Abstract
Abstract. First- and higher order-generation products formed from the oxidation of isoprene and methacrolein with OH radicals in the presence of NOx have been studied in a simulation chamber. Significant oxidation rates have been maintained for up to 7 h, allowing the study of highly oxidized products. Gas-phase product distribution and yields were obtained, and show good agreement with previous studies. Secondary organic aerosol (SOA) formation has also been investigated. SOA mass yields from previous studies show large discrepancies. The mass yields obtained here were consistent with the lowest values found in the literature, and more specifically in agreement with studies carried out with natural light or artificial lamps with emission similar to the solar spectrum. Differences in light source are therefore proposed to explain partially the discrepancies observed between different studies in the literature for both isoprene- and methacrolein-SOA mass yields. There is a high degree of similarity between the SOA mass spectra from isoprene and methacrolein photooxidation, thus strengthening the importance of the role of methacrolein in SOA formation from isoprene photooxidation under our experimental conditions (i.e., presence of NOx and long term oxidation). According to our results, SOA mass yields from both isoprene and methacrolein in the atmosphere could be lower than suggested by most of the current chamber studies.
Highlights
Isoprene (2-methyl-1,3-butadiene) is a biogenic volatile organic compound (VOC) emitted by vegetation
We investigate the formation of gas-phase first- and higher-generation products and Secondary organic aerosol (SOA) during isoprene and MACR + OH reactions in the presence of NOx
Gas-phase products and SOA formation from isoprene and MACR photooxidation were investigated in a stainless steel simulation chamber equipped with realistic artificial light sources (Fig. S1)
Summary
Isoprene (2-methyl-1,3-butadiene) is a biogenic volatile organic compound (VOC) emitted by vegetation. It is one of the most abundant non-methane hydrocarbons emitted into the troposphere, with annual global emissions of 440 to 660 TgC (Guenther et al, 2006). Because of its large emission rates and high reactivity, isoprene can have a strong influence on tropospheric photochemistry on the local, regional and global scales. Isoprene photooxidation in the presence of sufficient NOx is known to result in the production of significant quantities of ozone on regional scales, in rural as well as in urban areas during summer (Biesenthal et al, 1997; Starn et al, 1998; Wiedinmyer et al, 2001)
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