Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase as Examined by TPD MS and Inverse Gas Chromatography
The desorption non-isothermal kinetics of preliminary adsorbed Cl, Br, and I-containing volatile halocarbons from the surface of surrogates for atmospheric solid aerosols (fumed silica and alumina, silica gel and H-mordenite) was studied by TPD MS. The TPD spectra demonstrate high heterogeneity of t...
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| Zitieren: | Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase as Examined by TPD MS and Inverse Gas Chromatography / V.I. Bogillo, M.S. Bazylevska, B.G. Mischanchuk, V.A. Pokrovskiy // Хімія, фізика та технологія поверхні. — 2010. — Т. 1, № 4. — С. 401-414. — Бібліогр.: 38 назв. — англ. |
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Digital Library of Periodicals of National Academy of Sciences of Ukraine| _version_ | 1860230197748432896 |
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| author | Bogillo, V.I. Bazylevska, M.S. Mischanchuk, B.G. Pokrovskiy, V.A. |
| author_facet | Bogillo, V.I. Bazylevska, M.S. Mischanchuk, B.G. Pokrovskiy, V.A. |
| citation_txt | Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase as Examined by TPD MS and Inverse Gas Chromatography / V.I. Bogillo, M.S. Bazylevska, B.G. Mischanchuk, V.A. Pokrovskiy // Хімія, фізика та технологія поверхні. — 2010. — Т. 1, № 4. — С. 401-414. — Бібліогр.: 38 назв. — англ. |
| collection | DSpace DC |
| container_title | Хімія, фізика та технологія поверхні |
| description | The desorption non-isothermal kinetics of preliminary adsorbed Cl, Br, and I-containing volatile halocarbons from the surface of surrogates for atmospheric solid aerosols (fumed silica and alumina, silica gel and H-mordenite) was studied by TPD MS. The TPD spectra demonstrate high heterogeneity of the surface studied. The average desorption activation energies and half-widths of the halocarbons desorption energy rectangular distribution were calculated. The relationships between the average desorption activation energies and molecular descriptors for the halocarbons were derived for the solids. The partitioning of the halocarbons and additional volatile organics between surrogates for mineral and carbonaceous atmospheric aerosols (silica gel, Carbopack S, Carbosil) was examined by using the inverse gas chromatography method. These data indicate to the energetic heterogeneity of the solid surfaces. The average adsorption energies and variances of the adsorption energy rectangular distribution were calculated and connected with molecular descriptors of the volatiles. A relationship is observed between average desorption activation energies of halocarbons on the silica gel surface from TPD MS data and average adsorption energies in these systems determined using inverse gas chromatography method at finite concentrations.
Кінетика неізотермичної десорбції попередньо адсорбованих Cl, Br і I-вмістних галогенвуглеводнів (ГВ) з поверхні сурогатів атмосферних твердих аерозолів (пірогенні кремнезем і оксид алюмінію, силікагель і Н-морденіт) вивчена методом температурно-програмованої десорбційної мас-спектрометрії (ТПД МС). ТПД спектри демонструють високу неоднорідність вивчених поверхонь. Розраховані середні величини енергії активації десорбції та півширини прямокутних розподілів енергій десорбції ГВ. Отримані співвідношення між середніми енергіями активації десорбції ГВ і їх молекулярними дескрипторами для всіх вивчених твердих тіл. Розподіл ГВ і додаткових летких органічних сполук між сурогатами мінеральних і вуглецьвмісних атмосферних аерозолів (сілікагель, Карбопак і Карбосіл) досліджено методом оберненої газової хроматографії (ОГХ). Дані ОГХ вказують на енергетичну неоднорідність поверхні цих твердих тіл. Розраховані середні величини енергії адсорбції ГВ і дисперсії прямокутного розподілу поверхонь по енергіям адсорбції та знайдені зв’язки між цими величинами та молекулярними дескрипторами цих летких сполук. Встановлено співвідношення між середніми енергіями активації десорбції ГВ з силікагелю з даних ТПД МС і середніми енергіями адсорбції в цих системах, визначеними з даних ОГХ при скінченних концентраціях.
Кинетика неизотермической десорбции предварительно адсорбированных Cl, Br и I-содержащих галогенуглеводородов (ГУ) с поверхности суррогатов атмосферных твердых аэрозолей (пирогенные кремнезем и окись алюминия, силикагель и Н-морденит) изучена методом температурно-программированной десорбционной масс-спектрометрии (ТПД МС). ТПД спектры демонстрируют высокую неоднородность изученных поверхностей. Рассчитаны средние значения энергии активации десорбции и полуширины прямоугольных распределений энергий десорбции ГУ. Получены соотношения между средними величинами энергии активации десорбции ГУ и их молекулярными дескрипторами для всех изученных твердых тел. Распределение ГУ и добавочных летучих органических соединений между суррогатами минеральных и углеродсодержащих атмосферных аэрозолей (силикагель, Карбопак и Карбосил) исследовано методом обращенной газовой хроматографии (ОГХ). Данные ОГХ указывают на энергетическую неоднородность поверхности этих твердых тел. Рассчитаны средние энергиии адсорбции ГУ и дисперсии прямоугольного распределения поверхностей по энергиям адсорбции и найдены связи между этими величинами и молекулярными дескрипторами летучих соединений. Установлено соотношение между средними энергиями активации десорбции ГУ с силикагеля из данных ТПД МС и средними энергиями адсорбции в этих системах, определенными из данных ОГХ при конечных концентрациях.
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Хімія, фізика та технологія поверхні. 2010. Т. 1. № 4. С. 401–414
_____________________________________________________________________________________________
* Corresponding author vbog@carrier.kiev.ua
ХФТП 2010. Т. 1. № 4 401
UDC 544.723.3:543.51+543.544:543.27:544.772
PARTITIONING OF VOLATILE HALOCARBONS BETWEEN
SURROGATES FOR ATMOSPHERIC SOLID AEROSOLS
AND GAS PHASE AS EXAMINED BY TPD MS AND INVERSE
GAS CHROMATOGRAPHY
V.I. Bogillo1*, M.S. Bazylevska1, B.G. Mischanchuk2, V.A. Pokrovskiy2
1Department of Antarctic Geology and Geoecology
Institute of Geological Sciences of National Academy of Sciences of Ukraine
55B Oles' Gonchar Street, Kyiv 01054, Ukraine
2Chuiko Institute of Surface Chemistry of National Academy of Sciences of Ukraine
17 General Naumov Street, Kyiv 03164, Ukraine
The desorption non-isothermal kinetics of preliminary adsorbed Cl, Br, and I-containing volatile halo-
carbons from the surface of surrogates for atmospheric solid aerosols (fumed silica and alumina, silica gel
and H-mordenite) was studied by TPD MS. The TPD spectra demonstrate high heterogeneity of the surface
studied. The average desorption activation energies and half-widths of the halocarbons desorption energy
rectangular distribution were calculated. The relationships between the average desorption activation ener-
gies and molecular descriptors for the halocarbons were derived for the solids. The partitioning of the halo-
carbons and additional volatile organics between surrogates for mineral and carbonaceous atmospheric
aerosols (silica gel, Carbopack S, Carbosil) was examined by using the inverse gas chromatography
method. These data indicate to the energetic heterogeneity of the solid surfaces. The average adsorption en-
ergies and variances of the adsorption energy rectangular distribution were calculated and connected with
molecular descriptors of the volatiles. A relationship is observed between average desorption activation en-
ergies of halocarbons on the silica gel surface from TPD MS data and average adsorption energies in these
systems determined using inverse gas chromatography method at finite concentrations.
INTRODUCTION
The volatile F, Cl, Br and I-containing halo-
carbons (HCs) used as solvents and refrigerants
are important priority toxic pollutants because
exposure to the dangerous HCs can be injurious
to human health and ecosystems [1]. Many of
these compounds are toxic and exhibit mutagenic
and/or carcinogenic properties. Major potential
health effects of HCs exposure include acute and
chronic respiratory effects, neurological toxicity,
lung cancer, and eye and throat irritation.
The HCs participate in much heterogeneous
industrial and natural processes. So, heterogene-
ous reactions of the HCs on the surface of strato-
spheric cryoaerosols are responsible for the de-
velopment of the Antarctic ozone hole [2]. Re-
lease of chlorine during the HCs reactions with
constituents of rocket exhaust formed by solid
rocket motors (α- and γ-Al2O3) may provide an
additional source of active chlorine that may cata-
lytically destroy the stratospheric ozone [3].
Assessment of the importance of heterogene-
ous chemical reactions of HCs taking place on the
surface of particulates present in the troposphere is
an area of ongoing studies [4]. Heterogeneous
transformations of HCs may decrease tropospheric
oxidation potential which has been previously es-
timated from consideration of only gas-phase re-
actions of HCs with OH, NO3 radicals and ozone
[5, 6]. In case of such Langmuir-Hinshelwood
heterogeneous reactions, the reaction coefficient
depends on the adsorption energy of the HCs [7].
Potential of soils, sediments, ocean, snow and
vegetation as sources and sinks for HCs has
widely been discussed [8–11]. The volatile spe-
cies can be transported over long distances from
emission sources and be distributed between air
and these environmental compartments. Adsorp-
tion of the HCs on these surfaces is a first stage of
their removal from atmosphere and it determines
the effectiveness of subsequent transformations
such as photochemical, chemical and microbial
oxidation, etc. Knowledge of HCs adsorption
V.I. Bogillo, M.S. Bazylevska, B.G. Mischanchuk, V.A. Pokrovskiy
_____________________________________________________________________________________________
402 ХФТП 2010. Т. 1. № 4
characteristics from gas phase to such interfaces
as water, snow, plants, rocks, soils, and sedi-
ments, organic, carbonaceous and mineral aero-
sols is important for assessing the partitioning and
transport of the organics in our environment. The
air/interface partition coefficients are involved as
input parameters in current stationary and dy-
namic models of atmospheric and environmental
chemistry [12]. However, these data for most at-
mospherically abundant HCs on various envi-
ronmental interfaces are unknown.
Adsorption process is perhaps the most com-
mon method for the capture and recovery of HCs
vapors, such as cleaning solvent vapors, from gas
stream [13]. Most adsorbents play a role of catalyst
in heterogeneous transformations of HCs or cata-
lyst supports [14, 15]. Adsorption data for HCs are
essential in choice and development of appropriate
and selective adsorbents, solid sensors and in com-
prehension and the modeling of reaction kinetics
on solid catalysts. In all cases, a priori prediction
of the adsorption characteristics would be very
useful in order to reduce the experimental efforts.
Inverse gas chromatography (IGC) [16] and
thermal programmed desorption mass spectrome-
try (TPD MS) [17] would be appropriate methods
for quantitative study of the HCs partitioning be-
tween gas phase and the solid surfaces. In the pre-
sent work, we experimentally studied the partition-
ing of some Cl-, Br-, and I-containing volatile HCs
between surrogates of mineral and carbonaceous
aerosols and gas phase by using these methods.
EXPERIMENTAL
Materials. Following HPLC grade HCs
(Merck, Germany) were used in the IGC and TPD
MS study: dichloromethane (CH2Cl2), chloroform
(CHCl3), carbon tetrachloride (CCl4),
1,2-dichloroethane (C2H4Cl2), trichloroethylene
(C2HCl3), dibromomethane (CH2Br2), bromoform
(CHBr3), 1,2-dibromoethane (C2H4Br2),
1-bromobutane (C4H9Br), and methyl iodide
(CH3I). These HCs are emitted from industrial and
natural sources [1]. Most of them are present in the
troposphere in appreciable concentrations and,
therefore, they affect the atmospheric level of HOx
(HO, HO2) radicals and ozone. Furthermore, fol-
lowing volatile "test" compounds (Merck, Ger-
many) possessing different electronic polarizability
and acid-base characteristics of the molecules were
used in the IGC study: n-pentane, n-hexane, n-hep-
tane, benzene, carbon disulfide, acetonitrile, nitro-
methane, nitroethane, methanol, ethanol, acetone,
diethyl ether, tetrahydrofurane, and 1,4-dioxane.
The parameters of the Antoine equation and
the liquid densities at the standard temperature
(293 K) required to calculate their adsorption iso-
therms from IGC data are taken from [18].
Since the main component of terrigenous aero-
sols in the troposphere is silica [19] the silica gel
S60 (Fluka, Switzerland) with BET specific ad-
sorption surface area of SA = 336 m2/g (as deter-
mined from low-temperature nitrogen adsorption
measurements (77 K) by using an ASAP 2010
volumetric adsorption apparatus from Micromerit-
ics (Norcross, GA)) and fumed silica Aerosil 300
(Chlorovinyl Co, Kalush, Ukraine) with
SA =
267 m2/g are chosen as this component. Se-
cond main component of the mineral aerosols is
alumina [19] and the fumed alumina (Chlorovinyl
Co, Kalush, Ukraine) with SA = 159 m2/g was used
in the TPD MS study. Zeolites are widely used as
catalysts for dehalogenation processes of the HCs
[15] and similar reactions are possible in the tropo-
spheric conditions on the surface of mineral aero-
sols containing these minerals. A sample of com-
mercial hydrogen mordenite (H-mordenite from
Norton Co., USA) with SA = 380 m2/g and with
Si/Al = 10.7 was used in the TPD MS study.
Carbonaceous aerosols were imitated by
graphitized carbon black (Carbopack C; Supelco,
Bellefonte, PA, USA) with SA = 10 m2/g and the
silica gel modified by low-temperature carboniza-
tion of acetylacetone (Carbosil with 35 wt% car-
bon) with SA = 100 m2/g [20]. The latter was cho-
sen because the burning of solid fuels yields large
amount of silica [19].
TPD-MS procedure. TPD MS technique has
been developed, aimed at studies of adsorption-
desorption kinetics and chemical transformations
of HCs on the environmental surfaces starting
from very low temperature (100 K). The equip-
ment set included monopole mass analyzer MX-
7304A (Ukraine, Sumy), liquid nitrogen free vac-
uum system and pump NMD 0.16–1, precise
thermal regulator with heating element RIF-101,
quarts-molybdenum tube for samples and IBM
computer-guided system of registration and moni-
toring. Equipment parameters obtained in our
test experiments are: mass range is 1–400 Dalton,
resolving power is 10% intensity of 1/M, sensitiv-
ity is 10-8 g; the heating rate ranges from 0.05 to
30 K/min and average experiment duration is
1 hour. The adsorption capacity of the dispersed
Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase
_____________________________________________________________________________________________
ХФТП 2010. Т. 1. № 4 403
solids has been provided desorption of about 10-3
times the weight of sample. The result is a gain in
sensitivity of about 105 in comparison with bulk
samples. All the experimental scheme of TPD of
ultra-fine samples became similar to thermal
analysis experiment with mass spectrometric de-
tection of volatile products.
The dispersed samples of the solids each of
about 0.1–1 mg weight are placed into a quartz-
molybdenum tube and evacuated at 10-1 Pa and
then attached to the inlet system of the mass spec-
trometer. The reactor-to-mass spectrometer inter-
face included a high-vacuum valve with an orifice
of diameter 5 mm and the inlet tube of 20 cm
length which was kept at 150°C. The reaction
space is open in the ion-source direction and at the
heating rate used (about 0.1 K s-1) the observed
intensity of the ion current is expected to be pro-
portional to the desorption rate so that diffusion
retardation may be neglected. We assumed quasi-
stationary conditions when the shape and position
of desorption peaks did not depend on the tempera-
ture of the spectrometer interface, the sample dis-
persity and/or its size. The TPD data were not con-
sidered further if these conditions were not fulfilled.
In the typical TPD MS experiment the solid
sample was preliminarily pressed at 3·103 Pa. This
procedure, as it has been shown previously, does
not change specific surface area of the fumed ma-
terials. Preliminary vacuum treatment of the sam-
ples was provided at the temperature 970 K during
2 hours. Sample pellet of size 2×2×1 mm has been
introduced into quartz-molybdenum tube and
evacuated at 7.5·10-7 Pa for half of an hour. After
cooling the sample down to room temperature the
material has been exposed to a HC vapor in
amount of inner volume of quartz-molybdenum
tube i.e. about 10 cm3. Then the sample was cooled
down to the temperature of liquid nitrogen. Cool-
ing lasted approximately 10 minutes. When the
stationary temperature of the sample has been
achieved, the high-vacuum pumping started and
after five-minutes of pumping the cyclic record of
mass spectra was switched on. The temperature
has been recorded for each cycle and, correspond-
ingly, to each mass spectrum. At the first stage of
record the typical mass spectrum of a HC was ob-
served, further all a HC was pumped away and
only chemical background was observed in the
mass spectrum. For example, characteristic tem-
perature of 1,2-dichloroethane disappearance from
the Aerosil 300 surface was 246°K.
IGC procedure. The inverse chromatographic
measurements were carried out with gas chro-
matograph "LKhM 80" (Russia). Thermal con-
ductivity detector was used in the study. The ana-
log output from the detector was digitalized and
recorded on an IBM PC computer controlled by
original software (Turbo Pascal) to determine the
coordinates of chromatographic peak from those
measurements. Helium was used as the carrier
gas. Air, as a non-interacting marker, was em-
ployed to measure the dead volume of the chro-
matographic column. Injection of the volatile
compounds was repeated at least three times.
Flow rate was measured at the end of the column
with a bubble flow meter and its value was main-
tained in the range 30–40 cm3/min. Pressures
measured at the inlet and outlet of the column
(scaling factor was 0.15 Pa) were applied to cal-
culate the net retention volume. The molecular
probes were injected manually with Hamilton
glass micro syringes (Hamilton micro liter 700
and 7000 series syringe). The volume of injected
liquid probes varied from 0.1 to 5 µl.
Short stainless columns (400 mm long and
3 mm I.D.) were filled by the examined solids. The
columns were preliminary conditioned under he-
lium at 470 K for 12 h before their use to remove
the physically adsorbed water and other volatile
traces from the solid surface. Adsorption measure-
ments were carried out over a temperature range of
from 353 to 453 K (at the isothermal conditions,
scaling factor was 0.2 K) at 10 K interval. The tem-
peratures of the detector and injector were 473 K.
Calculation of primary IGC data. The specific
adsorption retention volume, VS
o (in cm3/m2) for the
examined molecular probes was calculated as
0
0
3
2
0
0
2
1
1
2
315,273
)(
P
PP
P
P
P
P
TwS
F
ttV
OH
o
i
i
rA
X
o
g
−
×
−
−
×××−=
(1)
where tX and t0 are the retention times of the mo-
lecular probe and of the non-interacting marker
(air) at column temperature T (in K), F is the flow
rate of the carrier gas through column measured
on the output at room temperature Tr, w is the
weight of a solid in the column, PH2O is the satu-
rated water vapor pressure at the Tr, Pi and PO are
the pressures of the carrier gas measured at the
inlet and outlet of the column.
The "multiple injection" and "one-peak"
methods are commonly applied to the analysis of
V.I. Bogillo, M.S. Bazylevska, B.G. Mischanchuk, V.A. Pokrovskiy
_____________________________________________________________________________________________
404 ХФТП 2010. Т. 1. № 4
the chromatographic peak dependence on the
known amount of the liquid probe injected into
the chromatographic column, and for the subse-
quent determination of the adsorption isotherm on
the surface of chromatographic support [21]. In
both methods a given amount of probe injected
quickly, inducing a peak. Adsorption or desorp-
tion may be followed by a mathematical examina-
tion of the front and tail of the recorded peak. The
first method analyses the dependence of specific
adsorption retention volume on the probe amount,
whereas second approach deals with co-ordinates
of the chromatographic peak at moderate or large
amount of the probe.
The calculation of the vapor pressure for
the molecular probes, Pcorr and the surface solid
coverage, acorr for the adsorption isotherms using
"one-peak" method with correction for multilayer
adsorption [22] was carried out from the data for
the peak’ profile (400–2000 points) as follows
i
corrpeak
p h
FSMW
TvR
P ×
××
×××
=
ρ
, (2)
)(adsi
Apeak
p S
wSSMW
v
a ×
×××
×
=
ρ
, (3)
1
11
2
3
3
2
2
−
−
×
−××
=
o
i
o
i
k
o
OH
corr
P
P
P
P
T
P
P
TF
F , (4)
S
corr PP
P
P
/1−
= , (5)
S
corr PP
a
a
/1−
= (6)
where R is the universal gas constant, vp is the vol-
ume of the liquid probe injected, ρ is the liquid den-
sity at Tk, MW is the molecular weight, Speak is the
total area of the chromatographic peak calculated by
its numerical integration, Fcorr is the flow rate cor-
rected by compressibility of the carrier gas in the
column and change of surface tension for water in
the bubble flow meter with the Tr value, hi is the
height for the point i localized on the descending
side of the peak’ tail, Si(ads) is the product of the dis-
tance on the chromatogram from the retention time
of non-interacting marker to the retention time for
point i on the height of the point, hi, PS is the satu-
rated vapor pressure for the liquid probe at T.
RESULTS AND DISCUSSION
TPD MS measurements and calculation of de-
sorption activation parameters. The desorption of
the HCs preliminary adsorbed on the surrogates for
mineral atmospheric particulates was studied by
TPD MS method from liquid nitrogen up to room
temperature. In all cases, observed mass spectra
included reliably identified lines of HCs as a main
component. The shape and temperature interval of
evolution of molecular ion varied depending on the
nature of the surrogate and adsorbed HCs. All mass
spectra included also line of water of medium inten-
sity, starting its evolution from the sample at the
temperature of about 150 K for all samples.
Fig. 1 presents desorption peaks for the HCs
from the silica gel surface. It is obvious that the
shape of the peaks, their width and temperature
maximum depend on the HCs structure.
120 160 200 240
0
40
80
120
CH
3
I
n-C
4
H
9
Br
C
2
HCl
3
1,2-C
2
H
4
Cl
2
CHCl
3
CH
2
Cl
2
CCl
4
I,
a
rb
. u
ni
ts
T, K
Fig. 1. TPD spectra of Cl, Br and I-containing volatile
halocarbons preliminary adsorbed on the silica
gel (Si60) surface. The heating rate was 0.1 K/s
For the interpretation of temperature depend-
encies of mass spectra we assume that the desorp-
tion equation may be expressed as a first-order
process from homogeneous solid surface
Θ−=Θ Dkdtd / (7)
where Θ is the surface coverage and the desorp-
tion rate coefficient, kD is
)/exp( RTEAk DDD −= (8)
where ED is the desorption activation energy and
AD is the pre-exponential factor.
Both Eqs. (7) and (8) constitute the Polanyi-
Wigner equation: )/exp(/ RTEAdtd DD −−=Θ . At the
initial condition Θ t = =0 1 we have the following
solution of equation (7)
)](exp[)( tt Φ−=Θ , (9)
∫=Φ
t
D dtkt
0
)( . (10)
Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase
_____________________________________________________________________________________________
ХФТП 2010. Т. 1. № 4 405
According to Eq. (9) desorption rate which is
proportional to ion current may be obtained in the
following form
)](exp[/)( tkdttd D Φ−−=Θ . (11)
The key equation (10) may be expressed in an
approximate analytical form for a slow heating rate
( β ≤ 0.1 K/s) and high values of the pre-
exponential factor (AD > 109 s-1) assuming a linear
heating rate, T = T0 + β t and expanding the tem-
perature dependence near the peak’ maximum Tmax
)exp()(
2
max
RT
E
A
E
RT
t D
D
D
−=Φ
β
(12)
which, in most cases, is valid within experimental
accuracy. The condition of the maximum value of
d dtΘ / (or ion current I t( ) ) is Φ( )t = 1 .
The behavior of I T( ) near the peak maxi-
mum may be used for calculating the parameters
of non-isothermal kinetics. The behavior of the
experimentally observed ion intensity I T( ) in the
neighborhood of Tmax may be written as
2
1/)(
2
max
TI
ITI
∆′′−= (13)
where maxTTT −=∆ and ′′I is the value of the sec-
ond derivative at the peak maximum of experi-
mental curve I = f(T).
Expanding, on the other hand, the expressions
for ion current taking into account Eq. (12) and
the condition Φ( )t = 1 in the neighborhood of Tmax
and comparing with the chosen experimental val-
ues TTT −=∆ max and corresponding
III −=∆ max one can easily obtain approximate
formulas for the calculation of the desorption ac-
tivation parameters
3
max 1027.8 −= DD TE σ [kJ/mol] (14a)
and
)exp(
max
DDD T
A σσβ= [s-1], (14b)
max
max2
I
I
T
T
D
∆
∆
=σ . (14c)
The determination of ∆T value and the cor-
responding
max/ II∆ from an experimental curve
depends upon two opposing factors. max/TT∆
should be chosen as small as possible to preserve
the validity of approximation made to derive
equation (12); II /∆ , on the contrary, should be
chosen as large as possible to decrease the error
of graphical measurement of ∆I . A typical com-
promise is the value ∆I/I of about 0.1–0.3; the
corresponding value of ∆T is found from the
experimental peak I = f(T). The values ∆I and
∆T should be derived from the low-temperature
side of desorption peak. The existence of differ-
ent adsorption sites on a solid surface being the
most common source of the more or less overlap-
ping peaks on the experimental TPD spectra. In
case of first-order desorption from energetically
heterogeneous surface it is necessary to introduce
a normalized distribution function for surface
sites over ED values: )( DEρ . Then the total de-
sorption rate dΘ/dt (and the total ion current, I)
should be calculated as an integral
∫
∞Θ
0
)(
)(
DD dEE
dt
td
dt
d ρθ
(15)
where dθ(t)/dt is the local desorption rate from
the surface sites with desorption activation energy
ED at point t.
Unfortunately, very little information is
available concerning ρ(ED) function in most cases
of adsorption of organic molecules on the solid
surfaces. In what follows condition Φ( )t = 1 is
applied to the simplest distribution function
ρ(ED). Let function ρ(ED) be a rectangle in the
interval ED(min), ED(max) of magnitude
1
(min)(max) )( −− DD EE . In this case
∫−
=Θ (max)
min)
)(1
(min)(max)
D
D
E
E
D
D
DD
dE
dt
Ed
EEdt
d θ
. (16)
Neglecting the weak pre-exponential dependen-
cies upon T and ED, and substituting ED and T
by average values Tmax and 2/)( (min)(max) DD EE + ,
the following approximate expression may be
obtained for this model
[ ]),(),(
)(
)(
(min)(max)
(min)(max)max
(max)(min)
tEtE
EET
EE
dt
d
DD
DD
DD
Θ−Θ×
×
−
+
=Θ β
. (17)
V.I. Bogillo, M.S. Bazylevska, B.G. Mischanchuk, V.A. Pokrovskiy
_____________________________________________________________________________________________
406 ХФТП 2010. Т. 1. № 4
Table 1. Average desorption activation energies (ED(av)) and half-widths (∆D/2) of the rectangular halocarbons de-
sorption activation energy distributions of surfaces for surrogates of mineral aerosols from TPD MS data
and evaporation enthalpies for the halocarbons, ∆Hvap from [18]
Halocarbon A-300 Silica gel Al2O3 H-mordenite
ED(av) ∆D/2 ED(av) ∆D/2 ED(av) ∆D/2 ED(av) ∆D/2 ∆Hvap
kJ/mol
CH2Cl2 50 20 70 10 64 10 67 17 28.0
CHCl3 53 15 75 10 60 20 70 8 29.7
CCl4 60 20 65 25 59 11 71 11 30.0
1,2C2H4Cl2 54 20 70 10 67 15 75 15 32.0
C2HCl3 51 15 60 20 55 17 69 9 31.4
n-C4H9Br 55 13 75 15 73 17 78 16 33.0
CH3I 42 12 60 10 27.2
Substitution of equations (9) and (12) in (17)
gives the analytical dependence of the ion current
upon the variables and parameters of the model
]exp
[exp
)(
)(
(min)
(max)
(min)
2
max
(max)
2
max
(min)(max)max
(max)(min)
−−
−
−×
×
−
+
=Θ
−
−
RT
E
D
D
RT
E
D
D
DD
DD
D
D
eA
E
RT
eA
E
RT
EET
EE
dt
d
β
β
β
.
(18)
The observed great width of the desorption
peaks (Fig. 1) points to the large energetic surface
heterogeneity of the solids studied. The Eq. (11) is
not reconcilable with experimental TPD spectra for
all systems examined. Then the average desorption
activation energies and half-widths of the rectan-
gular desorption activation energy distributions
were calculated assuming minimal pre-exponential
desorption factor AD = 1.0·1013 s-1 [23] with use of
Eq. (18). These data are presented in Table 1.
From the Table we notice that both the average
desorption activation energy and width of the dis-
tribution depend on the halocarbon structure and
the solid surface. Maximum ED(av) values are ob-
tained for H-mordenite and the minimum ones are
characteristic of the Aerosil-300 surface.
One would expect the proximity of a ED(min)
value for the physical desorption of preliminary
adsorbed volatile compounds to the evaporation
enthalpy of the compounds, ∆Hvap. However, as it
is evident from the Table, the difference between a
quantity ED(av)–∆D/2 and ∆Hvap varies from 2 to
30 kJ/mol. One of reason for this difference may
be choice of very large pre-exponential factor AD
for the evaporation process. Formerly we exam-
ined the non-isothermal desorption of water from
silica surfaces by TPD MS and DTG methods [24]
and for n-butanol desorption from silica gel sur-
face by Q-TG and Q-DTG methods under quasi-
equilibrium conditions [25]. The most calculations
of AD from the TPD spectra of water physically
adsorbed on silica by using the most popular Po-
lanyi-Wigner, Kissinger and Freeman methods
[26] give lower desorption pre-exponential factors,
ranging from 0.8 to 3.6·105 s-1, than the vibrational
frequency, 1013 s-1 [24]. The dramatic decrease of
AD was explained by limitations of the methods for
independent evolution of AD in the desorption kinet-
ics from the heterogeneous solid surface [25]. An
equation for estimation of the minimal AD value in
the TPD and Q-DTG studies of physically adsorbed
liquids was proposed in [25]
−
∆
+
∆
=
β
b
b
vap
b
vap
D
T
RT
H
RT
H
A lnlnexp(min)
(19)
where Tb is the boiling temperature of the liquid
at standard temperature, in K.
The calculation of the AD values for HCs from
Table 1 by Eq. (19) gives AD varied from 90 s-1
(CCl4) to 161 s-1 (n-C4H9Br). Because the ap-
proximate Redhead first-order desorption kinetic
equation [25] predicts that difference between two
desorption activation energies ED(1) and ED(2) is
( ))2()1(max)2()1( lnln DDDD AARTEE −=− , (20)
the decrease in AD value from 1013 s-1 to 102 s-1
leads to the difference of ∆ED up to 30 kJ/mol at
Tmax ∼ 150 K. Then the ED(av) values from Table 1
would be shifted of about 30 kJ/mol in the low
energy direction at AD ∼ 102 s-1.
Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase
_____________________________________________________________________________________________
ХФТП 2010. Т. 1. № 4 407
Almost all theoretical studies of TPD have
been based on the absolute rate theory (ART) [27].
The inapplicability of the classical Polanyi-Wigner
equation to describe the thermodesorption kinetics
from real solid surfaces was known long ago.
Various generalizations of the ART expressions,
toward taking into account interactions between
adsorbed molecules, energetic surface heterogene-
ity, existence of "precursor states" and other were
proposed [27]. For example, Nagai showed [27]
that the ART approach underestimates the role of
entropy changes as an important factor affecting
the kinetics of adsorption/desorption processes.
The pre-exponential term for desorption rate in-
cludes product of molecular partition function of
the adsorbed molecules, q0
s and a constant charac-
teristic for an adsorption system, ξ and they were
treated as the best fit parameters in the Nagai the-
ory whereas this term in the Kreuzer-Payne theory
is: sg
sD qqhmkTkTSA 000 /)/2( πα= where S0 is a
"sticking coefficient" on a "empty" surface, αs is
the "condensation" coefficient, q0
g is the partition
function of gas molecules related to the internal
degrees of freedom. Also, the pre-exponential fac-
tor )/exp()/( 00 kTqKK ss
gsD µ−= , where Kgs is a con-
stant related to the exchange rate between gas
phase and the solid surface once an isolated system
has reached equilibrium, µ0
s is the standard chemi-
cal potential of the adsorbed molecules, was pro-
posed for the thermodesorption kinetics by using
the Statistical Rate Theory of Interfacial Transport
(SRTIT) [27]. The most parameters in above ex-
pressions are unknown or make sense as purely
empiric. Then the AD values are not limited by
T/2πh ∼ 1013 s-1 as their downward boundary.
We attempt to describe the effect of HCs
structure on the ED(av) values from Table 1 by us-
ing the quantitative "structure-activity" relation-
ship (QSAR) similarly proposed in [28]
423221)( aaaaE HH
eavD +Σ×+Σ×+×= αβα
(21)
where αe is the molecular deformation polariza-
bility of a HC, Σα2
H and Σβ2
H are its acidity and
basicity for the H-bond formation in the Abraham
scale and coefficients a1, a2 and a3 characterize
average ability of surface solid sites to dispersive
interaction, and the interaction with acid and base
adsorbed molecules at H-bond formation while a4
is a constant for given solid surface. The αe, Σα2
H
and Σβ2
H values for the HCs were taken from
[29, 30]. The calculated coefficients are presented
in Table 2.
Table 2. Coefficients of Eq. (21) for thermodesorption
of halocarbons from the surface of surrogates
for atmospheric mineral aerosols
Coefficient A-300 Silica gel Al2O3 H-mordenite
a1, kJ/(mol A3) 1.5±1.1 1.7±1.4 0.9±0.8
a2, kJ/mol 54±42 113±43 51±25
a3, kJ/mol – 86±58 – –
a4, kJ/mol 41±13 45±16 60±15 61±9
R 0.756 0.668 0.897 0.916
As is evident from Table, the Eq. (21) ade-
quately describes the desorption kinetics of HCs
from the solids examined. The best result is ob-
tained for H-mordenite whereas worst result is
observed for silica gel (the lowest correlation co-
efficient R). High a1 and a2 coefficients denote
the contributions of polarizability of surface sites
and their acidity to desorption activation energy
of HCs. As to H-mordenite, the terminal silanols
(Si–OH), extra-framework AlOH groups and
framework bridged Si–OH–Al species are its
main Bronsted surface sites and their acidity in
H-bond formation decreases as: SiOH > AlOH >
Si–OH–Al [31]. This leads to the surface hetero-
geneity and to the high a2 coefficient for the solid.
IGC measurements and calculation of the ad-
sorption equilibrium parameters. The inverse
chromatographic measurements were performed for
23 volatile organic compounds including 9 HCs on
the surface of silica gel, Carbopack S and Carbosil.
For all systems examined, we observed an appre-
ciable dependence of the retention time on the probe
amount. One example is displayed in Fig. 2. That
the shapes of the tails of the peaks coincide for vari-
ous amounts of the probe suggest that the observed
asymmetry of the peaks has an equilibrium nature
associated with nonlinearity of the adsorption iso-
therm rather than the diffusion kinetic one.
In all cases, adsorption isotherms calculated
from the IGC data at various temperatures are
concave with respect to the surface coverage axis
(Fig. 3); i. e., they do not obey the Henry ad-
sorption isotherm equation even at low cover-
age (below 10% of a monolayer). Although the
Langmuir adsorption isotherm equation is
more suitable to describe the isotherms in this
coverage range, all the systems, except for
n-alkanes/Carbopack exhibit significant devia-
tions from the Langmuir equation.
V.I. Bogillo, M.S. Bazylevska, B.G. Mischanchuk, V.A. Pokrovskiy
_____________________________________________________________________________________________
408 ХФТП 2010. Т. 1. № 4
0 100 200 300 400 500
0
5
10
15
20
0.2 µµµµl
0.5 µµµµl
1.0 µµµµl
2.0 µµµµl
D
et
ec
to
r
R
es
po
ns
e
t
x
, s
Fig. 2. Dependence of retention time and peak profile
for CH2Br2/Carbosil system at 413 K on the
amount of the liquid probe
0.0 0.5 1.0 1.5 2.0 2.5
0.0
1.0x10-4
2.0x10-4
3.0x10-4 433 K423 K413 K
a
corr
, µµµµmole/m2
Y
A
xi
s
T
itl
e
P
corr
, Pa
Fig. 3. Adsorption isotherms at different temperatures
for CH2Br2 on the Carbosil surface calculated
from IGC data by using the "one peak" method
0.0 0.1 0.2 0.3 0.4 0.5 0.6
30
35
40
45
50
Q
A(iso)
, kJ mole-1
a
corr
, µµµµmole m-2
Fig. 4. Dependence of isosteric adsorption heat for
CH3I/Carbosil on the solid surface coverage
That the solid surfaces are heterogeneous is
confirmed by the exponential fall of calculated
isosteric adsorption heats as the surface coverage
raises (Fig. 4). Therefore, the partitioning of the
volatile organic compounds including HCs be-
tween the gas phase and the surface of the surro-
gates for solid atmospheric aerosols should be de-
scribed with regard to the energetic heterogeneity
of the surface similarly to above TPD MS data.
The common integral equation for the adsorp-
tion equilibrium from gas phase on the heteroge-
neous surface is [16]
∫=Θ
(max)
(min)
)(),,(),(
A
A
E
E
AAA dEEETPTP ρθ (22)
where Θ(P,T) = acorr/am is the total relative surface
coverage at Pcorr and T, am is the monolayer capac-
ity, θ(P,T,EA) is the relative surface coverage of sur-
face sites with adsorption energy EA, ρ(EA) is the
normalized differential adsorption energy distribu-
tion of the total surface, and EA(min) and EA(max) are
the lower and upper boundaries of the distribution.
To solve Eq. (22), it is necessary to determine
function θ(P,T,EA). Let it be described by the
Langmuir adsorption isotherm (lateral interaction
between adsorbed molecules is ignored)
+
=
RT
E
K
P
RT
E
K
P
ETP
A
A
A
exp1
exp
),,(
0
0θ
(23)
where K0 is the Langmuir constant, which is
given by [32]
( )RTHPK vapS /exp0 ∆= . (24)
Eq. (22) can be readily solved by the im-
proved regularization procedure [33]. Fig. 5a-c
show the adsorption energy distributions of 3
halocarbons on the surfaces of Carbopack (a),
Silica Gel (b) and Carbosil (c) calculated using
this method. As can be seen, the narrowest uni-
modal distributions are observed for Carbopack, a
solid with an energetically most homogeneous
surface. For the Silica gel and Carbosil, several
peaks in the distributions are observed. That sev-
eral peaks appear is indicative of the existence of
several types of adsorption sites with substan-
tially different strengths on the solid surface.
The position and the shape of the distribution
also depend on the halocarbon structure. In passing
from CH2Cl2 to 1,2-C2H4Cl2 and to n-C4H9Br, as the
polarizability of the molecules increases, the peaks
broaden and shift to higher adsorption energies.
Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase
_____________________________________________________________________________________________
ХФТП 2010. Т. 1. № 4 409
2x104 3x104 4x104 5x104 6x104
0.0
1.0x10-4
2.0x10-4
3.0x10-4
n-C
4
H
9
Br
1,2-C
2
H
4
Cl
2
CH
2
Cl
2
ρρρρ(E
A
), mole J-1
E
A
, J mole-1
a
3x104 4x104 5x104 6x104 7x104
0.0
1.0x10-5
2.0x10-5
3.0x10-5 n-C
4
H
9
Br
1,2-C
2
H
4
Cl
2
CH
2
Cl
2
ρρρρ(E
A
), mole J-1
E
A
, J mole-1
b
3x104 4x104 5x104 6x104 7x104
0.0
1.0x10-5
2.0x10-5
3.0x10-5
n-C
4
H
9
Br
1,2-C
2
H
4
Cl
2
CH
2
Cl
2
ρρρρ(E
A
), mole J-1
E
A
, J mole-1
c
Fig. 5. Adsorption energy distributions for 3 halo-
carbons calculated by using the improved regu-
larization procedure from IGC data a –on the
Carbopack S surface; b – on the Silica Gel sur-
face; c –on the Carbosil surface
Although the regularization procedure is effec-
tive in identifying the energetic heterogeneity of the
solid surfaces, it is unsuitable for quantitative rela-
tionship between the molecular descriptors and the
adsorption characteristics. Cumulants (semivariants)
of the adsorption energy (or free adsorption energy)
distributions, rather than the thermodynamic adsorp-
tion functions or the logarithms of the partition coef-
ficient (which are used in the Henri law region), play
the role of functions in the QSARs [34]. It is conven-
ient to use in the QSARs the distribution functions
that provide an analytical solution to Eq. (22). The
simplest distribution that makes it possible to obtain
an analytical solution is rectangular distribution
><
≤≤
−
=
(max)(min)
(max)(min)
(min)(max)
;,0
/(1
)(
AAAA
AAA
AA
A
EEEE
EEE
EE
Eρ
(25)
Using Eqs. (23) and (25), we obtain the solu-
tion to Eq. (22)
( )
( )
−+
−+
×
×
−
=
0(min)Acorr
0(max)Acorr
(min)A(max)A
m
corr
KlnRT/EexpP1
KlnRT/EexpP1
ln
EE
RTa
a
.
(26)
The first- and second-order cumulants of the distri-
bution (the average, KI, and the variance, KII) are given by
2/)( (min)(max))( AAavAI EEEK +== , (27)
.
4
)EE(
)EE(3
EE
K
2
(min)A(max)A
(min)A(max)A
3
(min)A
3
(max)A2
EaII
+
−
−
−
−
=σ= (28)
The calculated KI, and KII for the adsorption sys-
tems examined by IGC are presented in Table 3. They
are related to molecular descriptors for halocarbons
and other volatiles by Eq. (21). The table shows that,
in passing from carbon black (which has an energeti-
cally nearly homogeneous surface) to Silica Gel and to
Carbosil, the variances increase markedly. The results
of regression analysis for Eq. (21) are given in Table 4.
As can be seen from these data, the mean po-
larizability of the solid surface sites increases as Car-
bopack>Carbosil>Silica Gel, the mean acidity in the
H-bond formation as Silica Gel>Carbosil>Carbopack
and the mean basicity in the H-bond formation as
Carbosil≈Carbopack>Silica Gel. The last sequence is
explained by existence of strong basic sites, such as
basal faces of graphite, which can be considered as π-
electron condensed systems, ∼C=O and ∼C(O)OH
groups. The reason for decay of surface acidity from
Silica Gel to Carbosil is the decrease in the hydroxyl
groups concentration and their activity after carboni-
zation of silica surface.
V.I. Bogillo, M.S. Bazylevska, B.G. Mischanchuk, V.A. Pokrovskiy
_____________________________________________________________________________________________
410 ХФТП 2010. Т. 1. № 4
Table 3. Molecular descriptors of volatile organic compounds, their average adsorption energies (EA(av), in kJ mol-1)
and the adsorption energy variances (σ2
Ea, in kJ2 mol-2) on the solid surfaces
Molecular descriptors Carbopack Carbosil Silica Gel
Compound
αe,A
3
Σα2
H
Σβ2
H EA(av) σ
2
Ea EA(av) σ
2
Ea EA(av) σ
2
Ea
CH2Cl2 6.48 0.10 0.05 28.0 104.2 33.0 143.6 28.8 136.8
CHCl3 8.51 0.15 0.02 42.3 0.08 34.1 162.4 28.4 120.6
CCl4 10.48 0 0 41.7 0.03 37.0 150.2 28.7 88.6
1,2-C2H4Cl2 8.0 0.10 0.11 43.1 0.10 37.7 169.1 36.7 63.3
CH2Br2 9.32 0.10 0.10 36.0 1.60 34.0 156.9 29.5 124.2
CHBr3 11.82 0.15 0.09 44.0 0.31 39.3 181.3 30.5 115.2
1,2-C2H4Br2 11.26 0.10 0.17 46.7 0.14 40.9 165.9 33.3 129.2
C4H9Br 13.9 0 0.12 50.7 0.0045 46.0 168.4 35.5 151.8
CH3I 7.97 0 0.13 25.4 104.7 31.9 123.5 25.9 119.6
n-C5H12 9.99 0 0 43.8 0.00008 33.5 127.8 23.4 130.1
n-C6H14 11.76 0 0 48.4 0.00017 38.2 176.5 29.8 65.6
n-C7H16 13.61 0 0 53.3 0.00002 41.3 158.2 32.8 105.1
C6H6 10.33 0 0.14 47.7 13.2 38.0 160.1 35.4 61.2
CH3OH 3.29 0.43 0.47 32.0 103.6 45.6 156.4 41.8 140.2
C2H5OH 5.11 0.37 0.48 37.4 129.8 50.7 170.4 46.7 156.1
(CH3)2C=O 6.40 0.04 0.49 28.4 108.6 38.8 148.7 37.5 136.2
(C2H5)2O 10.2 0 0.45 41.6 8.3 37.4 149.8 33.5 157.4
C4H8O 8.2 0 0.48 31.1 29.5 39.6 165.8 39.8 138.4
C4H8O2 10.0 0 0.64 43.1 0.95 37.2 106.8 44.1 164.2
CH3CN 4.40 0.07 0.33 25.1 107.2 40.2 155.8 34.6 141.9
CH3NO2 7.37 0.06 0.32 26.6 0.00001 37.1 151.8 37.5 67.8
C2H5NO2 9.63 0.02 0.33 33.3 0.00001 41.6 173.6 38.0 121.3
CS2 6.9 0 0.07 37.3 120.3 32.1 141.3 26.9 115.6
Table 4. Coefficients of Eq. 21 for partitioning the
volatile organic compounds between gas
phase and solid surface
Function/
Coefficient
Carbopack S Silica Gel Carbosil
EA(av)
a1,
kJ/ (mol A3) 3.1±0.5 0.7±0.3 1.0±0.3
a2, kJ/mol – 25.3±3.6 11.6±3.8
a3, kJ/mol 29.2±10.6 19.4±6.8 30.0±7.0
a4, kJ/mol 9.8±5.4 21.1±3.4 24.4±3.6
R 0.85 0.88 0.77
σ
2
Ea
a1,
kJ2/(mol2 A6) -15.7±3.5 – 2.8±1.7
a2,
kJ2/mol2 – 84.0±33.0 –
a3,
kJ2/mol2 – – 89.0±37.0
a4,
kJ2/mol2 182.0±39.0 84.0±32.0 126.0±19.0
R 0.78 0.55 0.52
The proposed approach makes it possible to
establish how the variance of the adsorption en-
ergy distribution depends on the molecular de-
scriptors. The variance is determined by both the
chemical heterogeneity of the surface sites and
their topography. As can be seen, the largest con-
tribution to the variance for Carbopack comes
from the sites polarizability; for Carbosil the con-
tribution from basic sites is also important. Acidic
sites markedly influence the variance only for
Silica Gel, which surface contains various types
of silanol groups (single, vicinal and geminal).
Relationship between TPD MS and IGC
data. As it shown from Fig. 6, a relationship is
observed between average desorption activation
energies of HCs on the silica gel surface from
TPD MS data and average adsorption energies in
these systems determined using IGC method at
finite concentrations. More low EA(av) values in
comparison with ED(av) are explained by more
high temperatures in the IGC experiment (from
353 to 453 K) as against the TPD MS experiment
Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase
_____________________________________________________________________________________________
ХФТП 2010. Т. 1. № 4 411
(from 100 to 298 K) and by difference between
pre-exponential desorption factor used in the TPD
kinetics and average adsorption entropy for the
HCs in the IGC study.
60 65 70 75
25
30
35
CH
3
I
CCl
4
CH
2
Cl
2
1,2-C
2
H
4
Cl
2 n-C
4
H
9
Br
E
A
(a
v)
, k
J/
m
ol
e
(I
G
C
d
at
a)
E
D
(av), kJ/mole (TPD MS data)
Fig. 6. Relationship between average desorption acti-
vation energies (TPD MS data) and average ad-
sorption energies (IGC data) for halocarbons on
silica gel surface
The calculated coefficients a1, a2 and a3 of
Eq. (21) from TPD MS and IGC data lie within
the same order. Thus, the proposed approach
makes it possible to estimate average desorption
activation energy and adsorption energy for the
HCs on the basis of their molecular descriptors.
Compensation effect in the partitioning of
HCs on the heterogeneous solid surface. All
above calculations of KI and KII values from IGC
data were carried out in assumption that K0 con-
stant is independent on the surface coverage. In
case of dependence of К0 on the Θ(P,T) value, the
integral adsorption equation should include in
addition to (ρ(EA)) function, the surface distribu-
tion on the ln K0 value, ρ(ln K0) also
∫∫
∆∆
=Θ
0ln,
000 ln)(ln)()ln,,,(),(
KE
AAA
A
KddEKEKETPTP ρρθ .(29)
Two extreme variants for behavior of the K0
and EA values can be proposed: there are correla-
tion between these parameters and its lack. Be-
cause )/exp(0 RSK A∆−= where ∆SA is the molar
isosteric adsorption entropy, the decrease of mo-
lar isosteric adsorption enthalpy may lead to fall
of the adsorption entropy. Such relationship be-
tween enthalpy and entropy in phase transitions
and intermolecular complex formation is well
known as "compensation effect" or "isoequilib-
rium relationship" [35]. In first time the adsorbing
molecules interact with most active sites of the
heterogeneous surface at low vapor pressure
(high ЕА values). Then the Р value increases and
less active sites are filled up. This results in de-
crease of -∆SA function and the К0 constant. The
"isoequilibrium relationship" between EA and К0
may be written as
isoAiso RTEKK /lnln )(00 += (30)
where K0(iso) is the К0 value at isoequilibrium
temperature Tiso, when the Langmuir constant are
equal for all surface sites, i. e. the surface is ho-
mogeneous over these constants.
It has been shown that logarithm of the
Langmuir constant for HCs decreases with reduc-
ing the adsorption energy as the surface coverage
of Silica Gel increases and compensation effect
has been observed [36]. Such relationship be-
tween EA and ln K0 is displayed in Fig. 7 for
CH3I/Carbosil system.
30 35 40 45 50 55
15
16
17
18
ln K
0
, Pa-1
E
A
, kJ mole-1
Fig. 7. Variation of the Langmuir constant versus
adsorption energy for the CH3I/Carbosil system
The approaches based on the distribution
moments theory and condensation approximation
have been proposed to evaluate parameters of this
dependence from the adsorption data and the cal-
culation has been performed for the adsorption of
chloromethanes series (CHnCl4-n, n = 0÷3) and
methyl iodide on Silica Gel and Carbosil surface
[36]. For example, K0(iso) = 8.7·103 Pa-1 and
Tiso = 700 K were obtained for the CH3I/Carbosil
system. The range of the Langmuir constants at
several coverages exceeds noticeably ones calcu-
lated by Eq. (24): ln K0(calc) = 12.2 – 12.8 Pa-1 for
the chloromethanes series on Silica Gel and the
experimental ln K0(exp) values varied from 5.7 to
20.8 Pa-1 as the relative surface coverage falls
from 1.0 to 0. These variations should be taken
into account in the calculations of the ρ(EA) func-
tion from the adsorption data.
V.I. Bogillo, M.S. Bazylevska, B.G. Mischanchuk, V.A. Pokrovskiy
_____________________________________________________________________________________________
412 ХФТП 2010. Т. 1. № 4
Atmospheric implications. As it follows from
above TPD MS and IGC data, the surfaces of
components of atmospheric mineral and carbona-
ceous aerosols are energetically heterogeneous.
Only Langmurian adsorption equilibrium on the
homogeneous surfaces (or its initial linear part of
the isotherms, i. e. Henry region) is considered in
current models of heterogeneous atmospheric chem-
istry [37]. The approximation of homogeneous sur-
face may overestimate the partition coefficients and
adsorption enthalpies, since these quantities usually
calculated from adsorption measurements in the
Henry region, i. e., under conditions where only the
strongest adsorption sites are involved. The fraction
of such active sites at the surface of atmospheric
particles can be extremely small, and, therefore,
these quantities are not suitable for describing the
activity of their surface as a whole.
The surface of the atmospheric solid aerosols
is chemically and structurally heterogeneous
[7, 38], which can be explained by its containing
many types of adsorption sites with various activi-
ties, by difference in the topography of such sites
and by the specifics of the amorphous structure of
the surface layer and porous structure of the parti-
cles. Therefore, the partitioning of HCs and other
volatile impurities between the surface of aerosol
particles and air is convenient to calculate within
the framework of the above approaches developed
for describing the adsorption of species from the
gas phase on a heterogeneous solid surface. The
proposed approach (Eqs. (21), (26)–(28)) makes
possible to estimate the volatile structure, the tem-
perature influence the partition coefficients and the
surface concentrations on the aerosol particles.
Acknowledgements. This study was sup-
ported by National Science Foundation of USA
(COBASE program) and by Science and Tech-
nology Center in Ukraine (project #2196). The
authors are grateful to Prof. R. Leboda (Maria
Curie-Sklodowska University, Lublin, Poland)
for courteously providing Carbosil sample.
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Received 16.06.2010, accepted 06.09.2010
Дослідження розподілу легколетких галогенвуглеводнів між сурогатами атмосферних
твердих аерозолів і газовою фазою методами ТПД МС і оберненої газової хроматографії
В.Й. Богилло, М.С. Базилевська, Б.Г. Місчанчук, В.О. Покровський
Відділ геології та геоекології Антарктики, Інститут геологічних наук Національної академії наук України
вул. Олеся Гончара 55Б, Київ 01054, Україна, vbog@carrier.kiev.ua
Інститут хімії поверхні ім. О.О. Чуйка Національної академії наук України
вул. Генерала Наумова 17, Київ 03164, Україна
Кінетика неізотермичної десорбції попередньо адсорбованих Cl, Br і I-вмістних галогенвуглеводнів (ГВ) з поверхні
сурогатів атмосферних твердих аерозолів (пірогенні кремнезем і оксид алюмінію, силікагель і Н-морденіт) вивчена
методом температурно-програмованої десорбційної мас-спектрометрії (ТПД МС). ТПД спектри демонструють
високу неоднорідність вивчених поверхонь. Розраховані середні величини енергії активації десорбції та півширини
прямокутних розподілів енергій десорбції ГВ. Отримані співвідношення між середніми енергіями активації десорб-
ції ГВ і їх молекулярними дескрипторами для всіх вивчених твердих тіл. Розподіл ГВ і додаткових летких органічних
сполук між сурогатами мінеральних і вуглецьвмісних атмосферних аерозолів (сілікагель, Карбопак і Карбосіл) дослі-
джено методом оберненої газової хроматографії (ОГХ). Дані ОГХ вказують на енергетичну неоднорідність повер-
хні цих твердих тіл. Розраховані середні величини енергії адсорбції ГВ і дисперсії прямокутного розподілу поверхонь
по енергіям адсорбції та знайдені зв’язки між цими величинами та молекулярними дескрипторами цих летких спо-
лук. Встановлено співвідношення між середніми енергіями активації десорбції ГВ з силікагелю з даних ТПД МС і
середніми енергіями адсорбції в цих системах, визначеними з даних ОГХ при скінченних концентраціях.
Исследование распределения легколетучих галогенуглеводородов между суррогатами
атмосферных твердых аэрозолей и газовой фазой методами ТПД МС
и обращенной газовой хроматографии
В.И. Богилло, М.С. Базилевская, Б.Г. Мисчанчук, В.А. Покровский
Отдел геологии и геоэкологии Антарктики, Институт геологических наук Национальной академии наук Украины
ул. Олеся Гончара 55Б, Киев 01054,Украина, vbog@carrier.kiev.ua
Институт химии поверхности им. А.А. Чуйко Национальной академии наук Украины
ул. Генерала Наумова 17, Киев 03164, Украина
Кинетика неизотермической десорбции предварительно адсорбированных Cl, Br и I-содержащих га-
логенуглеводородов (ГУ) с поверхности суррогатов атмосферных твердых аэрозолей (пирогенные кремне-
зем и окись алюминия, силикагель и Н-морденит) изучена методом температурно-программированной де-
сорбционной масс-спектрометрии (ТПД МС). ТПД спектры демонстрируют высокую неоднородность изу-
ченных поверхностей. Рассчитаны средние значения энергии активации десорбции и полуширины прямо-
угольных распределений энергий десорбции ГУ. Получены соотношения между средними величинами энергии
активации десорбции ГУ и их молекулярными дескрипторами для всех изученных твердых тел. Распределе-
ние ГУ и добавочных летучих органических соединений между суррогатами минеральных и углеродсодер-
жащих атмосферных аэрозолей (силикагель, Карбопак и Карбосил) исследовано методом обращенной газо-
вой хроматографии (ОГХ). Данные ОГХ указывают на энергетическую неоднородность поверхности этих
твердых тел. Рассчитаны средние энергиии адсорбции ГУ и дисперсии прямоугольного распределения по-
верхностей по энергиям адсорбции и найдены связи между этими величинами и молекулярными дескрипто-
рами летучих соединений. Установлено соотношение между средними энергиями активации десорбции ГУ с
силикагеля из данных ТПД МС и средними энергиями адсорбции в этих системах, определенными из данных
ОГХ при конечных концентрациях.
|
| id | nasplib_isofts_kiev_ua-123456789-29023 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 2079-1704 |
| language | English |
| last_indexed | 2025-12-07T18:21:13Z |
| publishDate | 2010 |
| publisher | Інститут хімії поверхні ім. О.О. Чуйка НАН України |
| record_format | dspace |
| spelling | Bogillo, V.I. Bazylevska, M.S. Mischanchuk, B.G. Pokrovskiy, V.A. 2011-11-28T21:28:47Z 2011-11-28T21:28:47Z 2010 Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase as Examined by TPD MS and Inverse Gas Chromatography / V.I. Bogillo, M.S. Bazylevska, B.G. Mischanchuk, V.A. Pokrovskiy // Хімія, фізика та технологія поверхні. — 2010. — Т. 1, № 4. — С. 401-414. — Бібліогр.: 38 назв. — англ. 2079-1704 https://nasplib.isofts.kiev.ua/handle/123456789/29023 544.723.3:543.51+543.544:543.27:544.772 The desorption non-isothermal kinetics of preliminary adsorbed Cl, Br, and I-containing volatile halocarbons from the surface of surrogates for atmospheric solid aerosols (fumed silica and alumina, silica gel and H-mordenite) was studied by TPD MS. The TPD spectra demonstrate high heterogeneity of the surface studied. The average desorption activation energies and half-widths of the halocarbons desorption energy rectangular distribution were calculated. The relationships between the average desorption activation energies and molecular descriptors for the halocarbons were derived for the solids. The partitioning of the halocarbons and additional volatile organics between surrogates for mineral and carbonaceous atmospheric aerosols (silica gel, Carbopack S, Carbosil) was examined by using the inverse gas chromatography method. These data indicate to the energetic heterogeneity of the solid surfaces. The average adsorption energies and variances of the adsorption energy rectangular distribution were calculated and connected with molecular descriptors of the volatiles. A relationship is observed between average desorption activation energies of halocarbons on the silica gel surface from TPD MS data and average adsorption energies in these systems determined using inverse gas chromatography method at finite concentrations. Кінетика неізотермичної десорбції попередньо адсорбованих Cl, Br і I-вмістних галогенвуглеводнів (ГВ) з поверхні сурогатів атмосферних твердих аерозолів (пірогенні кремнезем і оксид алюмінію, силікагель і Н-морденіт) вивчена методом температурно-програмованої десорбційної мас-спектрометрії (ТПД МС). ТПД спектри демонструють високу неоднорідність вивчених поверхонь. Розраховані середні величини енергії активації десорбції та півширини прямокутних розподілів енергій десорбції ГВ. Отримані співвідношення між середніми енергіями активації десорбції ГВ і їх молекулярними дескрипторами для всіх вивчених твердих тіл. Розподіл ГВ і додаткових летких органічних сполук між сурогатами мінеральних і вуглецьвмісних атмосферних аерозолів (сілікагель, Карбопак і Карбосіл) досліджено методом оберненої газової хроматографії (ОГХ). Дані ОГХ вказують на енергетичну неоднорідність поверхні цих твердих тіл. Розраховані середні величини енергії адсорбції ГВ і дисперсії прямокутного розподілу поверхонь по енергіям адсорбції та знайдені зв’язки між цими величинами та молекулярними дескрипторами цих летких сполук. Встановлено співвідношення між середніми енергіями активації десорбції ГВ з силікагелю з даних ТПД МС і середніми енергіями адсорбції в цих системах, визначеними з даних ОГХ при скінченних концентраціях. Кинетика неизотермической десорбции предварительно адсорбированных Cl, Br и I-содержащих галогенуглеводородов (ГУ) с поверхности суррогатов атмосферных твердых аэрозолей (пирогенные кремнезем и окись алюминия, силикагель и Н-морденит) изучена методом температурно-программированной десорбционной масс-спектрометрии (ТПД МС). ТПД спектры демонстрируют высокую неоднородность изученных поверхностей. Рассчитаны средние значения энергии активации десорбции и полуширины прямоугольных распределений энергий десорбции ГУ. Получены соотношения между средними величинами энергии активации десорбции ГУ и их молекулярными дескрипторами для всех изученных твердых тел. Распределение ГУ и добавочных летучих органических соединений между суррогатами минеральных и углеродсодержащих атмосферных аэрозолей (силикагель, Карбопак и Карбосил) исследовано методом обращенной газовой хроматографии (ОГХ). Данные ОГХ указывают на энергетическую неоднородность поверхности этих твердых тел. Рассчитаны средние энергиии адсорбции ГУ и дисперсии прямоугольного распределения поверхностей по энергиям адсорбции и найдены связи между этими величинами и молекулярными дескрипторами летучих соединений. Установлено соотношение между средними энергиями активации десорбции ГУ с силикагеля из данных ТПД МС и средними энергиями адсорбции в этих системах, определенными из данных ОГХ при конечных концентрациях. This study was supported by National Science Foundation of USA (COBASE program) and by Science and Technology Center in Ukraine (project #2196). The authors are grateful to Prof. R. Leboda (Maria Curie-Sklodowska University, Lublin, Poland) for courteously providing Carbosil sample. en Інститут хімії поверхні ім. О.О. Чуйка НАН України Хімія, фізика та технологія поверхні Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase as Examined by TPD MS and Inverse Gas Chromatography Дослідження розподілу легколетких галогенвуглеводнів між сурогатами атмосферних твердих аерозолів і газовою фазою методами ТПД МС і оберненої газової хроматографії Исследование распределения легколетучих галогенуглеводородов между суррогатами атмосферных твердых аэрозолей и газовой фазой методами ТПД МС и обращенной газовой хроматографии Article published earlier |
| spellingShingle | Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase as Examined by TPD MS and Inverse Gas Chromatography Bogillo, V.I. Bazylevska, M.S. Mischanchuk, B.G. Pokrovskiy, V.A. |
| title | Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase as Examined by TPD MS and Inverse Gas Chromatography |
| title_alt | Дослідження розподілу легколетких галогенвуглеводнів між сурогатами атмосферних твердих аерозолів і газовою фазою методами ТПД МС і оберненої газової хроматографії Исследование распределения легколетучих галогенуглеводородов между суррогатами атмосферных твердых аэрозолей и газовой фазой методами ТПД МС и обращенной газовой хроматографии |
| title_full | Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase as Examined by TPD MS and Inverse Gas Chromatography |
| title_fullStr | Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase as Examined by TPD MS and Inverse Gas Chromatography |
| title_full_unstemmed | Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase as Examined by TPD MS and Inverse Gas Chromatography |
| title_short | Partitioning of Volatile Halocarbons between Surrogates for Atmospheric Solid Aerosols and Gas Phase as Examined by TPD MS and Inverse Gas Chromatography |
| title_sort | partitioning of volatile halocarbons between surrogates for atmospheric solid aerosols and gas phase as examined by tpd ms and inverse gas chromatography |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/29023 |
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