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Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Atmospheric pollution
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (1)
Gases:Natural and pollutants Liquids:
Natural and pollutants
Solids:Natural and pollutants
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (1)
RELEVANT COMPONENTS OF ATMOSPHERIC CHEMISTRY
gaseous oxides
atmospheric methane
hydrocarbons (photochemical smog)
particulate matter (PM)
primary and secondary pollutants (e.g. H2SO4, NO2)
The characteristics of the atmosphere are determined by the balance of energy and
mass transfer processes.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (1)
Primary pollutants: emitted directly (e.g. SO2)
Secondary pollutants: formed by the atmospheric processes
acting upon primary pollutants or not pollutants (generally
from the tendency of atmosphere to oxidize primary
pollutants)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (1)
Particles ranging from aggregates of a few molecules to pieces of dust readily visible
to the naked eye are commonly found in the atmosphere
Some atmospheric particles, such as sea salts formed by the evaporation of water from
droplets of sea spray, are natural and even beneficial atmospheric constituents (e.g.
condensation nuclei serve as bodies for atmospheric water vapor to condense upon and
are essential for the formation of rain drops).
Colloidal-sized particles in the atmosphere are called aerosols:
dispersion aerosol: formed by grinding up bulk matter.
condensation aerosol: particles formed from chemical reactions involving gases.
Particles & colloids
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (1)
Atmospheric trace
gases in dry air
near ground level
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (1)
Trace gases
Carbon dioxide is the most abundant. It is a natural atmospheric constituent and it is
required for plant growth. The level of carbon dioxide in the atmosphere (actually at
about 400 ppm by volume) is increasing by about 2 ppm per year: associated with the
so-called greenhouse effect. https://www.co2.earth/
http://www.epa.gov/climatestudents/basics/today/greenhouse-effect.html
Increased levels of carbon monoxide represents a serious health threat because it
prevents blood from transporting oxygen to body tissues (carboxyhemoglobin).
Oxides of carbon, sulfur, and nitrogen are important constituents of the atmosphere
and are pollutants at higher levels.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (1)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (1)
Nitrogen oxides (collectively denoted as NOx) are both naturally occurring and
anthropogenic gases: associated with the so-called photochemical smog.
Sulfur-containing gases, in particular sulfur dioxide (SO2), are increasing atmospheric
components as by-products of the combustion of fuels: associated with acid rains.
Methane (CH4) is the most abundant hydrocarbon in the atmosphere. It is naturally
released from underground sources as natural gas and produced by the fermentation
of organic matter. Although quite unreactive, like other atmospheric hydrocarbons is
produced by several sources (mainly exhaust emissions): associated with the
photochemical smog. It is a greenhouse gas.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Inorganic gaseous pollutantsIn addition to solid pollutants (metal derivatives and particulates, see next Lecture), a
number of gaseous inorganic pollutants enter the atmosphere as the result of human
activities:Element Atmospheric inorganic form(s)
Oxygen O3
Carbon CO2, CO
Sulfur H2S, SO2, SO3, CS2, OCS
Nitrogen NH3, N2O, NO, NO2, N2O5
Halogens (X = Cl, F) X-, X2, HX
CO, SOx, NOx several hundred millions tons/year
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Inorganic gaseous pollutantsIn addition to solid pollutants (metal derivatives and particulates, see next Lecture), a
number of gaseous inorganic pollutants enter the atmosphere as the result of human
activities:Element Atmospheric inorganic form(s)
Oxygen O3
Carbon CO2, CO
Sulfur H2S, SO2, SO3, CS2, OCS
Nitrogen NH3, N2O, NO, NO2, N2O5
Halogens (X = Cl, F) X-, X2, HX
CO, SOx, NOx several hundred millions tons/year
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Sulfur is mainly released into the atmosphere as either H2S or SO2, both toxic primary air
pollutants.
H2S is oxidized by HO· to SO2 (H2S + 3/2 O2 SO2 + H2O) in a three step process:
H2S + HO· HS· + H2O
HS· + O2 HO· + SO
SO + O2 SO2 + O
The primary source of anthropogenic sulfur dioxide is pyrite in coal:
4 FeS2 + 11 O2 2 Fe3O4 + 8 SO2
Essentially all sulfur is converted to SO2 (only 1-2% to SO3).
Sulfur dioxide (SO2)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Sulfur dioxide may react in the atmosphere in several ways:
photochemical reactions;
photochemical and chemical reactions in the presence of NOx and/or
hydrocarbons;
chemical processes in water droplets, particularly containing metal salts
and ammonia;
reactions on solid particles to form particulate matter and its reaction
products are thought to be responsible for some aerosol formation.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2) *
much of the sulfur dioxide in the atmosphere is ultimately oxidized to sulfuric
acid and sulfate salts, particularly ammonium sulfate and ammonium
hydrogen sulfate.
The most important gas-phase reaction leading to the oxidation of SO2 is the
addition of HO· radical:
HO· + SO2 HOSO2·
HOSO2· radical can then react with another hydroxyl radical to form water
and SO3 or H2SO4 .
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Sulfur dioxide dissolves in water droplets where it can react with oxygen:
SO2(aq) + H2O + 1/2O2(g) H2SO4(aq)
SO2(aq) can be also oxidized by other oxidants:
SO2(aq) + H2O2(aq) H2SO4(aq)
SO2(aq) + O3(aq) H2SO4(aq) + O2(g)
Eventually, sulfuric acid can react with atmospheric ammonia to form
ammonium bisulfate and/or sulfate.
Sulfuric acid and its ammonium salts are water soluble, so they are washed
out of the atmosphere with precipitations.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
The sulfuric acid generated from anthropogenic sulfur dioxide emissions results in
precipitation with low pH values (<3.0 in extreme cases), and the phenomenon known as acid
rain may induce:
direct phytotoxicity to plants and destruction of forests;
respiratory problems to humans and other animals;
acidification of waters and subsequent toxic effects;
corrosion of exposed structures, electrical relays, equipment, ornamental materials, and
soil (e.g. limestone CaCO3);
formation of sulfuric mist (aerosol).
SO2 and acid rains
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
All current technologies involve the exposition of combustion gases to SO2
absorbent substance.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (3)
In addition to H2S, carbonyl sulfide (COS) and carbon disulfide (CS2) are important
gaseous components of the atmosphere → increasing source of atmospheric pollution.
Both COS and CS2 are oxidized in the atmosphere by reactions initiated by the hydroxyl
radical:
HO· + COS CO2 + HS·
HO· + CS2 COS + HS·
The HS· radicals can undergo further reactions to sulfur dioxide and, eventually, to sulfate
species.
Reduced sulfur gases
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Carbonyl sulfide is so long-lived that significant amounts reach the
stratosphere where it can undergo photolysis:
COS + hn CO + S
S + O2 SO + O
SO + O2 SO2 + O
COS + O CO + SO
SO2 formed in this process is eventually oxidized to sulfuric acid and sulfate
aerosol, thus producing a stratospheric aerosol layer contributing to the
greenhouse effect.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
The “modern” sulfur cycle
Differs quite dramatically from the original
one because of the large portion of
anthropogenic sulfur added to the
atmosphere (mainly in the form of sulfur
dioxide produced upon combustion of fossil
fuels).
Vulcanoes and biological decay of matter
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Inorganic gaseous pollutantsIn addition to solid pollutants (metal derivatives and particulates, see next Lecture), a
number of gaseous inorganic pollutants enter the atmosphere as the result of human
activities:Element Atmospheric inorganic form(s)
Oxygen O3
Carbon CO2, CO
Sulfur H2S, SO2, SO3, CS2, OCS
Nitrogen NH3, N2O, NO, NO2, N2O5
Halogens (X = Cl, F) X-, X2, HX
CO, SOx, NOx several hundred millions tons/year
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Carbon monoxide (CO)
Overall atmospheric concentration: 0.1 ppm, can reach 50-100 ppm in metropoles
From methane oxidation (1.6 ppm)
Anthropogenic emissions: 6% of CO
Decay of plant masses
Engines (increase air-fuel ratio > 16:1, CO → CO2)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Carbon monoxide (CO)Carbon monoxide causes problems in cases of locally high concentrations (metropolitan
areas) because of its toxicity.
20% vol of the CO released the to the atmosphere each year comes from natural sources
(degradation of chlorophyll, decay of plant matter).
Anthropogenic sources account for ca. 6% vol of CO emissions (mainly from incomplete
combustion of fossil fuels).
The remaining atmospheric CO comes from largely unknown sources (CO is an intermediate
in the oxidation of methane by hydroxyl radicals, and the methane content of the atmosphere
is about 10 times that of CO).
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2) *
CO in the atmosphere reacts with hydroxyl radical:
CO + HO· CO2 + H·
Hydroperoxyl radical is subsequently formed:
O2 + H· HOO·
Hydroxyl radical is then regenerated:
HOO· + NO HO·+ NO2
HOO· + HOO· H2O2
H2O2 + hn 2 HO·
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Carbon dioxide (CO2)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Carbon dioxide (CO2)
Very strong connection between life forms on Earth and the nature of Earth’s climate, which
determines its suitability for life.
The Gaia hypothesis by James Lovelock: the atmospheric O2/CO2 balance established and
sustained by living organisms determines and maintains Earth’s climate and other
environmental conditions.
When the first primitive life molecules were formed approximately 3.5 billion years ago, the
atmosphere was very different from its present state: chemically reducing and containing N2,
CH4, CO2, NH3, H2O, H2 but no O2.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
The atmospheric O2/CO2 balance was supposed to be preserved by maintaining
atmospheric carbon dioxide at low levels through the action of photosynthetic
organisms.
Atmospheric carbon dioxide levels are determined by a long-term equilibrium
between CO2 in the air and CO2 dissolved in the oceans and surface water, releases
of CO2 from natural and anthropogenic sources, and losses by plant growth.
During the last 200 years human activities: increased levels of atmospheric CO2 due
to combustion of large quantities of fossil fuels, burning of biomass and vegetation,
vehicles exhausts.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Atmospheric CO2
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
CO2 and global warming
global warming: energy
balance of incoming solar
radiation.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (3)
The greenhouse effect
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (3)
conversion nm → wavenumber (cm-1)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (3)
The greenhouse effect
https://www3.epa.gov/climatechange//kids/basics/today/greenhouse-effect.html
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (3)
greenhouse gases
https://www.epa.gov/ghgemissions/global-greenhouse-gas-emissions-data
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (3)
Global Warming Potentials (GWP)
depends upon:
ability to absorb energy (their "radiative efficiency")
how long they stay in the atmosphere (also known as their "lifetime")
it is a measure of how much energy the emissions of 1 ton of a gas will
absorb over a given period of time, relative to the emissions of 1 ton of
carbon dioxide (CO2).
The larger the GWP, the more that a given gas warms the Earth compared
to CO2 over that time period.
https://www.epa.gov/ghgemissions/understanding-global-warming-potentials
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (3)
Global Warming Potentials (GWP) CO2, by definition, has a GWP of 1. CO2 remains in the climate system for a very long time: CO2
emissions cause increases in atmospheric concentrations of CO2 that will last thousands of years.
Methane (CH4) is estimated to have a GWP of 28–36 over 100 years. CH4 emitted today lasts
about a decade on average, which is much less time than CO2. But CH4 also absorbs much more
energy than CO2. The net effect of the shorter lifetime and higher energy absorption is reflected in
the GWP. The CH4 GWP also accounts for some indirect effects, such as the fact that CH4 is a
precursor to ozone, and ozone is itself a GHG.
Nitrous Oxide (N2O) has a GWP 265–298 times that of CO2 for a 100-year timescale. N2O
emitted today remains in the atmosphere for more than 100 years, on average.
Chlorofluorocarbons (CFCs), hydrofluorocarbons (HFCs), hydrochlorofluorocarbons (HCFCs),
perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) are sometimes called high-GWP gases:
they trap substantially more heat than CO2.
https://www.epa.gov/ghgemissions/understanding-global-warming-potentials
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Any substance absorbing re-emitted IR radiation would decrease the energy released
to space, leading to higher temperatures at Earth’s surface (greenhouse effect).
Water vapor, CH4 and CO2 are
very effective IR rays
absorbent: "greenhouse"
gases.
Increase of CO2 :
1-2 ppm/year
Doubled in this century: 1.5-
4.5°C increase
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
CO2 emissions: the carbon footprint
http://www.eea.europa.eu/
http://www3.epa.gov/carbon-footprint-calculator/
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Inorganic gaseous pollutantsIn addition to solid pollutants (metal derivatives and particulates, see next Lecture), a
number of gaseous inorganic pollutants enter the atmosphere as the result of human
activities:Element Atmospheric inorganic form(s)
Oxygen O3
Carbon CO2, CO
Sulfur H2S, SO2, SO3, CS2, OCS
Nitrogen NH3, N2O, NO, NO2, N2O5
Halogens (X = Cl, F) X-, X2, HX
CO, SOx, NOx several hundred millions tons/year
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (3)
Nitrogen oxides (NOx)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Nitrogen oxides (NOx)
Involved in
- photochemical smog
- stratospheric ozone layer depletion
- acid rain
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Three oxides of nitrogen are normally encountered in the atmosphere:
nitrous oxide (N2O), nitric oxide (NO), and nitrogen dioxide (NO2).
N2O: anesthetic known as “laughing gas,” is produced by microbiological
processes and is a component of the unpolluted atmosphere (ca. 0.3 ppm).
Relatively unreactive, does not seem to significantly influence the lower
atmosphere.
Concentration decreases rapidly with altitude in the stratosphere due to the
photochemical reaction
N2O + hn N2 + O
Nitrogen oxides (NOx)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
NO (colorless and odorless), NO2 (red-brown pungent): collectively
designated as NOx, these gases enter the atmosphere from natural sources
(lightning and biological processes) and from pollutant sources.
NO binds to hemoglobin, but concentration lower
Practically all anthropogenic NOx enter the atmosphere as a result of the
combustion of fossil fuels, mainly as NO generated from internal combustion
engines:
N2 + O2 2 NO (at very high temperature)
Rapidly converted to NO2 in the troposphere:
NO + ½ O2 NO2 / NO + O3 NO2 + O2
Nitrogen oxides (NOx)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
NO2 is a very reactive and significant species in the atmosphere
it absorbs light throughout the UV spectrum penetrating the troposphere:
NO2 + hn NO + O (l < 398 nm)
O + O2 O3
NO + O3 NO2 + O2
During daytime NO2 is rapidly converted back to NO
in the absence of photodissociation at night NO2 predominates over NO.
NO2 + hn NO2* (l > 430 nm)
In the stratosphere: HO· + NO2 HNO3 acid rain
Nitrogen oxides (NOx)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2) *
Atmospheric chemical reactions of NO2
First observed in the troposphere in 1980, nitrate radical (NO3·) is now recognized as
an important atmospheric chemical species, especially at night.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
nitrate radical (NO3·)
This species is mainly formed by the reaction
NO2 + O3 NO3· + O2
Levels of NO3· remain low during daylight (lifetime at sunlight: ca. 5 s) because of the
following two dissociation reactions:
NO3· + hn NO + O2 (l < 700 nm)
NO3· + hn NO2 + O (l < 580 nm)
It is likely that NO3· levels become high enough just before the sunset and strongly increase
at night.
[HO·] higher during daytime major oxidant
[NO3·] higher during the night major oxidant
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
NO3· exists in equilibrium with NO2:
NO2 + NO3· N2O5
N2O5 + H2O 2 HNO3 acid rain
HNO3 + HO· H2O + NO3· (in the stratosphere)
The chemistry of NOx in the troposphere is different from that in the
stratosphere: nitrogen chemistry at both levels is driven by the
photochemical dissociation of nitrogen dioxide, but the products formed
depend on other substances with which the photochemically excited NO2*
molecules can react.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Photochemical smog (=photochemically oxidizing atmosphere) formation is strictly
related conversion of nitrogen into many substances in the atmosphere through several
different reactions. Necessary requirements for the photochemical smog to be formed:
(i) nitrogen oxides (NOx),
(ii) hydrocarbons
react together due to:
(i) radiation (sunlight)
Hydrocarbons (originated from incomplete combustion of fossil fuels) react with NOx through
a sequence of reactions (all involving a free radical mechanism) to form oxidants (the final
product of photochemical smog).
NOx and the photochemical smog (troposphere)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
https://energyeducation.ca/encyclopedia/Photochemical_smog
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Photochemical smog
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
The final substances (aldehydes, peroxyalkylnitrates, peroxyacetylnitrates, etc.) are extremely
irritating to sensitive biological tissues and cause most of the health problems associated with
photochemical smog.
NOx and the photochemical smog
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)*
NO and hydrocarbon radicals released
from exhausts gases;
NO converted to NO2:
NO + ½ O2 NO2
NO + O3 NO2 + O2
NO + RO2· NO2 + RO·
NO2 reacts with hydrocarbon free
radicals:
NO2 + RC(O)O2· RC(O)O2NO2
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2) *
NO2 photodissociates:
NO2 + hn NO + O
Reactions of O:
O + H2O 2 HO·
O + O2 O3
Reactions of O3:
NO + O3 NO2 + O2
RH + O3 RO· + H2O
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)*
Formation of hydrocarbon radicals:
RH + HO· H2O + R·
R· + O2 RO2·
RO2· + NO NO2 + RO·
RO· + O2 RCHO + HO2·
RCHO + HO· RCO· + H2O
RCO· + O2 RC(O)O2·
Photochemical smog:
NO2 + RC(O)O2· RC(O)O2NO2
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Inorganic gaseous pollutantsIn addition to solid pollutants (metal derivatives and particulates, see next Lecture), a
number of gaseous inorganic pollutants enter the atmosphere as the result of human
activities:Element Atmospheric inorganic form(s)
Oxygen O3
Carbon CO2, CO
Sulfur H2S, SO2, SO3, CS2, OCS
Nitrogen NH3, N2O, NO, NO2, N2O5
Halogens (X = Cl, F) X-, X2, HX
CO, SOx, NOx several hundred millions tons/year
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Ozone (O3)
www.epa.gov
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Stratospheric ozone (O3) layer (15-35 km) depletion
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Ozone (O3)
Uses of ozone
For air purification at the crowded places like cinema halls and tunnel railways. Due to its strong
oxidizing power it also destroys the foul smell in slaughter houses.
In sterilizing drinking water by oxidizing all germs and bacteria.
For preservation of meat in cold storages.
For bleaching delicate fabrics such as silk, ivory, oils, starch and wax.
It helps to locate a double bond in any unsaturated organic compound by ozonolysis.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Ozone (O3)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Ozone layer depletion
Ozone (O3) forms a layer in the stratosphere (thinner on the equator, denser towards the
poles).
The amount of ozone above a point on Earth's surface is measured in Dobson Units (DU).
1 DU is 0.01 mm thickness slab at
standard temperature and pressure:
~260 DU near the tropics and higher
elsewhere, though there are large
seasonal fluctuations.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
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Ozone (O3)
www.theozonehole.com
absorbs very strongly in the region 220-
330 nm (filters UV-B radiation)
UV-A 320-440 nm less harmful
UV-C < 290 nm does not penetrate the
troposphere
Absorption converted to heat: increase
of T at 50 km
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
O3 layer forms when UV radiation strikes the stratosphere
O2 + hn O + O (l < 242.4 nm)
O2 + O + O3
It provides a shield from the potentially harmful UV radiation from the sun (at wavelengths
between 240 and 320 nm) by absorbing such rays:
O3 + hn O + O2 (l < 325 nm) (ozone photodissociation)
It can then reform through the following reaction:
O2 + O O3
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Ozone (O3)
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
It can also be destroyed by a series of reactions from which the net result is
O3 + O 2 O2
The concentration of ozone in the
stratosphere is a steady-state
concentration resulting from the
balance of ozone production and
destruction by the above processes.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Ozone (O3)
Although ozone is a desirable substance in the stratosphere, it is a major
environmental hazard at ground level (troposphere, smog):
it is formed naturally photochemically;
by-product of photochemical smog, the presence of nitrogen oxides (NOx) leads to
higher than normal background levels of ozone;
NO + ½ O2 NO2 / NO + O3 NO2 + O2
reacts with hydrocarbons to form peroxynitrates that damage eyes, nasal
passages, throat and lungs;
excessive levels are believed to be detrimental to plants through reactions with
chlorophyll.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Ozone (O3)
Number of days on
which ozone
concentrations
exceeded the
information
threshold during
the summer of 2014
http://www.eea.euro
pa.eu
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
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Chlorofluorocarbons (CFCs)Chlorofluorocarbons (e.g. CCl2F2, commonly called Freons) are volatile
one- or two-carbon compounds containing Cl and F atoms bound to C.
widely used in recent decades in the fabrication of flexible and rigid foams
and as fluids for refrigeration and air conditioning, blowing agents.
Halons are related compounds containing bromine (e.g. CBrClF2) and are
used in fire extinguisher systems.
CFCs are notably stable (lifetime 60-420 y), nontoxic, volatile (not
removed in the troposphere, ultimately diffuse to the stratosphere) and
inert (unless they are exposed to the intense solar radiation).
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (3)
In the stratosphere CFCs are exposed to the intense solar radiation that
cannot penetrate the ozone layer, and the CFCs become photochemically
active:
CCl2F2 + hn Cl· + CClF2·
Cl· + O3 ClO· + O2 (ozon destruction)
ClO· + ClO· ClOOCl (dimerization)
ClOOCl + hn ClOO· + Cl· / ClOO· Cl· + O2
2 Cl· + 2 O3 2 ClO· + 2 O2
This is a catalytic process (Cl·/ClO· is regenerated)!
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Each Cl· can catalyze the destruction of about 100,000 ozone molecules
before being converted into inert molecules of HCl and ClONO2:
Cl· + CH4 CH3· + HCl
HO· + ClO· O2 + HCl
NO2 + ClO· ClONO2
Both HCl and ClONO2 are stable non-ozone destroying molecules and remain
in the air. Eventually, winds carry them into the troposphere.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)The most prominent instance of ozone layer destruction is the so-called “Antarctic
ozone hole”. This phenomenon is manifested by the appearance during the
Antarctic’s late winter and early spring of severely depleted stratospheric ozone (up
to 50%) over the polar region.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)*
Why Antartica?
During the winter polar night, sunlight does not reach the south pole.
A strong circumpolar wind develops in the stratosphere (polar vortex)
sucking gaseous air components (including pollutants) and isolating the air
over the polar region.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)*
Since there is no sunlight, the air within the polar vortex can get very cold and
special clouds form (Polar Stratospheric Clouds - PSCs):
- when temperature drops to -78°C, HNO3, H2SO4 and H2O condense to
form type I PSCs containing small particles (1 mm) that remain in the
stratosphere;
- as temperature drops to -85°C, H2O further condenses to form type II
PSCs which contain particles large enough (1 mm) to fall out of the
stratosphere, removing nitric acid and water from the stratosphere.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)*
ClONO2 and HCl molecules in the air strike the type II cloud particles
attach to their surface where, although generally stable, they are
converted into Cl2, building up a reservoir of Cl2 and HOCl:
HCl + ClONO2 Cl2 + HNO3
ClONO2 + H2O HOCl + HNO3
During winter these compounds have no effect on ozone because of the
absence of UV radiation from the sun, required to convert these species
into reactive Cl· radicals.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
When the sunlight returns to the lower stratosphere above Antartica in Spring,
ClONO2 and Cl2 undergo photodissociation:
Cl2 + hn 2 Cl·
HOCl + hn HO· + Cl·
Cl· radicals thus formed trigger the reactions causing
ozone depletion.
Cl· + O3 ClO· + O2
ClO· + ClO· ClOOCl (dimerization)
ClOOCl + hn ClOO· + Cl· / ClOO· Cl· + O2
2 Cl· + 2 O3 2 ClO· + 2 O2
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Inorganic gaseous pollutantsIn addition to solid pollutants (metal derivatives and particulates, see next Lecture), a
number of gaseous inorganic pollutants enter the atmosphere as the result of human
activities:Element Atmospheric inorganic form(s)
Oxygen O3
Carbon CO2, CO
Sulfur H2S, SO2, SO3, CS2, OCS
Nitrogen NH3, N2O, NO, NO2, N2O5
Halogens (X = Cl, F) X-, X2, HX
CO, SOx, NOx several hundred millions tons/year
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
F2, HF and other volatile fluorides are produced in the manufacture of
aluminum
HF is a by-product in the conversion of fluorapatite (rock phosphate) to
phosphorous-based fertilizers. Highly corrosive (reacts even with glass),
irritating to the body tissues and the respiratory tract (brief exposure to HF
vapors at the part-per-thousand level may be fatal).
The acute toxicity of F2 is even higher than that of HF and causes fluorosis,
whose symptoms include mottled teeth and pathological bone conditions.
Gaseous halides
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Cl2 does not occur as an air pollutant on a large scale but is widely used as a
manufacturing chemical in the plastics industry, for water treatment and as
bleach.
Quite toxic, very reactive and a powerful oxidizing agent, it dissolves in
atmospheric water droplets, yielding hydrochloric acid and hypochlorous acid.
HCl is released to the atmosphere mainly as a combustion product during
incineration of chlorinated plastics (PVC).
Some compounds (e.g. SiCl4, AlCl3) may hydrolize and release HCl.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Organic pollutants (natural or anthropogenic)
- hydrocarbons (both alkyl and aromatic)
- carbonyl compounds (aldehydes, ketones, carboxylates)
- alcohols
- ethers
- nitrogen-, sulfur-, halide-containing organics.
may have a strong effect upon atmospheric quality:
direct effects, such as cancer caused by exposure to vinyl chloride;
formation of secondary pollutants, especially photochemical smog.
Organic gaseous pollutants
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Polychlorinated dibenzodioxins (PCDDs) are of considerable concern
because of their toxicity.
Numerous sources, including car engines, pesticides (by product of
organochloride pesticides production), steel and other metal production, and,
in particular, old municipal solid waste incinerators.
Formation in such incinerators results from the presence of chloro-
containing waste (such as PVC bottles) and of trace metals that can
catalyze reactions leading to their production.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
DioxinesClasse di composti che raggruppa 75 dibenzo-para-diossine policlorurate (PCDD)
e 135 dibenzo-furani policlorurati
Prodotte da processi di combustione di sostanze organiche in presenza di cloro
(T> 300°C)
Anche da incendi boschivi ed eruzioni vulcaniche
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
One of the most relevant environmental pollutant chemical is 2,3,7,8-tetrachlorodibenzo-p-
dioxin (TCDD), often known simply as “dioxin”.
Organic gaseous pollutants: PCDDs
It has been released in a number of industrial accidents, the most massive of which exposed
several tens of thousands of people to a cloud of chemical emissions spread over a 3-square-
mile area at the La Roche manufacturing plant near Seveso in 1976.
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Organic gaseous pollutants: PCDDs
Very low vapour pressure
High melting point (305°C )
Poorly water soluble
Chemically unreactive
Thermally stable up to 700°C
Poorly biodegradable
Stable, persistent environmental pollutant
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
DioxinesDiossina più tossica TCCD (valore 1 scala di tossicità in TEF = fattore di tossicità equivalente )
2,3,7,8-tetraclorodibenzo-p-diossina
Veleno di Seveso (1976)
Produzione di triclorofenolo
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
Dioxines: TEFI fattori di tossicità equivalente (TEF) si basano sulla
considerazione che PCDD, PCDF e PCB diossina simili sono
composti strutturalmente simili che presentano il medesimo
meccanismo di azione (attivazione del recettore Ah) e producono
effetti tossici simili: proprio il legame tra le diossine e il recettore Ah
è il passo chiave per il successivo innescarsi degli effetti tossici.
I TEF vengono calcolati confrontando l’affinità di legame dei vari
composti organoclorurati con il recettore Ah, rispetto a quella della
2,3,7,8-TCDD (2,3,7,8- tetraclorodibenzodiossina), la più tossica,
considerando l’affinità di questa molecola come il valore unitario di
riferimento.
Per esprimere la concentrazione complessiva di PCDD/PCDF e
PCB diossina simili nelle diverse matrici si è introdotto il concetto di
tossicità equivalente (TEQ), che si ottiene sommando i prodotti tra i
valori TEF dei singoli congeneri e le rispettive concentrazioni,
espresse con l’unità di misura della matrice in cui vengono
ricercate.
http://www.arpa.piemonte.it/approfondimenti/temi-
ambientali/microinquinanti/Diossine%2C%20PCB%2C%20IPA%20-
%20guida%20alla%20lettura%20dei%20risultati%20analitici
Environmental Toxicology, Master Sc. in Industrial Biotechnology Silvia Gross
Environmental toxicology: chemical aspects
Atmospheric chemistry (2)
In Europe, the catastrophic accident in the Italian
town of Seveso in1976 prompted the adoption of
legislation on the prevention and control of such
accidents. The so-called Seveso-Directive
(Directive 82/501/EEC) was later amended in
view of the lessons learned from later accidents
such as Bhopal, Toulouse or Enschede resulting
into Seveso-II (Directive 96/82/EC). In 2012
Seveso-III (Directive 2012/18/EU) was adopted
taking into account, amongst others, the changes
in the Union legislation on the classification of
chemicals and increased rights for citizens to
access information and justice. It replaces the
previous Seveso II directive.
The Directive now applies to more than 10 000
industrial establishments in the European Union
where dangerous substances are used or stored
in large quantities, mainly in the chemical,
petrochemical, logistics and metal refining sectors.
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