1. Announcements Reading assignment: S+P chaps. 2.7-2.9 and chap 8.
I might give an in-class quiz on the reading material this week or next

2. Tropospheric Ozone System
Adding NOx Ox
NOx XO O3 2a
NO2
The main source of that free O in the troposphere is NO2
We can think of NO as a “carrier” molecule for the free oxygen 2b hn M 2b 2a X O2 NO
Reactions:
(2a) NO2 + hn  NO + O
(2b) O3 + NO  NO2 +O2 M
We keep track of nitrogen with NOx = NO + NO2
The free O bound up in NO2 can be thought of as a “potential Ox”
XO = Ox + NO2

3. Tropospheric Ozone System
Hydrocarbons: CH4 Ox
NOx
HOx CO
CH4 XO O3 2a
NO2 3
HO2 4 CO 5
CH4 2b hn x3 hn M 2b 3 5 3 4 5 X O2 NO OH
Reactions:
(5a) CH4 + OH + O2  H2O+ CH3O2
CH4 has many pathways for its degradation.
Low NO  sink for HOx and minor source of CO
High NO  source of 2HOx, 4 XO, one CO
(5b) CH3O2 +NO + 3O2
CO + NO2 + 3HO2
(5c) CH3O2 + HO2  CH3OOH + O2
The potential for methane to steal free O from atmospheric O2 is potentially strong, if there’s lots of NO around, otherwise, it’s not as strong.
XO = Ox + NO2+ HO2 + CO + CH4f(NOx)

4. Sulfur Cycle

5. Atmospheric Aerosols Why are they important? Chemistry: Radiation:
Important endpoint for atmospheric nitrogen and sulfur chemical cycles
Site for aqueous and heterogeneous chemistry
Many aerosol types have adverse human health effects
Acidity of rain
Radiation:
Scatter and absorb solar radiation, reducing visibility
Influence greenhouse effect by absorbing and emitting infrared radiation (esp. dust)
Cloud Physics:
Aerosol particles are the CCN upon which clouds drops form
Aerosol chemistry and size can influence the freezing process in cold clouds, and hence rain/hail generation
Climate:
Aerosol “radiative forcing” has countered much of the GHG warming in the past century
Radiative forcing includes “direct” impacts on solar/IR radiation and “indirect” impacts through altered cloud optical properties, snow reflectivity, and perhaps atmospheric chemistry

6. Key Classifications Primary vs. Secondary: Natural Vs. Anthropogenic:
Primary: Directly emitted by the surface through mechanical processes
Secondary: Created in the atmosphere through gas-phase reactions and nucleation
Natural Vs. Anthropogenic:
About half of atmospheric aerosol < 1 mm is thought to be anthropogenic
Size Ranges:
Giant: Dp > 10 mm
Coarse: Dp between 1 – 10 mm
Fine: Dp between 0.1 – 1 mm
UltraFine: Dp < 0.1 mm
Modes:
Aerosol particles of similar sources and histories are often found within a relatively narrow range of sizes, called “modes”
Nucleation/Aitken Mode: Recently-formed, short-lived particles, < 30 nm
Accumulation: 50 nm – 200 nm – where most secondary aerosol exists
Coarse Mode: generally > 1 mm – where most primary aerosol resides

7. The Aerosol Cycle

9. Quantifying Primary Measures Other measures Distributions
Number Concentration, Na (cm-3)
Mass concentration, (usually mg/m-3)
Other measures
Volume concentration, Va
Surface area concentration, Aa
Distributions
By particle Diameter, Na(Dp)
Chemical breakdown, Mi

10. Size Distributions The Histogram
Di –Di+1 Ni
Ni = concentration of particles within size range for bin i
Di = Lower-bound particle diameter for bin i
N(Di) = Total concentration for particles smaller than Di

11. Size Distributions The Number Distribution
Di –Di+1 Ni
ni = aerosol number distribution for bin i
DDi = Di+1–Di is the bin width
Ni = niDDi
ni = has units of (cm-3 mm-1)
Area under the curve = total aerosol concentration, N

12. Histogram
Number distribution
Instruments with different Di would produce very different histograms, but similar number distributions

13. Size Distributions The Log Number Distribution
Aerosol distributions span orders of magnitude in size, and are often best shown as a function of log-diameter. Now, the area under curve is NOT equal to total concentration.
To remedy this, we can create a log number distribution

14. Size Distributions The Number Distribution Function
Distributions are often represented in models or analytically, as continuous functions of diameter.

15. Size Distributions The Number Distribution Function
Aerosol distributions span orders of magnitude in size, and are often best shown as a function of log-diameter. Now, the area under curve is NOT equal to total concentration.
To remedy this, we can create a log number distribution