《环境化学》课程PPT教学课件讲稿（英文版）Unit 2 Atmospheric Composition

Atmospheric composition

Atmospheric Composition

Composition of the atmosphere Gas %o by volume 78.08 02 20.95 Ar 0.93 Dry air C02 0.03 All other gases(Ne, He, 0.01 Kr, h, etc) Water Variable

Composition of the atmosphere Gas % by volume N2 78.08 O2 20.95 Ar 0.93 CO2 0.03 All other gases (Ne, He, Kr, H, etc) 0.01 Water Variable Dry air

Water vapor in the air The %volume of Water vapor is variable depending on temperature, precipitation rate of evaporation and other factors at a particular location The percentage of water vapor ranges from 0.1 5%. Generally it is 1-3%(the 3rd most abundant constituents in the air)

Water vapor in the air • The % volume of Water vapor is variable, depending on temperature, precipitation, rate of evaporation and other factors at a particular location. • The percentage of water vapor ranges from 0.1- 5%. Generally it is 1-3% (the 3rd most abundant constituents in the air)

Expressing the amount of substances in the atmosphere Concentration the amount(mass, moles, molecules, etc) of a substance in a given volume divided by that volume. The example concentration units are mg/m3 mol/m3 molecules /cc, and etc Mixing ratio the ratio of the amount of the substance in a given volume to the total amount of all constituents in that volume

Expressing the amount of substances in the atmosphere • Concentration – the amount (mass, moles, molecules, etc) of a substance in a given volume divided by that volume. – The example concentration units are mg/m3 , mol/m3 , molecules/cc, and etc. • Mixing ratio – the ratio of the amount of the substance in a given volume to the total amount of all constituents in that volume

Mixing ratio total n; is the molar concentration of /and nota is the total molar concentration of air. parts per million(ppm) 10-6 umol mol-1 parts per billion(ppb) 10-9 nmol mol-1 parts per trillion(ppt 10-1 pmol mol-1 (Ppm)=10°x total

Mixing Ratio ni is the molar concentration of i and ntotal is the total molar concentration of air. parts per million (ppm) 10-6 mmol mol-1 parts per billion (ppb) 10-9 nmol mol-1 parts per trillion (ppt) 10-12 pmol mol-1 total i i n n  = total i i n n ppm x 6  ( ) =10

Conversion between ppm and ug/m3 10m mol/m3 m: ug/m3 total V RT M;: g/mol mzxingratio in ppm=10 n M RT P RT RT mixing ratio in ppm=- p cOncentration_in_ug/m

Conversion between ppm and mg/m3 RT P V N ntotal = = i i i M m n 10−6 = ni : mol/m3 mi : mg/m3 Mi : g/mol total i n n mixing ratio in ppm 6 _ _ _ =10 i i i i m pM RT RT p M m = = −6 6 10 10 3 _ _ _ xConcentration _ in _ g / m pM RT mixing ratio in ppm i = m

RT mixing ratio In ppm cOncentration in ug /m M Pressure unit and r Constant P=1.01325X10^5 pascal R8. J/k mol for p in pa and volume in m3

3 _ _ _ xConcentration _ in _ g / m pM RT mixing ratio in ppm i = m Pressure unit and R Constant: P= 1.01325x10^5 pascal R= 8.314 J/k.mol for P in Pa and volume in m3

Conversion between ppm and ug/m3 Example: The Hong Kong Air Quality Objective for ozone is 240 ug/m. The U.S. National ambient Air Quality Standard for ozone is 120 ppb. Which standard is stricterat the same temperature (250C)and the pressure(latm)? 8.314x298 muxing ratio in ppm x2401g/m3=0.122ppm=122ppb 101325x103x48

Conversion between ppm and mg/m3 Example: The Hong Kong Air Quality Objective for ozone is 240 mg/m3 . The U.S. National Ambient Air Quality Standard for ozone is 120 ppb. Which standard is stricter at the same temperature (25oC) and the pressure (1atm)? x g m ppm ppb x x x mixing ratio in ppm 240 / 0.122 122 1.01325 10 48 8.314 298 _ _ _ 3 5 = m = =

Typical mixing ratios for some compounds of environmental importance Carbon dioxide 355 ppm Carbon monoxide 100 ppb to 20 ppm Ozone 1 to 100 ppb Methane 1.72 ppm Nonmethane hydrocarbon 1 ppt to 1 ppb Nitric oxide(no) 5 ppt to 1 ppb Nitrogen dioxide(no2) 1 to 150 ppb Nitrous oxide(n2o) 310 ppb Sulfur dioxide 1 to 100 ppb CFCI3(Freon 11 200 ppt CF2C12(Freon 12) 350 ppt

Typical mixing ratios for some compounds of environmental importance Carbon dioxide 355 ppm Carbon monoxide 100 ppb to 20 ppm Ozone 1 to 100 ppb Methane 1.72 ppm Nonmethane hydrocarbon 1 ppt to < 1 ppb Nitric oxide (NO) 5 ppt to 1 ppb Nitrogen dioxide (NO2) 1 to 150 ppb Nitrous oxide (N2O) 310 ppb Sulfur dioxide 1 to 100 ppb CFCl3 (Freon 11) 200 ppt CF2Cl2 (Freon 12) 350 ppt

ppm in solution vs ppm as mixing ratio for airborne substances ppm: Parts per million solution air weight of species mole of species i C(ppm) x weight of solution mole of air molecules ity_of dilute aqueous_ solution z density_of_water =1g/ml=10'g/liter=10 mg/L Img species i om 10° mg solution ng Img/L liter solution

ppm in solution vs. ppm as mixing ratio for airborne substances ppm: Parts per million solution 6 10 _ _ _ _ _ ( ) x weight of solution weight of Species i Ci ppm = air mole of air molecules mole of species i i _ _ _ _ _ _  = g ml g liter mg L density of dilute aqueous solution density of water 1 / 10 / 10 / _ _ _ _ _ _ 3 6 = = =  mg L liter solution mg mg solution mg species i ppm 1 / 1_ _ 1 10 _ 1 _ _ 1_ 6 = = =