V olatile O rganic C ompound measurements at SMEAR II station with P roton T ransfer R eaction – M ass S pectrometry Taina M. Ruuskanen 1, Risto Taipale 1, Maija Kajos 1, Janne Rinne 1, Hannele Hakola 2, Heidi Hellén 2, Anni Reissell 1, Markku Kulmala 1 Pasi Kolari 3, Jaana Bäck 3, Pertti Hari 3 1) University of Helsinki, Department of Physical Sciences 2) Finnish Meteorological Institute, Air Chemistry Laboratory 3) University of Helsinki, Department of Forest Ecology

PTR-MS measurements of VOCs at SMEAR II Introduction to measurements –Where? What? and Why? Measurements & results –instrument –methods used for VOC concentrations emissions (fluxes) on shoot and canopy level Summary

Where? SMEAR II station at Hyytiälä forestry field station About 200 km North of Helsinki Middle of forest, mainly Scots pine (mänty) and Norwegian spruce (kuusi)

Biogenic from forest –trees, grass, soil –e.g. monoterpenes Anthropogenic –car exhaust, solvents, industry etc –e.g. benzene VOCs are transported around the world in atmosphere, many react on the way and arrive as new compounds. What are V olatile O rganic C ompounds ? Where do they come from?

Why? measure VOCs at SMEAR II VOCs for Global climate change (models) because: VOCs have an important role in photochemistry, –e.g. formation of ozone (+ in upper, - in lower atmosphere) and PAN (e.g. role in growth of ozone hole) VOCs participate in aerosol formation and affect properties of aerosols and clouds –e.g. more clouds (+ global cooling of climate) Also, some VOCs have direct health effects Accurate information on the natural loading of VOCs needed to get predictions of global warming right –diurnal, seasonal and annual variation may be large, long time series needed SMEAR II: plant physiology and environment measurements –understanding how concentrations and why emissions vary

VOCs selected and detected at compound mass + 1 continuous, online (no sampling/ pretreatment) sec per VOC limitations in detecting VOCs: –proton affinity of VOC must be higher than that of H 2 O –identification of compound by mass P roton T ransfer R eaction - M ass S pectrometry Measurement:

Ambient concentration –measure air concentration inside and above canopy Emissions with chambers –automatic closing chambers, change in VOC concentration –unshaded top branches of trees Fluxes with D isjunct E ddy C ovariance –correlate momentary concentration with momentary vertical wind speed –above canopy Methods

VOC concentrations

Measurements at SMEAR II started 2004, Continuous: June 2006 – September 2007 –Measured at 5 minute interval, every second hour at heights 4 and 14 m inside canopy and 22 m above canopy –List of calibrated compounds methanol, acetonitrile, acetaldehyde, acetone, isoprene, benzene, monoterpenes, toluene, methacrolein + MVK, MEK, hexenal + cis-3-hexenol

VOC concentrations Methanol (M33) large variability (below hourly averages) ppb high during summer, low in winter

VOC concentrations Benzene (M79) usually below 0.1 ppb, momentary high higher in winter

VOC concentrations Monoterpenes (M137) average 0.5, high momentary peaks (10 x average) higher during summer

Emission with chambers

Ruuskanen et al. (2005) Emission with chambers Principles: –shoot inside chamber –emission determined from concentration before and during closure –requires fast measurements Automated pneumatic chambers –build for photosynthesis/respiration (CO 2 ) and transpiration (H 2 O) measurements –open between measurements and close for few minutes at a time

Emission with chambers Monoterpene from Scots pine

Disjunct Eddy Covariance Micrometeorological measurement technique vertical turbulent flux of a VOC above vegetation direct flux measurement determines flux in ecosystem scale does not disturb measured ecosystem

Principle –measure vertical wind speed above canopy with high frequency (10–20 Hz) –take short (0.1–0.5 s) samples of the VOC concentration from same place –VOC sampling disjunct, time intervals of 5–30 s (unlike in traditional Eddy Covariance) possible to use slow analyzers for measurement of a single VOC or fast for several VOCs. DEC measurement setup at SMEAR II. Disjunct Eddy Covariance

measurements above Scots pine forest 13.6.– Disjunct Eddy Covariance Emissions of non-terpenoid VOCs same order of magnitude as monoterpenes. Average emissions [μg m −2 h −1 ] methanol, M33186 acetaldehyde, M4550 acetone, M59110 monoterpenes, M137258

Comparing model with measurements Emission algorithm for monoterpenes (G93): Disjunct Eddy Covariance best fit: β = 0.08 °C −1, E 30 = 615 μg m −2 h −1 with a traditionally used (fixed) β = 0.09 °C −1 : E 30 = 675 μg m −2 h −1

Monoterpene emission –daily max at noon in modeled (with measured temperature) and measured Disjunct Eddy Covariance

VOC measurements with PTR-MS + excellent time resolution + enables very long time series - identification of compounds uncertain Automated measurement set up enables continuous long term measurements of VOCs –ambient air concentrations with meteorology and aerosols –in and above canopy profiles –emissions on shoot level with plant physiology with chambers –emissions on canopy (ecosystem) level with DEC Conclusions I NEW !

Conclusions II Emissions of Scots pine: –monoterpene emissions measured with PTR-MS agree well with emissions determined with well established chamber method –emissions of other VOCs (acetone, acetaldehyde and methanol) are same order of magnitude as terpenoids (many not possible to determine with generally used (GS-MS) methods) NEW !

Thank you for your attention.