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

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

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)

Sulfur Cycle

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

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

The Aerosol Cycle

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

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

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

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

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

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

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