Hexenols are known as one of the most important groups of biogenic volatile organic compounds (BVOCs). Their oxidation reactions in the atmosphere can affect the formation of ozone and secondary organic aerosols (SOA), thus causing significant effects on atmospheric environment. These effects may become increasingly significant because environment and climate changes are promoting the emissions of these compounds through O₃ concentrations increasing and global warming. Therefore, understanding their atmospheric chemistry, such as reaction rates and degradation processes, is important for accurate model simulation and for prevention and control purposes.

After their emission into the atmosphere, hexenols are expected to be degraded mainly by reactions with tropospheric oxidants, OH radical being the most dominant oxidant, which proceeds in principle through OH-addition channel and H-abstraction channel. H-abstraction channel was often considered to be with minor importance and thus ignored in the theoretical studies. However, large discrepancy was found in the literatures between the experimental and the theoretical results, causing a greater uncertainty in the model results based on these theoretical data. The possible reason for these disagreements may result from the neglect of the H-atom abstraction reaction pathway.

Recently, a research group led by Prof. ZHANG Weijun at Hefei Institutes of Physical Science, Chinese Academy of Sciences (CASHIPS) conducted a study to better understand the atmospheric reactions of a series of hexenols with OH radicals using both experimental and theoretical methods, and also evaluated the relative importance of the H-abstraction reaction channel.

The results showed that the presence of hydroxyl groups in the studied hexenols can make H-abstraction reactions more prone to occur, which greatly increased the proportion of H-abstraction reaction channels. By comparing the reaction rate constants of the OH-addition channel with those of the H-abstraction channel, H-abstraction channels were found to contribute more than 20% for most of the studied reactions, some even more than 50%. Thus, H-abstraction channels may have an important role in the reactions of these hexenols with OH radicals and cannot be ignored. The results of this study have an important guiding role in atmospheric theoretical research and model improvement.

A paper describing this work, entitled “Experimental and Theoretical Study of Reactions of OH Radicals with Hexenols: An Evaluation of the Relative Importance of the H Abstraction Reaction Channel” has been published in Environ. Sci. Technol.

This work was supported by the National Natural Science Foundation of China and the Natural Science Foundation of Anhui Province.

Atmospheric reaction mechanism of hexenols with OH radicals: OH-addition channel or H-abstraction channel (Imaged by GAI Yanbo)