1. NOx-mediated Chemistry - Climate Interactions via Atmospheric Aerosols Julie Fry, currently unemployed! (was UC Berkeley, starting at Reed College next week)
NO + oxyRO2
Climate effects?
RONO2(g)
NOx
RONO2
aerosol
NO3 + VOCs
So what I’ve been getting into in my post-doc research is following this nitrate into the aerosol. We’re interested in studying chemistry that leads to aerosol formation, which in turn influences Earth climate. I’ll start by discussing the big-picture aerosol-climate interactions that motivate us to think about aerosol, and then move backwards to the specific chemistry we’re looking at, but here’s a quick preview of the big picture. NOx in the atmosphere, emitted by human activities, can undergo daytime photochemistry or nighttime nitrate radical chemistry to form organic nitrates, some of which may be big and sticky enough to partition to the aerosol phase. This addition of organic nitrates to the aerosol affects the composition and therefore potentially the hydroscopic properties, and also just increases the total aerosol number and/or mass in the atmosphere, all of which have climate effects.
Chamber studies of SOA formation
AMS organic nitrate standard studies
Modeling regional importance of NOx-mediated SOA formation
Future: Measuring aerosol chemical composition with Hi-Vol samplers &
offline GC-MS, FTIR, NMR; regional modeling (WRF-Chem)
August 2008

2. NO3 in Juelich SAPHIR chamber, June 2007
NO3 TD-LIF
NO2 TD-LIF inlets
Our golden opportunity to study these NO3 reactions came when we were part of a group conducting experiments on NO3 at the SAPHIR chamber in Juelich, Germany last June. This is a really cool facility – it’s a giant 300 m3 teflon bag with some great infrastructure for simulating the atmosphere in a controlled way. This past summer, a bunch of collaborators converged with our instruments at the chamber, stuck all of our sampling inlets up through the floor, and did a series of experiments with NO3.
March 13, 2008

3. aerosol formation DRY Y~50% 60% RH Y~50% o N2O5 +NO3 + β-pinene
We can make the same comparison across the two experiments, this time focusing on total aerosol mass yield (note different units because we don’t know the molecular weight of the total aerosol). Aerosol mass yields are typically computed in terms of mass aerosol / mass hydrocarbon precursor reacted away.
60% RH
Y~50%

4. Modeling nitrate partitioning
estimated Pvap~6x10-4 Torr
Absorptive partitioning model requires Pvap = 4x10-6 Torr

5. Modeling NO3 + β-pinene Yield(Alkyl nitrates) = 30%
Emphasize: free-running model captures all of this part of the chemistry quite well with a single organic nitrates yield
Yield(Alkyl nitrates) = 30%

6. How much aerosol could NO3 + β-pinene make globally?
Mass yield of aerosol from NO3 + β-pinene: ~50%
Global annual β-pinene emissions: ~ 33 Tg yr-1
Fraction of β-pinene that reacts with NO3, based on relative NO3, O3, and OH lifetimes: ~ 30%
→ .3 x .5 x 33 Tg yr-1 = 5 Tg yr-1
What we DO know for sure is the 50% mass yield from b-pin + NO3. So what doest this mean in terms of potential
SOA source estimates:
Kanakidou et al, 2005: 12 – 70 Tg year-1
Goldstein & Galbally, 2007: 510 – 910 Tg year-1