Analytical Chemistry Seminar: Lea Hildebrandt Ruiz
Jointly sponsored by the Department of Chemistry and Biochemistry, CIRES, and the Environmental Program
Atmospheric Reactive Chlorine: Observations, Sources and Effects
Lea Hildebrandt Ruiz, Ph.D.- The University of Texas at Austin, Cockrell School of Engineering
Ambient measurements have detected tropospheric reactive chlorine concentrations much higher than predicted by state-of-the-art air quality models, challenging current understanding of the emissions and atmospheric chemistry of chlorinated compounds. For example, measurements in the Dallas Fort Worth (¬DFW) area routinely observed HCl concentrations of 1 ppb or more, peaking in the late afternoon. Modeling work has investigated several hypotheses for the source of HCl in DFW, and results suggest emissions of an organic chloride, potentially from hydraulic fracturing activity, as the most likely explanation. In the presence of particulate chloride reactive chlorine can also be formed from heterogeneous reactions on the particles’ surface. Laboratory chamber experiments were conducted to quantify the rate of heterogeneous production of chlorine, and results suggest that this path could explain observed sources of Cl2. Higher concentrations of reactive chlorine can lead to increased production secondary organic aerosol (SOA). Mass yields of SOA formed from chlorine-radical-initiated oxidation of hydrocarbons were measured in laboratory chamber experiments. Volatility basis set parameters from these experiments can be incorporated in air quality models to more accurately represent reactive chlorine concentrations and its effects on atmospheric composition.