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SO2 Flashcards

1
Q

What natural sources emit SO2?

A

Volcanic actions, sea salt over oceans, organic matter decomposition.

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2
Q

What anthropogenic sources emit SO2?

A

Coal/petroleum combustion, petroleum refining, nonferrous smelting., 95% of total coming from industry and stationary sources

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3
Q

What is Sulfur content of coals?

A

0.3-7% in organic and inorganic forms.

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4
Q

How is SO2 emitted when coal is burnt?

A

Pyrite (FeS2) oxidises to FeSO4 or Fe2O3/02.

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5
Q

What is its content in oil?

A

0.2-1.7%, in organic form.

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6
Q

What is SO2’s solubility?

A

11.3 g/100 mL, dissolving into fog or cloud droplets in the atmosphere, forming sulfurous acid, which is oxidised by O2 to sulfuric acid.

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7
Q

What can then be formed from this?

A

Ammonium sulfate

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8
Q

How is SO2 removed from the atmosphere?

A

Precipitation as bisulfate, dissolution into water droplets, incorporation into fog or cloud droplets, and diffusion to plant surfaces.

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9
Q

How is SO2 uptaken by plants?

A

Stomatal diffusion

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10
Q

What influences stomatal aperture closure impact?

A

Light, humidity, stomatal aperture/ammount, temperature, and wind velocity (due to influence on guard cells)

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11
Q

How can SO2 impact stomatal conductance?

A

Injuring epidermal/guard cells, elevating stomatal conductance, increasing gaseous entry.

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12
Q

How does SO2 alter guard cell physioloy?

A

The process of stomatal aperture regulation dpends on K and Cl ions alongside ion channels and trasnporters. Ion gradient alterations through SO2 can impact guard cell turgor pressure.

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13
Q

How does SO2 impact potassium channels?

A

Inhibition of inward-rectifying potassium channels, which are important in potassium ion fluxes important in stomatal opening.

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14
Q

How does SO2 imapct pH?

A

Acidification of cytoplasm affects proton pump and ion transporter activity, disrupting ion homeostasis thus impairing stomatal function.

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15
Q

How do guard cells regulate stomatal aperture?

A

Transportation of K and Cl ions across membranes creates osmotic gradients driving water movement in or our of guard cells, influencing turgor pressure. Influx of water results in swelling and srhinking, where guard cell expansion opens stomata.

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16
Q

How does SO2 impact internal biochemistry following guard cell interactions?

A

Low concentration elevates photosynthesis and transpirtation, which then decreases with concentration increase.

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17
Q

What plant injuries may manifest as a result of pollution?

A

Leaf chlorosis and spotty necrotic lesions.

18
Q

How does SO2 impact photosynthesis?

A

Inhibition of enzymes, damaging chloroplast structure, ETC disruption, and oxidative stress.

19
Q

How are enzymes inhibited by SO2?

A

Rubisco catalysing carbon fixation in calvin cycle is inhibited, done by binding to active sites, competing for CO2 and interfering carboxylation.

20
Q

How is the ETC disrupted?

A

Interaction with cytochrome b6f and Photosystem 2

21
Q

What is the mechanism of ETC disruption?

A

Direct interaction of SO2 with Fe-S clusters in PS1 and PS2, disrupting electron transfer between pigments and electron carriers, meaning decreased efficiency of ATP and NADPH production.

22
Q

How does SO2 damage to chloroplast structure?

A

Oxidation of lipids/proteins in the membrane, especially unsaturated fatty acids, leading to lipid peroxidation and membrane damage, compromising thylakoid membrane integrity which houses photosynthetic machinery, like pigments and protein complexes in light.

23
Q

How does SO2 generate ROS?

A

Through stimulation of NADPH oxidases which is an ROS generating enzymes, leading to ROS acumulation and photosynthesis inhibition in Strawberries (Muneer et al., 2013)

24
Q

What causes leaf chlorosis?

A

Decrease in chlorophyll content.

25
Q

How does SO2 induce this?

A

Inhibition of enzymes involved in chlorophyll synthesis, like oxidiative stress and subsequent damage to glutamyl-tRNA reductase, which is the first step in chlorophyll biosynthesis.

26
Q

What is a case study of SO2 impact on crop yield?

A

In china where there is extensive coal burning, there is a negative correlation between SO2 concentrations and rice prodcutivity.

27
Q

How is SO2 expected to increase in Asia?

A

From 34 x 106t in 1990 to 110x106t by 2020 (Imran et al., 2020)

28
Q

What’s an example of synergistic pollutive impacts?

A

SO2 and O3.

29
Q

What is a study showing synergistic pollution impacts?

A

Experiments on Chinese guger-tree seedlings in field chambers exposed to 325 ppb of SO2 for for weeks decreased photosynthetic rate, root weight, and total seedling weight, with 75% increase in SH groups.

30
Q

Why are O3/SO2 synergistic?

A

Their overlapping mechanisms of action

31
Q

What is an example of syngerism of O3/SO2?

A

Both generate ROS species, SO2 to superoxide radicals and hydrogen peroxide, whilst O3 of singlet oxygen and peroxyl radcials.

32
Q

Why do O3 and SO2 mechanisms of action overlap?

A

Common properties like high oxidation potential meaning readily reacting to organic molecules through oxidation.

33
Q

How is SO2 also synergistic with CO2?

A

Studies show that photosynthesis also decreases with increasing SO2 cocnentration at 300, 45, and 600 ppm CO2, larger reductions occuring at lower CO2 (Carlson, 1983)

34
Q

What is the chemical fate of SO2 when absorbed onto leaves?

A

Ready dissolution in intercellular water forming bisulfite, sulfite, and other ionic species.

35
Q

How are these metabolites phytotoxic?

A

They have lone pair of electrons on sulfur atom, favouring electron-deficient sites on molecules

36
Q

What happens when metabolites are oxidised?

A

Toxicity decreases by enzymes, metals, cytochrome oxidase, UV, and O3 stimulate oxidation.

37
Q

What enzymes catalyse this?

A

Sulfite oxidase enzymes containing a catalytic molybdenum cofactor, catalysing transfer of electrons from sulfite to O2, forming sulfate ions.

38
Q

How can metals oxidise them?

A

SO2 adsorb onto metal oxide particles, weakening the sulfur-oxygen bonds making them further susceptible to oxidation, where O2 reacts with it to form sulfur trioxide.

39
Q

How is plant metabolism impacted by SO2?

A

Foliar Cp concentration decrease, P metabolism stimulation, lipid biosynthesis inhibition in pine needles…

40
Q

What enzymes are impacted?

A

Alanine/aspartate aminotransferases, glutamate dehydrogenase, malate dehydrogenase, glycolate oxidate, GAH-3-P…

41
Q
A

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