You are here
Harvard Forest Symposium Abstract 2005
- Title: Fast time response measurements of volatile organic compound (VOC) concentrations and fluxes at Harvard Forest
- Primary Author: Karena McKinney (Harvard School of Engineering and Applied Sciences)
- Additional Authors: Heidi Fuchs (Amherst College); Anna Mari Lone (Amherst College)
- Abstract:
Volatile organic compounds (VOCs) are a ubiquitous component of the lowermost atmosphere, and, through reactions with the major atmospheric oxidizing agents and NOx, play a key role in determining the oxidizing capacity of the atmosphere. These processes lead to production of ozone and secondary organic aerosols, which affect local air quality and global climate. Essential factors regulating the atmospheric chemistry of VOCs that remain poorly understood include the identity and quantity of emitted species, the detailed mechanisms and products of hydrocarbon oxidation reactions, and the role of various VOCs in ozone and aerosol formation. Harvard Forest is itself a large source of biogenic hydrocarbons, and is also regularly impacted by anthropogenic hydrocarbon emissions from nearby urban and industrial areas. We plan to quantify sources and sinks of hydrocarbons at Harvard Forest and investigate their reactivity in the atmosphere by making direct field observations of ambient concentrations, concentration gradients, and fluxes of VOCs using Proton Transfer Reaction Mass Spectrometry (PTR-MS), an on-line technique with high sensitivity (~10 – 100 pptv) and fast time response (> 1 Hz), capable of monitoring multiple VOCs. We will focus specifically on the emission rates and oxidation processes of unsaturated biogenic hydrocarbons such as isoprene and monoterpenes, and on the factors that determine the concentrations of oxygenated VOCs such as acetone and methanol. Together, these two classes of compounds dominate the OH reactivity of non-methane hydrocarbons in the atmosphere.
We obtained preliminary PTRMS measurements of many VOCs, including isoprene, monoterpenes, methyl vinyl ketone, methacrolein, benzene, tolulene, xylenes, acetone, and acetaldehyde at the Harvard Forest Environmental Measurement Station during August, 2004. Isoprene concentrations exhibited a strong diurnal cycle, varying from less than 100 pptv at night to midday maxima of up to ~3.5 ppbv, and were strongly correlated with solar radiation. The observations are consistent with previous measurements of isoprene mixing ratio made at the same site using an on-line gas chromatograph technique, and with research indicating biogenic emissions of isoprene are highly dependent on radiation levels (Goldstein et al. 1998). In contrast, acetone has a longer atmospheric lifetime (~50 days) than does isoprene (~1 hour), and has distinctly different sources, including direct anthropogenic emissions and secondary photochemical production in addition to biogenic emissions (Singh et al. 1994). Observed acetone mixing ratios varied from ~0.5 to ~2 ppbv, and showed only a weak diurnal cycle. Acetone abundances were reasonably well correlated with ozone mixing ratios measured at the same location (B. Munger, personal communication), indicating a significant fraction of the observed acetone was likely a result of in situ photochemical production upwind of the measurement site. Measurements of VOC concentrations, concentration gradients, and fluxes over the course of a full growing season are planned for 2005.
Goldstein, A. H., M. L. Goulden, et al. (1998). "Seasonal course of isoprene emissions from a midlatitude forest." J. Geophys. Res. 103(D23): 31045-31056.
Singh, H. B., D. O'Hara, et al. (1994). "Acetone in the atmosphere: Distribution, sources, sinks." J. Geophys. Res. 99(D1): 1805-1819. - Research Category:
