1. Aerosols By Elizabeth Dahl (2005) Edited by Ted Dibble (2008)

2. What’s driving aerosol research? transport of bomb radionuclides geochemical cycles –metals, nutrients, organics acidification (sulfur, nitrogen) climate change –direct/indirect effects –aerosol optical properties, aerosol/cloud interactions human health –air quality, airborne pathogen transport

3. Terminology Aerosol – a dispersion of solid and liquid particles suspended in gas (air). note: “aerosol” is defined as the dispersion of both particles and gas, but in common practice it is used to refer to the particles only! Primary aerosol – atmospheric particles that are emitted or injected directly into the atmosphere. Secondary aerosol – atmospheric particles that are created by in situ aggregation or nucleation from gas phase molecules (gas to particle conversion). Either type may be natural or anthropogenic or both How much aerosol is there? typically ~10’s of ug/m 3 (air density ~1kg/m 3 )

4. Global Particle Production (Table 2.19 from Seinfeld and Pandis)

5. Log-normal distributions Aitken mode Accumulation mode Coarse mode Number distribution  n n (log D p )=dN/d log D p Surface area distribution  n s (log D p )= dS/d log D p Volume distribution  n v (log D p )=dV/d log D p

6. Aitken mode – 0.01-0.1  m Accumulation mode – 0.1-1  m Coarse mode - >1  m and sometimes, the elusive nucleation mode <0.01 um The Aerosol Modes

7. Removal mechanisms... gravitational settling 10  m particle  1000 cm hr -1 1  m particle  10 cm hr -1 coarse particles

8. fine particles You can estimate the distance a particle will diffuse in a given time from the equation: where D is the diffusion coefficient Diffusion/Coagulation

9. Why is there an “accumulation” mode? impaction, settling diffusion, coagulation

10. So lifetimes are …. Aitken nuclei – hours to days (diffusion/coagulation) Accumulation mode – weeks Coarse mode – hours to days (deposition) Ultrafine – minutes to hours

11. Secondary organic aerosol (SOA)formation SOA is produced in gas phase from oxidation of parent organic gases. Partitioning to aerosol phase depends on vapor pressure –High equilibrium vapor pressure  tendency to stay in gas phase –Low equilibrium vapor pressure  partitions to aerosol phase – non-volatiles Production of the organic aerosol compound depends on the gas phase chemistry of it’s parent (on aerosol phase chemistry too!) Large organics (C> 6) tend form aerosols while organics C<6 do not.

12. Aerosol chemistry…

13. Aqueous Aerosol Partitioning between gas and aerosol phases (A g  A aq ) depends on –liquid water content (L=g of H 2 O/m 3 of air) L=0.1-0.3 in clouds L=0.02-0.5 in fogs –Henry’s law constant (H) H A =[A] (M)/P A (atm)

14. H O2 =1.3x10 -3 M/atm H O3 =1.1x10 -2 M/atm H NH3 =62 M/atm H H2O2 =7x10 4 M/atm H H2CO =2.5 M/atm Calculate the concentration of ozone in 1 ml of pure water for 10 ppbv ozone, assume ideal gas. A few Henry’s law constants…

15. Formaldehyde in aqueous aerosol In water, H 2 CO mostly adds H 2 O to form H 2 C(OH) 2

16. The chemical perspective... a chemical size distribution 1. chemical size distributions resemble mass, not number 2. sulfate and organics dominate the accumulation mode, but there’s a surprising amount of seasalt 3. there are a lot of unidentified organics 4. the coarse mode has the expected mechanically generated aerosols, but also nitrate and sometimes sulfate Mass (C. Leck)

17. Dust (mineral aerosols)  diameter size: 2-300 µm  main material: sand, silt, clay  includes essential trace metals such as Fe  consists of insoluble and soluble fractions Mineral Dust

18. “brown carbon”: sugars alcohols aromatics di/tri acids ketoacids hydroxyacids soot – “elemental carbon” formed in flames little spectral dependence carbon-only Organic aerosols - burning

19. Seasalt aerosols... seasalt production via bubble bursting... film drops (many, small, organics) jet drops (fewer, larger) wind  bubbles  spray whitecap coverage W α U 3+