Atmospheric Chemistry of CF3CN: Kinetics and products of reaction with OH radicals, Cl atoms and O3

Long path length FTIR-smog chamber techniques were used to study the title reactions in 700 Torr of N2, oxygen or air diluent at 296 ± 2 K. Values of k(Cl...

Secondary aerosol formation from dimethyl sulfide – improved mechanistic understanding based on smog chamber experiments and modelling

Dimethyl sulfide (DMS) is the dominant biogenic sulfur compound in the ambient marine atmosphere. Low-volatility acids from DMS oxidation promote the formation and growth of sulfur aerosols and ultimately alter cloud properties and Earth's climate. We studied the OH-initiated oxidation of DMS in the Aarhus University Research on Aerosol (AURA) smog chamber and the marine boundary layer (MBL) with the aerosol dynamics and gas- and particle-phase chemistry kinetic multilayer model ADCHAM. Our work involved the development of a revised and comprehensive multiphase DMS oxidation mechanism, capable of both reproducing smog chamber and atmospheric relevant conditions. The secondary aerosol mass yield in the AURA chamber was found to have a strong dependence on the reaction of methyl sulfinic acid (MSIA) and OH, causing a 82.8 % increase in the total PM at low relative humidity (RH), while the autoxidation of the intermediate radical CH3SCH2OO forming hydroperoxymethyl thioformate (HPMTF) proved important at high temperature and RH, decreasing the total PM by 55.8 %. The observations and modelling strongly support the finding that a liquid water film existed on the Teflon surface of the chamber bag, which enhanced the wall loss of water-soluble intermediates and oxidants dimethyl sulfoxide (DMSO), MSIA, HPMTF, SO2, methanesulfonic acid (MSA), sulfuric acid (SA) and H2O2. The effect caused a 64.8 % and 91.7 % decrease in the secondary aerosol mass yield obtained at both dry (0 % RH–12 % RH) and humid (50 % RH–80 % RH) conditions, respectively. Model runs reproducing the ambient marine atmosphere indicate that OH comprises a strong sink of DMS in the MBL (accounting for 31.1 % of the total sink flux of DMS) although less important than the combined effect of halogen species Cl and BrO (accounting for 24.3 % and 38.7 %, respectively). Cloudy conditions promote the production of SO42- particular mass (PM) from SO2 accumulated in the gas phase, while cloud-free periods facilitate MSA formation in the deliquesced particles. The exclusion of aqueous-phase chemistry lowers the DMS sink as no halogens are activated in the sea spray particles and underestimates the secondary aerosol mass yield by neglecting SO42- and MSA PM production in the particle phase. Overall, this study demonstrated that the current DMS oxidation mechanisms reported in literature are inadequate in reproducing the results obtained in the AURA chamber, whereas the revised chemistry captured the formation, growth and chemical composition of the formed aerosol particles well. Furthermore, we emphasize the importance of OH-initiated oxidation of DMS in the ambient marine atmosphere during conditions with low sea spray emissions.

Estimation of secondary organic aerosol formation parameters for the Volatility Basis Set combining thermodenuder, isothermal dilution and yields measurements

<p>Secondary organic aerosol (SOA) constitutes a major fraction of the total organic aerosol (OA) in the atmosphere. SOA is formed by the partitioning onto pre-existent particles of low vapor pressure products of the oxidation of volatile, intermediate volatility, and semivolatile organic compounds. Oxidation of the precursor molecules results a myriad of organic products making the detailed analysis of smog chamber experiments difficult and the incorporation of the corresponding results into chemical transport models (CTMs) challenging. The volatility basis set (VBS) is a framework that has been designed to help bridge the gap between laboratory measurements and CTMs. It describes the volatility distribution of the OA and the SOA. The parametrization of SOA formation for the VBS has been traditionally based on fitting yield measurements of smog chamber experiments. To reduce the uncertainty of this approach we developed an algorithm to estimate parameters such as volatility product distribution, effective vaporization enthalpy, and accommodation coefficient combining SOA yield measurements with thermograms (from thermodenuders) and areograms (from isothermal dilution chambers) from different experiments and laboratories. The algorithm was first evaluated with “pseudo-data” produced from the simulation of the corresponding processes assuming SOA with known properties. The results showed excellent agreement and low uncertainties when the volatility range and the mass loadings range of the yield measurements coincide. One of the major features of our approach is that it estimates the uncertainty of the resulting parameterization for different atmospheric conditions (temperature, concentration levels, etc.). In the last step of the work, the use of the algorithm with realistic smog laboratory data is demonstrated.</p>