and campus life of Howard Payne College in Brownwood, Texas

Bulletin, Daniel Baker College, Series 14, Number 2, June 1923

Catalog describes the governance, history, course offerings, and campus life of Daniel Baker College in Brownwood, Texas

Bulletin, Howard Payne College, Volume 12 Number 2, June 1924

Catalogue describes the history, governance, admission requirements, course offerings, and campus life of Howard Payne College in Brownwood, Texas

Bulletin, Howard Payne College, Volume 8, Number 1, June 1920

Catalogue describes the history, governance, admission requirements, course offerings, and campus life of Howard Payne College in Brownwood, Texas

Bulletin, Daniel Baker College, Series 16, Number 3, July 1925

Catalog describes the governance, history, course offerings, and campus life of Daniel Baker College in Brownwood, Texas