Abstract
Abstract. Reaction of stabilized Criegee intermediates (SCIs) with SO2 was proposed as an additional pathway of gaseous sulfuric acid (H2SO4) formation in the atmosphere, supplementary to the conventional mechanism of H2SO4 production by oxidation of SO2 in reaction with OH radicals. However, because of a large uncertainty in mechanism and rate coefficients for the atmospheric formation and loss reactions of different SCIs, the importance of this additional source is not well established. In this work, we present an estimation of the role of SCIs in H2SO4 formation at a western Mediterranean (Cape Corsica) remote site, where comprehensive field observations including gas-phase H2SO4, OH radicals, SO2, volatile organic compounds (VOCs) and aerosol size distribution measurements were performed in July–August 2013 as a part of the project ChArMEx (Chemistry-Aerosols Mediterranean Experiment). The measurement site was under strong influence of local emissions of biogenic volatile organic compounds, including monoterpenes and isoprene generating SCIs in reactions with ozone, and, hence, presenting an additional source of H2SO4 via SO2 oxidation by the SCIs. Assuming the validity of a steady state between H2SO4 production and its loss by condensation on existing aerosol particles with a unity accommodation coefficient, about 90 % of the H2SO4 formation during the day could be explained by the reaction of SO2 with OH. During the night the oxidation of SO2 by OH radicals was found to contribute only about 10 % to the H2SO4 formation. The accuracy of the derived values for the contribution of OH + SO2 reaction to the H2SO4 formation is limited mostly by a large, at present factor of 2, uncertainty in the OH + SO2 reaction rate coefficient. The contribution of the SO2 oxidation by SCIs to the H2SO4 formation was evaluated using available measurements of unsaturated VOCs and steady-state SCI concentrations estimated by adopting rate coefficients for SCI reactions based on structure–activity relationships (SARs). The estimated concentration of the sum of SCIs was in the range of (1–3) × 103 molec. cm−3. During the day the reaction of SCIs with SO2 was found to account for about 10 % and during the night for about 40 % of the H2SO4 production, closing the H2SO4 budget during the day but leaving unexplained about 50 % of the H2SO4 formation during the night. Despite large uncertainties in used kinetic parameters, these results indicate that the SO2 oxidation by SCIs may represent an important H2SO4 source in VOC-rich environments, especially during nighttime.
Highlights
Sulfuric acid, H2SO4, is an important atmospheric component identified as playing a key role in formation of secondary atmospheric aerosol through new particle formation processes (Dunne et al, 2016; Paasonen et al, 2010; Sipilä et al, 2010; Weber et al, 1997)
Despite large uncertainties in used kinetic parameters, these results indicate that the SO2 oxidation by stabilized Criegee intermediates (SCIs) may represent an important H2SO4 source in volatile organic compounds (VOCs)-rich environments, especially during nighttime
Based on the OH, H2SO4, SO2 and particle number density measurements and assuming validity of a steady state between H2SO4 production and its loss by condensation on existing aerosol particles with a unity accommodation coefficient, we have found that the contribution of the SO2 + OH reaction accounts for (86 ± 4) % and only for (9 ± 2) % of the H2SO4 production during the day and night, respectively
Summary
H2SO4, is an important atmospheric component identified as playing a key role in formation of secondary atmospheric aerosol through new particle formation processes (Dunne et al, 2016; Paasonen et al, 2010; Sipilä et al, 2010; Weber et al, 1997). H2SO4 is considered to be a major precursor of newly formed atmospheric nucleationmode particles and may play a significant role in their subsequent growth (Boy et al, 2005; Smith et al, 2005; Zhang et al, 2012). It is important to understand well the atmospheric mechanisms determining the H2SO4 concentrations in different atmospheric environments. It was assumed that H2SO4 atmospheric concentrations are determined predominantly by this source and the loss of sulfuric acid on the surface of existing particles, with the loss rate depending on the efficiency of H2SO4 uptake.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
