Photochemical reactions in the atmosphere – a source of secondary pollutants
In the atmosphere polluting agents are involved in different reactions which lead to secondary pollutants. Secondary pollutants are mainly generated by photochemical and thermal reactions. These reactions occur in the atmosphere and they generate photochemical smog. We studied the variations of pr...
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2006
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| Cite this: | Photochemical reactions in the atmosphere – a source of secondary pollutants / R. Cuciureanu, G. Dimitriu // Проблеми програмування. — 2006. — N 2-3. — С. 682-687. — Бібліогр.: 5 назв. — англ. |
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| citation_txt | Photochemical reactions in the atmosphere – a source of secondary pollutants / R. Cuciureanu, G. Dimitriu // Проблеми програмування. — 2006. — N 2-3. — С. 682-687. — Бібліогр.: 5 назв. — англ. |
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| description | In the atmosphere polluting agents are involved in different reactions which lead to secondary pollutants. Secondary pollutants are mainly
generated by photochemical and thermal reactions. These reactions occur in the atmosphere and they generate photochemical smog. We
studied the variations of primary and secondary pollutants concentrations by photochemical modeling systems. All the test problems
(denoted models A-F) were coded in Fortran and are based on the Carbon Bond Mechanism IV consisting of 32 chemical species involved
in 70 thermal and 11 photolytic reactions. The numerical integration of the stiff systems was carried out using a Rosenbrock solver.
|
| first_indexed | 2025-11-24T11:45:40Z |
| format | Article |
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Прикладне програмне забезпечення
© K. Georgiev, E. Donev, 2006
ISSN 1727-4907. Проблеми програмування. 2006. №2-3. Спеціальний випуск 682
UDC 004.75
PHOTOCHEMICAL REACTIONS IN THE ATMOSPHERE
– A SOURCE OF SECONDARY POLLUTANTS
Rodica Cuciureanu, Gabriel Dimitriu
University of Medicine and Pharmacy “Gr. T. Popa” Iasi, Faculty of Pharmacy,
Department of Food and Environment Chemistry, Department of Mathematics and Informatics
16 Universitatii street, 700115 Iasi, Romania
Е-mail: rcuciur@lycos.com, dimitriu@umfiasi.ro
In the atmosphere polluting agents are involved in different reactions which lead to secondary pollutants. Secondary pollutants are mainly
generated by photochemical and thermal reactions. These reactions occur in the atmosphere and they generate photochemical smog. We
studied the variations of primary and secondary pollutants concentrations by photochemical modeling systems. All the test problems
(denoted models A-F) were coded in Fortran and are based on the Carbon Bond Mechanism IV consisting of 32 chemical species involved
in 70 thermal and 11 photolytic reactions. The numerical integration of the stiff systems was carried out using a Rosenbrock solver.
Introduction
Atmosphere pollution may have natural causes (forest fires, vulcanic eruptions, pollen, dust). It may also be
caused by human activities (industrial processes, traffic, agriculture, thermal stations).
Each source/process which causes changes in normal composition of air releases so-called primary polluting
agents in the atmosphere. These are compounds which are released in the atmosphere as they are: carbon oxides, nitric
oxides, sulphur oxides, hydrocarbons (methane and non methane, volatile organic compounds, aldehides, ketones, total
suspended particulates).
Chemical species resulted from microbial metabolism and organic compounds released by trees in low
atmosphere are also considered primary polluting agents.
These compounds are implied in hydroxyl radical production in the atmosphere. As an example, isoprene
reacts with HO radicals generating O3 and other chemical species. These reactions open a new pathway in studying
models’ predict. But the researchers found that chemicals in air masses that come from the forested area did change
with a change in temperature. Forest-generated emissions change a lot with temperature. Isoprene is the forest generated
chemical with the largest piece of the emission pie, but it is produced only in during day. Other compounds, terpene
respectively, are produced around the clock and are also temperature sensitive (5).
In the atmosphere molecules of primary polluting agents can take part in different reactions (thermal,
photochemical) which lead to new compounds – secondary polluting agents; these are more dangerous for human body
than the substances which generated them.
Structure of secondary polluting agents differs from the structure of primary polluting agents and it depends on
nature and concentration of primary polluting agents, atmospheric conditions (temperature, humidity, solar radiations)
and the reaction cycle they take part in. The majority of secondary polluting agents are formed in photochemical
reactions which occur in atmosphere and generate photochemical smog. The generation of photochemical smog is
conditioned by simultaneous presence of nitric oxides, hydrocarbons and solar radiation. The oxidant capacity of some
secondary polluting agents which generate photochemical smog (O3, peracyl nitrates) explain the name of oxidant
smog.
Sources of primary polluting agents
The main primary polluting agents which are present in the air and generate oxidant smog are: CO, NO,
hydrocarbons, sulphur dioxide.
Carbon monoxide (CO)
In the atmosphere there are both natural and anthropogenic sources of CO. Natural emissions are important
(they are 10 times more intensive than the emissions generated by human activities). Natural emissions are produced by
superior plants, alga, plankton and human breathing. The average natural concentration of CO is 0,1 mg/m3 air. In
atmosphere the lifetime of CO is 30 days.
In urban regions of Europe 90% of CO emission is caused by road traffic.
CO is involved in atmosphere - occurring chemical processes by which it indirectly influences the climate.
Interaction of CO with hydroxyl radicals elevates the methane concentration in the atmosphere. In presence of nitric
oxides, CO is involved in generating tropospheric ozone.
Nitric oxides (NOx)
N2O, NO and NO2 are nitric oxides which occur in atmosphere. The mixture of NO and NO2 is represented by
NOx symbol. In the atmospheric air nitric oxides proceed from natural sources and human activity.
Прикладне програмне забезпечення
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Natural sources: atmospheric nitrogen is fixed as nitrate by plants and bacteria; anaerobic bacteria convert
nitrates in N2, N2O and low amounts of NO and NO2.
Natural emissions of NOx are 10 times more intensive than the ones caused by human activity; at soil level the
natural concentration of NOx is 3 - 4µg/m3 air. NOx is formed by reaction between N2 and O2 during electric discharges.
In stratosphere N2O is oxidized to NO2 under the influence of O3 and UV radiations. In atmosphere the main source of
NOx are the combustion processes (road traffic, thermal stations, industrial processes).
In Europe, almost half of NOx emissions are generated by road traffic. In urban air, in stable meteo conditions
(absence of air currents), high concentrations of NOx are present. If nitric oxides are generated directly in the air, at high
altitudes (by airplanes motors), they contribute to diminution of stratospheric O3 level. In the presence of sunlight, NOx
together with volatile organic compounds (VOC) are precursors for secondary polluting agents – oxidant smog.
Lifetime of NOx is about one day. A part of NOx converts into HNO3 which forms acidic depositions (4).
Volatile organic compounds
This group of primary polluting agents includes different compounds: methane and other organic compounds
except methane (NMVOC) – ethane, propane, butane, aldehides, ketones, alcohols, complex molecules (biphenyl
policlorurates, dioxines, furans). NMVOC influence climate changes in two ways: as with CO they indirectly increase
atmospheric methane concentrations through reduction of hydroxyl radicals and generation of tropospheric O3.
Increases in NMVOC concentrations decrease hydroxyl radicals values by decreasing the oxidant atmospheric
concentrations of methane.
Toxic organic micropollutants
Globally it is considered that VOC natural emissions (metabolism and decomposition of plants) are 5 times
higher than the emissions generated by human activity.
Anthropogenic emissions are generated by road traffic, fuel burns, industrial processes, solvents evaporation.
Oxidant smog – mechanism of ozone generation
Mechanisms of O3 generation are different as the reactions occur in troposphere or stratosphere.
In stratosphere, O3 is generated by O2 photolysis in presence of UV radiations with λ < 240 nm:
⋅+→ ⋅
ν O OO h
2 and O2 + O· → O3
In presence of UV radiations with λ < 310 nm O3 decomposes: 23 3O
h
O2 → ν
In troposphere O3 is generated by the same reaction: O2 + O· → O3
As solar radiations with λ < 240 nm can not reach the troposphere, oxygen atom can be generated only by NO2
photolysis: NO2 → NO + O
Reaction rate depends on light intensity; the reaction does not occur during night. NO2 photolysis does not
quantitatively generate O3; O3 reacts with NO and generates NO2. Thus, O3 generation competes with oxidation of NO
to NO2. This competition implies generation of radicals with high oxygen content (hydroperoxy and organic peroxy
radicals).
Organic compounds and CO are important sources of peroxyl radicals. Lifetime of organic compounds is short
because they are involved in radical reactions in which hydroxyl radicals take part. These reactions are combustions at
low temperatures; in these conditions CH4, H2 and CO are oxidized to CO2 and H2O.
The presence of hydrocarbons and nitric oxides in the air increases the availability of free radicals. This
mechanism of reaction allows the evaluation of maxim number of O3 molecules which are generated by a certain
compound oxidation. Theoretically, each carbon atom in saturate hydrocarbons generates three molecules of O3. For
substituted organic compounds (alcohols) carbon atom which is linked to OH is partially oxidized and it is less implied
in O3 generation (1).
The high reactivity of O3 molecule makes possible its consumption in reactions with other chemical influence
O3 stability which can persist in the atmospheric from several hours to several days.
Tropospheric O3 tends to concentrate in high populated urban regions in which important amounts of VOC, O3
precursors, accumulate.
Other chemical species are involved in photochemical decomposition of organic compounds. As the organic
molecule is attacked by a free radical, the radical reactions cycle generates O3 only if NO concentration is 10 - 40 ppt at
least. During these reactions, decomposition of peracetyl nitrate is a source of NOx.
Nitric oxides are not consumed during elementary photochemical processes which generate O3. Although, in
photochemical systems, the lifetime of nitric oxides is limited because the hydroxyl radicals react very fast with NO2
and generate HONO2.
If NOx concentration is higher than the organic compounds concentration, hydroxyl radicals can be consumed
stopping O3 generation. During a photochemical episode, 1 - 3 ozone molecules are generated for each NO molecule. In
unpolluted troposphere (free troposphere), O3 generation is elevated (10 - 100 O3 molecules for one NOx molecule).
Although, in free atmosphere O3 generation is limited by NOx decreased availability (in non-urbane continental regions
NOx concentrations vary between 50 and 1000 ppt; in free troposphere it varies between 10 and 100 ppt) (3,4)..
Прикладне програмне забезпечення
684
O3 stability in atmosphere
The diminution of O3 concentration in atmosphere occurs by its decomposition and deposition on the ground,
at the surface of seas and oceans, plants. Plants are the main receiver for O3 which destroys organic molecules in
vegetal tissue, especially during day and the intensive vegetation period. Ozone decomposition by photolysis generates
O2 and oxygen atoms which can restart the cycle with generation of new O3 molecules which can react with water
vapors generating hydroxyl radicals or they can react with other molecular species.
Oxidant smog – mechanism of peroxyacyl nitrates generation
In the atmosphere peroxyacyl nitrates are not generated as they are; they are generated in situ by
photochemical reactions having NOx and VOC as precursors.
Depending on organic radical, peroxyacyl nitrates can be: peroxy acetyl nitrates (PAN): CH3C(O)OONO2;
peroxy propionyl nitrates (PPN): CH3CH2C(O)OONO2; peroxy n-butyryl nitrates (PnBN): CH3CH2CH2C(O) OONO2
etc. Among these, PAN plays an important in atmospheric chemistry.
The reactions of PAN formation are based on generation of acetyl radicals by radiation of some VOC
(hydrocarbons, alcohols, aldehides). For example:
⋅+→⋅+ CO - CH OH HO CHO - CH 323 (1)
(2)
(3)
In addition to the reaction with NO2, peracetyl radical can also react with NO generating NO2 and CH3
radicals. These species generate formaldehyde by oxidation.
(4)
(5)
PAN decomposition occurs only in the presence of NO. The rate of PAN decomposition increases fast with the
temperature. In the atmosphere PAN concentration depends on temperature, NO2/NO ratio (competition between
reaction 3 and 4 and VOC availability and reactivity VOC can generate acetyl radicals). Therefore, the relationship
between PAN in the air and the emission of its precursors (VOC and NOx) is not linear and, in the same time dependent
on O3, VOC and NOx concentrations.
Acyl radicals having a higher number of carbon atoms (propionyl-, n-buthyryl-) generates PPN or PnBN, and
not PAN. Ethanol as direct precursor can be oxidized to acetaldehyde.
PPN/PAN ratio can be an index of the impact of using ethanol as an additive for vehicles fuels compared to
using gasoline. Both PPN day variation and ratio PPN/O3 are similar to those for PAN.
PAN stability in the atmosphere
As it has already been shown, PAN stability in the atmosphere is limited (35 minutes). The daytime evolution
of oxidant smog composition is expressed by PAN/O3 ratio. The ratio decreases with increasing temperatures. This
confirm of PAN thermal decomposition mechanism (1). This ratio has a maximum value during night (the temperature
diminution promotes PAN stability) and a minimum value at now (mid-day), when temperature is higher. A secondary
maximum is noticed in the morning when hydroxyl radicals availability is increased (a more intensive road traffic)
promoting PAN generation.
Exposure to PAN
PAN impact upon human health, plants and environment in general justifies specialists’ interest for the study
of this compound. The conversion of human exposure expressed by ppb (µg/person/day). 1 ppb PAN = 4,95 µg/m3 la
25ºC and 1 atm and for the 23 m3 of air which are daily represent 114 µg/person/day inhaled. The inhaled doze would
be 570 µg/person/day if PAN concentration in inhaled air is 5 ppb.
Comparative numerical study
In this work we studied the variations of primary and secondary polluting agents concentrations by
photochemical modeling systems.
All the test problems (denoted models A-F) were coded in Fortran and are based on the Carbon Bond
Mechanism IV, consisting of 32 chemical species involved in 70 thermal and 11 photolytic reactions. We used for the
numerical integration of the stiff systems a Rosenbrock solver implementing a number of 4-stage (3) pairs. The
C H 3 C O O 2 C H 3 C
O
O O
+
C H 3 C
O
O O
+ N O 2 C H 3 C
O
O O N O 2
C H 3 C
O
O O
+ + N O N O 2 C O 2 C H 3 +
C H 3 O O O 2
+
+ (5a)
N O N O 2
C H 3
+ C H 3 O O (5b)
C H 3 O
C H 3 O
+ O 2 H O O + H C H O (5c)
Прикладне програмне забезпечення
685
problems were run for five days. This time interval is sufficiently large for taking into account several diurnal cycles of
the photochemical reactions. The five day interval is split up in 120 one hour subintervals. The unit of time is seconds
and the unit for the concentrations is number of molecules per cm3. The test problems A-D describe urban scenarios and
simulate a heavily polluted atmosphere. The test problems E-F describe a rural atmosphere.
For urban regions (Fig. 1a-h) the models B, C and D were performed by adding emissions of some polluting
agents (CO, NO, NO2, HO radicals, CH2O, isoprene, O3, PAN) with some multiplying factors, with respect to the model
A, as indicated below:
Model B: NO + 2; NO2 + 0.4; CO + 4; CH2O + 0.4; PAR + 4.
Model C: NO + 2; NO2 + 0.4; CO + 4; CH2O + 0.4; PAN + 2; PAR + 4.
Model D: O3 + 2; PAN + 2.
For rural regions (Fig. 2a-h) Model F was constructed from Model E, increasing twice the emissions of the
following polluting agents:
Model E: NO + 0.01; NO2 + 0.01; isoprene + 0.1.
Model F: NO2 + 0.02; isoprene + 0.2.
Прикладне програмне забезпечення
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Прикладне програмне забезпечення
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1. Adelman Z. E. A reevaluation of the carbon bond-IV photochemical mechanism. Master of Science Thesis – Department of Environmental
Sciences and Engineering, Schol of Public Health, University of North Carolina at Chapel Hill, 1999.
2. Atkinson R. D. L., Baulch R. A., Cox R. F., Hampson Jr. J. A., Kerr M. J., Rossi and Troe J. Kinetic and photochemical data for atmospheric
chemistry, Organic species: Supplement VII. J. Phys. Chem. Ref. Data. 1999, 28 : 191 - 393.
3. Cocheo V. Polluting agents and sources of urban air pollution. Ann Ist Super Sanita. 2000;36(3):267-74.
4. Gaffney J. S., Marley N. A. Atmospheric chemistry and air pollution. ScientificWorld Journal. 2003; 7(3) :199 - 234.
5. Loreto F. Emission of isoprenoids by plants: their role in atmospheric chemistry, response to the environment, and biochemical pathways. J
Environ Pathol Toxicol Oncol. 1997;16(2-3):119-24.
|
| id | nasplib_isofts_kiev_ua-123456789-1580 |
| institution | Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| issn | 1727-4907 |
| language | English |
| last_indexed | 2025-11-24T11:45:40Z |
| publishDate | 2006 |
| publisher | Інститут програмних систем НАН України |
| record_format | dspace |
| spelling | Cuciureanu, R. Dimitriu, G. 2008-08-26T13:22:37Z 2008-08-26T13:22:37Z 2006 Photochemical reactions in the atmosphere – a source of secondary pollutants / R. Cuciureanu, G. Dimitriu // Проблеми програмування. — 2006. — N 2-3. — С. 682-687. — Бібліогр.: 5 назв. — англ. 1727-4907 https://nasplib.isofts.kiev.ua/handle/123456789/1580 004.75 In the atmosphere polluting agents are involved in different reactions which lead to secondary pollutants. Secondary pollutants are mainly generated by photochemical and thermal reactions. These reactions occur in the atmosphere and they generate photochemical smog. We studied the variations of primary and secondary pollutants concentrations by photochemical modeling systems. All the test problems (denoted models A-F) were coded in Fortran and are based on the Carbon Bond Mechanism IV consisting of 32 chemical species involved in 70 thermal and 11 photolytic reactions. The numerical integration of the stiff systems was carried out using a Rosenbrock solver. en Інститут програмних систем НАН України Прикладне програмне забезпечення Photochemical reactions in the atmosphere – a source of secondary pollutants Article published earlier |
| spellingShingle | Photochemical reactions in the atmosphere – a source of secondary pollutants Cuciureanu, R. Dimitriu, G. Прикладне програмне забезпечення |
| title | Photochemical reactions in the atmosphere – a source of secondary pollutants |
| title_full | Photochemical reactions in the atmosphere – a source of secondary pollutants |
| title_fullStr | Photochemical reactions in the atmosphere – a source of secondary pollutants |
| title_full_unstemmed | Photochemical reactions in the atmosphere – a source of secondary pollutants |
| title_short | Photochemical reactions in the atmosphere – a source of secondary pollutants |
| title_sort | photochemical reactions in the atmosphere – a source of secondary pollutants |
| topic | Прикладне програмне забезпечення |
| topic_facet | Прикладне програмне забезпечення |
| url | https://nasplib.isofts.kiev.ua/handle/123456789/1580 |
| work_keys_str_mv | AT cuciureanur photochemicalreactionsintheatmosphereasourceofsecondarypollutants AT dimitriug photochemicalreactionsintheatmosphereasourceofsecondarypollutants |