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These are notes describing the discussions we had on the telecom today. Present: (I think) Mat Evans, Jingqiu Mao, Barron Henderson, Fabien Paulot, Daniel Jacob, Chris Miller, Eloise Marais (anybody else?)

1) Model engineering We currently have 2 different modes of using the chemistry in the model. KPP and SMVgear. There are diagnostics in SMVgear that don't exist for KPP so people would rather use the SMVgear for chemistry development work. KPP offers quite a lot of flexibility in the way that it deals with modular chemistry and so is an attractive route forwards for increasingly complex chemistry (Isoprene / Monoterpene / Bromine etc).

Outcome: Mat, Barron, Mike Long to investigate how we can take KPP forwards in GEOSChem

2) Isoprene chemistry There have been a variety of advances in the isoprene chemistry over the last couple of years. Where these are available they should be included as the standard version of the model. There needs to be some pragmatic thought about which species should be included as tracers in the model.

Outcome: Fabien, Eloise to make their work on the 'best' available isoprene chemistry scheme available to the support team for inclusion in a future version of the model.

3) RO2 + HO2 --> ROOH The rates for large (C>2) RO2 radicals is currently based on the value for C2H5O2+HO2 but there is evidence for a carbon number dependence in the rate constant. The MCM includes such a dependence [1] . Fabien has implemented this already into a version of the model.

Outcome: Fabien to included these updates into a version of the model

4) ROOH +OH The reaction ROOH+OH has two pathways. One where the OH attacks the peroxide H (ROOH)and one where the OH attacks an organic H (RHOOH). The attack on the peroxide H leads to a recycling of the initial RO2 radical and thus provides a catalytic sink for OH. The GEOS-Chem chemistry for peroxides often seems to favour this catalytic loss route which doesn't appear to be borne out by experimental evidence for the larger ROOHs.

"Outcome: Mat, Fabien Once the new isoprene chemistry is in the model check the ROOH+OH chemistry to ensure that we are happy with the products"

5) RO2 + NO3--> RO+NO2 I've had a post-doc looking at fast night time chemistry over western europe. This comes out as being important in controlling the NO3 concentrations and the N2O5 concentrations. It would be relatively simple to put into the model. Propene isn't the dominant species reacting with NO3 at night so the radical concentration in GC are probably too low at night. We might want to include a higher alkene in the future but at the moment putting in RO2 + NO3 --> RO + NO2 would not be that much work and would improve the model

Outcome: Mat to provide the new reactions. Probably put them in with the RO2+HO2 changes

6) N2O5 hydrolysis Some evidence that this isn't fast enough in the model as night time N2O5 appears too high. Parameterization for the Nitrate inhibition of uptake is available but doesn't change things too very much. The inclusion of RO2+NO3 into the model chemistry will act to reduce the N2O5 concentration so this may help.

Outcome: Harvard to include nitrate inhibition into a new version of the model. Impact of chemistry changes on night time N2O5 and HNO3 to be monitored

7) NO2 + OH Recent paper in Science [2] suggests a ~10% change in the rate constant for this reaction. Work done by Barron and Mat suggests that this has commensurate impact of species such as O3 and OH. However the evidence that this "improves" the model performance is weak. Given that the model is already high on OH and this would only make things higher it is not obvious that inclusion of this rate should be exbedited faster than the standard procedure of including updates to JPL and / or IUPAC.

8) HO2 on aerosol Jingqiu has been working on updates to the uptake of HO2 on aerosol. This seems to improve the global simulation. Once a paper has been submitted we should consider whether to include these updates in the model.

9) What is a tracer? There was some discussion about the nature of a tracer in the model vs a species. it was felt that the choice is rather arbitrary and based on historical decisions rather than any rigorous approach. Also the definition may be different between a 4x5 simulation and a 0.25x 0.33 simulation. It would be nice if a model diagnostic could be developed which would evaluation the lifetime of a spies and compare this to the dynamical time step and factor in the flux through that species.

10) Future meetings It was felt that the telecom was a useful way of people being able to get together to talk about the chemistry in the model and that we should have another one in the medium term. (March?)