Abstract
Abstract. Saturated aldehydes, e.g. 2-methylbutanal (2 MB, CH3CH2CH(CH3)C(O)H), are emitted into the atmosphere by several biogenic sources. The first step in the daytime atmospheric degradation of 2 MB involves gas-phase reactions initiated by hydroxyl (OH) radicals, chlorine (Cl) atoms, and/or sunlight. In this work, we report the rate coefficients for the gas-phase reaction of 2 MB with OH (kOH) and Cl (kCl), together with the photolysis rate coefficient (J), in the ultraviolet solar actinic region in Valencia (Spain) at different times of the day. The temperature dependence of kOH was described in the 263–353 K range by the following Arrhenius expression: kOH(T)=(8.88±0.41)×10-12 exp[(331±14)/T] cm3 molec.−1 s−1. At 298 K, the reported kOH and kCl are (2.68±0.07)×10-11 and (2.16±0.32)×10-10 cm3 molec.−1 s−1, respectively. Identification and quantification of the gaseous products of the Cl reaction and those from the photodissociation of 2 MB were carried out in a smog chamber by different techniques (Fourier transform infrared spectroscopy, proton transfer time-of-flight mass spectrometry, and gas chromatography coupled to mass spectrometry). The formation and size distribution of secondary organic aerosols formed in the Cl reaction were monitored by a fast mobility particle sizer spectrometer. A discussion on the relative importance of the first step in the daytime atmospheric degradation of 2 MB is presented together with the impact of the degradation products in marine atmospheres.
Highlights
The saturated aldehyde 2-methylbutanal (2 MB, CH3CH2CH(CH3)C(O)H) is emitted into the low atmosphere from several sources
The experimental set-up employed in this work has been described in detail elsewhere (Blázquez et al, 2020). This system consists of a deuterium-tungsten light source (DT-200, StellarNet) placed at the entrance of a 107.15 cm jacketed Pyrex® cell, connected by an optical fibre to a f/2 spectrometer that possesses a concave holographic grating (590 grooves mm−1)
This work presents a comprehensive study on the relative importance of the most important diurnal atmospheric degradation routes of 2-methylbutanal (2 MB) and on the formation of secondary pollutants
Summary
The saturated aldehyde 2-methylbutanal (2 MB, CH3CH2CH(CH3)C(O)H) is emitted into the low atmosphere from several sources. It is known that 2 MB is formed during the fermentation and drying processes of cocoa beans (Utrilla-Vázquez et al, 2020), the manufacturing process of tea leaves (e.g. Camellia Sinensis, Flaig et al, 2020), and as a consequence of the stress suffered by grapevine leaves due to drought (Griesser et al, 2015). This aldehyde is emitted into the atmosphere from wildland fires (Urbanski et al, 2008) and many industrial activities, such as poultry rendering operations during which animal by-products are processed (Kolar and Kastner, 2010).
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