A First Look at the Effect of Heating on Aerosol Optical Properties Chris Cappa, Dan Mellon *, Tim Onasch, Paola Massoli CalNex-Atlantis Data Workshop January 2011 UC Davis Windmills CaLNex A t n t i s l *Now at Thorlabs Funding:

Aerosol Volatility and Optical Properties [Lack and Cappa, ACP, 2010] Light absorption by particles from black carbon (soot) and brown carbon Coatings on BC can enhance absorption in climatically important ways [e.g. Jacobson, Nature, 2001] Enhancement factor can be calculated from Mie theory, but limited validation from ambient measurements Objective: to directly measure the absorption enhancement factor for ambient particles at multiple wavelengths

AmbientReally hot Large EnhancementSmall Enhancement Highly Scattering Less Scattering Brown CarbonNo Brown Carbon Absorption by brown carbon should contribute more to total absorption at short UCD PAS measures absorption (and extinction) at 405 nm and 532 nm Approach: Heat Particles to Drive Off Coatings

Measurements Thermo- denuder HR-ToF- AMS SP-AMSPAS/CRDSMPSSP2 MAST or Note: PM1 cutoff Non-refractory particle composition BC & coating composition Particle absorption & extinction Size Distribution BC mass distribution Env. Ca Aerodyne UC Davis Env. Ca SP2 and SPAMS should tell us something about how coating thickness has changed upon heating SP2 BC measurement can tell us about particle losses through the TD

Particle Transmission Correction Similar results to Huffman et al. (2008): Tr = 0.98 – *Temp Need to do using particle # (instead of mass) and for entire data set

Influence of heating on particle extinction (532 nm)

Influence of heating on particle extinction

Lines are binned data over different time periods Total aerosol volatility varies greatly with time/location Excludes Sea Sweep periods Influence of heating on particle extinction Start of Campaign End of Campaign

Influence of heating on particle absorption Note: only included periods when s abs > 1 Mm -1

Influence of heating on particle absorption Limitation: FR ext does not account for mixing state

Model: Mie Core-Shell D p = 250 nm SSA i = 0.95; D core = 25 nm

Model: Mie Core-Shell D p = 250 nm SSA i = 0.95; D core = 25 nm SSA i = 0.88; D core = 35 nm SSA i = 0.77; D core = 45 nm SSA i = 0.67; D core = 55 nm

Model: Mie Core-Shell SSA i = 0.95 SSA i = 0.88 SSA i = 0.77 SSA i = 0.67; vary D p SSA i = 0.58 D p = 150 nm D p = 100 nm D p = 80 nm

Mie “Core-Shell” Results

Since we are talking about California anyway… same experiment done at CARES, but with fixed TD temperature (225 °C) and PM 2.5 Note: variation in FR ext from atmosphere, not temperature

An update on (very important) other matters… These guys apparently do not qualify as “all-stars” But the good news is… Applications for the next season opened this week! We are already saving up for all our carbon offsets (and accepting donations).