Māris kļaviņŠ, azamat azizov, JĀnis zaļoksnis environment, pollution, development: the case of uzbekistan

 7.7. 
 Acid precipitations
The increased entry of various acid-forming oxides (NO, NO
2
, 
SO
2
, SO
3
)  into  the  atmo sphere  causes  an  effect  that  the  pH  of 
precipitation may decrease, but at the same time the composition of 
atmo spheric precipitation can be significantly altered. 
Precipitation acidification is caused by photochemical oxidation 
of sulfur and nitrogen oxides in the atmo sphere, the subsequent 
reaction with water vapour present in the atmo sphere to form 
sulfuric acid, nitric acid and sulfurous acid, and the fall with the 
precipitation in the form of rain or snow. If rain water contains 
acid, its pH is lowered. Acidification of precipitation also causes the 
surface water acidification.
A  significant  volume  of  gases,  which  may  cause  acidification 
of atmo spheric precipitation, is generated in the industrialized 
countries (Figure 7.28). As such precipitation falls, it may affect the 
overground water, soil and vegetation. Pure water has a pH of ~5.7, 
determined by atmo spheric carbon dioxide dissolution and formation 
of weak acid – carbonic acid. Due to the impact on the atmo sphere of 
sea salt aerosols, as well as the aerosols generated by soil erosion, the 
atmo spheric precipitation pH may increase even up to a pH value 8. 
However, as a result of industrial contamination the acid rain may 
be typically formed with a pH of less than 5.6.
Precipitation in the form of rain and snow is created in the upper 
layers of the tropo sphere by condensation of water evaporating from