VolatileOrganicCompound

measurements at SMEAR II station with ProtonTransferReaction – MassSpectrometry

Taina M. Ruuskanen1, Risto Taipale1, Maija Kajos1, Janne Rinne1, Hannele Hakola2, Heidi Hellén2, Anni Reissell1, Markku Kulmala1

Pasi Kolari3, Jaana Bäck3, Pertti Hari3

1) University of Helsinki, Department of Physical Sciences2) 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

Ta m p e re

St Pe te rsb u rg

SM EA R I I

SM EA R I

S t o c k h o lm

O s lo

H e ls i n k i

C o p en h a g e n

M i n s k V il n i u s

R i g a

T a ll in n

R u s s i a

F i n la n d

S w e d e n

N o r w a y

D en m a rk

E s to n ia

L a t v ia

L i th ua n ia

B e la r u s

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 Volatile Organic Compounds ? 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)

• 0.1 - 60 sec per VOC• limitations in detecting

VOCs:– proton affinity of VOC must

be higher than that of H2O– identification of compound

by mass

Proton Transfer Reaction - Mass Spectrometry

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 DisjunctEddyCovariance – correlate momentary concentration with momentary

vertical wind speed– above canopy

Methods

VOC concentrations

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) 0.5 - 6 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

(CO2) and transpiration (H2O) 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.–19.7.2006

Disjunct Eddy Covariance

Emissions of non-terpenoid VOCs same order of magnitude as monoterpenes.

Average emissions

[μg m−2 h−1]

methanol, M33 186

acetaldehyde, M45 50

acetone, M59 110

monoterpenes, M137 258

Comparing model with measurements• Emission algorithm for monoterpenes (G93):

Disjunct Eddy Covariance

• best fit: β = 0.08 °C−1, E30 = 615 μg m−2 h−1

• with a traditionally used (fixed) β = 0.09 °C−1: E30 = 675 μg m−2 h−1

o30 exp 30 CE E T

• 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!

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.