Environmental Chemistry

Atmospheric concentrations Atmospheric Pressure: 1 atm = 760 torr = 101325 Pa = 1.01325 bar = 1013.25 mbar Atmospheric abundances can be measured in pressure or “number density” (# molecules/volume): 𝑃 𝑅𝑇 = 𝑛 𝑉 moles/volume = molar concentration (moles/L) 𝑃 𝑁 𝐴 𝑅𝑇 = 𝑛 𝑁 𝐴 𝑉 # molecules/volume = number concentration or number density (molecules cm-3) Mole fraction or “mixing ratio”: 𝑋 𝑖 = 𝑃 𝑖 𝑃 𝑡𝑜𝑡𝑎𝑙 = 𝑁 𝑖 𝑉 𝑁 𝑡𝑜𝑡𝑎𝑙 𝑉 (mole fraction is unitless!) To convert mole fraction to ppmv (or ppbv, etc.): ppmv = 𝑋 𝑖 × 106 ppbv = 𝑋 𝑖 × 109 pptv = 𝑋 𝑖 × 1012

Miniscule concentrations Parts Per Million (PPMV) A unit of concentration often used when measuring levels of pollutants in air, water, body fluids, etc. One ppm is 1 part in 1,000,000. The common unit mg/liter is equal to ppm. Four drops of ink in a 55-gallon barrel of water would produce an "ink concentration" of 1 ppm. Parts Per Billion (PPBV) One part per billion is 1 part in 1,000,000,000. One drop of ink in one of the largest tanker trucks used to haul gasoline would represent 1 ppb. Parts Per Trillion (PPTV) A unit of concentration used to measure vanishingly small levels of pollutants or contaminants. One ppt is 1 part in 1,000,000,000,000. One drop of ink distributed through the water contained in a 12-million-gallon reservoir would result in a final concentration of 1 ppt.

Brasseur, Orlando, and Tyndall, Atmospheric chemistry and global change, 1999.

Lifetime and variability Hobbs, IAC, 2000.

Blackbody Radiation https://phet.colorado.edu/sims/blackbody-spectrum/blackbody-spectrum_en.html

Intercepted solar radiation Jacob, Intro to Atmospheric Chemistry, 1999

Solar irradiance spectrum Graedel and Crutzen, Atmospheric Change, 1993

Absorption and Reflection of Radiation

Albedo http://visibleearth.nasa.gov/

Solar and terrestrial blackbody spectra

Solar and terrestrial blackbody spectra

Outgoing long-wave radiation http://visibleearth.nasa.gov/

Terrestrial radiation spectrum 290 K Jacob, Intro to Atmospheric Chemistry, 1999

IR spectrum of CO2 http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Vibrational_Spectroscopy/Vibrational_Modes http://www2.ess.ucla.edu/~schauble/molecular_vibrations.htm

IR spectrum of H2O bending modes stretching modes

Typical IR absorption frequencies http://chem.unl.edu/powers/

Absorption by atmospheric gases atmospheric window 5 μm