Cost effective new methods to quantify emissions of trace gases benefit society, because pollution poses a costly risk to human health. For example, wildfires are important for ecosystems, but are also a major source of airborne smoke and pollution that poses a risk to human health and property; yet difficulties to quantify fire emissions arise from limitations with access to plumes that often travel decoupled from ground-level, complex terrain, plume heterogeneity, and uncertain plume rise and transport. 

This project explored Solar Occultation Flux (SOF), based on infrared absorption spectroscopy from aircraft, as a high risk and potentially transformative approach to study biomass burning emissions using aircraft. An early airborne SOF prototype, developed at the University of Colorado at Boulder, was successfully flown on research aircraft. The use of SOF to quantify emissions of harmful ammonia (NH3), an aerosol precursor, and nitrogen oxides (NOx = NO + NO2) from agricultural soils was further demonstrated using a ground-based prototype. Better knowledge about emissions is pre-requisite to protecting society from the harmful impacts of pollution. It is shown that NOx emissions from agricultural soils, most likely due to microbial activity, are missing in National Emission Inventories. Such unaccounted NOx sources are likely to gain relative importance in the future as other sources continue to decrease. Further, the emissions of NH3 were underestimated during our case studies. Airborne SOF is a versatile tool that in principle is capable to measure many other gases. 

Professor Volkamer, an academic professor and CIRES Fellow who lead the project, spent a productive sabbatical stay in Europe. In collaboration with KIT, Germany his research group explored creative new ways to quantify and disentangle methane emissions from natural and anthropogenic sources by relatively low-cost COCCON type networks of column sensors, and simultaneous measurements of chemical tracers by CU SOF. In a proof-of-concept study it is shown that the relative contributions of different source sectors can be disentangled using small networks designed for longer-term operation on regional scales. 

Furthermore, in collaboration with Dr. Michael Hoepfner at KIT, infrared emission spectroscopy was used to detect NH3 in the free troposphere (FT). There are no previous measurements of NH3 in the upper troposphere, where even small amounts of NH3 can form ammonium sulfate aerosol, and have potential to strongly modify new particle formation and growth at cold temperatures in the upper troposphere.

Aerosols are harmful to human health, and their properties can modify clouds and rain fall. The oxidation of sulfur dioxide and isoprene in cloud droplets were studied at the CLOUD simulation chamber at CERN, Switzerland, in bench-top experiments in Boulder, and through modeling. We have measured Setschenow salting constants of glyoxal and methyl glyoxal, and estimated that of isoprene epoxide. These three molecules are formed from isoprene, and are deemed responsible to form aerosol mass from multiphase chemistry in suspended droplets (aerosols and clouds) over forests. The laboratory findings were incorporated into the CMAQ model (collaboration with Professor Carlton, now UC Irvine), and suggest that anthropogenic sulfate could regulate biogenic aerosol formation in ways not presently included in atmospheric models. In collaboration with Professor Amman at the Paul Scherrer Institute, Switzerland, surface reactions of light absorbing products from glyoxal multiphase chemistry were shown to be a source of radical species at aqueous interfaces. Finally, fatty acid photochemistry as a source of small oxygenated volatile organic carbon (OVOC) molecules found over oceans were explored in a photochemical reactor that simulates the ocean surface in collaboration with Dr. George at IRCELYON, France. 

The broader impacts of this project are that a principal investigator engaged new disciplines through collaborations with experts in infrared spectroscopy, aerosol formation and growth, and photocatalysis. Five graduate students, one postdoc, and one undergraduate student received training on the development of instrumentation for use from mobile platforms (ground, aircraft), conducted field observations and laboratory research as part of interdisciplinary teams, engaged novel disciplines, and interacted with researchers in National Laboratories in Germany, France, Switzerland, and the US. The project has contributed to the development of a globally engaged work force in environmental science, and provided training beyond the laboratory bench that is useful for careers in academia, government and/or industry.

Last Modified: 12/18/2017
Modified by: Rainer M Volkamer