discerning mercury-halogen chemistry from diurnal cycles of rgm christopher holmes, daniel jacob,...
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Discerning mercury-halogen chemistry from diurnal cycles of RGM
Christopher Holmes, Daniel Jacob, Noelle Eckley SelinHarvard University
Dan Jaffe, Phil SwartzendruberUniversity of Washington
Rob MasonUniversity of Connecticut
Observations of RGM in the Marine Boundary Layer
Major features of RGMdiurnal cycles- Fast morning rise - Peak 11:00-13:00 LT- Fast decline in afternoon- No significant change 20:00-4:00 LT- Amplitudes 1-3X mean
Jaffe et al. JGR 2005
Laurier et al. JGR 2003 Laurier & Mason JGR 2007
All RGM Observations
Smoothed Diurnal Cycle
Obs GEOS-Chem
Selin et al. JGR 2007
Okinawa diurnal cycle
Δ Phase due to halogens?
Hg0 RGMOH, O3
Deposition (~1d)
Sea salt (7h)
hv Reduction (~1d)
Standard GC Mechanism
Inconsistent with nighttime RGM > DL
Okinawa DLCruise DL
Okinawa
Hg0 RGMO3
Deposition (~1d)
Sea salt (7h)
hv Reduction (~1d)
“Excess” Oxidation OH, Br, Cl…
Simple Model
Calculating [Br] from RGM observations
Other oxidants, e.g. Cl, OH, also contribute
Pacific Cruise
[Br] < 1 x 107 cm-3 in MOCCA and MISTRA(Dickerson et al. 1999; von Glasow et al. 2002)
Hg0 RGMBr, Cl, O3, (OH?)
Deposition (~1d)
Sea salt (slower)
hv Reduction (<1d?)
Revised MBL Mechanism
Implications
Major features of RGM diurnal cycles
- Fast morning rise oxidation of Hg0 by Br and Cl
- Peak 11:00-13:00 LT oxidation of Hg0 is primarily in the morning
- Fast decline in afternoon rapid sink could be photochemical reduction
- No significant change 20:00-4:00 LT direct deposition (1st order) is a minor RGM sink
- Amplitudes 1-3X mean different RGM sink rates
Smoothed Diurnal Cycle