Atmospheric environmental assessment of next generation fuel

Research Project , Research Report 2007

Kenichi TONOKURA Environmental Science Center, Univ. of Tokyo

Abstract

Reactions of ?-hydroxyalkyl radicals (RCHOH) with molecular oxygen are important elementary reactions in environmental and atmospheric chemistry. In particular, the oxidation reaction of the simplest ?-hydroxyalkyl radical ? the hydroxymethyl radical (CH2OH) ? plays a significant role on the methanol oxidation processes in troposphere. The kinetics and absolute rate constants of the gas-phase reaction of the hydroxymethyl radical (CH2OH) with molecular oxygen have been studied using laser photolysis/ near-IR absorption spectroscopy. The reaction was tracked by monitoring the time-dependent changes in the production of the hydroperoxy radical (HO2) concentration. For sensitive detection of HO2, two-tone frequency modulation absorption spectroscopy was used in combination with a Herriott-type optical multipass absorption cell. Rate constants were determined as a function of temperature (236 K < T < 600 K) at 50 torr of N2. The experimental results exhibit a slight negative temperature dependence in the measured temperature region. Microcanonical variational transition state theory was used to estimate the rate constants of the investigated reaction. The results of the theoretical calculations also suggest a negative temperature dependence of the reaction rate constant in the measured temperature region. The temperature dependences of the rate constants of the reaction of the hydroxymethyl radical with molecular oxygen determined in the present study have an impact in the estimate of the atmospheric formation of HO2 and CH2O.

Keywords:

urban atmosphere, next generation fuel, methanol, atmospheric lifetime