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You are here: Home / SARP / SARP 2015 / 2015 Student Presentations / Whole Air Sampling / Estimation of Tropospheric OH and Cl Concentrations Inferred from NMHC ratios over Southern California

Estimation of Tropospheric OH and Cl Concentrations Inferred from NMHC ratios over Southern California

Karimar Ledesma, University of Puerto Rico at Mayagüez
00:12:40
2015

Abstract: Non Methane Hydrocarbons (NMHC) play an important role as chemical precursors to ozone and secondary organic aerosol (SOA) in the troposphere via their photochemical oxidation. In turn, ozone and SOA affect global climate, air quality, and human health. Though oxidation of NMHCs generally occurs via reaction with the hydroxyl radical (OH), oxidation can also occur via reaction with atomic chlorine (Cl), often at rates that are orders of magnitude greater than with OH. During the 2015 NASA Student Airborne Research Program (SARP), whole air samples (WAS) were collected onboard the NASA DC-8 over Southern California. In this study, four regions were focused on: The Los Angeles area, the Central Valley, the Salton Sea, and Santa Barbara (which also include samples collected on the ground). Using ratios of select NMHCs that react with OH and Cl at different rates, Cl concentrations over the four study regions were estimated to be 1.49 X 104, 1.1 X 104 , 8.83X 103 , 1.23 X 104 and 1.77X 104 molecules cm-3 respectively. These results were used to calculate theoretical OH radical concentration, which were in the range of 1.1 X105 to 9.053 X105 molecules cm-3 over the whole study region. These values were compared with WAS collected during the 2014 NASA SARP project and the concentration of OH and Cl vary considerably. Despite of this variability, the magnitude of OH and Cl concentrations for both years has reasonable impact on ozone formation. Although the Central valley is far away from the ocean we estimated a relatively high Cl concentration, indicating the importance of Cl in ozone production even in inland regions of California.