《环境化学》课程PPT教学课件讲稿（英文版）Unit 12 Water in the atmosphere-Acid rain

Water in the atmosphere-Acid rain

Water in the atmosphere- Acid rain

Ions in pure water autoionization H20 H+ OH neutralization Kea= [h] w=Keglh2O [H2O] =HOH =10 14

Ions in pure water H2O autoionization neutralization H+ + OH- [ ] [ ][ ] H2 O H OH Keq + − = 14 2 2 10 [ ][ ] [ ] M H OH Kw Keq H O − + − = = =

pH value of pure water HOH log Kw=-log h]-log oH] oK w=pH+pOH In pure water, autoionization is the only source of ions, therefore [F]=[OH]=107M pH=7 A pH of 7 defines neutrality pH7 is basic

pH value of pure water pK pH pOH K H OH K H OH w w w = + − = − − = + − + − log log[ ] log[ ] [ ][ ] In pure water, autoionization is the only source of ions, therefore: 7 [ ] [ ] 10 7 = = = + − − pH H OH M A pH of 7 defines neutrality, pH7 is basic

What is the pH of natural rain water? pH of natural rain water is determined by acidic and basic species that are CO2(8)+H20=H2CO3 naturally present in the TH2CO3 Unit: M atmosphere K ICOL,OI Equilibrium IH,CO3 constant Kell,oi CO2 partial pressure 1015=H2CO in unit of atm 370x10 C02: 370 ppm [H2CO3]=10-M

What is the pH of natural rain water? H CO M x H CO p H CO K H O CO H O H CO K CO g H O H CO CO eq eq 4.9 2 3 6 1.5 2 3 2 3 2 2 2 2 3 2 2 2 3 [ ] 10 370 10 [ ] 10 [ ] [ ] [ ][ ] [ ] ( ) 2 − − − = = = = + = pH of natural rain water is determined by acidic and basic species that are naturally present in the atmosphere. Equilibrium constant CO2 partial pressure in unit of atm Unit: M CO2: 370 ppm

What is the pH of natural rain water? ( Continued) H2CO3=H++HCO3(K=1064 K-[H* I lH,CO3 k=[+2 [H]≈[HCO31 [H,CO [H+]=K[H2CO3]=10-64x10-9 [H+]=10-37 pH=5.7 Rainwater is naturally acidic because its equilibrium with carbon dioxide

What is the pH of natural rain water? (Continued) 5.7 [ ] 10 [ ] [ ] 10 10 [ ] [ ] [ ] [ ][ ] ( 10 ) 5.7 6.4 4.9 2 3 2 2 3 2 2 3 3 6.4 2 3 3 = = = = = = = + = + − + − − + + − + − − pH H H K H CO x H CO H K H CO H HCO K H CO H HCO K a a a a Rainwater is naturally acidic because its equilibrium with carbon dioxide. [ ] [ ] 3 + − H  HCO

Acid rain Rainwater has a pH of 5.7 if Co2 is the only species hat affects its acidity. When additional acidic species are present at appreciable levels as a result of man-made activities, pH of rain water becomes lower than 5.7.>Acid rain H2S04 and hno3 are the major contributors to acid rain

Acid rain • Rainwater has a pH of 5.7 if CO2 is the only species that affects its acidity. • When additional acidic species are present at appreciable levels as a result of man-made activities, pH of rain water becomes lower than 5.7.→ Acid rain. • H2SO4 and HNO3 are the major contributors to acid rain

pH of acid rain Normal Background Rain Battery Acid Distilled Water Ammonia Lemon Juice Human Blood Vinegar Baking soda ACIDIRAIN 01234567891011121314 ACIDIC NEUTRAL ALKALINE H2SO4 and hno3 are the major contributors to acid rain

pH of acid rain H2SO4 and HNO3 are the major contributors to acid rain

Sources for h2so4 and hno3 in the air Both substances are formed in the air Precursor to H2S04: S02 Precursor to hno3 No2 Concentrations of the precursors so2 and NO2 are greatly increased by man-made activities, especially fossil fuel combustion

Sources for H2SO4 and HNO3 in the air • Both substances are formed in the air – Precursor to H2SO4: SO2 – Precursor to HNO3: NO2 • Concentrations of the precursors SO2 and NO2 are greatly increased by man-made activities, especially fossil fuel combustion

Role of nh3 in acid rain Ammonia dissolved in rainwater scavenges h+ NH3 (aq)+H+t=NH4+ Ammonia input lowers the acidity in rain Ion Rural New York Southwest Minnesota (μeq/) μeq/) H+(pH)46(4.34) 0.5(6.31) SO245 416 NO3- 25 24 HCO 0.1 10 NH+ 8.3 38 The larger input of NH3 in MN is responsible for the lower rain acidity than in NY

Role of NH3 in acid rain • Ammonia dissolved in rainwater scavenges H+: – NH3 (aq) + H+ = NH4+ • Ammonia input lowers the acidity in rain. Ion Rural New York Southwest Minnesota (meq/l) (meq/l) H+(pH) 46 (4.34) 0.5 (6.31) SO4 2- 45 46 NO3 - 25 24 HCO3 - 0.1 10 NH4 + 8.3 38 The larger input of NH3 in MN is responsible for the lower rain acidity than in NY

Production of nh3 Animal waste ammonification of humus followed by emission from soils losses of nh3-based fertilizers from soils industrial emissions

Production of NH3 • Animal waste, • ammonification of humus followed by emission from soils • losses of NH3-based fertilizers from soils • industrial emissions