Atmospheric reactions of substituted butanes with OH radicals: kinetics and atmospheric implications.

Abstract

2-Chlorobutane (2CB) and 2-aminobutane (2AB) are chiral compounds, which play a crucial role in biological complexity. These compounds can be released into the air through natural and man-made processes. Their emission into the atmosphere may influence the air quality and climate significantly. In the present work, the kinetics for the reactions of 2AB and 2CB were investigated experimentally and computationally at various temperatures. The rate coefficients for both reactions were evaluated using the SAR approach at 298 K. In addition, their impacts on the atmosphere have been discussed using atmospheric parameters. The experiments were performed using a pulsed laser photolysis - laser induced fluorescence technique for both reactions over 268-363 K. The rate coefficients were measured to be (2.42 ± 0.08) × 10^-12 and (3.03 ± 0.05) × 10^-11 cm³ molecule^-1 s^-1, for OH-initiated reactions of 2CB and 2AB, respectively. The computational calculations for these reactions were performed at the CCSD(T)/aug-cc-pVDZ//M06-2X/6-311+G(d,p) level of theory for 2CB and 2AB over 200-400 K. The rate coefficients were compared with changing the substituent on the butane chain. Cumulative atmospheric lifetime, radiative forcing, global warming potential, and acidification potential were calculated using the experimental and theoretical rate coefficients. In addition, the secondary organic compounds formed due to the reactions were analysed qualitatively using GC-MS and then compared with the theoretical results of the individual group contribution to the overall rate coefficients.