Relying on the Kindness of Strangers

Last week I left Seattle on a ferry for a whirlwind tour of the Olympic Peninsula.

The first stop upon arrival in Port Townsend was this farmstand staffed by industrious hippy relics.

It's such a cool and cloudy climate that tender crops like cucumbers and tomatos are raised in protected tents.

Even these sheltered nasturtium leaves exhibit signs of chlorosis.

But the flowers are very pretty!

I have been puzzling over why the relatively pristine Pacific Northwest appears to have nearly as much damage on leaves from toxic greenhouse gases as those I find in much more severely polluted, industrial regions. These cucumber vines in the greenhouse are perfect examples.

I do not know the answer, but it occurred to me that although there is less pollution, perhaps it is held, suspended, in acid fog - thereby bathing foliage in toxins for longer periods of time - and so I looked it up on the marvelous intertubes.

I stumbled upon a blog written by a botany professor from India, Dr. Pradeep Garg, called Environment of Earth, with a wealth of information about the effects of acid rain, including wet and dry and fog deposition.

There doesn't appear to be anything added more recently than September 2009, and I cannot find any links to original research, or attributions to other supporting evidence for his statements.

Nevertheless his blog has become my bible of pollution effects on vegetation, and I'm going to post a number of excerpts along with some photos of the grand trees and spectacular scenery in the Olympic National Park and Hoh Forest.

But first I have to say thank you to my hosts, who I had never met before, but who overwhelmed me with their generous hospitality. Joan and Leif, THANK YOU!

While in Port Townsend, Leif offered his hand-crafted boat as home base, which was marvelous - I like nothing better than to wake up very early and see a harbor.

Leif built the Raven himself - and it is a miracle of ingenious design. Every nook and cranny serves multiple purposes and allows for a luxurious sense of spaciousness.

Each morning we had a scrumptious breakfast on the dock.

The locals roll in for coffee at 6 am. Every time somebody refills their own cup, they wander around the room, offering to pour for everyone else.

Nobody seemed to mind our disheveled, rumpled early morning arrival where we would wake up slowly, reading the funny bumpersticker wall, and checking the news on the laptop.

I would go back to Port Townsend in a heartbeat - if only just for the home-made hash browns with fried peppers, onions and mushrooms and cheese - and the best bacon I ever tasted.

The mornings start off cool and foggy. This eagle was a reliable guardian at the top of a post.

As the hours passed the fog usually burned off and we had sunny afternoons to explore the ancient woods.

THANK YOU Leif and Richard Pauli, wonderful companions who squired me around to a succession of locations each more magical than the one before...and helped me explore the myriad questions urgently raised by climate change, like - is it at all possible to address global warming without a concurrent, and radical, and likely impossible reorganization of society?

We stopped to admire the long boats of the First Nation people, some of them very old and carved from a single tree trunk.

Leif is very knowledgeable about the construction and has been on the annual canoe trip many times in the past.

We were never far from exquisite scenes of water.

Here is the world's largest spruce tree.

It is about 1,000 years old - 58'11" in circumference, 191 feet in height.

That's me, perched on the roots!

These pictures are only the most paltry homage to the staggeringly immense and complex density of these untouched virgin tracts.

The heights are dizzying.

There are almost 200 different types of epiphytes that are hosted by the trees, all tangled together in a majestic volley of symbiotic life.

They hang from branches and cling to bark.

This is my idea of a pagan cathedral and a unique natural museum, rolled into one.

It is like wandering through a living sculpture garden.

Every step reveals more fascinating formations.

The well-trodden paths led over footbridges above transparent streams that were home to brilliant green algae - and precisely reflected the azure blue sky.

Lichens add to the color palette.

Leif is doing an excellent gnome impersonation. The ferns are so ginormous they make him look as though he is far shorter than his 6 feet!

This copse of maples shrouded in mosses looked like the perfect set for a performance of A Midsummer Night's Dream.

The shades of green and textures of leaves, ferns, mosses and bark were incredibly lush,

and I will never forget how truly peaceful and quiet it was.

Here is Richard standing on a fallen trunk.

Fallen trees become home to younger trees that colonize the nurse logs, and remain arranged in long straight rows.

Trees continue to grow even when there is just a small fraction remaining.

Here a fallen giant dwarfs the staircase.

Leif brought us to a favorite, venerable specimen.

He is standing about 8 feet above ground level, on the gnarled roots.

The hollowed interior is large enough for several people to stand comfortably inside, and peer up to see light from the sky above.

The forest floor was a spongy peat, covered with ferns.

Lake Quinault is a famous destination.

We also stopped to explore the historic lodge at Lake Crescent, which is impeccably maintained, plus enchanting and romantic.

A particularly long moss hung from the branches of an alder tree,

which was also host to various intriguing lichens.

Alder trees have superbly mottled bark and look somewhat like birches.

Small cabins nestled in groves of enormous trees are available to rent.

People paddled on the waters - there were no motor boats to mar the silence.

We admired the crystal clarity and then resumed our treks through the woods.

Even though I was only here for a long weekend, I will remember it forever. It has been days since I left and I am still disoriented both from the intensity of being in a truly sacred place and the unusual experience of spending time in conversation with people who inhabit the same parallel universe that I do.

This specimen is particularly grand.

It is sometimes difficult to tell which parts are original tree and which are merged neighbors.

Unfortunately, the forest has far too many standing dead - in fact they are ubiquitous, as these photos will demonstrate. Even the National Park Tour Guide says: "Acid Rain and Fog generated in the Puget Sound area, and carried toward the park by winds, have caused high ozone levels at Mount Rainier." The foresters are, of course, studying the situation. Following are several samples interspersed with italicized notes from Dr. Garg's blog (...of course Blogger detests cut and paste so some of the passages will be garbled...).

Acid rains, acid fog and acid mist cause quite serious damages to natural and man-made things.

Effects on terrestrial ecosystems

Acid deposition on land affects the forests and crops directly as well as indirectly through alteration of the chemistry and microbiology of soil. Though effects of acid deposition on crops have important economic consequences, the effects on forests have been very dramatic and ecologically damaging. However, the study of the effects of acid deposition on land is a very complex problem because of the following two factors:

1. There is a very wide range and large number of possible interactions between atmosphere, soil and plants in terrestrial ecosystems.

2. Effects of acid deposition on soil and vegetation take very long time (decades in case of trees) to reach detectable levels.

Despite the constraints mentioned above, studies have yielded much information about the effects of acid rains on various aspects of terrestrial ecosystems. These may be categorized as following:

Effects on soil chemistry: Following acid deposition, a series of complex chemical reactions take place in the soil. General consequences of these reactions are:

1. Increasing nutrient deficiency in the soil: In the acidified soil, basic cations are replaced by hydrogen and aluminium ions. These liberated cations are rapidly leached down and out of the soil solution alongwith sulphate from the acid input. Basic cations are essential plant nutrients, particularly the K⁺, Na⁺, Ca²⁺ and Mg²⁺ which are taken up by plants from the soil in quite large amounts (macronutrients). Loss of essential nutrient cations from the soil adversely affects the plant growth. Poorly buffered soils are highly susceptible to acid-induced nutrient deficiency e.g. soils of Swedish forests have shown progressively decreasing levels of K⁺, Na⁺, Ca²⁺and Mg²⁺ over a ten-year period of acid deposition. Replacement of nutrient cations by hydrogen and aluminium ions further increases the soil acidity. Setting up a vicious cycle.

Mobilization and increase in heavy metal content of soil: Increase in soil acidity is often associated with increased soil concentration of toxic heavy metals. Most common such heavy metals are Al, Cd, Mn, Hg, Pb, Fe and Zn. In the soil of normal pH, these metals remain chemically ‘bound up’ in the soil. However, acidic pH of soil frees these metals and the mobilized metals can now rapidly spread throughout the soil alongwith natural flow of soil water.

1. Damage to mineral structure of soil:Soil acidification also increases the weathering of silicate minerals during liberation of metals and thus causes loss of mineral structure of the soil.

Effects on soil microbes: Acid deposition on land results in acidification of soil which causes damage to various decomposing bacterial and fungal populations in the soil. As a result, rate of decomposition of organic matter is slowed down and, therefore, the nutrient recycling in the ecosystem is blocked. Since return of essential nutrients back to the soil is blocked, the soil progressively becomes impoverished. Experimental studies have shown that soil acidity strongly reduces the decomposition of the litter of pine, spruce, birch and other cellulose-rich materials. Such reduction in decomposition of organic matter also results in reduced respiration of soil microbes including nitrogen-fixing bacteria and blue-green algae. This increases the levels of ammonia in the soil due to reduced mobilization of nutrients previously released by decomposition and the soil nitrate levels are considerably reduced due to ammonification. Such changes in the soil having pH below 3.0 bring about marked changes in the population sizes and species composition of soil microbes. For example, total abundance of acid-sensitive enchytraeids decreases and that of tolerant springtails increases. Further, soil acidification causes significant damage to other soil fauna also, particularly the earthworms. Reduced earthworm population markedly alters the soil structure and consequently the soil productivity is reduced.

One morning we stopped at Ruby Beach when it was still shrouded in mist.

Some of the bleached logs lying on the sand are escapees from logging operations.

Whether there should be so many I cannot say - but one passer-by said he had never seen so many piles before.

Here are more effects of acid rain from Dr. Garg:

Effects on terrestrial plants and ecosystem:

Effects on higher plants

All types of plants are adversely affected by acid rain and the damage is caused in two ways; firstly through shoot system, particularly the foliage which are directly exposed to acid rain, acid fog or acid mist and secondly through root system via deficiency of soil nutrients and toxicity of heavy metals in the acidified soil. Visible symptoms in plants can assume various forms depending on the character and level of acid deposition and the buffer capacity of the soil. The symptoms also vary between species and with the age of plant and tissue. Younger tissues and young plants are generally more susceptible to acid rain damage. In general, acid rain damage in plants is manifested as reduced plant growth and hence decline in yields, reduced canopy cover, reduced reproductive capacity etc.

1. Increased susceptibility to pathogens: Acid rains damage the surface cuticle of leaves and other plant organs and thereby make the plant more susceptible to attack by pathogenic fungi and bacteria which can now enter through the damaged surface.

2. Reduced growth: As discussed above, increasing soil acidity result in decreased availability of essential plant nutrients in the soil due to decreased nutrient cycling. Further, high aluminium released in soil following soil acidification has been reported to damage root hairs and thus adversely affect nutrient uptake. As a result of these, plants growing in land areas affected by acid deposition generally show poor growth. The availability of nutrients to the trees and other plants is also influenced by the exchange processes that take place on the surface of leaves. Ammonia and nitrogen landing on the leaf surface via acid deposition pass through the semi-permeable membranes of epidermal cells of leaves and are incorporated into the leaf tissue. This results in cation exchange in leaf tissues and the abundant plant nutrients present in leaf tissues such as K, Ca, Mg and S are leached and washed off the leaf surface. This foliar leaching due to acid deposition also causes depletion of essential plant nutrients and, therefore, reduced plant growth.

Foliar injury: Various visible leaf injury symptoms develop in leaves of plants growing in areas affected by acid rains. In general, visible leaf injury symptoms depend on the density of trichomes and stomata. Due to plasmolysis of palisade cells in leaves, structural damage in chloroplasts are common. In leaves of several species galls are produced in response to acid deposition.

Trees are falling over above the sand - and not just old trees at the end of their natural longevity.

The tips of evergreens are burnt in classic symptom of exposure to toxins, whether via fog, rain, dry deposition, or atmospheric.

From Dr. Garg:

Reduction in symbiotic balances: In the plants growing in land areas affected by acid deposition, formation of root nodules is drastically reduced and other symbiotic associations like ectotrophic and endotrophic mycorrhizae are also adversely affected.

Foliage is not as uniformly damaged as that of New Jersey - but samples are readily detected in any location.

Reduction in reproductive capacity: Decrease in flowering, reduced pollen germination, inhibition of pollen tube growth and inhibition of seed germination has been reported due to acid rains. In Norway spruce, Scots pine and Silver birth, seed germination is inhibited between pH 3.8 and 5.4. In these plants initial establishment of seedling is highly sensitive to soil pH and rapidly decreases below pH 4.2. All these effects of acid rains ultimately result in reduced reproductive success of the affected plants and, therefore, in reduced population size of the affected sensitive species. With gradual decrease in reproductive potential of affected species, the tolerant species gain upper hand and due to better reproductive success, gradually spread in the area.

Effects on forests:

Damage to forests due to acid rains is a complex problem. The available evidence suggests that the damage is caused due to a combination of a variety of contributory factors in addition to acid deposition. Such factors include dry deposition of the oxides of sulphur and nitrogen, ozone, heavy metal content of soil, parasites and plant diseases, extreme climatic conditions like very high or very low rainfall and temperature extremes (particularly frost), site factors e.g. soil drainage, soil characteristics, general state of health and age of trees, surge of naturally produced acids, acid flushes (e.g. during spring snow-melt or after prolonged draught) and forest management practices.

Such factors also contribute to damages to crops caused by acid rains. Ozone has been found to increase the vulnerability of trees to acid-induced damage by increasing their susceptibility to poisoning and nutrient loss. Ozone might play significant role at high altitudes where sunshine required for photo-chemical production of ozone is more intense.

Vegetation above 10,000 ft. line in West Germany shows many damaged trees. Much of the damage to vegetation remains undetected until it reaches a critical, perhaps irreversible stage. Species of coniferous and deciduous trees generally exhibit much genetic variability in their populations due to which all the individuals of a species do not show equal sensitivity to acid rains. Such variability is particularly marked in Scots pine and Norway spruce.

Further, different species in a forest have different dose-response relationship. All these factors make generalizations about the acid-rain induced damage to forests quite different. However, most evident effects of acid rains on forests have been observed in the form of Crown-dieback and Waldsterben.

Crown-dieback: In forest systems, damage to trees which is most extensive in West Germany, is spreading alarmingly throughout Europe and is gradually building up in U.S.A. and Canada. Visible damage tends to be concentrated in older and established trees and appears to be species-specific. Scots pine is the most sensitive species in which needles become shorter, duration of needles on the tree decreases from three to one year, top buds dry, annual growth of shoot decreases and shape of crown changes. Damaged conifers, in general, show yellowing of needles, loss of needles, distortion of branches, thinning of tree tops, injuries in bark, changes in trunks and damage to fine roots. In deciduous trees, main symptoms include discolouration of deformation of leaves, early shedding of leaves, bark injuries, death of tree tops and lack of natural regeneration. In extreme condition of damage, tree tops in all types of trees die earlier than the branches further downwards. This condition has been termed crown die-back.


Waldsterben: In 1980s, German scientists first observed the wasting disease of trees attributed to acid rains and termed it waldsterben which literally means ‘death of trees’ or ‘dying tree syndrome’ that blighted trees and forests. The extent and rate of spread of such damage is quite alarming in industrialized countries. By 1985 about 52% forest area was affected in West Germany and about 86% of woodland in East Germany showed such damage. The damage has also been found in forest of France, Switzerland, Sweden, Italy, Hungary, Poland, Czechoslowakia, Russia, U.K. Canada and U.S.A. Tree death occurs within five weeks of the appearance of first symptoms. Further, waldsterben affects young saplings as well as mature trees. In forests of areas affected by acid rains, first signs of damage were reported in Abies alba in early 1970s and in Picea abies by late 1970s. Pinus sylvestris and Fagus sylvetica were affected by early 1980s and the damage spread to other species like larch, red oak, maple, ash and rowan showing that disease affects almost all tree species. Greatest absolute damage was found in spruce and greatest relative damage occurred in silver fir in which over 87% of the trees were damaged. Three stages have been identified in this damage process:

1. Nitrates or nitrogen oxide in the acid rain initially provide soil nutrients and the trees grow more rapidly.

2. In next stage, soil progressively loses the ability to neutralize the increased acidity and the acids begin to accumulate and cause leaching of nutrient cations leading to slowing down of tree growth and yellowing or discolouration of needles or leaves. Sulphate combines with metals in soil and increases heavy metal concentration in the soil.

3. In the last stage, toxic aluminium is released at pH 4.2 leading to destruction of tree roots and deterioration of natural defense mechanisms of trees that prevent the entry of pathogenic bacteria, fungi and viruses. The trees thus gradually die due to nutrient deficiency, heavy metal toxicity and various pathogenic diseases.

I learned that clear-cutting in and of itself will drastically and irrevocably damage forests, even absent the slow poisoning from pollution.

It stands to reason that young trees whether planted as replacements, or spontaneously sprouting, will be subjected to very different conditions of light and moisture than the environment under a mature canopy in which they have evolved to thrive.

I call these views the Killing Fields.

If you allow the full horror to penetrate, it is quite unbearable.

Foxglove spring up in the barren wasteland the loggers leave behind.

But even their leaves have the common symptoms of exposure to toxic greenhouse gases.

At this port a huge ship stands ready to take the timber away - probably to Japan.

The Hoh River is a joyous torrent,

But the banks are lined with dead trees.

The steep inclines above are covered with trees that will be tumbling down as well, sooner or later.

There is no natural reason for so many trees to die.

We saw another bald eagle on our journey, but on the whole, very few birds or other wild creatures.

I expect there is little for them to eat.

When we stopped at a roadside cafe, the birch across the street were bare of leaves.

The potted flowers had leaves lacking chlorophyll, like this columbine.

The hydrangea flowers were luminous but the leaves were turning black.

Our last expedition before leaving Port Townsend was a guided tour by Joan and Leif, of a former military installation which is now a delightful park.

The bunkers were so well concealed that they were't visible from looking at the hill where they were installed.

But the interiors were vast echoing caverns.

I liked the pattern of this decrepit linoleum remaining on the floor.

The surrounding slopes have a disturbing percentage of bare trees.

The woods won't last very long at this rate of decline.

A yellow flower clinging tenaciously to life in a crack of the concrete is a hopeful sign - if only people would pay attention to our collapsing biosphere before it is too late to halt!

In any event, I am so grateful that I was able to journey to this wonderful place where the trees have never been cut.

And I am especially happy to have made the acquaintance of such marvelous and sympathetic friends as Leif, an unrepentant optimist

and Richard Pauli, a stalwart ally in the epic struggle to save the trees - and our own species from self-destruction.

Following are other passages from Dr. Garg that I think are important - there is far more on his blog, especially technical discussions that are beyond my ability to comprehend:

1. There is a very wide range and large number of possible interactions between atmosphere, soil and plants in terrestrial ecosystems.

2. Effects of acid deposition on soil and vegetation take very long time (decades in case of trees) to reach detectable levels.

   Reduction in symbiotic balances: In the plants growing in land areas affected by acid deposition, formation of root nodules is drastically reduced and other symbiotic associations like ectotrophic and endotrophic mycorrhizae are also adversely affected.

1. Effects on ecosystem

   Among terrestrial plants, the sequence of the sensitivity to acid rains is herbaceous dicots> woody dicots>monocots>conifers. The acid rain induced damage to trees, which are most important primary produces in the terrestrial ecosystems, reduces the food availability to animals in higher trophic levels. As a result, the population sizes of various animal species is adversely affected. In general, acid rains result in changes in relative abundance of populations in all the trophic levels and also the reduced species diversity of terrestrial ecosystems. In all the trophic levels, sensitive species are gradually eliminated and are replaced by tolerant species.

   The acid rains is caused by emission of large quantities of sulphur dioxide and oxides of nitrogen in the atmosphere due to burning of fossil fuel in various industrial and other activities of human beings. Allied to acid rains are phenomena of acid mist and acid fog, both of which come under the category of occult precipitation. The cause of acid mist or acid fog is high concentration of sulphates and nitrates in the form of fine aerosol particles (dust or soot) in wind-driven ground-level clouds which causes condensation of tiny water droplets around these particles. These droplets being tiny fraction of normal rain drops, do not fall as rain water but remain suspended in the atmosphere forming acid mist or acid fog.

2. The problem of acid rain has attracted worldwide attention only since 1980s. However, the term ‘acid rain’ was first used by first Alkali Inspector of Britain,, Robert Angus in 1872. His work largely remained ignored until 1950s when Canadian ecologist Dr. Eville Gorham undertook detailed studies of rainwater quality and its control in Lake District in north-west England. By mid 1960s, early damage symptoms of acid rains begun to appear in Scandinavia and Swedish worker Svente Oden begain a concerted scientific effort in 1967 to bring awareness about acid rain problem. He is considered to be the father of modern acid rain studies.

   GEOGRAPHY OF ACID RAIN

   Primary pollutants causing acid rain problem are blown over long distances by the wind and thus spreading the problem over whole of the Earth’s surface. However, till now most of pollutants responsible for acid rain problem are produced in the highly industrialized nations, the areas of the impact of acid rains are few, noticeable, few and predictable. Common properties observed in areas affected seriously by acid rain problem are:

   1. Heavy concentration of industries producing pollutants responsible for acid rain problem.

   2. Downwards flow of winds from pollutant-producing areas.

   3. Upland-mountainous position of pollutant-producing areas having thin glaciated bedrock and high rainfall-snowfall.

   4. Numerous lakes and streams and rich forest cover in pollutant-producing area.

   Areas sharing the above common properties are termed acid rain hot spots and include many parts of Scandinavia, upland Britain, West Germany and many parts of Northern Europe. Across Atlantic, such areas include Nova Scotia, Canadian Shield around southern Ontario and Quebec, Adriaondack Mountains, Great Smoky Mountains, parts of Wisconsin and Minnesota, Pacific Northwest U.S.A., Colorado Rockies and Pine Barrens of New Jersey. Japanese islands are also included in this category.

   Areas having severest acid rain damage are glaciated Pre-Cambrian shield areas of Scandinavia, glaciated parts of upland Britain having thin soils, eastern Canada and resistant Canadian Shield and northwest U.S.A. Problems of acidification develop much acutely on granite and similar other resistant rocks.

   Acid rain as global problem

   Though at present acid rain problem is mainly concentrated in highly industrialized areas, the long-range transport of concerned air pollutants results in gradual globalization of the problem. As a result of slow transport of acid rain causing pollutants from heavily industrialized areas to areas till now free from this problem, the latter areas are also beginning to show acidification damage. Such damage has been reported from many developing nations like Zambia, South Africa, Malaysia, Venezuela, India and China. Most productive farmlands of China and India, paddy fields of South-east Asia and forests of Amazon in South America have soils which are highly susceptible to acidification.

   Global dimension of acid rain problem was established beyond doubt in 1981 with discovery of Arctic haze. It is bluish-gray haze developing in Arctic areas similar to that frequently found over and downwind of large industrial areas in western Europe and eastern North America. Haze layers often cover a horizontal area of upto 1000 km and are caused by scattering of solar radiation by minute suspended particles in the atmosphere. These particles vary in the size range of 0.1-1.0 micrometer and mostly comprise of sulphate aerosols. These aerosols are transported by jet streams in upper atmosphere and may reach upto 8000 km away from their industrial sources. Hazes are found to be thickest in Alaska’s North Slope extending atleast to Norway. Hazes mainly affect visibility and are not as damaging as the smog.

   CAUSE AND FORMATION OF ACID RAIN

   SO₂ and oxides of nitrogen (NO_x) emitted into the atmosphere due to industrial, commercial and other anthropogenic activities are the basic cause of acid rain formation. Therefore, the problem of acid rains has accompanied the rise of emission of these gases into the atmosphere.

   SO₂ is emitted from three principal man-made sources:

   1. Combustion of coal produces about 60% of total SO2 emitted into atmosphere.

   2. Combustion of petroleum products which adds 30% of total emission.

   3. Industrial activities like smelting of iron, zinc, nickel, copper ores, manufacture of sulphuric acid and operation of acid concentrators in petroleum industry. These produce the remaining 10% of this gas.

   Overall emission of oxides of nitrogen is small in comparison with SO₂, their importance in formation of acid rains is very high. Most of the oxides of nitrogen (NO₃, NO₂, NO etc.) are produced from:

   1. Combustion of fossil fuels.

   2. Industrial chimneys and thermal power stations.

   3. Motor vehicles in urban areas.

   Man-made sources of SO₂ and NO_x emission are point sources (e.g. thermal power stations and industrial chimneys) and the emission from these occurs as a plume of gases. The plume of gases emitted from high stacks usually travels downwind for about 12 km as a straight line without much dispersion. Afterwards, its shape evolves by diffusion and changes progressively downwind into a widening cone. The direction, speed, distance of travel of the plume and its dispersal and diffusion depend upon meteorological conditions such as direction, velocity and pattern of propelling wind, air temperature (especially the vertical temperature gradient), air turbulence and atmospheric stability. Under stable atmospheric conditions, for example, at night over land and during day over snow covered ground, there is very little vertical dispersal for very long distance and the acidification may occur at quite far away place from the source of emission.

   Dispersal of the plume of SO₂ and NO_x occurs in the mixing layer of atmosphere that extends from ground level upto 1-2 km altitude. The dispersal is triggered by diffusion and atmospheric turbulence, normally between 5 to 25 km from the point of source. The rate of diffusion and mixing of oxides into air is faster when flow of air is turbulent. The lower portion of the dispersing cone of oxide plume first touches the ground level at about 5 km distance form the point source while middle and upper portions are thoroughly dispersed in the air leading to dilution and chemical transformation.

   The deposition of pollutant oxides from the plume onto the ground is of two types: dry deposition and wet deposition.

   1. Dry deposition: The acidic oxides deposited from the bottom of the plume between 5-25 km from the source in the form of gases and particles constitute the dry deposition. Though such deposition is not acid rain in strict sense, it produces acidification of soils and surface water bodies similar to acid rain. This dry deposition also causes direct SO₂ and NO_xpoisoning of the vegetation. Dry deposition of sulphur and nitrogen oxides and undissolved acids on lakes and steams straightaway dissolve in the water and acidify the water bodies. Such dry deposition on land and on vegetation remains inactive till dew or rainfall when these dry deposited acids dissolve in the dew or rain water and form active acids. Such sudden addition of high concentration of acids into an otherwise stable environment causes acid shocks, acid flushes or acid surges. These terms indicate increasing levels of acidification and decreasing time period in which such acidification takes place. During winters, SO₂ and NO_x pollutants are dry-deposited on snow and ice in the catchment areas of many lakes and rivers. In the following spring season, when this snow and ice melt, the acids accumulated in the snow and ice over long period are suddenly released over a period of few days to a week causing acid surges in the lakes and streams.

   2. Wet deposition: It is the deposition of acidic oxides of the plume over land or vegetation after being dissolved in the rainwater, snow or ice forming acid rains, acid snow, acid mistor acid fog. Today’s industrial chimneys are normally 100-300 meters high and, therefore, such wet deposition normally occurs beyond 25 km from the point source. The prevailing wind pattern and the length of time over which oxides are transported in the wind system is of great importance in the geographical distribution of acid rains. Longer the SO₂ and NO_xremain in the atmosphere, greater is the possibility of their transformation to produce sulphuric and nitric acids.

   The practice of increasing the height of chimneys and installation of electrostatic precipitators to reduce the air pollution appears to have magnified the problem of acid deposition in two ways. Firstly, tall stacks of pollutant-emitting units now emit pollutant gases at much greater heights so that these gases are now dispersed over much wider areas increasing the geographical extent of acid deposition. Secondly, installation of electrostatic precipitators and other mechanisms to remove alkaline particulates in chimneys has resulted in increased emission of acidic gases. It is because prior to installation of such mechanisms, acidic gases were neutralized to a large extent by alkaline particulates being emitted alongwith them.

   The complex pattern of acid deposition has following six stages:

   1. The atmosphere receives SO₂and NO_x from natural and man-made sources.

   2. Some of these oxides fall on the ground as dry deposition within 5-25 km from their parent sources.

   3. Formation of photo-oxidants like ozone, is stimulated in the atmosphere.

   4. The photo-oxidants interact with SO₂ and NO_x to produce acids (H₂SO₄ and HNO₃) by oxidation.

   5. The oxides of sulphur and nitrogen, photo-oxidants and other gases (including NH₃) dissolve in the cloud and rain-droplets to produce acids (H⁺and NH4⁺) and sulphates (SO₄^2-) and nitrates (NO₃^-).

   6. Acid rain containing ions of sulphate, nitrate ammonium and hydrogen falls as wet deposition.

   The most important step in this chain of reactions is the catalytic conversion of SO₂ and NO_x. This may take from a few hours to a few days in the atmosphere and can not occur without photo-oxidants (precurssors). Ozone is the most readily available and abundant photo-oxidant in the atmosphere . Hydrocarbons and NO added to the atmosphere as pollutants are the two main precurssors of ozone. The acid rain is the final product of the loading of SO₂ and NO_x coupled with photochemistry and physical dynamics of stratosphere.

   Chemistry of acid fog

   More recently, measurements at sites in parts of Europe, California and eastern U.S.A. have shown that in most circumstances, acid fog and water in low clouds has a lower pH value than equivalent acidic rainwater. Average pH values of acid fog in areas of heavy air pollution are about 3.4 and range from 2.8 to over 5.0 On average, mean concentrations of H+ and acid ions are 3 to 7 times higher in fog-water than in equivalent rainwater. Acid fog-water also has higher concentration of anions and cations. There are following five main reasons for the above describe differences:

   Fog being located nearer to the ground, is often exposed to higher pollutant concentrations for longer periods of time than the rainwater during below-cloud scavenging. This exposure allows more time for extensive aqueous-phase chemical processes to take place.

   Smaller fog and mist particles saturate with gaseous pollutants more quickly than the larger raindrops, allowing greater aqueous ion production.

   The smaller droplets in fog and mist have a greater combined surface area compared to raindrops. As a result, acid gas diffusion is enhanced and higher concentrations of the resultant ions are produced.

   The fog remains in the air mass in which it is formed while precipitation is often associated with changing air masses in frontal situations when much of the gaseous and aerosol material in the atmosphere is removed.

   Pollutant aerosols originating several hundred kilometers away often act as nuclei for fog or cloud droplets and enhance aqueous chemical processes. The size and number of water droplets formed and the resultant chemistry depend on the number of aerosol nuclei available in the cloud. Greater number of these generally produce smaller and more numerous fog droplets. Ion concentrations in mist tend to be lower than in fog because mist contains a lesser number of droplets and this limits the chemical reactions.

   However, fog-water shows wide variations in ion concentrations between sites and events. In stable atmosphere, low altitude fog masses are more likely to interact with pollutant emissions near the surface e.g. NO_x from automobiles. On the other hand, mountain fogs occurring in a well mixed atmosphere and at times, isolated from low-altitude pollutant emissions due to inversions, tend to be cleaner having pH values of 5.0 and above. On minor scale, dew from polluted atmosphere can also be acidic with free H+ comprising about 80% of acidity while species of sulphur and nitrogen may contribute about 60% and 30% respectively to the acidity.

   On this page:

   In conditions of sufficient moisture, two climatic factors i.e. photosynthetically active radiation and temperature are particularly important in relation to productivity of plant cover.

   The influence of radiation and temperature on productivity of plant cover is quite complex. In real natural situations, radiation is always a factor whose value is a ‘minimum’ because radiation available to leaves in lower layers of canopy is always insufficient. Therefore, increase in radiation flux always results in increased productivity of plant cover.

   With increase in temperature, the productivity of plant cover increases initially. After attaining a certain maximum value that depends on the value of radiation flux, productivity begins to decrease with further increase in temperature. Thus productivity of plant cover substantially decreases above a certain threshold value of temperature which is determined by the radiation flux.

   And on this page:

   Plants can effectively be used as cheap and naturally available monitoring systems or bioassays of the level and type of air, soil and water pollution in an area. The type and concentration of a pollutant can be reliably found out by various characteristics damage symptoms produced in the plants because such damage symptoms are pollutant specific as well as concentration specific. For example, in young needles of Pinus, chlorois indicates SO₂pollution, necrosis indicates HF pollution, beaching indicates NO₂ pollution while chlorotic mottle indicates Cl₂pollution in the atmosphere. These characteristic symptoms of damage in young pine needles appear only when concentration is 0.3 ppm for SO₂, 0.07 ppm for HF and 1.0 ppm for Cl₂. Similarly, browning in moss leaves due to fluoride accumulation is 5% in 65 ppm dry weight accumulation but rises to 90% in 4500 ppm dry weight accumulation. However, certain precautions have to be taken while using plants as pollution indicators...

   
   

   Leaves of sensitive species generally produce highly specific and characteristic visible injury symptoms in response to pollutants. The study of such symptoms can reliably indicate the type and level of pollutant(s) present in the environment. For such analysis, leaves of same age are collected at same time of the day and at different localities in the area from plants of a particular sensitive species. Most common symptoms studied are chlorosis, necrosis, discolouration, tip-burn, bleaching, bronzing, stipples and mottles in the leaves. Characteristic colours and patterns of these symptoms in particular plant species indicate the type and level of pollutant present.

   
   

   I also recommend this comprehensive section on the chemical formation of tropospheric ozone.

   On another note, following is an exchange of comments on the ClimateProgress post, "Obama's Failed Presidency" (wahhhhhhh!)

   Remember the outrage on the left when Obama reneged on his promise to expose and prosecute the torturers? Why did he do that? Probably because AFTER he came into office, he found out just how bad the evidence was – so bad that revealing it in trials would incite all sorts of attacks on Americans, for which he would be blamed, and his presidency would end in impeachment.

   What do you suppose he has learned about climate change since he came into office? If anybody in the military or in the Department of Agriculture has told him the truth, he knows something everybody who reads Climate Progress knows but doesn’t like to confront – we’re already screwed. There is enough heating in the pipeline to turn the vast majority of the Earth uninhabitable through desertification and rising seas. The carbon sinks are finished, the food chain in the oceans is collapsing – so the climate bill is irrelevant – Obama’s desk is crowded with issues like climate refugees, the breakdown of civil society, violent weather events creating disasters of one sort or another, massive, widespread crop failure, and resource wars

   #77 Wit’sEnd

   I have to agree here. When Obama came to office I’m sure he was presented with a list of the facts beyond the secret codes, Area 51, where Jimmy Hoffa was really buried and other such assumed conspiracy nonsense.

   In the case of climate change it may be just a matter of triage. Was the real truth finally exposed, that it’s beyond any one nation’s ability to control climate change. That we are in reality past the point of no return? That we may have just simply run out of time? After all he has all the best information and the brightest minds on the planet to present it to him. If so, it makes sense, why expend the effort at the sacrifice to solutions for other short term programs and problems that will make people feel good and have the possibility to be realized.

   Thanks Lore. I think above all he and those privy in his administration have as top priority – avert panic, or at least avoid it for as long as possible. Plain talk and the unvarnished truth could quickly lead to hysteria. The same is true for the economy. Our capitalistic system is unsustainable, no matter how much bank reform is legislated, but it would be political suicide to say so.

   The best case is that after one or two Pearl Harbor events, people go through the huge emotional discombobulations that accompany climate enlightenment – and still have enough trust in Obama to take the drastic steps necessary to salvage some semblance of civilization – that is going to include draconian rationing of water, fuel, food and some very restrictive emergency limits on the kind of freedoms we are used to.