The role of biogenic organic compounds in SOA formation

In order to better understand the sources and the atmospheric fate of organic aerosols and precursor gases the National Center for Atmospheric Research (NCAR) in Boulder USA is establishing the research initiative BEACHON (http://www.tiimes.ucar.edu/beachon/index.htm). This initiative is focusing on biogenic gas and particle flux measurements and simulations at the monitoring station in Colorado-USA. Accurate quantification of concentrations and fluxes of volatile (VOC) and semi-volatile organic compounds (SVOC) is a crucial component for understanding the formation and evolution of secondary organic aerosol (SOA). While conventional methods for measuring VOC composition based on GC-MS sampling are available during atmospheric field measurement campaigns, a critical research need is the quantification of all VOCs and SVOCs closely linked to SOA formation. A high mass resolution proton transfer reaction time-of-flight mass spectrometer (PTR-TOFMS) was recently developed at the University of Innsbruck. This instrument will open a new frontier for measuring biogenic VOC and SVOC that have previously not been measured. The PTR-TOFMS would complement the suite of highly sophisticated instrumentation deployed during BEACHON field projects and contribute an unparalleled broadness of quantitative VOC and SVOC data. In order to assess the feasability of SVOC flux determination by PTR-TOFMS NCAR scientist Thomas Karl, who is an expert in flux mesurements, will visit Innsbruck. He will instruct and train PhD students and scientists and support them in the development of SVOC flux measurement methods. The students will test and evaluate these methods in two field campaigns at the NCAR facility BEACHON with support of Thomas Karl. The results will be presented in front of a scientific and industrial audience.

An incredibly large amount of VOCs is steadily emitted into the shallow atmospheric layer of our planet. VOC stands for "volatile organic compounds". VOCs are carbon-containing compounds that will evaporate easily. VOCs are released by the burning of fossil fuels, forest fires and of solvent. Plants are considered as the main source. Oxidation of VOCs in the presence of nitrogen oxides produces ground-level Ozone, which is harmful in high concentrations. VOCs are also considered gas-phase precursors in the formation of aerosols. Aerosols (particulate matter suspended in air) can act as condensation nuclei and play a crucial role in cloud formation and hence have a strong impact on climate.To detect almost all VOCs in real-time, i.e. recognized immediately, is only possible by the recently developed Innsbruck PTR-TOF method. Previously, for the investigation of air quality time and cost-intensive chemical process were necessary, which provided only a posteriori results. The Innsbruck PTR-MS technique provides immediately results in real time, and with extremely high sensitivity and low limits of detection. PTR-MS stands for proton transfer reaction mass spectrometry, and is called a soft ionization method. This method was first used to determine the biogenic VOC emissions from a ponderosa pine forest in cooperation with scientists from the University of Innsbruck and the National Center for Atmospheric Research (NCAR) in Boulder, USA. The two years each summer through measurements have confirmed that biogenic VOC emissions are driven from sunlight and temperature. The conifers (Ponderosa Pine) emit a series of VOCs that are of great importance for aerosol formation. Following a severe hail storm branches and twigs of pine trees were demolished, that increased emissions of monoterpenes, which was detected with the PTR-TOF. Monoterpenes are produced by conifers and stored in the needles and branches. The hailstorm damaged the monoterpene storage pools in the trees releasing these substances in great abundance into the atmosphere. These increased monoterpene emissions were observed for several days after the hailstorm and analyzed in detail.