10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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The Role of Criegee Intermediates in Secondary Sulfate Aerosols Formation in Nocturnal Power-Plant Plumes in South Eastern USA
Daphne Meidan, Steven S. Brown, YINON RUDICH, Weizmann Institute of Science
Abstract Number: 473 Working Group: Aerosol Chemistry
Abstract Criegee Intermediates from ozonolysis of biogenic volatile organic compounds (BVOC) have been suggested to be important atmospheric oxidants. However, due to low atmospheric concentrations, possible high reactivity with water vapor, SO2, NO2 and unconstrained thermal decomposition rates, their impact on the atmosphere remains largely unidentified.
In this study, we investigate the formation of Secondary Sulfate Aerosols (SSA) in nocturnal power plant plumes in the South-Eastern USA, which is characterized by high background of BVOCs. At these conditions (high SO2, NOx, BVOCs concentrations and no photochemical OH) CI reactions may contribute to the formation of SSA. Under the high concentrations of SO2 in power plant plumes, the CI + SO2 reaction can compete with other pathways, such as water vapor reactions and thermal decomposition. In such cases it is possible to test the current understanding of the role of CI in SO2 oxidation that can then be extrapolated to the broader atmosphere.
We will present a dispersion model that includes nighttime and CI gas phase chemistry to simulate plume evolution during nighttime. The model results are compared to aircraft measurements of different power-plant plumes to evaluate the primary-secondary ratio and the CI impact on the SSA.
The results suggest that despite a high background of primary sulfate aerosols, Secondary Sulfate Aerosols formation increases by a factor of 3.5 when considering the CI contribution, accounting to up to 35% of the total sulfate aerosol in the plume. This effect decreases when the thermal decomposition rate is set to the higher measured CH2OO rate, 200 s-1 yet the CI chemistry still contributes to SSA formation through the additional OH produced in the CI thermal decomposition. These results may change if different rate coefficients for different CI’s are considered. The most important CI is the C1 (CH2OO) that consists up to 50% of the CI’s produced from isoprene. C4 CI’s may consist up to 45% of the CI’s produced and are expected to have much slower thermal decomposition rates and water reaction rate coefficients. This suggests that the model results presented here may be a lower limit to the CI contribution to SSA.