Kinetic analysis of the gas-phase reactions of methacrolein with the OH radical in the presence of NOx

Abstract

Um mecanismo explícito para a reação da metacroleína (MTA) com radicais OH, numa mistura NOx -ar, foi simulado resolvendo as equações diferenciais ordinárias usando o método RungeKutta-4-semi-implícito. Os resultados simulados são consistentes com os dados experimentais publicados e o modelo explica as principais vias de reação para a oxidação da MTA com radicais OH na presença de NOx -ar. Usando uma análise dos autovetores e autovalores dos coeficientes de sensibilidade, para todas as espécies químicas envolvidas em diferentes tempos de reação, foi extraída informação cinética do sistema. Este método foi utilizado para reduzir o modelo cinético de forma objetiva. Foi utilizado, também, o método tradicional de análise de velocidade de produção (ROPA) para estudar a importância relativa das reações individuais. Usando a informação da análise de componente principal e da análise de velocidade de produção, foram identificadas as principais reações individuais.An explicit chemical mechanism for the reaction of methacrolein (MTA) with OH radicals in NOx-air systems, was simulated by solving the corresponding ordinary differential equations using Runge-Kutta-4-semi-implicit method. The simulated results are consistent with the published experimental data and the model accounts for all the major pathways by which MTA reacts in NOx-air systems. An eigenvalue-eigenvector analysis is used to extract meaningful kinetic information from linear sensitivity coefficients computed for all species of the chemical mechanism at several time points. This method is used to get an objective condition for constructing a minimal reaction set. Also, a classic method called rate of production analysis (ROPA) was used for the study of the reactions relevance. Using the principal component information as well as the rate of production analysis the main paths of reaction are identified and discussed.

In-cloud processes of methacrolein under simulated conditions – Part 1: Aqueous phase photooxidation

“…The comparison between the branching ratios observed in the aqueous phase and those known for the gas phase oxidation of methacrolein via OH gives some interesting information on the mechanism of the first step OH-attack. The branching ratio of the hydrogen abstraction pathway (B) is only 4.8±3.0% in the aqueous phase while it is between 45 and 50% in the gas phase (Pimentel and Arbilla, 1999;Orlando et al, 1999;Chuong and Stevens, 2004). This difference can be explained by the findings of Mellouki et al (2003) and Smith and Ravishankara (2002) who proposed that, in the gas phase, OH radicals form strong hydrogen bonds with the carbonyl groups.…”

In-cloud processes of methacrolein under simulated conditions – Part 1: Aqueous phase photooxidation

“…The comparison between the branching ratios observed in the aqueous phase and those known for the gas phase oxidation of methacrolein via OH gives some interesting information on the mechanism of the first step OH-attack. The branching ratio of the hydrogen abstraction pathway (B) is only 4.8±3.0% in the aqueous phase while it is between 45 and 50% in the gas phase (Pimentel and Arbilla, 1999;Orlando et al, 1999;Chuong and Stevens, 2004). This difference can be explained by the findings of Mellouki et al (2003) and Smith and Ravishankara (2002) who proposed that, in the gas phase, OH radicals form strong hydrogen bonds with the carbonyl groups.…”

Atmospheric Reaction of Cl + Methacrolein: A Theoretical Study on the Mechanism, and Pressure- and Temperature-Dependent Rate Constants

“…The biogenic volatile organic compounds, especially isoprene can undergo photolysis or chemical degradation by many species such as OH, O 3 , NO 3 , and Cl atoms. As one of isoprene’s major oxidation products, methacrolein (MACR) is also highly reactive toward OH, − O 3 , − NO 3 , − and Cl, − and is mainly degraded by the reaction with OH radical in atmosphere. However, large amounts of reactive chlorine compounds (ClNO 2 ), gaseous photolytic Cl atoms precursor, have been observed in continental regions far from marine and coastal regions .…”