AQ Modeling Fundamentals photochemistry Gustavo Sosa Iglesias WMO

AQ Modeling Fundamentals: photochemistry Gustavo Sosa Iglesias WMO GURME Training Course on Air Quality Modeling for Latin American Cities Project SEMARNAT, Mexico City August 10, 2009

Solar radiation: energy source for the Earth n n Matter-to-energy conversion 4 Tg/s in the core Sun´s average temperature 5783 K Energy's Sun fraction entering to the Earth 4. 5 x 10 -15 Solar constant 1370 W/m 2 (solar energy flux) at the top of the Earth's atmosphere

Geometrical dependence of solar radiation

Radiative flux in the Atmosphere Sun Reflected outward

Photochemical reactions in the Atmosphere 1. Available light j AB + h A + B 2. Absorptions spectrum h = hc/ j light frequency light wavelength photolysis rate Examples: Strong bond O-O (O 2) 119 Kcal/mol; = 240 nm Weak bond O-O 2 (O 3) NIR, Vis, UV 25 Kcal/mol; =1122 nm 3. Quantum yield

Ozone formation mechanism

Tropospheric photochemistry modeling

Model’s Formulation Change in = Advection by Winds Concentration Turbulent Diffusion + Ri Chemical Reaction + Si Emissions + Li Surface Removal/Deposition

Chemical Mechanism (SAPRC 99) Reaction Number Reactants Products K 298 (ppm–n min– 1) 1 NO 2 NO + O Photolysis 2 O + O 2 + M O 3 + M 2. 105 E-05 3 O + O 3 2 O 2 1. 175 E+01 4 5 SPRC 99 Lumped Mechanism O + NO + M NO 2 + M 3. 676 E-03 O + NO 2 NO + O 2 1. 435 E+04 9 NO + NO 3 2 NO 2 3. 849 E+04 10 NO + O 2 2 NO 2 7. 104 E-10 11 NO 2 + NO 3 N 2 O 5 2. 268 E+03 6 7 8 217 O chemical reactions + NO 2 NO 3 2. 690 E+03 76 O 3 species (explicit and lumped) 2. 682 E+01 + NO NO 2 + O 2 Gas. O 3 and aerosol phases + NO 2 + NO 3 5. 202 E-02

Air Quality Inputs C Initial Conditions (ICs) q q C model spinup role of ambient measurements Boundary Conditions (BCs) q q q Lateral boundaries (time, space varying) Concentrations aloft (time, space invariant) Based on clean air background, observations+clean air, and/or continental model simulations

Outputs from an Air quality Model O 3 CO