[show abstract][hide abstract] ABSTRACT: We have conducted seasonal ambient and emission measurements of a series
of biogenic VOCs such as monoterpenes (MT), sesquiterpenes (SQT),
isoprene, methanol, methyl chavicol and acetaldehyde. Therefore a plant
enclosure technique was applied in order to investigate a Central
European spruce forest and its emissions responses to meteorological and
environmental parameters. A healthy ≈15m tall Norway spruce tree was
selected and a vegetation enclosure technique was applied from April to
November 2011. VOCs are measured by PTR-MS, while samples have also been
analyzed with GC-MS (Gas Chromatography - Mass Spectrometry) techniques
for intercomparison and identification of individual VOCs. E/N ratio was
adjusted at 117Td and the primary ion signal (H3O+) was continuously
above 4×10^7cps, implying a high sensitivity to our measurements.
Temperature, relative humidity, ozone, photosynthetic active radiation
(PAR) and CO2 concentrations were continuously measured inside the plant
cuvette. Meteorological and environmental parameters (radiation,
atmospheric pressure, wind velocity, wind direction, temperature, O3,
relative humidity, soil moisture, precipitation, global radiation, H2O,
NO, NO2) were measured by HLUG (Hessian Agency for Environment and
Geology) and DWD (German Weather Service), 50 meters away from the
measuring site. In a peculiar season, which was characterized by a warm
spring (temperature anomaly >40C), a wet summer (precipitation
anomaly 126-150%) and an extremely dry autumn (precipitation anomaly
<50%), VOC emissions were analyzed and studied in order to discern
different driving forces for the individual compounds. The suggested
empirical beta factor for MT found to be in a reasonable range but the
temperature dependency was almost double for daytime compared to
nighttime measurements, suggesting that light is also influencing MT
emissions. On the contrary, SQT emissions showed similar temperature
dependency for both day and night measurements. The beta factor showed a
different behavior during the seasons for different compounds implying
different driving forces and storage inside the tree. Especially for
SQT, there are indications that a storage pool that is getting empty
while moving towards winter. Interestingly, it has been found that SQT
emissions are not only correlated with ambient temperature but also with
high ambient ozone levels. In a wide range of meteorological conditions
and ozone concentrations, we found different emission behavior when
ozone values are exceeding a critical threshold.  Goldstein, A. H.
and Galbally, I. E.: Known and unexplored organic constituents in the
earth's atmosphere, Environ. Sci. Technol., 41, 1514-1521, 2007.
 Kim, S., Karl, T., Helmig, D., Daly, R., Rassmusen, R. and Guether,
A. : Measurement of atmospheric sesquiterpenes by proton transfer
reaction-mass spectrometry (PTR-MS), Atmos. Meas. Tech., 2, 99-112,
2009.  Guenther, A.B., Zimmerman, P.R., Harley, P.C., Monson, R.K.,
Fall, R., 1993. Isoprene and monoterpene emission rate variability:
model evaluations and sensitivity analyses, Journal of Geophysical
Research., 98, 12609-12617, 1993.
[show abstract][hide abstract] ABSTRACT: New particle formation in number and mass is a quite ubiquous phenomenon
in the atmospheric boundary layer. However, different locations provide
different mechanisms for the initial particle production steps.
Investigating the formation aims usually in explaining two aspects, the
initial formation process and the contribution to cloud condensation
nuclei production. In this study we focus on the latter. Once these
particles are formed they grow further on until they reach cloud
effective sizes. This is the size, where those particles can affect
local climate via the indirect aerosol effect. This study deals with the
processes mentioned at Mt. Kleiner Feldberg (810 m a.s.l.) about 50 km
northwest of Frankfurt activation diameters. We have been determined
using a CCN-counter (DMT, Boulder, U.S.) [Roberts and Nenes, 2005] and a
SMPS (TSI 3936) with a long DMA (TSI 3081) and a UCPC (TSI 3025A).
Particles were assumed to be equal in chemical composition since the
vast majority of particles were smaller than 300 nm in diameter, i.e.
secondary of nature. Therefore, measured CCN concentrations were
intercompared with section wise integrated particle number
concentrations starting at the largest size towards the smaller ones.
The best match of integrated and CCN concentration was assumed to be the
activation diameter (Dp,active). With this set-up the activation
diameters were determined for five supersaturations (0.1, 0.2 0.3, 0.4
and 0.6%) during a two weeks period. This resulted in the expected
detcrease in activation size with increasing supersaturation from about
130±10 nm at 0.1% to 70±5 nm at 0.6% supersaturation. The
empirically fitted kappa-value [Petters and Kreidenweis, 2007] was
obtained as 0.16±0.03 indicating aerosols of lower
water-solubility. Second, measurements of ice nuclei [Klein et al.,
2010] were conducted once per day during the same time period, which
indicate that IN concentrations, were about one per mill of the CCN.
Interestingly the cross-correlation between both cloud nuclei indicated
at maximum at the same time, i.e. no time shift, and it was tentatively
seen that CCN concentration pattern could explain 60% of the IN pattern.
However the dataset available is to short to draw final conclusions and
more detailed work is needed in the future.  Klein, H., Nickovic,
S., Haunold, W., Bundke, U., Nillius, B., Ebert, M., Weinbruch, S.,
Schuetz, L., Levin, Z., Barrie, L. A., and Bingemer, H. (2010): Saharan
Dust And Ice Nuclei Over Central Europe. Atmos. Chem. Phys., 10,
10211-10221.  Petters, M.D., and Kreidenweis, S. M. (2007): A
single parameter representation of hygroscopic growth and cloud
condensation nucleus activity. Atmos. Chem. Phys., 7, 1961-1971. 
Roberts, G. C., and Nenes, A. (2005): A continuous-flow streamwise
thermal-gradient CCN chamber for atmospheric measurements. In: Aerosol
Science and Technology,39, 206-221.
[show abstract][hide abstract] ABSTRACT: Oxidation capacities of ecosystems are important to facilitate an
ecosystem feedback on oxidation stress and in order to survive. We have
conducted seasonal ambient measurements of a series of biogenic VOCs
using a plant enclosure technique and determined the ambient levels of
ozone, NOx as well as basic meteorological parameters at a managed
spruce forest site in Central Germany (Mt. Kleiner Feldberg). The site
is 810 m a.s.l. and faces distinct anthropogenic contributions from the
Rhine-Main-area including the airport and major traffic routes in from
the southeast. The opposite direction is moderately polluted and can be
classified as Central German background condition. Since atmospheric
chemistry and pollutants become very important especially for this site,
which is the most polluted one in Germany with respect to ozone we
approximated the sink terms for the atmospheric oxidation agents of
interest at this site, i.e ozone, OH and NO3 using the measurements and
box model steady state calculations for intermediate species not
measured directly between the first of April and the start of November
2011. BVOC measurements were obtained with PTR-MS every 36 s and
averaged for 30 min intervals afterwards to facilitate the inclusion of
the monitoring data of the Hessian Agency for the Environment and
Geology (HLUG) in Wiesbaden, Germany: temperature, humidity, global
radiation, ozone and NOx. Analysis was performed with Matlab (Mathworks
Inc.) and included the gas-phase chemistry set-up described by the
Master Chemical Mechanism (MCM, v3, ). This resulted in the following
outcome for sinks of oxidants: Ozone: Significant contributions were
found for mono- and sesquiterpenes as well as for NOx. The individual
contributions vary notably with the time of the day and the year and the
emission strength of biogenic VOCs. Especially for the early season in
April sesquiterpene reactions dominated the sink by up to 80% during
nighttime, while NOx reactions dominated the sink terms during daytime.
The contributions of monoterpene and isoprene reactions strengthened
towards the summer period, while sesquiterpene reactions slowed down.
Hydroxyl radical: The picture becomes much more complex for OH. Besides
the reaction with nitrogen dioxide, isoprene and monoterpenes were key
destructing agents of OH with estimated contributions of about 50-60%,
increasing towards the summertime. Contributions of their oxidation
products to the total sink of OH are supposed to be less than 20% but
showing more intense during summer and less towards cooler periods.
Sesquiterpene OH-reactions only contributed to 10% with a maximum of
about 20% at the early April. Nitrate radical: NO3 displayed a
mixture of the sinks of OH and ozone. The dominant destruction takes
place via NOx-reactions (about 50%) and the remainder primarily via
monoterpene (36±20%), sesquiterpene (11±8%) and isoprene
(2±1%) OH-reactions. From our observations at this particular
site it is apparent that the spruce forest provides a quite efficient
variety of pathways to compensate oxidation stress. This is essentially
displayed in the variation of emission pattern of different compound
classes with different reactivity for the three major oxidation agents.
One needs to be aware of the fact that the sink is highly variable in
space, too. Therefore we conclude: In order to understand and describe
the oxidation tolerance of a certain ecosystem one needs to detect at
least the reactive hydrocarbons.  Jenkin, M.E., Shallcross, D.
E., and Harvey, J. N.: Development and application of a possible
mechanism for the generation of cis-pinic acid form the ozonolysis of
α- and β-pinene. Atmos.Environ., 34, 2837-2850, 2000.
[show abstract][hide abstract] ABSTRACT: Atmospheric new particle formation is a general phenomenon observed over coniferous forests. So far nucleation is either parameterised as a function of gaseous sulphuric acid concentration only, which is unable to explain the observed seasonality of nucleation events at different measurement sites, or as a function of sulphuric acid and organic molecules. Here we introduce different nucleation parameters based on the interaction of sulphuric acid and terpene oxidation products and elucidate the individual importance. They include basic trace gas and meteorological measurements such as ozone and water vapour concentrations, temperature (for terpene emission) and UV B radiation as a proxy for OH radical formation. We apply these new parameters to field studies conducted at conducted at Finnish and German measurement sites and compare these to nucleation observations on a daily and annual scale. General agreement was found, although the specific compounds responsible for the nucleation process remain speculative. This can be interpreted as follows: During cooler seasons the emission of biogenic terpenes and the OH availability limits the new particle formation while towards warmer seasons the ratio of ozone and water vapour concentration seems to dominate the general behaviour. Therefore, organics seem to support ambient nucleation besides sulphuric acid or an OH-related compound. Using these nucleation parameters to extrapolate the current conditions to prognosed future concentrations of ozone, water vapour and organic concentrations leads to a significant potential increase in the nucleation event number.
ATMOSPHERIC CHEMISTRY AND PHYSICS 01/2009; · 5.51 Impact Factor
[show abstract][hide abstract] ABSTRACT: Atmospheric new particle formation is a general phenomenon observed over coniferous forests. So far nucleation is described as a function of gaseous sulfuric acid concentration only, which is unable to explain the observed seasonality of nucleation events at different measurement sites. Here we introduce a new nucleation parameter including ozone and water vapor concentrations as well as UV-B radiation as a proxy for OH radical formation. Applying this new parameter to field studies conducted at Finnish and German measurement sites it is found capable to predict the occurrence of nucleation events and their seasonal and annual variation indicating a significant role of organics. Extrapolation to possible future conditions of ozone, water vapor and organic concentrations leads to a significant potential increase in nucleation event number.
Atmospheric Chemistry and Physics 01/2009; · 4.88 Impact Factor