Gas-phase reaction of dichlorvos, carbaryl, chlordimeform, and 2,4-D butyl ester with OH radicals

Article abstract of DOI:10.1002/kin.20129

Widespread use of pesticides has caused serious environmental concern. In order to evaluate the fate of organic pesticides in the atmosphere, rate constants for gas phase reactions of OH radicals with dichlorvos, carbaryl, chlordimeform, and 2,4-D butyl ester were measured using the relative rate method at ambient temperature and 101 kPa total pressure. On-line FTIR spectroscopy was used to monitor the concentrations of pesticides as a function of time. The reaction rate constants with OH radicals (in units of cm ³ molecule^-1 s^-1) have been determined as (2.0±0.4) × 10^-11 for dichlorvos, (3.3±0.5) × 10^-11 for carbaryl, (3.0±0.7) × 10 ^-10 for chlordimeform, and (1.5 ± 0.2) × 10 ^-11 for 2,4-D butyl ester. These rate constants agree well with those estimated based on the structure-activity relationship. The group rate constant for N=C group (k(N=c)) was estimated as 2.7 × 10^-10 cm³ molecule^-1 s^-1. Dimethyl phosphite has been tentatively identified as a product of the reaction of dichlorvos with OH radicals. Atmospheric lifetimes due to the reactions with OH radicals were also estimated (in units of h): 14±3 for dichlorvos, 8±1 for carbaryl, 1.0±0.3 for chlordimeform, and 19±3 for 2,4-D butyl ester. These short atmospheric lifetimes indicate that the four organic pesticides degrade rapidly in the atmosphere, and they themselves are unlikely to cause persistent pollution. Further studies are needed to identify the potential hazard of their degradation products.

Full text of DOI:10.1002/kin.20129

Gas-Phase Reaction
of Dichlorvos, Carbaryl,
Chlordimeform, and 2,4-D
Butyl Ester with OH Radicals
F. SUN, T. ZHU, J. SHANG, L. HAN
State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences,
Peking University, Beijing 100871, People’s Republic of China
Received 25 January 2005; accepted 15 June 2005
DOI 10.1002/kin.20129
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: Widespread use of pesticides has caused serious environmental concern. In order to
evaluate the fate of organic pesticides in the atmosphere, rate constants for gas phase reactions
of OH radicals with dichlorvos, carbaryl, chlordimeform, and 2,4-D butyl ester were measured
using the relative rate method at ambient temperature and 101 kPa total pressure. On-line FTIR
spectroscopy was used to monitor the concentrations of pesticides as a function of time. The
3
−1 −1
s ) have been deter-
for carbaryl, (3.0 ± 0.7) × 10
reaction rate constants with OH radicals (in units of cm molecule
mined as (2.0 ± 0.4) × 10− for dichlorvos, (3.3 ± 0.5) × 10
11
−11
−10
−
11
for chlordimeform, and (1.5 ± 0.2) × 10
for 2,4-D butyl ester. These rate constants agree well
with those estimated based on the structure–activity relationship. The group rate constant for
−
10
3
−1 −1
N C group (k(N C)) was estimated as 2.7 × 10
cm molecule s . Dimethyl phosphite has
been tentatively identified as a product of the reaction of dichlorvos with OH radicals. Atmo-
spheric lifetimes due to the reactions with OH radicals were also estimated (in units of h): 14 ± 3
for dichlorvos, 8 ± 1 for carbaryl, 1.0 ± 0.3 for chlordimeform, and 19 ± 3 for 2,4-D butyl ester.
These short atmospheric lifetimes indicate that the four organic pesticides degrade rapidly in
the atmosphere, and they themselves are unlikely to cause persistent pollution. Further stud-
ies are needed to identify the potential hazard of their degradation products. ꢀC 2005 Wiley
Periodicals, Inc. Int J Chem Kinet 37: 755–762, 2005
INTRODUCTION
Correspondence to: T. Zhu; e-mail: tzhu@pku.edu.cn.
Contract grant sponsor: National Outstanding Young Scholar
Organic pesticides are used widely throughout the
world and have short and/or long term hazardous
effects on the environment. Most of these organics are
so-called “semivolatile organic compounds” (SOCs)
with vapor pressures between 0.1 and 1 Pa at ambient
temperature [1]; they are ubiquitous in the atmosphere
Fund.
Contract grant number: 49925513.
Contract grant sponsor: Chinese Natural Science Foundation.
Contract grant number: 20077001.
Contract grant sponsor: Chinese Ministry of Science and
Technology.
Contract grant number: 2002CB410802.
Contract grant sponsor: Key Project of Chinese Ministry of
[2,3] and can be transported in the atmosphere to
remote areas. For example, polychlorinated biphenyls
(PCBs), dichlorodiphenyltrichloroethane (DDT),
Education.
ꢀ
c 2005 Wiley Periodicals, Inc.

756
SUN ET AL.
hexachlorocyclohexane (HCH), and hexachloroben-
zene (HCB) were found in Arctic and Antarctic regions
EXPERIMENTAL METHODS
The Relative Rate Method
[4–6].
Upon entering the atmosphere, gas-phase reactions
The reaction rate constants were determined by the rel-
ative rate method assuming that the pesticides and ref-
erence compounds are lost solely via reaction with OH
radicals:
of SOCs with the atmospheric oxidants (such as O3,
OH, and NO3) are the main removal processes for these
compounds [7], and the reaction with OH radicals is
likely the most important one [8]. Nevertheless, these
reactions have received much less attention than the
reactions of OH radicals with volatile organic com-
pounds, mostly because the low volatility and strong
wall effect of SOCs seriously complicate the kinetic
experiments. The wall effects can partly be overcome
by (1) raising the reaction temperature, (2) employing
Teflon-coated chambers, and (3) selecting an OH radi-
cals generating method that is less sensitive to the wall
surface [9]. However, due to technical difficulties, up
to now only a limited number of SOCs have been stud-
ied for their reactions with OH radicals [7,9–12]. In
these studies, researchers either selected organic com-
pounds with relatively high vapor pressures or raised
the temperature to minimize the wall effect.
k
OH + Pesticide −→ Products
(1)
(2)
kr
OH + Reference −→ Products
where k and kr are the rate constants of the reactions
(1) and (2).
Gas phase pesticides in the reactor could be also lost
through wall adsorption and photolysis. Assuming the
loss of pesticides due to wall effect and photolysis fits
the first-order kinetics:
kwall/photo
Pesticide −−−−→ Products
(3)
where kwall/photo is the rate constants due to the wall
effect and possible photolysis reaction. If there is no
wall loss of the reference compound, then the relation-
ship between the concentrations of the pesticides and
the reference compounds at time t is
This paper reports our experimental results on the
reactions of dichlorvos, carbaryl, chlordimeform, and
2
,4-D butyl ester with OH radicals. The relative rate
method was used with cyclohexane and styrene as the
reference compounds. The structure and physiochemi-
cal properties of the pesticides are shown in Table I. The
reasontochoosethesefourpesticidesisthatdichlorvos,
carbaryl, and chlordimeform are the three representa-
tive pesticides among the “Priority Pollutants” List of
China, and 2,4-D butyl ester is a typical herbicide in-
tensively used in 60s and now is still used in some
developing countries.
ꢀ
ꢀ
[Pesticide]0
[Pesticide]t
k
[Reference]0
ln
t = ln
t + kwall/photo
kr [Reference]t
{1}
where [Pesticide] , [Reference] , [Pesticide] , and
[Reference] denote the concentrations of the organic
pesticides and reference compounds at time zero and
t, respectively.
0
0
t
t
Table I Structure and Physicochemical Properties of Four Organic Pesticides
Name
Molecular Formula
Structure
Vapor Pressure
293 K: 1.6 Pa
Dichlorvos
C4H7Cl2O4P
Carbaryl
C12H11O2N
298 K: 670 mPa
Chlordimeform
C10H10ClN
293 K: 47 mPa
2
,4-D butyl ester
C12H14Cl2O3
298 K: 0.133 mPa

GAS-PHASE REACTION OF DICHLORVOS, CARBARYL, CHLORDIMEFORM, AND 2,4-D BUTYL ESTER
757
A plot of ln [
Pesticide]
0
/t versus ln
[Reference]
0
/t has
[Reference]
t
Analytical Procedures
[
Pesticide]
t
a slope with the ratio of the rate constants (k/kr) and an
intercept of kwall/photo. Since the reference rate constant
kr is known, the rate constants of a pesticide k can be
easily calculated.
In this study, styrene was chosen as the reference
compounds for dichlorvos, carbaryl, and chlordime-
form, and cyclohexane for 2,4-D-butyl ester, because
their rate constants are well determined [13] and are
close to those of the pesticides.
The pesticides and reference compounds were moni-
tored with the FTIR at a 1 cm resolution. Spectra
were recorded every 2–4 min over a period of 20 min,
−1
following the initiation of the reaction by turning on
−1
the light. From the IR spectra, the peaks at 1060 cm
,
−1
−1
−1
−1
1
9
230 cm , 1102 cm , 1201 cm , 2864 cm , and
10 cm were used to quantify dichlorvos, carbaryl,
−1
chlordimeform, 2,4-D butyl ester, cyclohexane, and
styrene, respectively.
An off-line method was employed to identify the
products of the reaction between dichlorvos and OH
radicals. About one third of the gas in the reactor was
drawn out by a pump and passed through an alcohol-
Apparatus and Reaction Experiments
The reactions were carried out in a 28.5 L cylindri-
cal quartz reactor (16 cm in diameter, 1.2 m in length)
connected to a Fourier transform infrared spectrometer
◦
liquid nitrogen cold trap (−80 C). Five milliliter of
acetone was added into the cold tube to wash its inner
wall and then 1 ꢀL from the 5 mL acetone solution was
injected into a GC/MS (Polaris Q, Thermo Finnigan)
equipped with a DB-5 column. The GC oven temper-
(FTIR, Nicolet Nexus) equipped with a liquid nitrogen
cooled mercury-cadmium-tellurium (MCT) detector.
The reactor was equipped with a multireflection white-
mirror system (path length 29.5 m). Eight black light
lamps (40 W each, with the peak wavelength at 365 nm)
were used as the light source. Before each experiment,
the reactor was purged three times with ultrahigh purity
◦
ature was initially held at 70 C for 2 min and then in-
◦
◦
creased at 5 C /min to 100 C, after holding for 1 min,
it was increased at 25 C/min to 200 C and held for
min. The ion trap mass spectrometer was operated in
◦
◦
5
the selective ion mode.
(UHP) N2, then evacuated to 10 Pa using a high vacuum
diffusion pump (PD180, Leybold–Heraeus Company,
Germany). To minimize wall memory effects, the reac-
tor was washed with UHP N2 several times after each
experiment. To check wall memory effects, the reactor
was then filled with UHP N2 and the IR spectra showed
no characteristic peaks from the compounds used in the
experiments.
Regents
All compounds were used as received and had the
following purities from Sigma-Aldrich Chemical Co:
dichlorvos (98%), 2,4-D-butyl ester (98%), cyclohex-
ane (analytical grade), and acetone (HPLC grade);
from the Chinese Standard Chemicals Center: carbaryl
(95%) and chlordimeform (95%); from the Beijing
Chemical Reagents Company: styrene (analytical
grade); from the Beijing Chemical Plant: H SO (ana-
The pesticides were introduced into the reactor by
placing a few milligrams of pesticide sample on a tem-
perature controllableheater;afterinserted intothe reac-
tor, the temperature of the heater was increased gradu-
2
4
lytical grade), NaNO (analytical grade), CH OH (an-
2
3
◦
ally up to 150 C. In the meantime, the reactor was filled
alytical grade), NaOH (analytical grade), and CaCl2
(analytical grade); from the Department of Mechan-
ics and Engineering Science of Peking University: N2
(99.999%); from Huayuan Gases & Chemicals Co. Lit:
with a gentle flow of UHP nitrogen and oxygen mix-
ture (N2:O2 = 4:1 by volume) up to 101 kPa and left to
mix and stabilize in the dark for about 2 min. OH radi-
cals were generated by the photolysis of methyl nitrite
2
O (99.999%) and NO (99.5%).
(CH3ONO) in air at a wavelength longer than 300 nm,
Methyl nitrite was synthesized by dripping H SO4
2
NO was added to suppress the formation of O3 and
NO3 radicals [14]. Gaseous CH3ONO and NO were
introduced into the reactor with a syringe. The initial
concentrations of the compounds were approximately
(50%) into the mixture of NaNO , CH OH, and H O.
After passing through a 40% NaOH solution and anhy-
2
3
2
drous CaCl , the methyl nitrite was purified to greater
2
than 99% by vacuum distillation and stored in liquid
nitrogen.
1
4
−3
(10 molecule cm ): CH3ONO, 8; NO, 1; pesticide,
1
;andreference, 2. Alltheexperimentswerecarriedout
at room temperature (296 ± 1 K) and made at one level
of concentrations. For the three replicate experiments,
the initial concentrations of pesticides in each experi-
ment were slightly different, no attempt was made to
change concentration ratio of reference compound and
pesticide.
RESULTS AND DISCUSSION
Wall Effects and Photolysis
In order to evaluate their wall effect and photolysis,
each pesticide and reference compound was introduced

758
SUN ET AL.
into the reactor, mixed with 101 kPa air, and irradiated
for 30 min. After 30 min irradiation, a total loss of
about 30–35% of the gaseous pesticide was recorded
with FTIR, and a straight line was derived from the
[
Reactant]
t
plot of − ln
versus t (see Fig. 1). This con-
[
Reactant]
0
firmed our assumption that the loss of pesticides due
to the wall effect and photolysis fits the first-order
kinetics.
[
Pesticide]t
ln
= −kwall/photot
Pesticide]0
{2}
[
(c)
Based on Eq. {2}, the rate constants and standard
deviations of wall effect and photolysis, kwall/photo, for
dichlorvos, carbaryl, chlordimeform, and 2,4-D butyl
ester were calculated and are listed in Table II.
While no loss was observed for cyclohexane, 3%
loss of styrene was observed during 30 min irradiation,
which was negligible.
(d)
Figure 1 Continued.
Reactions of the Pesticides
with OH Radicals
Figure 2 shows the plots of Eq. {1} for the reactions of
thepesticideswithOHradicals, basedonthreereplicate
measurements for each pesticide. The data were fitted
to a straight line using the least-squares regression, and
the slopes (k/kr) and intercepts are given in Table II.
Based on k/kr and the rate constants of the reac-
tions between OH radicals and styrene at 295 K (5.2
(a)
−
11
3
−1 −1
s ) and cyclohexane
±
0.5 × 10
at 298 K (7.95 ± 0.43 × 10
13], the rate constants of the reaction of OH radicals
cm molecule
−
12
3
−1 −1
cm molecule s )
[
with dichlorvos, carbaryl, and 2,4-D butyl at 296 ± 1 K
were calculated as (2.0 ± 0.4), (3.3 ± 0.5), and (1.5
−
11
3
−1 −1
±
0.2) × 10
cm molecule s , respectively, and
the rate constants for chlordimeform at 295 ± 1 K was
−
10
3
−1 −1
3
.0 ± 0.7 ×10
cm molecule s . Here the er-
rors are based on two standard deviation of the slope
of the fitted line. The relative errors of the rate con-
stants for the reaction of OH radicals with dichlorvos,
carbaryl, chlordimeform, and 2,4-D butyl ester were
± 20%, ± 15%, ± 23%, ± 13%, respectively. Consider-
ing the experimental difficulties associated with wall
(b)
Figure 1 The effect of wall adsorption and photolysis on
the concentrations of gaseous pesticides over time (the line
shows the linear regression): A for dichlorvos, B for carbaryl,
C for chlordimeform, and D for 2,4-D butyl ester.

GAS-PHASE REACTION OF DICHLORVOS, CARBARYL, CHLORDIMEFORM, AND 2,4-D BUTYL ESTER
759
Table II Experimental Conditions, Rate Constants, and Relevant Parameters for the Reactions of Pesticides with OH
Radicals
Slopea
krb (cm
3
k (cm3
molecule
Intercept
c
kwall/photod
−1
−
1
−1
−1 −1
−1
Pesticide
Reference T (K) (k/kr ± 2SD) molecule
s
)
s
)
(s
)
(s
)
−
−
−
−
11
11
11
12
−11
−11
−10
−11
Dichlorvos
Carbaryl
Chlordimeform
Styrene 296 ± 1 0.38 ± 0.08
Styrene 296 ± 1 0.63 ± 0.10
Styrene 295 ± 1 5.7 ± 1.4
5.2 × 10
5.2 × 10
5.2 × 10
7.95 × 10
(2.0 ± 0.4) × 10
(3.3 ± 0.5) × 10
(3.0 ± 0.7) × 10
(1.5 ± 0.2) × 10
0.016 ± 0.003 0.013 ± 0.002
−0.017 ± 0.003 0.013 ± 0.002
−0.02 ± 0.03 0.068 ± 0.006
0.019 ± 0.001 0.026 ± 0.002
2
,4-D butyl ester Cyclohexane 296 ± 1 1.9 ± 0.2
a
b
c
d
Slope of Eq. {1}.
From Xu et al. [15].
Intercept of Eq. {1}.
k
wall/photo is the slope of Eq. {2}.
effect, the precision of the results is within acceptable
levels.
2,4-D butyl ester. Dichlorvos has a higher vapor pres-
sure than the other three pesticides, so we were able to
carry out experiments on the reaction with OH radicals
at a higher concentration of dichlorvos and collected
more products for GC-MS analysis.
Formation of (CH3O)2P(O)OH from the reaction
between (CH3O)2P(O)H and (CH3O)2P(O) with OH
radicals has been confirmed by Martin et al. [16].
Dichlorvos has a similar structure as (CH3O)2P(O)H
and (CH3O)2P(O), therefore (CH3O)2P(O)OH could
be also a product of the reaction between OH and
dichlorvos. A possible reaction pathway is shown in
Fig. 3.
To our knowledge, this is the first report about the
rate constants of the reactions between OH radicals
and carbaryl, chlordimeform, and 2,4-D. The rate con-
stant of the reaction of dichlorvos with OH radicals
−
11
3
−1 −1
s , which
was (2.0 ± 0.4) × 10
cm molecule
−
11
agrees well with the value of (3.06 ± 0.46) × 10
3
−1 −1
cm molecule
15]. The system and methods used in the previous
s reported previously by our group
[
study on dichlorvos are slightly different from those in
the current one: in previous study FTIR from Bio-Rad
(FTS-65A) was used, HNO2 was used as the source of
OH radicals, and dichlorvos was vaporized before in-
troduced into the chamber; while in the current study,
FTIR from Nicolet (Nexus) was used, CH3ONO was
used as the source of OH radicals, and dichlorvos was
vaporized inside the reactor. Considering the differ-
ences between the previous and current studies, the
experiment results agree with each other well.
GC/MS analysis of the products collected from the
reaction between OH and dichlorvos showed two ions
(m/z = 125 and m/z = 110) had large peaks at 6.36 min
retention time; these ions could be attributed to
From Eqs. {1} and {2}, we had assumed that
kwall/photo from Eq. {2} or Fig. 1 should be the same as
the intercept from Eq. {1} or Fig. 2; this seems true for
dichlorvos and 2,4-D butyl ester (see Table II). How-
ever, for carbaryl and chlordimeform, negative inter-
cepts were obtained from Eq. {1}, while their kwall/photo
values from the wall and photolysis experiments were
positive. This might be because of the release of car-
baryl and chlordimeform from the wall, when their gas-
phase concentrations in the reactor decreased due to the
reactions with OH radicals. However, considering the
complicated nature of the wall effect, the difference
between kwall/photo and the intercepts of carbaryl and
chlordimeform could also be caused by experimental
errors.
(
m/z = 125) and
(m/z = 110). This provides supporting evidence for
our hypothesis that (CH O) P(O)OH was a product of
3
2
the reaction between OH and dichlorvos.
The co-product of the reaction is the radical
OCH CCl . It is reasonable to expect that OCHCl2
will further react to form dichloroketene (OC CCl2)
2
Efforts have been made to identify the reaction prod-
ucts of OH radicals with the pesticides. Due to low
efficiency of the offline sampling, no product infor-
mation was obtained for carbaryl, chlordimeform, and
and HO . Dichloroketene has very sharp and strong IR
2
−
1
absorptions in the 2000–2200 cm region. However,
this band was not observed in our study and the reason
is not clear at current stage.

760
SUN ET AL.
Figure 3 Scheme of a possible reaction mechanism be-
tween OH radicals and dichlorvos.
Estimating k with Structure-Activity
Relationship
A structure-activity relationship (SAR) has been de-
veloped to estimate the reaction rate constants of OH
radicals for gas-phase organic compounds [17,18]. For
the newly measured reaction rate constants of carbaryl,
chlordimeform, and 2,4-D butyl ester with OH radi-
cals, it is interesting to compare them with the SAR
estimated values.
By using the group rate constants and the substi-
tute factors from [17,18], the reaction rate constants
of dichlorvos, carbaryl, and 2,4-D butyl ester with OH
−
12
radicals at 298 K were estimated to be 8.2 × 10
,
−
11
−10
3
−1 −1
6
.8 × 10 , and 5.1 × 10
cm molecule s , re-
spectively (Table III). These estimated rate constants
are of the same magnitude as those determined with
experiments. Since the four pesticides contain multi-
functional groups, and the group rate constants for P,
O, N, and Cl-containing groups were derived from lim-
ited experimental values, the agreements between es-
timated and measured rate constants are actually quite
good.
For chlordimeform, the reaction rate constants with
OH radicals could not be estimated, because no report
of the group rate constant for the N C group (k(N C))
was found in the literature. However, we can calcu-
late the k(N C) by using the reaction rate constants of
Table III Experimental and SAR Estimated Rate
Constants for the Gas-Phase Reactions of OH Radicals
with Dichlorvos, Carbaryl, and 2,4-D Butyl Ester
ka (10
−11
cm3
s
kb (10 cm3
−11
−
1
−1
−1 −1
molecule s )
Pesticide
molecule
)
Dichlorvos
Carbaryl
2.0 ± 0.4
3.3 ± 0.5
1.5 ± 0.2
0.82
6.8
0.51
(
d)
Figure 2 Experimental results of the reactions between OH
radicals and the pesticides at 296 ± 1 K and 101 kPa. The line
shows the linear regression from three replicate experiments
data.
2
,4-D butyl ester
a
Experimental values.
Structure–activity relationship (SAR) estimated values.
b

GAS-PHASE REACTION OF DICHLORVOS, CARBARYL, CHLORDIMEFORM, AND 2,4-D BUTYL ESTER
761
−
11
−11
chlordimeform with OH radicals (kchlordimeform) mea-
sured in our experiment:
± 0.4) × 10 , (3.3 ± 0.5) × 10 , (3.0 ± 0.7) ×
−
10 3
−11
−1 −1
10 , and (1.5 ± 0.2) × 10
cm molecule s ,
respectively. To our knowledge, this is the first report
of the rate constants of the gas-phase reactions of car-
baryl, chlordimeform, and 2,4-D butyl ester with OH
radicals. The reaction rate constant of dichlorvos with
OH radicals agreed well with the previous measured
value by our group [15]. These rate constant data are
critical to evaluate whether these pesticides could have
long atmospheric lifetimes and pose a broad threat to
the environment through long-range atmospheric trans-
port. The short atmospheric lifetimes estimated with
these rate constants indicate that in the gas phase, the
pesticides studied are unlikely to be transported long
distances in the atmosphere.
kchlordimeform
=
2 × kprim F(R-N) + kAromatic + kprim F(Aromatic)
−
12
+
+
k(N C) = 2 × 0.144 × 10
× 9.3
× 1 + k(N C)
−
12
−12
31 × 10
+ 0.144 × 10
3.0 × 10− cm molecule
10
3
−1 −1
s
=
then
k(N C) = 2.7 × 10− cm molecule
10
3
−1 −1
s
The large k(N C) indicates that the reaction of OH
radical with chlordimeform mainly happens through
the addition of OH radicals at the N C double
bond. The k(N C) value should be very important for
the SAR database to estimate the reaction rate con-
stants of molecules containing N C group with OH
radicals.
The authors wish to thank Devon Worth and reviewers for
comments that improved the manuscript.
BIBLIOGRAPHY
Atmospheric Lifetimes
1
2
. Bidleman, T. F. Environ Sci Technol 1988, 22, 361–
67.
. Hillery, B. R.; Simcik, M. F.; Basu, I.; Hoff, R. M.;
Strachan, W. M. J.; Burniston, D.; Chan, C. H.; Brice,
K. A.; Sweet, C. W.; Hites, R. A. Environ Sci Technol
Atmospheric lifetimes are necessary to evaluate
whether these pesticides could pose a broad threat to
the environment through long-range atmospheric trans-
port. By using the rate constants in Table II along with
3
6
an assumed atmospheric OH concentration (1.0 × 10
1998, 32, 2216–2221.
−3
molecule cm ) [19], the atmospheric lifetimes of the
pesticides due to the reaction with OH radicals were
estimated to be 11 ± 3, 8 ± 1, 1.0 ± 0.3, and 19 ±
3. Cortes, D. R.; Hites, R. A. Environ Sci Technol 2000,
34, 2826–2829.
4. Malmquist, C.; Bindler, R.; Renberg, I.; Bavel, B. V.;
Karlsson, E.; Anderson, N. J.; Tysklind, M. Environ Sci
Technol 2003, 37, 4319–4324.
3
h for dichlorvos, carbaryl, chlordimeform, and 2,4-D
butyl ester, respectively.
5
. Hung, H.; Halsall, C. J.; Blanchard, P.; Li, H. H.; Fellin,
P.; Stern, G.; Rosenberg, B. Environ Sci Technol 2002,
The atmospheric lifetimes of these pesticides are
less than 1 day, indicating that the gas-phase reaction
with OH radicals is an important removal process for
these pesticides, and in the gas phase they are unlikely
to be transported long distance in the atmosphere. How-
ever, further studies are required to determine if the
reaction products of these pesticides with OH radicals
were more hazardous than the pesticides themselves
and if the pesticides in particulate phase could be trans-
ported long distance in the atmosphere.
3
6, 862–868.
6
7
. Dickhut, R. M.; Cincinelli, A.; Cochran, M.; Ducklow,
H. W. Environ Sci Technol 2005, 39, 465–470.
. Lee, W.; Stevens, P. S.; Hites, R. A. J Phys Chem A 2003,
1
07, 6603–6608.
8. Crutzen, P. J.; Ramanathan, V. Science 2000, 290, 299–
304.
9. Anderson, P. N.; Hites, R. A. Environ Sci Technol 1996,
3
0, 301–306.
0. Anderson, P. N.; Hites, R. A. Environ Sci Technol 1996,
0, 1756–1763.
1. Brubaker, W. W. Jr.; Hites, R. A. Environ Sci Technol
998, 32, 766–769.
1
1
1
3
CONCLUSION
1
2. Atkinson, R.; Guicherit, R.; Hites, R. A.; Palm, W. U.;
Seiber, J. N.; Voogt, P. D. Water Air Soil Pollution 1999,
Using the relative rate method and on-line FTIR spec-
trometer, the rate constants of the gas phase reactions
of OH radicals with dichlorvos, carbaryl, chlordime-
form, and 2,4-D butyl ester at ambient temperature and
1
15, 219–243.
13. Atkinson, R. Chem Rev 1985, 85, 69–201.
14. Atkinson, R.; Tuazon, E. C.; Aschmann, S. M. Environ
Sci Technol 2000, 34, 623–631.
1
01 kPa total pressure have been determined to be (2.0

762
SUN ET AL.
1
1
1
5. Xu, Y. P.; Zhu, T.; Li, S. J. Prog Nat Sci (Chinese) 2001,
2, 1258–1262.
6. Martin, P.; Tuazon, E. C.; Atkinson, R.; Maughan, A. D.
J Phys Chem A 2002, 106, 1542–1550.
18. Kwok, E. S. C.; Atkinson, R. Atmos Environ 1995,
29(14), 1685–1695.
19. Prinn, R. G.; Huang, J.; Weiss, R. F.; Cunnold, D. M.;
Fraser, P. J.; Simmonds, P. G.; McCulloch, A.; Harth, C.;
Salameh, P.; O’Doherty, S. R.; Wang, H. J.; Porter, L.;
Miller, B. R. Science 1995, 292, 1882–1888.
1
7. Atkinson, R. Environ Sci Technol 1987, 21, 305–
3
07.