Vol. 45 No. 5
SCIENCE IN CHINA (Series B)
October 2002
Quantification of acetone emission from pine plants
SHAO Min (J
;)1 & Jürgen Wildt 2
1. State Joint Key Laboratory of Environmental Simulation and Pollution Control, Center for Environmental Sciences,
Peking University, Beijing 100871, China;
2. Institut für Chemie der Belasteten Atmosphäre, ICG-2, Forschungszentrum Jülich, 52425, Germany
Correspondence should be addressed to Shao Min (email: [email protected])
Received April 8, 2002
Abstract Acetone emission from pine plants (pinus sylvestris) is measured by continuously stirred
tank reactor. Under a constant light intensity, acetone emission rates increase exponentially with
leaf temperature. When leaf temperature is kept constant, acetone emission increases with light
intensity. And acetone emission in darkness is also detected. Acetone emitted from pine is quickly
labeled by 13C when the plants are exposed to air with 630 mg/m3 13CO2. However, no more than
20% of acetone is 13C labeled. Acetone emission from pine may be due to both leaf temperaturecontrolled process and light intensity-controlled process. Based on these understandings, an algorithm is used to describe the short term acetone emission rates from pine.
Keywords: biogenic emission, carbonyl compound, 13C labeling, simulation.
Carbonyl compounds have been of increasing concern in recent years. They are intermediates
of atmospheric oxidation process. Their photolysis is significant source of free radicals in troposphere[1]. It was reported that OH and HO2 concentration could not be explained by the chemistry
of water vapor, and ozone and methane in upper troposphere, carbonyls as well as peroxide compounds transported from lower troposphere must be taken into accounts. Carbonyls may play
more important roles in the atmosphere than that we understood[2].
Till now not many studies have been performed on carbonyls. Preliminary measurements
show that acetone is the most abundant and also long-live carbonyls in the atmosphere[3,4]. One
question that needs to be answered is the direct emission of acetone from biogenic sources. MacDonald[5] reported the acetone emission from conifer buds, but the emission was not detected from
conifer needles nor any angiosperm vegetative tissues. Few data are available up to now about the
biogenic sources of acetone, and less is known about the mechanism of acetone releasing from
vegetation.
Acetone emission from pine (pinus sylvestris) was measured in continuously stirred tank reactor (CSTR) for about half a year. The diurnal variation of acetone emission rates, and the influence of leaf temperature and light intensity on emission rates were obtained. By feeding 13CO2 to
pine plants, the labeling of acetone by
13
C was investigated. Based on the understanding of con-
trolling factors of acetone emission rates, an algorithm was used to quantify acetone emission
rates.
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QUANTIFICATION OF ACETONE EMISSION FROM PINE PLANTS
533
Experimental
Acetone emission from pine was measured in a continuously stirred tank glass reactor
(CSTR). The CSTR system was a 1600 L volume glass chamber with inlet of purified air at one
side and outlet at the other side. The chamber was mounted in a temperature-controlled cell.
Twelve discharge lamps (Orsam HQI T 1000W) were used as light source in the chamber. The
lamps were adjusted so that each lamp contributed 30 µEm−2s−1 to pine plants at mid canopy
height. Four pines aged between 23 a were put in the chamber with stem and leaf. The plant
roots and soil were separated from the stem at the bottom of the chamber by a PTFE sheet to prevent possible adsorption of organics and interruption of ambient CO2 and H2O in the chamber.
The concentrations of CO2, H2O, and volatile organic compounds (VOCs) at chamber inlet
and outlet were measured continuously. As other VOC species, acetone was analyzed by a gas
chromatography with flame ionization detector (GC-FID, Airmotec HC 1010). 3 L of air in the
chamber was first adsorbed and enriched on a carbtrap/carbosieve tube in the GC, after thermal
desorption air sample was captured on the injection tube for secondary absorption and desorption,
and then entered GC column for analysis. The flow rate of air and hydrogen was 120 and
12 mL/min respectively. The detection limit of Airmotec was 0.05 ng, and time resolution of
on-line acetone measurement was 30 min.
The emission rate of acetone from pine was calculated by
Φ acetone =
F
([acetone]out − [acetone]in ) + Φwall ,
AL
(1)
where Φacetone is acetone emission rate (molcm−2s−1), F is the flow rate of air through the
chamber, AL is leaf area of pine (cm2, one side), [acetone]out and [acetone]in are the acetone mixing
ratios at chamber inlet and outlet respectively, and Φwall is the wall loss for acetone.
The wall loss of acetone in the CSTR was observed by measuring the acetone concentration
differences at chamber inlet and outlet when a constant concentration of acetone was added to the
empty chamber. Acetone concentrations at chamber outlet were 10% to 20% lower than that at
chamber inlet. Because it was impossible to obtain an exact value for the wall losses of acetone,
and the measured wall losses were not significant, the Φwall was neglected for acetone. Therefore,
the emission rates of acetone presented in this paper were underestimated and could be considered
as lower limits.
Similarly, net photosynthesis (ΦCO2, in molcm−2s−1) of plants was calculated by
ΦCO2 =
F
([CO 2 ]out − [CO 2 ]in ),
AL
(2)
where [CO2]out and [CO2]in are mixing ratios of CO2 at chamber outlet and inlet.
Synthetic air containing 630 mg/m3 13CO2 was prepared by diluted 99% 13CO2 with CO2 free
air, and then used to feed pine plants. A three-way valve was used to connect the channel of 13CO2
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SCIENCE IN CHINA (Series B)
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and normal CO2 at chamber inlet. Thus we can switch quickly from 13CO2 to normal CO2 or vice
versa. The air flow was set at 25 L/min, so the residence time of air in the chamber was about 1 h.
The 13CO2 was fed for 8 h, then the valve was switched back to normal CO2. The whole measurement lasted for 48 h. During the period of
−2
13
CO2 fumigation, light intensity was set at 300
−1
µEm s and leaf temperature was 20. In the 13CO2 exposure experiment, acetone concentrations were measured on a gas chromatography/mass spectrometer system (GC-MS, Fisons MD
800, GC: Carlo Erba CE 8060).
2 Results and discussion
2.1 Emission rates and diurnal variation
Emission rates of acetone are calculated by eq. (1). Under leaf temperature of 25 and light
intensity of 360 µEm−2s−1, acetone emission rates from April to August have been obtained
(fig. 1). Isoprene emission rates at the same duration are also given in fig. 1 for comparison. Fig. 1
shows that acetone emission rates range from 3.2 × 10−15 to 7.3 × 10−15 molcm−2s−1, or can be
expressed as 0.150.34 µgh−2g−1 (fresh weight). This number is relatively lower than that of
acetone emission of (7.4 ± 1.5) µgh−2g−1 (fresh weight) from deciduous tree Abies Concolor
before budbreak[5]. The carbon loss by acetone emission from pine accounts for about 0.0015%
0.0039% of C fixed by photosynthesis. This is comparable to the carbon loss due to acetone emission ranged from 0.003% to 0.02 of carbon fixed by photosynthesis estimated by Singh[6]. As pine
is an evergreen and global distributed species, the plant has active photosynthesis in whole year,
and could be a significant acetone emitter.
Fig. 1. Variation of emission rates of acetone and isoprene from pine (pinus sylvestris) under leaf temperature of
25k and light intensity of 360 µECm−2Cs−1.
It is also shown in fig. 1 that pine emits acetone and isoprene with different variation patterns.
Isoprene has peak emission rates around mid of May, and then drops steadily afterwards. Under
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535
the same condition (leaf temperature, and light intensity), the maximum isoprene emission rate is
3 times as the minimum. While acetone has rather stable emission rates during our measurements,
it starts to decrease from mid of July. The different seasonal variations of isoprene and acetone
may be due to the emission mechanisms of these two compounds.
Acetone emission rates have distinct diurnal variation (measured data are shown in fig. 2).
Over a time period of 4 d, acetone emission rates are high in daytime and low at night. It is noteworthy that nighttime emission rates are not negligible. Daytime emission rates are far higher than
that in darkness, which is caused by both leaf temperature and light intensity. By using the leaf
temperature dependence of acetone emission rates, the daytime and nighttime emission rates could
be normalized to the temperature of 25, then the nocturnal emission rates are about 1/3 of that
in daytime. This discrepancy is probably due to the role of light intensity.
Fig. 2. The measured and calculated diurnal variation of acetone emission rates. Daytime: leaf temperature 22.8k,
light intensity 360 µECm−2Cs−1; night time: leaf temperature 15.0k.
2.2 Impact factors of acetone emission rates
The most important environmental parameters influencing biogenic VOCs emissions are
temperature and light intensity[7,8]. It is found that under the same light intensity, acetone emission
rates change exponentially with leaf temperature. The dependency is described as
 CT (T − Ts ) 
•
,
 R T • Ts 
s
Φacetone = Φacetone
• exp 
(3)
s
are acetone emission rate (molCcm−2Cs−1) at leaf temperature T (K) and
where Φacetone and Φacetone
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standard temperature Ts (298 K) respectively, and CT/R is empirical constant.
By setting constant light intensity, the variation of acetone emission rates with leaf temperature was measured. And the measurements were repeated by changing light intensity. A total of 7
measurements were conducted from April to December to obtain the temperature dependence of
acetone emission rates in daytime. The CT /R values do not show evident change under different
light intensities, and the CT /R level was measured to be (4791±1082) K (1δ ). Interestingly, acetone emission in darkness also changes with leaf temperature as described in eq. (3), and the
nocturnal CT / R values are (4498 ±1310) K (1δ ).
Similarly the light intensity dependence of acetone emission was measured by setting leaf
temperature constant and changing light intensity. Measurements show that emission rates of acetone increase with increasing of light intensity (fig. 3). It can be seen from fig. 3 that response of
acetone emission rates with light intensity is not linear. When light intensity is low, acetone emission rates change almost linearly with light. But with the elevation of light intensity, the increasing
rate of acetone emissions with light goes down, showing a tendency of saturation. Numbers of
measurements prove that acetone emission in darkness is considerable, nocturnal acetone emission
rates are about 1/3 of that under full illumination, which is in good agreement with the data from
diurnal variation measurement.
Fig. 3. Change of acetone emission rates with light intensity ( leaf temperature: 28).
2.3
13
CO2 exposure experiment
The mass spectra of acetone were measured before, during, and after 13CO2 being fed to the
plants. The mass spectra before 13CO2 fumigation are used as background for analysis of 13C labeling of acetone molecules during and after 13CO2 exposure. The most abundant mass of acetone
is its 2-carbon fragment at m/z = 43, and the second abundant ion is the molecular ion at m/z = 58.
The calculation of acetone labeling is done based on molecular ion. Fig. 4 presents the mass spectra variation of 13CO2 (m/z = 45) and acetone molecular ion at chamber outlet.
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QUANTIFICATION OF ACETONE EMISSION FROM PINE PLANTS
537
Fig. 4 indicates that relative abundances of acetone molecular ions change greatly during
CO2 exposure. Before 13CO2 being added, the percentage of ion 58 is above 95%. During 13CO2
exposure, the percentage of ion 58 decreases by about 15%, correspondently, as the acetone
molecules are labeled by 13C, the relative abundances of ions 59, 60 and 61 increase simultaneously. It is important to note that ion 59 remains high level as that in the process of 13CO2 exposure even long time after 13CO2 being switched back to normal air, and then drops slowly.
13
Fig. 4. The variation of molecule mass ion of emitted acetone from pine before, during and after 13CO2 exposure.
Following the change of relative abundance of acetone mass ions in fig. 4, the percentages of
acetone molecule labeled by 13C could be calculated. We did the calculation for the data during
13
CO2 exposure and also the data were obtained at 12ü36 h after the 13CO2 being switched back
to normal air (fig. 5). During the period of 13CO2 fumigation, the aggregated labeling possibility of
all possible patterns is only about 20%, in which full labeling (all carbon atoms of acetone molecule are labeled by 13C) is preferential pattern. And when 13CO2 supply was replaced by normal air,
the total labeling possibility drops to 3%, in which only one carbon atom labeling is predominant
pattern.
Fig. 5. Comparison of label percentage of various label patterns during and after 13CO2 exposure. (a) During 13CO2 fumigation,
(b) 1236 h after 13CO2 was replaced by normal air.
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From the data of 13CO2 exposure experiment, we can find that the acetone emitted from pine
is labeled at the mean time when plants are exposed to 13CO2. At present, the evidence of direct
linkage between carbon fixed by photosynthesis and acetone emission is not available, and the
experimental data indicate rapid and close relationship of photosynthesis and acetone release
process. Furthermore, in the period of 13CO2 exposure and 12ü36 h after the exposure, the contribution from direct photosynthesis related process is only a small portion of acetone emission.
Acetone emitted from pine is still labeled by 13C long time after 13CO2 being replaced, hinting the
existence of big carbon reservoir inside pine plants as precursor of acetone formation and release.
2.4 Algorithm of acetone emission
From the experimental results above, acetone emission is partly originated from processes in
parallel to photosynthesis and therefore is influenced by light intensity, and partly from light independent processes and then only affected by leaf temperature. Numbers of studies have been
performed on each process. Guenther et al.[8] established algorithm to describe isoprene emission
from deciduous trees, and Tingey et al.[9] set up a model to simulate terpene emission from coniferous trees. As acetone emission has contribution to both processes, we combine the algorithm of
Guenther and Tingey to compute acetone emission from pine by assuming that these two processes work separately inside plants. This method is employed to estimate VOCs emission from
sunflower and beech[7].
c
 T − Ts  
exp  T1

(4)
R  TTs  
 cTP  T − Ts  


αL
P,s
B,s

= Φacetoneexp  
,

  + ΦacetonecL
2
2
 1 + α L  1 + exp  cT2  T − TM  
 R  TTs  
 

 R  TTs  
2
Φacetone
where Φ acetone is acetone emission rate, consisting of temperature-controlled process (the first
B,s
term ) and light intensity-controlled process (the second term), Φ P,s
acetone and Φ acetone are standard
emission rate of temperature-controlled process and light intensity-controlled processes at standard condition (leaf temperature 298 K, light intensity of 360 µEm−2s−1 when under illumination); T is leaf temperature, L is identical to light intensity. α, CTP, CT1, CT2 and TM are all empirical parameters for temperature dependence description; CL is a factor to force Φ B,s
VOC to be 1
at standard condition. TM is temperature of maximum enzyme activity of plant. As leaf temperature is generally lower than TM, the second denominator of the second term is set as 1.
P,s
In eq. (4), Φ acetone
is obtained from average of nocturnal emission rates at leaf temperature
Ts (298 K). Φ B,s
acetone is the difference between emission rates under illumination and in darkness at
standard condition. The empirical parameters are derived from regression of eq. (4) with input of
data from temperature dependent experiments and light intensity dependent experiments. Based
on these calculations, the measured diurnal variation of acetone emission rates in fig. 2 is repro-
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QUANTIFICATION OF ACETONE EMISSION FROM PINE PLANTS
539
duced by using eq. (4). It can be seen that the simulation results are in good agreement with the
nocturnal measurement data, but the modeled daytime emission rates are 14.5% higher than
measured values in average. It is interesting to note from fig. 2 that the shapes of measured data
and simulated data at daytime are also different, showing that simulated data are very sensitive to
the variation of leaf temperature. But the measured data do not change evidently when leaf temperature changes only by 12. It seems that small fluctuation of leaf temperature has no measurable change in acetone emission from pine plants.
As indicated in fig. 1, acetone emission rates under constant condition would change with
season, and adequate data of seasonal acetone emission rates at standard condition are not obtained yet. Eq. (4) could not be used to predict long-term variation of acetone emission rates.
3 Conclusions
Pine plant (pinus sylvestris) releases acetone into atmosphere with a significant emission rate.
Acetone emission rates have distinct diurnal variation, and are higher in daytime and lower at
night. Under illumination or in darkness, acetone emission rates change exponentially with leaf
temperature. Emission rates of acetone increase with light intensity under a constant leaf temperature. In this paper, the maximum light intensity where acetone emission rates are saturated is not
found, and the response of emission rates with light intensity is nonlinear. Only temperature-controlled process or light intensity-controlled process alone could not be satisfactory explanation of
our experimental phenomena.
During 13CO2 exposure experiment, acetone is labeled simultaneously when pine is fed with
630 mg/m3
13
CO2, suggesting the fast relationship between carbon fixed by photosynthesis and
acetone emission. Preliminary estimation indicates that only about 20% of acetone emitted from
pine is 13C labeled. In measurement after 13CO2 fumigation, acetone is still labeled but with much
lower labeling percentage. Labeling patterns are found to be very different from that during 13CO2
exposure. However, acetone could be labeled by 13C for more than 36 h after 13CO2 supply stops,
revealing that precursor of acetone formation may be more than one source inside pine plants.
The quantitative contribution of photosynthesis related process to acetone emission is obtained from measurement of acetone emission rates, giving 66%, and also
13
CO2 exposure ex-
periment which shows value of 20%. The reason for such a big discrepancy needs to be investigated further. And all these experimental results prove that acetone emission comes from both
temperature-controlled process and light intensity-controlled process. Assuming that these two
processes work separately, an algorithm is established by combining the models of Guenther[8] and
Tingey[9], and is applied in simulation of acetone emission rates from pine. The algorithm reasonably reproduces diurnal variation of acetone emission rates. If accurate seasonal variation of
acetone emission rates could be obtained, the algorithm is possible to be used as a tool for long
term acetone emission prediction.
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