Biogenic Volatile Organic Compounds
Volatile organic compounds (VOCs) are a ubiquitous component of the lowermost atmosphere and play a key role in determining its chemistry and composition. Through reactions with the major atmospheric oxidizing agents and NOx, VOCs control the oxidizing capacity of the atmosphere. These reactions lead to production of O3 and secondary organic aerosols, which affect local air quality and global climate. Many essential factors regulating the atmospheric chemistry of VOCs remain poorly understood. These include the identification and quantification of emitted species, elucidation of the mechanisms and products of hydrocarbon oxidation reactions, and determination of the role of specific VOCs in oxidant and aerosol formation. One goal of my research is to determine the net effects of these processes on the environment by investigating the sources and sinks of VOCs and their reactivity in the atmosphere through direct field observations of ambient concentrations, concentration gradients, and fluxes of these compounds. In collaboration with researchers at Harvard University, we are also conducting studies of the reactivity of biogenic VOCs under controlled laboratory conditions to better define the reaction mechanisms of individual chemical species. Proton Transfer Reaction Mass Spectrometry (PTRMS), an on-line technique with high sensitivity and fast time response capable of simultaneously monitoring multiple VOCs, is our primary analytical tool. The PTRMS measurements are complemented by gas chromatography (GC) and gas chromatography – mass spectrometry (GC-MS) measurements of in situ and collected samples, which provide additional structural information on some VOCs.
Since 2004, my research group has measured VOCs at the Environmental Measurement Station at Harvard Forest. We are focusing specifically on unsaturated biogenic hydrocarbons such as isoprene and monoterpenes and their derivatives, and oxygenated VOCs such as acetone and methanol. Together, these classes of compounds dominate the emissions of non-methane hydrocarbons to the atmosphere. We are using the extensive data sets we have collected on gas-phase concentrations of these species to test currently accepted mechanisms for photochemical loss of primary emissions, investigate hydrocarbon oxidation mechanisms and products and their fates, identify previously unobserved but highly reactive functionalized biogenic hydrocarbons, and develop relationships between environmental variables such as temperature, radiation, and season and emission rates.