EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmos. Chem. Phys., 13, 3865–3879, 2013 Atmospheric Atmospheric www.atmos-chem-phys.net/13/3865/2013/ doi:10.5194/acp-13-3865-2013 Chemistry Chemistry © Author(s) 2013. CC Attribution 3.0 License. and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Open Access Oxidation of SO2 by stabilized Criegee intermediate (sCI) radicals Open Access as a crucial source for atmospheric sulfuric acid concentrations Biogeosciences Biogeosciences Discussions M. Boy1, D. Mogensen1,2, S. Smolander1, L. Zhou1, T. Nieminen1, P. Paasonen1,7, C. Plass-Dulmer¨ 3, M. Sipila¨1, T. Petaj¨ a¨1, L. Mauldin1,4,5, H. Berresheim6, and M. Kulmala1 Open Access 1Department of Physics, P.O. Box 48, University of Helsinki, 00014 Helsink, Finland Open Access 2Helsinki University Centre for Environment, P.O. Box 27, University of Helsinki, 00014 Helsink, Finland Climate 3 Climate Hohenpeissenberg Meteorological Observatory, German Weather Service, Hohenpeissenberg, Germany of the Past 4Department of Atmospheric and Oceanic Sciences, University of Colorado at Boulder, P.O. Boxof 311,the Boulder, Past Colorado 80309-0311, USA Discussions 5Institute for Arctic and Alpine Research, University of Colorado at Boulder, P.O. Box 450, Boulder, Colorado 80309-0450, Open Access USA Open Access 6Center for Climate and Air Pollution Studies, School of Physics, National University of IrelandEarth Galway, System Galway, Ireland Earth System 7International Institute for Applied Systems Analysis (IIASA), Schlossplatz 1, 2361 Laxenburg, Austria Dynamics Dynamics Correspondence to: M. Boy (michael.boy@helsinki.fi) Discussions Open Access Received: 24 September 2012 – Published in Atmos. Chem. Phys. Discuss.: 22 October 2012 Open Access Revised: 3 March 2013 – Accepted: 17 March 2013 – Published: 12 April 2013 Geoscientific Geoscientific Instrumentation Instrumentation Methods and Methods and Abstract. The effect of increased reaction rates of stabi- together with these resultsData show that Systems the inclusion of this new Data Systems lized Criegee intermediates (sCIs) with SO2 to produce sul- oxidation mechanism could be crucial in regional as well as furic acid is investigated using data from two different loca- global models. Discussions Open Access Open Access tions, SMEAR II, Hyytial¨ a,¨ Finland, and Hohenpeissenberg, Geoscientific Germany. Results from MALTE, a zero-dimensional model, Geoscientific Model Development show that using previous values for the rate coefficients of Model Development sCI + SO2, the model underestimates gas phase H2SO4 by 1 Introduction Discussions up to a factor of two when compared to measurements. New particle formation in the troposphere is important for Open Access Using the rate coefficients recently calculated by Mauldin Open Access et al. (2012) increases sulfuric acid by 30–40 %. Increas- the global concentrationHydrology of cloud condensation and nuclei (CCN) Hydrology and (Spracklen et al., 2008; Makkonen et al., 2009; Pierce and ing the rate coefficient for formaldehyde oxide (CH2OO) Adams, 2009; Wang andEarth Penner, System 2009; Merikanto et al., Earth System with SO2 according to the values recommended by Welz 2010). Recently, Makkonen et al. (2012) presented the ef- et al. (2012) increases the H2SO4 yield by 3–6 %. Taken to- Sciences Sciences gether, these increases lead to the conclusion that, depend- fect of new particle formation on anthropogenic climate forc- Discussions Open Access ing on their concentrations, the reaction of stabilized Criegee ing in present-day and future (year 2100) conditionsOpen Access and concluded that with total aerosol forcing diminishing in re- intermediates with SO2 could contribute as much as 33– sponse to air pollution controls taking effect (especially re- Ocean Science 46 % to atmospheric sulfuric acid gas phase concentrations at Ocean Science ground level. Using the SMEAR II data, results from SOSA, ductions in sulfur dioxide (SO2)), warming from increased Discussions a one-dimensional model, show that the contribution from greenhouse gas concentrations can potentially increase at sCI reactions to sulfuric acid production is most important in a very rapid rate. According to several studies (e.g. Kul- Open Access the canopy, where the concentrations of organic compounds mala and Pirjola, 2000; Paasonen et al., 2010;Open Access Sipila¨ et al., 2010; Zhao et al., 2010; Lauros et al., 2011; Kirkby et al., are the highest, but can have significant effects on sulfuric Solid Earth acid concentrations up to 100 m. The recent findings that the 2011), sulfuric acid (H2SO4)Solid is one of Earth the initial or required molecules in the nucleation mechanism. In order to quantify Discussions reaction of sCI + SO2 is much faster than previously thought future atmospheric sulfuric acid concentrations, a complete Open Access Open Access Published by Copernicus Publications on behalf of the European Geosciences Union. The Cryosphere The Cryosphere Discussions 3866 M. Boy et al.: Oxidation of SO2 by sCI radicals understanding of the sink and source terms is crucial. Al- Finnish station SMEAR II. In the last two sections we will though the precursors for sulfuric acid (at least some of give a short discussion about the uncertainties in the calcula- them), as well as the main sink term (condensation on atmo- tions of different parameters and present a sensitivity study spheric aerosols) have been measured in several places, the on the effect of the reaction rates between Criegee interme- closure between measured and calculated sulfuric acid con- diates and water on the overall budget of sulfuric acid. centrations has rarely been investigated (Eisele et al., 1993; Weber et al., 1997; Boy et al., 2005). Criegee intermediate (CI) radicals can play a crucial role 2 Measurements in tropospheric oxidation, as suggested more than a decade ago by Calvert et al. (2000). The CI formation mechanism For our model investigations, we used data from two differ- starts from the ozonolysis of alkenes, with an addition of ent stations. These data included: measured concentrations of ozone to the double bond forming a primary ozonide with volatile organic compounds (VOC), hydroxyl radical (OH), high excess energy. The excess energy causes the primary sulfuric acid, and other inorganic gases in addition to parti- ozonide to decompose instantaneously to the Criegee inter- cle size distributions and basic meteorological data. The next mediate, which will still posses excess energy. In order to three subsections will present information about the stations release its excess energy, the Criegee intermediate either de- and the used data sets. composes into different products or collisionally stabilizes 2.1 Hyytial¨ a¨ (we refer to the latter as a stabilized Criegee intermediate (sCI)). The stabilized CI can then react with various atmo- Measurements in Hyytial¨ a¨ were performed at the Univer- spheric compounds, particularly H2O, NOx, SO2, CO and sity of Helsinki’s SMEAR II station (Station for Measur- many others. ing Ecosystem–Atmosphere Relations; Hari and Kulmala Recently, Welz et al. (2012) pointed out that ozonolysis of (2005); 61◦ 510 N, 24◦ 170 E). The surroundings of the sta- unsaturated hydrocarbons (e.g. terpenes) is a major removal tion are a rather homogeneous Scots pine (Pinus sylvestris) process in the troposphere for organic compounds and pro- forest, which was sown in 1962. The station is equipped ceeds via Criegee intermediate radicals. In their work, the au- with permanent instrumentation for measuring basic meteo- thors reported a more than three orders of magnitude higher rological parameters, aerosol concentrations, photosynthesis reaction rate constant for formaldehyde oxide (CH2OO) with and soil properties. In this work, we utilize measurements sulfur dioxide than was reported in the literature until today of temperature, wind speed, spectral irradiance, global and (k = 3.9 × 10−11 ± 0.7 × 10−11 cm3 s−1 at 298 K and 4 torr). diffuse solar radiation intensity, SO2, CO, NO, NOx,O3, The potential for different CIs to oxidize compounds like VOC, OH and H2SO4 concentrations. Furthermore, particle SO2 is much stronger than previously expected and is thus size number concentrations from DMPS (differential mobil- crucial to be included in all chemical models. ity particle sizer) and APS (aerodynamic particle sizer) are New atmospheric observations supported by laboratory included. A detailed description of the station and instru- experiments and theoretical considerations point to the ex- mentation (name, branch and detection limit) can be found istence of compounds (most probably stabilized CIs) which under Kulmala et al. (2001a) and at http://www.atm.helsinki. have significant capacities to oxidize atmospheric trace gases fi/SMEAR/index.php. like sulfur dioxide (Mauldin III et al., 2012). These authors For Hyytial¨ a¨ we first selected 7 days (29 July to 4 August) claimed rate constants for Criegee intermediate radicals orig- during the HUMPPA-COPEC-2010 (Hyytial¨ a¨ United Mea- inating from the ozonolysis of α-pinene and limonene to be surement of Photochemistry and Particles – Comprehensive −13 3 −1 −13 3 −1 6×10 cm s and 8×10 cm s , respectively. These Organic