A perspective on the requirements forEmission Inventories of Short-Lived Climate Forcers
needed to assess human role and to project SLCFs

M. J. Prather

IPCC Expert Meeting on Short-Lived Climate Forcers -- Geneva 28 May 2018

The step from human activities/emissions to radiative forcing:Emission ► Production/Loss ► Abundance/Burden ►RF•

All steps are diurnally, seasonally, geographically variant•

Many steps depend on local chemical-physical environment•

Many steps depend on co-emitted species•Many steps are not linearly scalable•

No simple, fungible rate-of-exchange (like CO2-eq for WMGHG)

O. Wild et al., 2001, Indirect long-term global cooling from NOx emissions, GRL 28:1719-1722

This seminal paper by Oliver Wild demonstrated that:
1. location of emissions (latitude, altitude) and co-species emitted (CO, VOCs)changed the SLCF RF, and2. emissions excite chemical modes, producing indirect effects across most SLCFs
0.5 Tg-N of NOx  short-lived trop-O3 vs. long-lived CH4 & O3

depends
strongly on
location ofemissions

O. Wild, et al., 2004, Chemical transport model ozone simulations for spring 2001 over the western
Pacific: Regional ozone production and its global impacts, JGR 109(D15): D15S02.

This paper followed the O3 caused by SLCF emissions for several E.
Asian metropolitan regions, following the steps from the first slide anddemonstrating how they can differ by day and type of pollution.

Altitude and amount of the O3
increase depends depends onthe meteorology of the day, andeven the decay (lifetime) of O3.

O. Wild, et al., 2004, Chemical transport model ozone simulations for spring 2001 over the western
Pacific: Regional ozone production and its global impacts, JGR 109(D15): D15S02.

This paper followed the O3 caused by SLCF emissions for several E.
Asian metropolitan regions, following the steps from the first slide anddemonstrating how they can differ by day and type of pollution. #2

Tokyo has much lower COand VOC emissions
The O3 burden (closest toRF) is much larger

M.J. Prather et al,(2017) Global Atmospheric Chemistry – Which Air Matters, ACP, 17(14), 9081-9102.

RESOLUTION: As we move to higher resolution chemistry models we see
incredible granularity in SLCF-critical chemistry, and this is also seen with the insitu observations. Below shows the fine-grain structure in column CH4 loss by OH.
We will need SLCF emissions inventory on the model grid.

from UCI
1º modelLu Hu et al., (2018). Global simulation of tropospheric chemistry at 12.5 km resolution: performance and evaluationof the GEOS-Chem chemical module (v10-1) within the NASA GEOS Earth System Model (GEOS-5 ESM),
GMDD, gmd-2018-111.

RESOLUTION: As we move to higher resolution chemistry models we see
incredible granularity in SLCF-critical chemistry, and this is shown with midtropospheric O3 below

fromGEOS-Chem
0.1º modelFigure 2. 500 hPa ozone distribution on August 1, 2013 at 0Z simulated by GEOS-5 with theGEOS-Chem chemical module at cubed-sphere C720 (~12.5×12.5km) resolution

C.D. Holmes et al. (2014) The climate impact of ship NOx emissions: an improved estimate accounting for plumechemistry, ACP 14:6801–6812, acp-14-6801-2014.

Intermediate modeling of SLCF emissions:
Even with <1º resolution, there will
be a need to model the complex,
non-linear processes that occur
within fresh plumes.
Work by Chris Holmes shows theimportance of plume models vs.
instant dilution over the grid cell.
It also shows failings of previous
plume models that calculated
O3 production and NOx loss,
but NOT CH4 loss.
LESSON: We will always develop moreaccurate models for the SLCF inventories.
If you build it they will come!

M.J. Prather (1994) Lifetimes and eigenstates in atmospheric chemistry, GRL, 21, 801-804.
M.J. Prather, J. Hsu (2010) Coupling of N2O and CH4 by global atmospheric chemistry, Science,330:952-954

Chemical feedbacks affect residence times and perturb other gases:

CO makes CH4
A perturbation to CO alone, δ[CO]=1, causes a significant perturbation to CH4that is “unmasked” in a few months:

δ[CO](t) ≈ + 0.005 e -t/13.6 + 0.995 e -t/0.285
δ[CH4](t) ≈ + 0.15 e -t/13.6 - 0.15 e -t/0.285

eigenvactors

M.J. Prather (1994) Lifetimes and eigenstates in atmospheric chemistry, GRL, 21, 801-804.
M.J. Prather, J. Hsu (2010) Coupling of N2O and CH4 by global atmospheric chemistry, Science,330:952-954

Chemical feedbacks affect residence times and perturb other gases:
N2O destroys CH4

Due to Interactions of N2O with stratospheric O3 chemistry,a relatively large reduction in CH4 (-3.6 ppb) is tied to anincrease in N2O (+10 ppb) that decays with a 108-yr time scale.
Thus N2O’s climate impact through radiative forcing is reduced*:(i) -8.4% because the decay of a pulse is faster than the e-foldof the steady-state lifetime and(ii) a further -4.5% to account for the reduction in CH4.

Some thoughts on SLCF inventories:
Emission ► Production/Loss ► Abundance/Burden ►RF•

Be consistent on co-emitted species•

Maintain full traceability, so that previous work can be adapted to newknowledge and so that the modeling/assessment community canscale by sectors/etc.

•Use as high resolution as possible, sometimes avoiding fixed regulargrid results that cannot be disaggregated.

•A full inventory of all species that the modeling community would ‘like’is simply not practical, so keep track of key marker species by sourcetype of emission, allowing emission factors to be used by the models.