[Committee] suphur dioxide

Tue Feb 13 17:05:55 UTC 2007

I was very disturbed to hear the speaker today suggested that Sulphur
Dioxide is a greenhouse gas. In fact the opposite is true: it is an aerosol
which cools the earth [1] and may well have had a significant effect in
masking the impact of much of the Carbon Dioxide that we have already
produced. [2] [3]
Please find enclosed a graphic which shows the past effect of SO2 (the main
aerosol) in masking global warming. The area below the x axis is the
negative impact of the gas, offsetting increased CO2 in the twentieth
century. The y axis (Radiative forcing) is a measure of the warming effect
of the greenhouse gases. It measures the degree of committed climate change,
depending on stabilisation scenarios. All the scenarios require very strong
action to be taken.

It is important not to let a lie propagate: I feel that we should send
information to all participants correcting this untruth

*Further information:*
 [1] FROM IPCC (2001)
 "Aerosols are liquid or solid particles suspended in the air. "
"Aerosols have most likely made a significant negative contribution to the
overall radiative forcing. An important characteristic of aerosols is that
they have short atmospheric lifetimes and therefore cannot be considered
simply as a long-term offset to the warming influence of greenhouse gases."
"Sulphate aerosols are produced by chemical reactions in the atmosphere from
gaseous pr  ecursors (with the exception of sea salt sulphate and gypsum
dust particles)."
"The two main sulphate precursors are SO2 from anthropogenic sources and
volcanoes, and DMS from biogenic sources, especially marine plankton (Table
5.2 <http://www.grida.no/climate/ipcc_tar/wg1/167.htm#tab52>). Since
SO2emissions are mostly related to fossil fuel burning, the source
distribution
and magnitude for this trace gas are fairly well-known, and recent estimates
differ by no more than about 20 to 30%"
 [2] Also see: http://www.zerocarbonnow.org/GHG.xls

[3] Furthermore, James Lovelock has proposed production of Di-methyl
Sulphide by cool-water algae which decomposes to sulphates as being the main
mechanism behind the biological regulation of climate: why we live on a
living planet (in thermodynamic dis-equilibrium) rather than a dead one.

On 13 Feb 2007 15:13:50 +0000, A.L. Stephenson <als53 at cam.ac.uk> wrote:

> Yes, I was right, suphur dioxide is an aerosol which does the opposite to
> Global Warming! It also causes acid rain but not global warming. I am
> going
> to email this to the engineering bloke and ask him to send it to the exxon
> woman. She should at least know something about global warming!
>
> Sulphur dioxide (SO2) Sulphur dioxide is produced when coal and some
> petroleum products containing sulphur impurities are burnt. Sulphur
> dioxide
> is an acid gas which can cause harm to people. It causes damage to
> ecosystems and buildings when deposited as acid rain.
>
> Aerosols:
>
> An argument against the idea that global warming is due to mankind's
> emissions of carbon dioxide goes as follows: the warming this century
> occurred mostly between 1910 and 1940, when the carbon dioxide
> concentration grew slowly from 293 to 300 ppm. On the other hand, the
> temperature remained steady between 1940-1980, while the carbon dioxide
> concentration increased from 300 to 335 ppm. The most likely answer to
> this
> inconsistency is atmospheric aerosol. Aerosols are emitted by industrial
> processes, transport, etc, and their increased concentration offset
> simultaneous warming due to increasing greenhouse gases. However the
> warming overtook the cooling by mid 1970's (8).
>
> Tropospheric aerosols reduced solar radiation to the ground by about 0.5
> W/m2, as a global average, between 1940-1992 (5). Unlike greenhouse gases,
> which are generally long-lived, aerosols fall out of the atmosphere fairly
> rapidly, either dry ('sedimentation') or within rain (as condensation
> nuclei). Therefore aerosol concentrations are not uniformly mixed across
> the globe. They have been so high in some regions that the cooling effect
> may have exceeded the warming due to greenhouse gases. In fact the lack of
> warming between 1940-1980 is only found in the northern hemisphere, where
> most manmade aerosols are emitted.
>
> Manmade aerosols include soot and sulphur dioxide emitted by coal burning
> plants, for instance. The Mt Pinatubo eruption in the Philippines in 1991
> produced 30m tonnes of SO2 in a few hours, almost twice as much as the
> entire USA produces in a year. The cooling effect could be felt for the
> following two years.

 MORE INFO FROM IPCC (2001) 5.2.2.6 Sulphates

Sulphate aerosols are produced by chemical reactions in the atmosphere from
gaseous precursors (with the exception of sea salt sulphate and gypsum dust
particles). The key controlling variables for the production of sulphate
aerosol from its precursors are:

   1. the source strength of the precursor substances,
   2. the fraction of the precursors removed before conversion to
   sulphate,
   3. the chemical transformation rates along with the gas-phase and
   aqueous chemical pathways for sulphate formation from SO2.

The atmospheric burden of the sulphate aerosol is then regulated by the
interplay of production, transport and deposition (wet and dry).

The two main sulphate precursors are SO2 from anthropogenic sources and
volcanoes, and DMS from biogenic sources, especially marine plankton (Table
5.2 <http://www.grida.no/climate/ipcc_tar/wg1/167.htm#tab52>). Since
SO2emissions are mostly related to fossil fuel burning, the source
distribution
and magnitude for this trace gas are fairly well-known, and recent estimates
differ by no more than about 20 to 30% (Lelieveld et al., 1997). Volcanic
emissions will be addressed in Section
5.2.2.8<http://www.grida.no/climate/ipcc_tar/wg1/175.htm>
.

Estimating the emission of marine biogenic DMS requires a gridded database
on its concentration in surface sea water and a parametrization of the
sea/air gas transfer process. A 1ºx1º monthly data set of DMS in surface
water has been obtained from some 16,000 observations using a heuristic
interpolation scheme (Kettle et al., 1999). Estimates for data-sparse
regions are generated by assuming similarity to comparable biogeographic
regions with adequate data coverage. Consequently, while the global mean
surface DMS concentration is quite robust because of the large data set used
(error estimate ± 50%), the estimates for specific regions and seasons
remain highly uncertain in many ocean regions where sampling has been sparse
(error up to factor of 5). These uncertainties are compounded with those
resulting from the lack of a generally accepted air/sea flux
parametrization. The approach of Liss and Merlivat (1986) and that of
Wanninkhof (1992) yield fluxes differing by a factor of two (Kettle and
Andreae, 2000). In Table
5.2<http://www.grida.no/climate/ipcc_tar/wg1/167.htm#tab52>,
we use the mean of these two estimates (24 Tg S(DMS)/yr).

The chemical pathway of conversion of precursors to sulphate is important
because it changes the radiative effects. Most SO2 is converted to sulphate
either in the gas phase or in cloud droplets that later evaporate. Model
calculations suggest that aqueous phase oxidation is dominant globally (Table
5.5 <http://www.grida.no/climate/ipcc_tar/wg1/172.htm#tab55>). Both
processes produce sulphate mostly in sub-micron aerosols that are efficient
light scatterers, but the precise size distribution of sulphate in aerosols
is different for gas phase and aqueous production. The size distribution of
the sulphate formed in the gas phase process also depends on the interplay
between nucleation, condensation and coagulation. Models that describe this
interplay are in an early stage of development, and, unfortunately, there
are substantial inconsistencies between our theoretical description of
nucleation and condensation and the rates of these processes inferred from
atmospheric measurements (Eisele and McMurry, 1997; Weber et al., 1999).
Thus, most models of sulphate aerosol have simply assumed a size
distribution based on present day measurements. Because there is no general
reason that this same size should have applied in the past or will in the
future, this lends considerable uncertainty to calculations of forcing. Many
of the same issues about nucleation and condensation also apply to secondary
organic aerosols.

Two types of chemical interaction have recently been recognised that can
reduce the radiative impact of sulphate by causing some of it to condense
onto larger particles with lower scattering efficiencies and shorter
atmospheric lifetimes. The first is heterogeneous reactions of SO2 on
mineral aerosols (Andreae and Crutzen, 1997; Li-Jones and Prospero, 1998;
Zhang and Carmichael, 1999). The second is oxidation of SO2 to sulphate in
sea salt-containing cloud droplets and deliquesced sea salt aerosols. This
process can result in a substantial fraction of non-sea-salt sulphate to be
present on large sea salt particles, especially under conditions where the
rate of photochemical H2SO4 production is low and the amount of sea salt
aerosol surface available is high (Sievering et al., 1992; O'Dowd, et al.,
1997; Andreae et al., 1999).

Because the models used to estimate sulphate aerosol production differ in
the resolution and representation of physical processes and in the
complexity of the chemical schemes, estimates of the amount of sulphate
aerosol produced and its atmospheric burden are highly model-dependent. Table
5.4 <http://www.grida.no/climate/ipcc_tar/wg1/171.htm#tab54> provides an
overall model-based estimate of sulphate production and Table
5.5<http://www.grida.no/climate/ipcc_tar/wg1/172.htm#tab55>emphasises
the differences between different models. All the models shown in
Table 5.5 <http://www.grida.no/climate/ipcc_tar/wg1/172.htm#tab55> include
anthropogenic and natural sources and consider at least three species, DMS,
SO2 and SO42-, B and D consider more species and have a more detailed
representation of the gas-phase chemistry. C, F and G include a more
detailed representation of the aqueous phase processes. The calculated
residence times of SO2, defined as the global burden divided by the global
emission flux, range between 0.6 and 2.6 days as a result of different
deposition parametrizations. Because of losses due to SO2 deposition, only
46 to 82% of the SO2 emitted undergoes chemical transformations and forms
sulphate. The global turnover time of sulphate is mainly determined by wet
removal and is estimated to be between 4 and 7 days. Because of the critical
role that precipitation scavenging plays in controlling sulphate lifetime,
it is important how well models predict vertical profiles.

The various models start with gaseous sulphur sources ranging from 80 to 130
TgS/yr, and arrive at SO2 and SO42- burdens of 0.2 to 0.6 and 0.6 to
1.1TgS, respectively. It is noteworthy that there is little
correlation between
source strength and the resulting burden between models. In fact, the model
with the second-highest precursor source (B) has the lowest SO2 burden, and
the model with the highest sulphate burden (J) starts with a much lower
precursor source than the model with the lowest sulphate burden (E). Figures
5.2(a) <http://www.grida.no/climate/ipcc_tar/wg1/168.htm#fig52> and
(b)<http://www.grida.no/climate/ipcc_tar/wg1/168.htm#fig52>show the
global distribution of sulphate aerosol production from
anthropogenic SO2 and from natural sources (primarily DMS), respectively
(see also Table 5.4 <http://www.grida.no/climate/ipcc_tar/wg1/171.htm#tab54>
).

The modelled production efficiency of atmospheric sulphate aerosol burden
from a given amount of precursors is expressed as P, the ratio between the
global sulphate burden to the global sulphur emissions per day. At the
global scale, this parameter varies between the models listed in Table
5.5<http://www.grida.no/climate/ipcc_tar/wg1/172.htm#tab55>by more
than a factor of two, from
1.9 to 4.5 days. Within a given model, the potential of a specific sulphur
source to contribute to the global sulphate burden varies strongly as a
function of where and in what form sulphur is introduced into the
atmosphere. SO2 from volcanoes (P=6.0 days) is injected at higher altitudes,
and DMS (P=3.1 days) is not subject to dry deposition and can therefore be
converted to SO2 far enough from the ground to avoid large deposition
losses. In contrast, most anthropogenic SO2 (P=0.8 to 2.9 days) is released
near the ground and therefore much of it is lost by deposition before
oxidation can occur (Feichter et al., 1997; Graf et al., 1997). Regional
differences in the conversion potential of anthropogenic emissions may be
caused by the latitude-dependent oxidation capacity and by differences in
the precipitation regime. For the same reasons P exhibits a distinct
seasonality in mid- and high latitudes.

This comparison indicates that in addition to uncertainties in precursor
source strengths, which may be ranging from factors of about 1.3 (SO2) to 2
(DMS), the estimation of the production and deposition terms of sulphate
aerosol introduces an additional uncertainty of at least a factor of 2 into
the prediction of the sulphate burden. As the relationship between sulphur
sources and resulting sulphate load depends on numerous parameters, the
conversion efficiency must be expected to change with changing source
patterns and with changing climate.

Sulphate in aerosol particles is present as sulphuric acid, ammonium
sulphate, and intermediate compounds, depending on the availability of
gaseous ammonia to neutralise the sulphuric acid formed from SO2. In a
recent modelling study, Adams et al. (1999) estimate that the global mean NH
4+/SO42- mole ratio is about one, in good agreement with available
measurements. This increases the mass of sulphate aerosol by some 17%, but
also changes the hydration behaviour and refractive index of the aerosol.
The overall effects are of the order of 10%, relatively minor compared with
the uncertainties discussed above (Howell and Huebert, 1998).
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.zerocarbonnow.org/pipermail/committee_zerocarbonnow.org/attachments/20070213/c9dfd0c1/attachment-0002.html 
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.zerocarbonnow.org/pipermail/committee_zerocarbonnow.org/attachments/20070213/c9dfd0c1/attachment-0003.html 