Wednesday, December 11, 2019
04:55 AM (GMT +5)

Go Back   CSS Forums > CSS Compulsory Subjects > General Science & Ability > General Science Notes

Reply Share Thread: Submit Thread to Facebook Facebook     Submit Thread to Twitter Twitter     Submit Thread to Google+ Google+    
 
LinkBack Thread Tools Search this Thread
  #1  
Old Sunday, December 17, 2006
Qurratulain's Avatar
Economist In Equilibrium
Medal of Appreciation: Awarded to appreciate member's contribution on forum. (Academic and professional achievements do not make you eligible for this medal) - Issue reason: she won the Essay competitionBest Moderator Award: Awarded for censoring all swearing and keeping posts in order. - Issue reason: Best ModMember of the Year: Awarded to those community members who have made invaluable contributions to the Community in the particular year - Issue reason: For the year 2006
 
Join Date: Feb 2006
Location: The Devil's Paradise
Posts: 1,742
Thanks: 118
Thanked 402 Times in 145 Posts
Qurratulain has a spectacular aura aboutQurratulain has a spectacular aura aboutQurratulain has a spectacular aura about
Default Acid Rain

Acid rain


Precipitation that incorporates anthropogenic acids and acidic materials. The deposition of acidic materials on the Earth's surface occurs in both wet and dry forms as rain, snow, fog, dry particles, and gases. Although 30% or more of the total deposition may be dry, very little information that is specific to this dry form is available. In contrast, there is a large and expanding body of information related to the wet form: acid rain or acid precipitation. Acid precipitation, strictly defined, contains a greater concentration of hydrogen (H+) than of hydroxyl (OH?) ions, resulting in a solution pH less than 7. Under this definition, nearly all precipitation is acidic. The phenomenon of acid deposition, however, is generally regarded as being anthropogenic, that is, resulting from human activity.

Theoretically, the natural acidity of precipitation corresponds to a pH of 5.6, which represents the pH of pure water in equilibrium with atmospheric concentrations of carbon dioxide. Atmospheric moisture, however, is not pure, and its interaction with ammonia, oxides of nitrogen and sulfur, and windblown dust results in a pH between 4.9 and 6.5 for most “natural” precipitation. The distribution and magnitude of precipitation pH in the United States (illustration) suggest the impact of anthropogenic rather than natural causes. The areas of highest precipitation acidity (lowest pH) correspond to areas within and downwind of heavy industrialization and urbanization where emissions of sulfur and nitrogen oxides are high. It is with these emissions that the most acidic precipitation is thought to originate.

Source:Science & Technology Encyclopedia
__________________
||||||||||||||||||||50% Complete
Reply With Quote
  #2  
Old Sunday, December 17, 2006
Qurratulain's Avatar
Economist In Equilibrium
Medal of Appreciation: Awarded to appreciate member's contribution on forum. (Academic and professional achievements do not make you eligible for this medal) - Issue reason: she won the Essay competitionBest Moderator Award: Awarded for censoring all swearing and keeping posts in order. - Issue reason: Best ModMember of the Year: Awarded to those community members who have made invaluable contributions to the Community in the particular year - Issue reason: For the year 2006
 
Join Date: Feb 2006
Location: The Devil's Paradise
Posts: 1,742
Thanks: 118
Thanked 402 Times in 145 Posts
Qurratulain has a spectacular aura aboutQurratulain has a spectacular aura aboutQurratulain has a spectacular aura about
Default

Distribution of rainfall pH in the eastern United States
Attached Images
File Type: gif CE004760FG0010.gif (16.7 KB, 304 views)
__________________
||||||||||||||||||||50% Complete
Reply With Quote
  #3  
Old Sunday, December 17, 2006
Qurratulain's Avatar
Economist In Equilibrium
Medal of Appreciation: Awarded to appreciate member's contribution on forum. (Academic and professional achievements do not make you eligible for this medal) - Issue reason: she won the Essay competitionBest Moderator Award: Awarded for censoring all swearing and keeping posts in order. - Issue reason: Best ModMember of the Year: Awarded to those community members who have made invaluable contributions to the Community in the particular year - Issue reason: For the year 2006
 
Join Date: Feb 2006
Location: The Devil's Paradise
Posts: 1,742
Thanks: 118
Thanked 402 Times in 145 Posts
Qurratulain has a spectacular aura aboutQurratulain has a spectacular aura aboutQurratulain has a spectacular aura about
Default

The transport of acidic substances and their precursors, chemical reactions, and deposition are controlled by atmospheric processes. In general, it is convenient to distinguish between physical and chemical processes, but it must be realized that both types may be operating simultaneously in complicated and interdependent ways. The physical processes of transport by atmospheric winds and the formation of clouds and precipitation strongly influence the patterns and rates of acidic deposition, while chemical reactions govern the forms of the compounds deposited.

There are a number of chemical pathways by which the primary pollutants, sulfur dioxide (SO2) from industry, nitric oxide (NO) from both industry and automobiles, and reactive hydrocarbons mostly from trees, are transformed into acid-producing compounds. Some of these pathways exist solely in the gas phase, while others involve the aqueous phase afforded by the cloud and precipitation. As a general rule, the volatile primary pollutants must first be oxidized to more stable compounds before they are efficiently removed from the atmosphere. Ironically, the most effective oxidizing agents, hydrogen peroxide (H2O2) and ozone (O3), arise from photochemical reactions involving the primary pollutants themselves.

The effect of acid deposition on a particular ecosystem depends largely on its acid sensitivity, its acid neutralization capability, the concentration and composition of acid reaction products, and the amount of acid added to the system. As an example, the major factors influencing the impact of acidic deposition on lakes and streams are (1) the amount of acid deposited; (2) the pathway and travel time from the point of deposition to the lake or stream; (3) the buffering characteristics of the soil through which the acidic solution moves; (4) the nature and amount of acid reaction products in soil drainage and from sediments; and (5) the buffering capacity of the lake or stream.

Acid precipitation may injure trees directly or indirectly through the soil. Foliar effects have been studied extensively, and it is generally accepted that visible damage occurs only after prolonged exposure to precipitation of pH 3 or less (for example, acid fog or clouds). Measurable effects on forest ecosystems will then more likely result indirectly through soil processes than directly through exposure of the forest canopy. Many important declines in the condition of forest trees have been reported in Europe and North America during the period of increasing precipitation acidity. These cases include injury to white pine in the eastern United States, red spruce in the Appalachian Mountains of eastern North America, and many economically important species in central Europe. Since forest trees are continuously stressed by competition for light, water, and nutrients; by disease organisms; by extremes in climate; and by atmospheric pollutants, establishing acid deposition as the cause of these declines is made more difficult. Each of these sources of stress, singly or in combination, produces similar injury. However, a large body of information indicates that accelerated soil acidification resulting from acid deposition is an important predisposing stress that in combination with other stresses has resulted in increased decline and mortality of sensitive tree species and widespread reduction in tree growth.

Acidic deposition impacts aquatic ecosystems by harming individual organisms and by disrupting flows of energy and materials through the ecosystem. The effect of acid deposition is commonly assessed by studying aquatic invertebrates and fish. Aquatic invertebrates live in the sediments of lakes and streams and are vitally important to the cycling of energy and material in aquatic ecosystems. These small organisms break down large particulate organic matter for further degradation by microorganisms, and they are an important food source for fish, aquatic birds, and predatory invertebrates.

Currently, there are concerns that acid deposition is causing the loss of fish species, through physiological damage and by reproductive impairment. While fish die from acidification, their numbers and diversity are more likely to decline from a failure to reproduce.The effects of acid deposition on individuals in turn elicit changes in the composition and abundance of communities of aquatic organisms. The degree of change depends on the severity of acidification, and the interaction of other factors, such as metal concentrations and the buffering capacity of the water. The pattern most characteristic of aquatic communities in acidified waters is a loss of species diversity, and an increase in the abundance of a few, acid-tolerant taxa.

Community-level effects may occur indirectly, as a result of changes in the food supply and in predator-prey relations. Reduction in the quality and amount of periphyton may decrease the number of herbivorous invertebrates, which may in turn reduce the number of organisms (predatory invertebrates and fish) that feed upon herbivorous invertebrates. The disappearance of fish may result in profound changes in plant and invertebrate communities. Dominant fish species function as keystone predators, controlling the size distribution, diversity, and numbers of invertebrates. Their reduction alters the interaction within and among different levels of the food web and the stability of the ecosystem as a whole.

The impact of acid deposition on terrestrial and aquatic ecosystems is not uniform. While increases in acid deposition may stress some ecosystems and reduce their stability and productivity, others may be unaffected. The degree and nature of the impact depend on the acid input load, organismal susceptibility, and buffering capacity of the particular ecosystem.
__________________
||||||||||||||||||||50% Complete
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Solved Everyday Science Papers Dilrauf General Science & Ability 7 1 Week Ago 07:28 PM
Geography One - PRECIPITATION and RAINFALL Bhalla Changa Geography 0 Wednesday, November 14, 2007 03:07 PM
Formation of rain Hurriah Islam 0 Friday, November 09, 2007 06:22 PM
Sahih_Bukhari hellowahab Islam 39 Wednesday, September 26, 2007 10:59 AM


CSS Forum on Facebook Follow CSS Forum on Twitter

Disclaimer: All messages made available as part of this discussion group (including any bulletin boards and chat rooms) and any opinions, advice, statements or other information contained in any messages posted or transmitted by any third party are the responsibility of the author of that message and not of CSSForum.com.pk (unless CSSForum.com.pk is specifically identified as the author of the message). The fact that a particular message is posted on or transmitted using this web site does not mean that CSSForum has endorsed that message in any way or verified the accuracy, completeness or usefulness of any message. We encourage visitors to the forum to report any objectionable message in site feedback. This forum is not monitored 24/7.

Sponsors: ArgusVision   vBulletin, Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.