Gaseous products and secondary organic aerosol formation during long term oxidation of isoprene and methacrolein

摘要

First- and higher order-generation products formed from the oxidationofisoprene and methacrolein with OH radicals in the presence of NO_x havebeen studied in a simulation chamber. Significant oxidation rates have beenmaintained for up to 7 h, allowing the study of highly oxidized products.Gas-phase product distribution and yields were obtained, and show goodagreement with previous studies. Secondary organic aerosol (SOA) formationhas also been investigated. SOA mass yields from previous studies show largediscrepancies. The mass yields obtained here were consistent with the lowestvalues found in the literature, and more specifically in agreement withstudies carried out with natural light or artificial lamps with emissionsimilar to the solar spectrum. Differences in light source are thereforeproposed to explain partially the discrepancies observed between differentstudies in the literature for both isoprene- and methacrolein-SOA massyields. There is a high degree of similarity between the SOA mass spectrafrom isoprene and methacrolein photooxidation, thus strengthening theimportance of the role of methacrolein in SOA formation from isoprenephotooxidation under our experimental conditions (i.e., presence of NO_xand long term oxidation). According to our results, SOA mass yields fromboth isoprene and methacrolein in the atmosphere could be lower thansuggested by most of the current chamber studies.