Minutes of the aerosol working group meeting 12/12/2013

Next UKCA aerosol teleconference to be held Thursday 22nd November between Leeds & MO

Present: to appear.

Relevant Files for Discussion

Latest GA4 sensitivity results:
Scavenging coefficient sensitivity The scavenging coefficients for accumulation and coarse modes in convective regimes were reduced from 1.0 --> 0.5

• Impact on AOD
  - does not have a large impact on tropical AOD, with detrimental increased to AOD in high latitudes
• Impact on Burdens
  - small increases in BC/OC burdens but increases in accumulation and coarse mode sea salt and sulphate are most noticeable
• Budgets Expt Budgets Control - reflects findings above, v. small impact on BC burdens/lifetimes while you see a large increase in the seasalt and sulphate burdens and lifetimes. A large increase in the nucleation mode Sulphate loss timescales??

Doubling BB emissions
In this experiment BB emissions and SOA yield from monoterpene were both doubled, as an attempt to increase AOD in the tropics.

• Mass loading of BC and OC has increased by almost a factor of 2.
• The aitken insoluble mass pretty much doubles
• The accumulation soluble mode is pumped up a little, particularly over tropical continents.
• AOD has moved in the right direction -now ~ 0.05 higher over tropical continents. I think we still need a further 0.05 - 0.1 increase to match observations.
• The AOD also increases by a similar amount (~0.05) in some N. hemisphere mid-latitude regions where there are monoterpene and BB emissions.
• This is a little suprising as the emissions of BB and monoterpene are much smaller in these mid-latitude regions
• AOD increase in the tropics is quite limited to the continental source regions - indicating that the lifetime of the aerosol in the tropics is still quite low.

burden_ajkzi_anmad.pdf aod_maps_ajkzi_anmad.pdf

Decreasing ageing rates
Attached are the annual-mean results from the test to decrease the ageing rate of carbonaceous aerosols. The Control is amtj-u, the Experiment is amtj-w.

Bottom line: carbonaceous burdens are

• decreased slightly in the nucleation mode (OC -11%)
• increased in both Aitken modes (BC[sol] +28%; OC[sol] +23%; BC[ins] & OC[ins] both more than +200%)
• increased in the coarse mode (BC +60%; OC +18%)

....but sadly, the accumulation mode burdens for both BC and OC are decreased (both c. -4%), so there's little impact on AOD, and such changes as there are could easily be due to interannual variability.
AODs_amtjw_cf_amtju.pdf burdens_etc_amtjw_cf_amtju.pdf

Initial results from Offline Chemistry: Offline_chem_GA4.pdf

GA6 Performance:

Latest GA6 AODs Earlier GA6 AODs with GA4 for comparison - for information, sorry uses different colorscale!

Summary of discussion:

Things will be discussed.