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Environmental Environmental Chemistry Chemistry
APCH211 APCH211 Dr PG Ndungu Dr PG Ndungu
Acid rain Acid rain
Acid Rain Acid Rain
“Acid
cid rai rain" – " – General eral term appl rm applied ied t to an any f form o rm of wet prec precipitation, usua usually in in the the tr trop
- posphere, w
with a acid idic ic spec species str stronger tha than CO CO2
Includes r
es rain, s sleet, s , snow
- w,
, fog, o
- r dew
Na
Natu tural ral pH pH of ra rain in water r ~ ~ 5.6 5.6 (f (from d m dissolved CO CO2)
Can ha
n have deposi deposition
- n of
- f dr
dry y gases and gases and com compou
- unds –
– so
- calle
called dr dry y dep deposition
Aqueo
eous us and and dr dry dep deposi sition ar are e col collectively t termed aci med acid dep deposi sition
The
e precur ursors rs or chemical f al forerunne rerunners o rs of ac acid r rain f formation rmation res result fr from
- m both
th na natur tural sour sources, such such a as volc lcanoes a and deca caying vege getation a and ma man- n-made sour sources, prim primarily emi emissions of sulf
- f sulfur
di dioxide (S e (SO2) an and d nitrog
- gen
en ox
- xid
ides (N es (NOx) r ) resulti sulting f ng from fossil ssil fuel comb mbust ustio ion. n.
Acid
id ra rain is in is pa partic icularly d dama magi ging t to la lakes, str streams, a and fore rests an and t d the pl e plan ants ts an and d an animals t that l at live i in these ese e ecosys
- systems
ms. .
Acidic Deposition Acidic Deposition
Wet deposition
refers to acidic rain, fog and snow. If the acidic chemicals in the air are
blown into areas where the weather is wet, the acids can fall to the ground in the form of rain, snow, fog, or mist. Dry deposition
In areas where the weather is dry, the
acid chemicals may become incorporated into dust or smoke and fall to the ground through dry deposition sticking to the ground, buildings, homes, cars, and trees. Later, when moisture content i id l ti i d d g increases, acid solution is produced.
Main Culprits in Acidic Precipitation Main Culprits in Acidic Precipitation
Nit Nitrogen spec species:
NOx
NOx
Sou
Sources incl include b burn rning of
- f
fo fossil f fuels, s, b biomas ass, s, e etc
Natural S
tural Sour urce ces; s; A Anorexic ic t i t il t Sul Sulfur Spec Species
SO
SO2
Foss
ssil f il fuels & els & sulfur o fur ore s e smeltin elting
H2S,
S, & & CS CS2:
Wetlands a
and sub submerged soi soils wa waters, ers, so soil ils, s, etc
NH
NH3
Animal exc
excret eta, a, fertiliz izer ers a and micr crobio
- biolo
logical r gical release ase
Wetlands a
and sub submerged soi soils
Dim
Dimethylsulfide, ( (CH3)2S, c S, carbon
- nyl
yl sul sulfi fide, COS, COS, me methyl mer mercaptan, CH CH3SH a and Dime Dimethyl disu isulfide, CH CH3SS SSCH CH3. .
Ocean an
Ocean and d soils. ils.
Atmosph mospheric c Pr Production
- duction Of Nitric A
Of Nitric Acid id Atmosph mospheric c Pr Production
- duction Of Nitric A
Of Nitric Acid id
The principle reaction sequence contributing to production of nitric acid starts with nitric
- xide,
NO from combustion processes. Nitric tric oxide ide Chemis hemistry: Dayti time me
NO is oxidized by O2, O3 or ROO – e.g.
NO + O3 NO2 + O2
3 This NO2 radical can then contribute to
- zone and OH radical production i.e.
plays a role in smog formation
- Short lifetime, thus smog events don’t last,
& not that frequent
- Main removal sequence for NO is via
catalyst (M), OH rxns
NO2 + OH + M HNO3 + M